Epidemiologic Reviews
ª The Author 2011. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health.
All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
Vol. 33, 2011
DOI: 10.1093/epirev/mxr008
Advance Access publication:
June 27, 2011
Genetic Screening
Wylie Burke*, Beth Tarini, Nancy A. Press, and James P. Evans
* Correspondence to Dr. Wylie Burke, Department of Bioethics and Humanities, A204 Health Sciences Building, Box 357120,
University of Washington, Seattle, WA 98195 (e-mail: wburke@u.washington.edu).
Current approaches to genetic screening include newborn screening to identify infants who would benefit from
early treatment, reproductive genetic screening to assist reproductive decision making, and family history assessment to identify individuals who would benefit from additional prevention measures. Although the traditional goal of
screening is to identify early disease or risk in order to implement preventive therapy, genetic screening has always
included an atypical element—information relevant to reproductive decisions. New technologies offer increasingly
comprehensive identification of genetic conditions and susceptibilities. Tests based on these technologies are
generating a different approach to screening that seeks to inform individuals about all of their genetic traits and
susceptibilities for purposes that incorporate rapid diagnosis, family planning, and expediting of research, as well
as the traditional screening goal of improving prevention. Use of these tests in population screening will increase
the challenges already encountered in genetic screening programs, including false-positive and ambiguous test
results, overdiagnosis, and incidental findings. Whether this approach is desirable requires further empiric
research, but it also requires careful deliberation on the part of all concerned, including genomic researchers,
clinicians, public health officials, health care payers, and especially those who will be the recipients of this novel
screening approach.
genetic testing; genetics, medical; genomics; heterozygote detection; neonatal screening; prenatal diagnosis
disease risk and can provide information about genetic susceptibilities to many different health risks. Some marketing
claims emphasize the health value of single nucleotide polymorphism screening—for example, ‘‘By understanding
your genetic predispositions, you can start looking at your
health in a new way. You can also learn if certain medications work with your genetic makeup’’ (13). Tests of this
kind are often referred to as ‘‘genome-scale’’ because they
analyze genetic variation across the full complement of human genetic material or genome. Numerous genome-scale
tests are now available (Table 2) (12, 14, 15), each using
different methods to measure multiple genetic differences
simultaneously.
The ultimate genome-scale test is whole genome sequencing, which ascertains an individual’s complete DNA
sequence (15). Costs of whole genome sequencing are rapidly diminishing. The first human genome sequence was the
end product of the Human Genome Project, a multinational
scientific effort that took almost 15 years to complete and
cost about $3 billion. However, costs (in the research setting)
are now in the range of $10,000–$50,000 per genome. The
‘‘thousand-dollar genome’’—perhaps even a hundred-dollar
INTRODUCTION
Screening is conventionally described as the evaluation
of asymptomatic people in a defined population to detect an
unsuspected disease or risk in order to improve health outcome (1). Newborn screening to identify infants who would
benefit from early treatment is an example and represents
a prominent public health service. Genetic screening is also
performed in clinical settings to detect carriers of genetic
diseases and for prenatal diagnosis, with a different goal: to
assist reproductive decision making. Both types of screening
were started with a focus on specific conditions (Table 1)
(2–9) but have expanded substantially as a result of technological advances.
New technologies allow multiple genetic risks to be ascertained simultaneously and offer new genetic screening
opportunities—for example, the potential to detect genetic
susceptibilities to common diseases at a level far exceeding
that of conventional family history assessment (10). One
example of such testing, single nucleotide polymorphism
microarray testing, is now available directly to consumers
(11). This type of screening uses an array-based platform
(12) to measure multiple gene variants associated with
148
Epidemiol Rev 2011;33:148–164
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Accepted for publication March 4, 2011.
Genetic Screening
genome—is expected soon. Whole exome sequencing is a
less expensive, but similar testing approach, in which just
the protein-coding regions of the genome are sequenced
(Table 2). Some experts predict that as costs fall, whole
genome sequencing and related genome-scale tests will
usher in an era of ‘‘genomic medicine’’ (12, 16).
Population screening is a central component of this vision. In this review, we explore the experience with newborn
and reproductive genetic screening. We also consider the
insights these screening programs provide as genomescale tests are contemplated for application in the general
population.
Newborn screening is now implemented in all developed
countries. In the United States, most states screen for at least
29 conditions (Table 3) (17, 18) within the first few days of
life as part of state public health programs that have developed over the last half century. For infants with out-of-range
findings, the program includes confirmatory testing and referral for medical follow-up (19, 20).
Historical background
Newborn screening began in the 1960s to address a specific disease, phenylketonuria (Table 1). The concept of
screening newborns for phenylketonuria was derived from
a 30-year research effort to define its biochemical basis (21),
develop a diet therapy (22–24), and create a reliable testing
mechanism (25). In this context, newborn screening provided an unprecedented opportunity to prevent cognitive
impairment in affected infants by rapid initiation of a phenylalanine-poor, tyrosine-enriched diet.
Several factors converged to promote newborn screening
for phenylketonuria (26–28). Advocacy organizations, particularly the National Association for Retarded Children,
embraced the potential of diet therapy to prevent the
complications of phenylketonuria (26). Political will was
spurred by the strong interest of the John F. Kennedy family
and presidential administration in the issue (27, 29). The
result was an alliance among disability advocates, genetics
specialists, and political leaders to establish newborn
screening state by state. This effort marked a sharp departure from the earlier association of genetics with the
eugenics movement (30), and it provided politicians with
an attractive opportunity to advocate for child health.
Newborn screening for phenylketonuria also represented
an important new connection between genetics and public
health. A distinctive feature of phenylketonuria screening
was time urgency: infants with phenylketonuria must be
identified within 2–3 weeks of birth to derive the full benefit
from diet therapy. Thus, a successful newborn screening
program requires both a suitable test, with attention to laboratory quality standards, and effective follow-up to assure
that all identified children have rapid access to treatment
(19, 20). These requirements led to implementation of
newborn screening as a legislatively mandated public health
program in most states.
Epidemiol Rev 2011;33:148–164
The groundswell of advocacy was sufficient to overcome
cautions expressed by many in the medical community that
the evidence for benefits from newborn screening was weak
(31). These cautions were not unreasonable: one historian
has estimated that newborn screening for phenylketonuria
was promoted on the basis of experience with diet therapy
in fewer than 20 infants with the disease (32). In addition,
although phenylketonuria screening is considered highly
successful, a full understanding of the implications of screening emerged only over time (29, 33). A randomized trial
established that diet therapy needed to be lifelong rather
than limited to a period of neurologic development in childhood (34), and a stringent diet is required in pregnancy to
prevent serious problems in children of women with phenylketonuria (35). Also foreshadowing the complexity of many
subsequent newborn screening tests, phenylketonuria screening led to the identification of infants with ‘‘physiologic
hyperphenylalanemia’’ who were not at risk of cognitive
impairment and could potentially be harmed by the diet
(29, 36).
Expansion of newborn screening
Gradual growth in testing panels occurred in the years
following initiation of phenylketonuria screening. The next
condition to be added in most states was congenital hypothyroidism, a nongenetic condition with a time urgency
similar to that of phenylketonuria; early treatment of congenital hypothyroidism prevents growth failure and cognitive impairment (37). Testing panels were further expanded
as screening tests became available to detect other conditions, mostly genetic, that required treatment in the newborn
period.
Many added conditions involved less time urgency or less
benefit than phenylketonuria and congenital hypothyroidism. For example, most states implemented newborn screening for sickle cell disease (Table 1) in the 1980s based on
evidence that early treatment with antibiotics reduces the
risk of sepsis (38). However, initiation of treatment is recommended within the first 4 months (39) rather than the first
2–3 weeks of life. Similarly, many states adopted screening
for cystic fibrosis based on randomized trial data showing
improved nutritional outcomes among cystic fibrosis infants
identified by newborn screening versus clinically (40). Newborn screening is also estimated to provide a small mortality
benefit (41, 42). However, a follow-up study of patients
in the randomized trial of newborn screening, now between
8 and 18 years of age, showed no benefit from newborn
screening for pulmonary disease or health-related quality
of life (43). The evolution toward screening that offered
less dramatic benefit was described by one expert as moving
from ‘‘public health emergency’’ to ‘‘public health service’’
(44).
A new testing technology introduced in the 1990s, tandem mass spectrometry, dramatically increased the number
of results available for newborn screening. Tandem mass
spectrometry enables measurement of numerous metabolites and more than 50 metabolic disorders, some still poorly
characterized or lacking definitive treatment (17, 45). In
addressing technology of this scope, policy makers need
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NEWBORN SCREENING
149
Role in Development of
Genetic Screening
Beta-thalassemia
(2)
Pioneering carrier
screening programs
in the Mediterranean
region
Reduced synthesis of
hemoglobin beta chain
Severe anemia and
hepatosplenomegaly,
leading to failure to thrive
(milder forms of disease
occur with mutations causing
milder impairment)
Transfusions and chelation
therapy; bone marrow
transplant
Autosomal recessive
inheritance of
mutations in the
HBB gene
Carrier and prenatal
screening
Cystic fibrosis (3)
First carrier screening
guideline for
nonminority
population; first
condition for which
randomized
controlled trial of
newborn screening
conducted
Abnormality in cystic
fibrosis transmembrane
conductance regulator
function
Progressive loss of lung
function related to thick lung
secretions and recurrent
infections; malnutrition;
male infertility; increased risk
of diabetes, pancreatitis,
liver failure (milder forms of
disease occur with mutations
causing milder impairment;
some mutations have
variable effects)
Antibiotic and nutritional
therapy; lung transplant
Autosomal recessive
inheritance of
mutations in the
CFTR gene; >1,000
mutations identified,
with different levels
of functional
impairment
Newborn screening,
carrier and prenatal
screening
Sickle cell disease
(4)
Unsuccessful
population-based
carrier screening
programs in the
1970s; carrier
screening now
offered in prenatal
care; newborn
screening initiated
in the 1980s
Functional impairment of
hemoglobin beta chain
Hemolytic anemia; vasoocclusive events; increased
risk of infections; clinical
course variable
Fluids; pain management;
transfusions; prophylactic
antibiotic and hydroxyurea
therapy; bone marrow
transplant
Autosomal recessive
inheritance of
hemoglobin S or of
hemoglobin S in
combination with
other beta-chain
mutations
Newborn screening,
carrier and prenatal
screening
Neural tube defects
(5)
First effort to develop
prenatal maternal
serum screening;
first test offered to
all pregnant women
regardless of risk
status
Unknown; results in
failure to close neural
tube during embryologic
development
Variable neurologic impairment
Supportive care and
symptom management
Multifactorial; genetic
studies identify
potential genetic
contributors to risk
Prenatal screening
Phenylketonuria (6)
First newborn
screening programs
in the 1960s
Total or near-total
deficiency of
phenylalanine
hydroxylase
Severe cognitive impairment
(milder presentations occur
for mutations causing partial
enzyme deficiency)
Phenylalanine-poor,
tyrosine-enriched diet
Autosomal recessive
inheritance of
mutations in the
PAH gene
Newborn screening
Spinal muscular
atrophy (7)
Most recent carrier
screening
recommendation
Degeneration and loss of
lower motor neurons in
the spinal cord and the
brain
Progressive muscle weakness;
different subtypes vary in
age at onset and range of
clinical manifestations
Supportive care and
symptom management
Autosomal recessive
inheritance of
mutations in the
SMN1 or SMN2 gene
Carrier and prenatal
screening
Tay-Sachs
disease (8)
First population-based
carrier screening
programs in the
1970s
Total or near total
deficiency of
hexosaminidase A
Neural degeneration beginning
at 6 months; death by 4–6
years (milder presentations
occur for mutations causing
partial enzyme deficiency)
Supportive care
Autosomal recessive
inheritance of
mutations in the
HEXA gene
Carrier and prenatal
screening
Trisomy 21 (Down
syndrome) (9)
First screening use
of amniocentesis
and prenatal
chromosome studies
Unknown; chromosomal
imbalance results in
impairment
Cognitive impairment;
increased incidence of
congenital heart defects,
hypothyroidism
Educational intervention;
other surgical and
medical therapy as
indicated
Trisomy 21 (small
percentage of cases
due to chromosomal
rearrangements
resulting in partial
trisomy 21)
Prenatal screening
Disease Mechanism
Clinical Findings
Treatment Options
Genetics
Current Screening
Abbreviations: CFTR, cystic fibrosis transmembrane conductance regulator; HBB, hemoglobin, beta; HEXA, hexosaminidase A (alpha polypeptide); PAH, phenylalanine hydroxylase;
SMN1, survival of motor neuron 1, telomeric; SMN2, survival of motor neuron 2, centromeric.
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Epidemiol Rev 2011;33:148–164
Condition
(Reference No.)
150 Burke et al.
Table 1. Conditions in the Development of Genetic Screening
Could identify rare mutations for a
wide range of disorders that benefit
from intervention
Likely a powerful diagnostic tool
for enigmatic familial disorders
Generates large amounts of
uninterpretable data; high
cost because of time- and
expertise-intensive analysis;
likely to reveal unwanted
information
Less sensitivity than whole
genome sequencing because
of lack of analysis of
noncoding regions of genome;
otherwise, similar to whole
genome sequencing
Comprehensive analysis; theoretically
highest sensitivity; will detect both
common and rare variants
High sensitivity; will detect both
common and rare variants; fewer
nonspecific findings than whole
genome sequencing (but still a
formidable problem); lower cost
than whole genome sequencing
Whole genome sequencing
(12, 15)
Whole exome sequencing
(12, 15)
Likely a powerful diagnostic tool
for enigmatic familial disorders
Could identify rare mutations for a
wide range of disorders that benefit
from intervention
Potentially useful if single nucleotide
polymorphisms chosen for
screening purposes
No established clinical utility at
present
Choice of gene variants included
in test determines value;
current tests generally
measure gene variants with
low predictive value
Rapid; adaptable to high throughput/
automation; high sensitivity and
specificity for measurement of
specific gene variants
Array-based single nucleotide
polymorphism assessment
analysis (12)
Evaluation of multiple congenital
anomalies and developmental
delay
Prenatal
Does not detect balanced
chromosomal rearrangements
Rapid; adaptable to high throughput/
automation; sensitive and specific
when validated array used
Array-based comparative
genomic hybridization (14)
Use in Clinical Management
Strengths
Test (Reference No.)
Table 2. Genome-scale Tests
Epidemiol Rev 2011;33:148–164
151
explicit criteria to determine whether to add a test to the
newborn screening panel. In an attempt to develop such
criteria, the American College of Medical Genetics recommended a core panel of 29 conditions for newborn screening, most identifiable using tandem mass spectrometry
technology (Table 3) (17). The report also recommended
including an additional 25 conditions as ‘‘secondary targets’’ because they are part of the differential diagnosis
for the 29 core conditions (Table 4). In developing these
recommendations, the report considered 3 categories of
evidence: clinical characteristics of the condition; analytical
characteristics of the test; and options for diagnosis, follow-up,
treatment, and management.
Because outcome data are limited or absent for many
conditions, the analysis relied heavily on expert opinion
and generated considerable debate (46, 47). Lack of data
has been a persistent difficulty for newborn screening policy
makers: the conditions in question are rare, making systematic observation difficult; and the clinical presentations
often require immediate action, making implementation
of clinical trials difficult and sometimes unethical (45, 48).
However, the Secretary’s Advisory Committee on Heritable
Diseases in Newborns and Children endorsed the American
College of Medical Genetics recommendations (49), as did
other organizations concerned with child health (50, 51); most
states now screen for the recommended conditions (Table 3).
Perhaps more importantly, the debate generated new approaches to evidence evaluation. The Secretary’s Advisory
Committee on Heritable Diseases in Newborns and Children
commissioned an Evidence Review Group to assist the
Committee in its appraisal of new candidate disorders
(52). This multidisciplinary group performs systematic
reviews of all available evidence (both published and unpublished) for candidate conditions. The Committee utilizes
this analysis in making recommendations to states regarding
the addition of new tests to newborn screening panels. In
addition, the Eunice Kennedy Shriver National Institute of
Child Health and Human Development has expanded efforts
to support and implement research related to newborn
screening (53).
Goals of newborn screening
The work of the Evidence Review Group, like the original
phenylketonuria example that precipitated newborn screening, is anchored in traditional screening goals: identifying
tests that enable early treatment to improve infants’ health
outcomes. However, growing test capacity has led to calls
to expand not only the number of disorders screened for
but also the goals of newborn screening. Several additional
goals of newborn screening are proposed (54–56): parents
may be spared the ‘‘diagnostic odyssey’’ that often occurs
when a child has a rare disease; identification of the condition may allow for early initiation of supportive or palliative
therapy when curative therapy is not possible; and because
the diseases identified by tandem mass spectrometry are often
genetic, early detection can inform future reproductive decisions. Finally, systematic identification of infants with rare
diseases through population screening can enhance research
to improve treatments.
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Limitations
Current or Proposed Screening Use
Genetic Screening
152 Burke et al.
Table 3. Incidence of Conditions Recommended for Universal
Newborn Screening (Incidence in the US Population) (17, 18)
Amino acid disorders
Phenylketonuria (1:20,000)
Maple syrup urine disease (1:250,000)
Homocystinuria (1:250,000)
Citrullinemia (1:200,000)
plemented with minimal information provided to parents.
Although most states provide informational brochures,
many parents are unaware that their infant has been tested
unless they are notified of a positive result (59, 60). As
testing panels expand to include conditions with less
time urgency or opportunity for definitive treatment,
many argue that greater efforts are needed to inform
parents, and potentially to obtain consent for screening
(57, 59–62).
Argininosuccinic acidemia (1:200,000)
Tyrosinemia type I (1:500,000)
Challenges in evaluating newborn screening results
Fatty acid oxidation disorders
Very long-chain acyl-CoA dehydrogenase deficiency (1:75,000)
Long-chain 3-OH acyl-CoA dehydrogenase deficiency (1:50,000)
Trifunctional protein deficiency (1:100,000)
Carnitine uptake defect (1:50,000)
Hemoglobinopathies
Sickle cell anemia (>1:5,000)
Hemoglobin S/beta-thalassemia (>1:50,000)
Hemoglobin SC (>1:25,000)
Organic acid disorders
Isovaleric academia (1:75,000)
Glutaric acidemia type I (1:100,000)
3-Hydroxy 3-methylglutaric aciduria (1:250,000)
Multiple carboxylase deficiency (1:250,000)
Methylmalonic academia (A, B) (1:100,000)
3-Methyl-crotonyl-CoA carboxylase deficiency (1:50,000)
Methylmalonic academia (Mut) (1:100,000)
Propionic acidemia (1:150,000)
ß-Ketothiolase deficiency (1:300,000)
Endocrine disorders
Congenital hypothyroidism (>1:5,000)
Congenital adrenal hyperplasia (>1:25,000)
Other
Biotinidase (>1:75,000 – lack of consensus)
Classical galactosemia (>1:50,000)
Hearing loss (>1:5,000)
Cystic fibrosis (>1:5,000)
If these goals were to become part of the rationale for
newborn screening, they would alter the evidence required
for new tests: Good analytic validity and a high predictive
value would be sufficient, without any obligation to assess
treatment benefit. This approach is controversial (57, 58).
A white paper from the President’s Council on Bioethics
(58) concluded that mandatory screening programs should
be limited to conditions that offer the opportunity to improve the health outcome of newborns. The Council recommended that newborn screening for other purposes be
offered to parents as voluntary programs only.
An important corollary of this debate concerns communication about newborn screening. Testing is often im-
Policy discussions about the goals of newborn screening
and associated communication strategies must take into
account challenges in evaluating test results, including
false-negative and false-positive results, ambiguities in the
information provided by screening, and incidental findings.
These challenges are common to all screening programs, but
the nature of genetic information influences the form they
take in newborn screening and other genetic screening.
False-negative and false-positive results. Newborn screening seeks to identify all affected infants, minimizing falsenegative results. Thus, thresholds for quantitative traits are
set to maximize sensitivity. False-negative results are also
minimized by ensuring that the sample is collected at least
24 hours after birth, and some states collect a second sample
1–2 weeks after birth (19). This effort appears to be successful, in that false-negative rates for most conditions appear to
be very low (63–66).
However, false-positive results are an inevitable feature
of a screening process that seeks to maximize sensitivity. As
more independent tests are added to newborn screening
panels, the overall number of false positives increases (67).
The definition of ‘‘false positive’’ varies across programs
(68). For example, some states may designate a result that
generates retesting of the same sample (without notification
of the family) a false positive, while others categorize a false
positive only if additional confirmatory testing is conducted;
still others categorize any situation in which a repeat specimen is obtained from the child as a false positive.
Although false positives are an unavoidable part of the
testing process, they must be managed to minimize harms
from both an economic (e.g., cost of additional testing) and
potential psychosocial impact. Anxiety, depression, and
parent-child dysfunction may occur among parents of children who received false-positive results (Table 5) (69–71).
Importantly, this anxiety appears related to poor parental
understanding of newborn screening (70). Studying the
psychosocial effect of false positives is complicated by
both the process and content of communication between
providers and parents, including the sense of urgency with
which an initial positive result is reported. Relatively few
studies have been reported. As a result, a number of unanswered questions remain about the type and scope of harms
(Table 5).
Overdiagnosis. Overdiagnosis is an emerging challenge
with particular importance for genetic screening. The term
refers to a screening-based diagnosis in a person who is
destined to remain asymptomatic or whose course is not
changed by early diagnosis. The potential benefits and
Epidemiol Rev 2011;33:148–164
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Medium-chain acyl-CoA dehydrogenase deficiency (1:15,000)
Genetic Screening
Table 4. Incidence of Secondary Targets Recommended for
Universal Newborn Screening (Incidence in the US Population)
(17, 18)
Amino acid disorders
Benign hyperphenylalaninemia (1:30,000)
Defects of biopterin cofactor biosynthesis (1:250,000)
Defects of biopterin cofactor regeneration (1:500,000)
Hypermethioninemia (1:200,000)
Citrullinemia type II (1:200,000)
Tyrosinemia type II (1:500,000)
Tyrosinemia type III (1:250,000)
Fatty acid oxidation disorders
Dienoyl reductase deficiency (1:2,000,000)
Carnitine palmitoyl-transferase Ia deficiency (1:300,000)
Carnitine palmitoyl-transferase II deficiency (1:250,000)
Carnitine/acyl-carnitine translocase deficiency (1:300,000)
Glutaric acidemia type II (1:250,000)
Medium/short-chain 3-OH acyl-CoA dehydrogenase deficiency
(1:2,000,000)
Medium-chain ketoacyl-CoA dehydrogenase deficiency
(1:2,000,000)
Carnitine/acyl-carnitine translocase deficiency (1:300,000)
Hemoglobinopathies
Variant hemoglobinopathies (>1:50,000)
Organic acid disorders
2-Methylbutyryl-CoA dehydrogenase deficiency (1:500,000)
2-Methyl-3-hydroxybutyric aciduria (1:1,000,000)
3-Methyl-glutaconic aciduria (1:200,000)
Methylmalonic acidemia (Cbl C,D) (1:100,000)
Isobutyryl-CoA dehydrogenase deficiency (1:100,000)
Malonic aciduria (1:500,000)
Other
Galactokinase deficiency (1:25,000)
harms of overdiagnosis are influenced by treatment options,
as illustrated by 2 newborn screening examples.
Most state newborn screening programs test for medium
chain acyl-CoA dehydrogenase deficiency (Table 3) (19).
Epidemiologic data suggest that 25% or more of infants
diagnosed with this deficiency by newborn screening will
remain asymptomatic; however, treatment consists primarily of dietary measures and is estimated to prevent death or
disability in another 20%–25% (72). Thus, most states have
determined that overdiagnosis is an acceptable burden for
medium chain acyl-CoA dehydrogenase deficiency. In contrast, newborn screening for Krabbe disease, a rare neurogenerative disorder, is controversial because the course is
highly variable and the treatment (bone marrow transplant)
may be life threatening (73). In New York State, where
testing for Krabbe disease is mandatory, all children with
positive newborn screening results for this disease are folEpidemiol Rev 2011;33:148–164
lowed clinically, with transplant usually offered only to those
with particularly severe biochemical and genetic phenotypes
and/or those with clinical findings of Krabbe disease. However, even for those ‘‘high-risk’’ children for whom follow-up
data are available, more than half have remained asymptomatic (73). These factors led the Secretary’s Advisory
Committee on Heritable Diseases in Newborns and Children
to recommend against adding Krabbe disease to its recommended newborn screening panel (74).
The issue is an important one for genetic screening programs because the penetrance (or likelihood that an individual will have clinical manifestations of disease) is often
incomplete for individuals with a disease-associated genotype. Therefore, screening for most genetic conditions will
identify some individuals who would do well if their conditions had remained undetected.
Findings of uncertain significance. Newborn screening
has a significant potential to yield indeterminate results.
Some abnormal metabolite levels detected by tandem mass
spectrometry have unclear clinical significance, and the introduction of DNA-based technologies in newborn screening can generate additional uncertainty. For example, most
screening protocols for cystic fibrosis include DNA-based
testing and yield some findings of uncertain clinical
significance—that is, infants with genotypes not diagnostic
of cystic fibrosis yet not clearly normal (Table 1). When the
confirmatory test, a measurement of sweat chloride, is
normal, the infant is assigned to an indeterminate category
now referred to as ‘‘Cystic Fibrosis Transmembrane
Conductance Regulator-related Metabolic Syndrome’’
(75). The prognosis for these infants is unclear, but
a substantial proportion are likely to remain symptom free.
As with false-positive results, results of this kind can
generate anxiety. Parents may also experience long-term
concern because of the lack of a clear prediction about their
child’s prospects. An observational study of parents and
health care providers coping with such uncertainties found
that multiple health care interactions may occur without
resolution, during which time the infant is perceived as
neither sick nor fully well (76).
Incidental findings. Screening may also identify clinical
findings unrelated to the screening goal. The most conspicuous example in newborn screening is the identification of
carrier status for genetic conditions—that is, individuals
with a single mutation for a condition (called autosomal
recessive) that manifests only when 2 mutations are present.
The carrier is healthy but has the potential to give birth to
a child with the disease if her mate is also a carrier. The tests
used to screen for sickle cell disease and cystic fibrosis
identify both affected infants and carriers. Because the
carrier state occurs more commonly than the disease, the
majority of ‘‘positive’’ results are for carriers (77).
Knowledge about the carrier status of an infant may lead
to further testing in the family, providing information for
parents or other relatives regarding reproductive risks.
Whether learning about a carrier state is a benefit or cost
of newborn screening has been a matter of debate. Some
have argued that newborn screening programs should report
results on carrier status (78, 79) and that these findings
represent an ancillary benefit of testing (54–56). Others
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Argininemia (1:250,000)
153
154 Burke et al.
Table 5. Psychosocial Effects of False-Positive Results From Newborn Screening
Current Findings (Reference No.)
Knowledge Gaps
Parents experience increased anxiety between receiving an
initial positive result and determination that the result is a false
positive (69).
How can parents best be supported during this period?
Some parents develop persistent psychosocial distress
(e.g., depression, anxiety, parent-child dysfunction) after
receiving a false-positive result (70).
Which parents are at risk of developing persistent psychosocial
distress?
Poor understanding of the testing process is associated with
persistent psychosocial distress (70).
What aspects of communication will optimize understanding?
Parents of children with false-positive results do not appear to
utilize more health care services (71).
What are the short-term and long-term health outcomes of parental
psychosocial distress after receipt of false-positive results?
REPRODUCTIVE GENETIC SCREENING
In contrast to newborn screening, reproductive genetic
screening occurs in clinical settings, usually as part of obstetric care. Two types of reproductive genetic screening are
in routine use: tests during pregnancy to identify fetuses
with trisomy 21 or neural tube defects (Table 1), and carrier
tests to identify couples at risk of having children with
specific autosomal recessive conditions. Screening is performed not to implement therapy but to allow parents the
opportunity to terminate (or avoid) a pregnancy to prevent
the birth of an affected child. Social concerns, in particular,
parents’ reproductive autonomy and physicians’ interests in
avoiding litigation, have played an important role in the
development of these screening programs.
Because the decision to terminate a pregnancy is highly
personal and societally controversial, experts characterize
prenatal and carrier tests as optional, in sharp contrast to
mandated newborn screening. In keeping with this difference, genetics professionals have developed a counseling
approach that avoids recommendations about testing and
instead has the goal of assisting couples to determine their
own preferred course of action (81, 82). Genetics professionals have also helped to justify reproductive genetic
services by de facto practice norms that seek to limit reproductive testing to early-onset diseases that cause severe,
untreatable impairment (83–85). Case reports of prenatal
testing for other purposes—for example, for sex selection
(86) or to assure a sibling match for organ donation
(83)—demonstrate the willingness of some to push beyond
these boundaries, but these uses of genetic testing have not
been part of routine prenatal screening.
Even when limited to severe childhood-onset conditions,
prenatal screening raises questions both because abortion is
controversial and because judgments differ regarding the
severity of conditions for which prenatal screening is offered. Disability advocates argue that selective abortion of
fetuses with disorders such as trisomy 21 brings 2 social
harms: it deflects attention away from the needs of people
living with disabilities and it implies a diminished social
value for such individuals (87). Some advocates consider
any use of selective pregnancy termination morally objectionable. Others support the right of individuals to make
autonomous decisions about pregnancy termination, but
they argue that prospective parents have a right to receive
complete and balanced information about persons with disabilities, including their potential for a good quality of life,
to ensure that decisions are not based on inappropriately
negative views of genetic disorders.
Historical background: prenatal screening for
trisomy 21
Prenatal identification of trisomy 21 was reported in 1970
(84), utilizing genetic analysis of fetal cells derived from
amniotic fluid (88). With the legalization of abortion and the
recognition of an increasing risk of trisomy 21 with maternal age (89), prenatal screening for trisomy 21 became an
accepted practice for women of ‘‘advanced maternal age’’
(90). Lawsuits claiming ‘‘wrongful birth’’ also had an impact on practice standards. These suits claim harm based on
the failure to offer prenatal testing to a pregnant women who
subsequently gives birth to a child with a genetic disorder
(91, 92); in essence, they are malpractice claims, arguing
a failure to disclose information pertinent to prenatal care.
Wrongful birth suits are frequently successful in the United
Epidemiol Rev 2011;33:148–164
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argue that routine reporting of carrier results violates the
right ‘‘not to know’’ and is of no direct benefit to the infant
(80). Furthermore, offering carrier results without prior
counseling or the opportunity for informed consent is contrary to current clinical practice (62). State practices vary
regarding notification of parents about carrier status, reflecting the unresolved debate about expanded goals for newborn
screening (77).
Implications of genome-scale tests. The debate regarding
expanded goals is likely to intensify as new technologies are
developed. Newborn screening currently utilizes DNAbased testing in a limited fashion—for example, as a confirmatory test in some screening protocols for cystic fibrosis.
However, as costs decrease, new genome-scale tests (Table 2)
may be applied to newborn screening. Some experts advocate
moving toward this approach as a means to achieve more
comprehensive identification of infants with genetic disorders
(54). Using genome-scale tests in newborn screening would,
however, greatly expand identification of carriers of genetic
diseases, the risk of overdiagnosis, incidental findings such as
genetic susceptibilities to common adult-onset disorders, and
findings of uncertain significance.
What proportion of parents of children who receive false-positive
results are affected?
Genetic Screening
Historical background: carrier screening
Concurrent with the development of prenatal screening
programs, community-based carrier screening programs
were developed among populations with an increased incidence of specific genetic diseases (77). The first carrier
screening program, for Tay-Sachs disease (Table 1), was
made possible by the discovery of the underlying biochemical deficit (98). Over a 5-year period from 1971 to 1976,
Tay-Sachs disease carrier screening programs were implemented in Jewish communities in more than 50 US cities
(85). Several factors contributed to this process, including
the high rate of carriers in Jewish populations (Table 1),
advocacy on the part of scientists/clinicians who were
deeply involved with at-risk families, and the existence
within the Jewish community of organizations willing to
help coordinate early testing programs (85). Many early
screening programs were implemented in synagogues or
other community centers. By 1977, prenatal diagnosis for
Tay-Sachs disease had been performed in an estimated 461
pregnancies (85). Of these, 371 involved couples with a previous affected child, and 90 involved couples identified by
Tay-Sachs disease carrier screening, resulting in identification of Tay-Sachs disease in 118 pregnancies. Elective pregnancy termination occurred in 93 of 97 pregnancies of
couples with a previously affected child and in 21 of 21
pregnancies in couples identified by carrier screening.
Tay-Sachs disease carrier screening served as a model for
screening programs in the Mediterranean region to identify
Epidemiol Rev 2011;33:148–164
beta-thalassemia carriers (Table 1). These programs, like
those for Tay-Sachs disease, were community based, focused on a genetic disease with increased prevalence, and
resulted in dramatic reductions in births of affected children
through pregnancy termination (99). As with Tay-Sachs disease, carrier screening received strong community support
and incorporated access to genetic counseling, prenatal diagnosis for couples at risk, and abortion services (99–101).
Carrier screening for sickle cell disease was also begun in
the 1970s in US African-American communities, but this
effort was ultimately viewed as a failure. There are likely
many contributors to this outcome, including racial tensions,
discriminatory insurance practices directed at sickle cell
disease carriers, testing procedures that failed to distinguish
between carriers and those with the disease, and problematic
screening procedures (102–104). For example, many programs screened school-age children under legislative mandates; educational, counseling, and follow-up procedures
were often weak and sometimes absent; and many screening
programs were initiated without community involvement
or support. In addition, prenatal diagnosis was not yet an
option when sickle cell disease carrier screening programs
were initiated (105); by comparison, the availability of prenatal diagnosis and the option to terminate affected pregnancies was seen as a central element in the success of
carrier screening programs for Tay-Sachs disease and
beta-thalassemia (85, 99).
Carrier testing before pregnancy
Although most carrier screening programs have been
focused on identifying carrier couples for prenatal diagnosis
(and the option of pregnancy termination), there has always
been interest in offering carrier testing before pregnancy.
Preconception testing offers couples a wider range of reproductive options if they wish to prevent the birth of an
affected child: they can choose not to have children, or, if
they have access to the technology, they can choose sperm
donation or in vitro fertilization utilizing either egg donation
or preimplantation genetic diagnosis. Carrier testing prior
to mate selection can also provide carriers the opportunity
to choose a partner who is not a carrier to avoid reproductive
risk, but this approach has been implemented only in rare
social circumstances (106).
Practice guidelines
As reproductive genetic screening became established, it
influenced practice standards, particularly obstetrics practice (97, 107–113). Most practice guidelines for carrier
screening continue to be directed toward population groups
at highest risk of specific genetic diseases, requiring health
care providers to make judgments about which patients
are candidates for screening. For example, screening for
Tay-Sachs disease carriers is generally performed as part
of a testing panel offered to women of Ashkenazi descent.
In its most recent practice guideline on Tay-Sachs disease
screening, the American College of Obstetricians and
Gynecologists recommends that Jewish women be screened
for Tay-Sachs disease and 3 additional conditions more
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States, in contrast to the more controversial claim of
‘‘wrongful life,’’ in which the child, as plaintiff, claims
she or he should not have been born (92).
In the early 1970s, researchers in the United Kingdom
found an association between elevated levels of alphafetoprotein in maternal blood and fetal neural tube defects
(Table 1), suggesting that screening for alpha-fetoprotein in
maternal blood could be used to detect pregnancies at higher
risk of neural tube defects (93). Ultrasound could then be
used to determine whether a neural tube defect was present.
As with trisomy 21, legal considerations played a role in
establishing routine prenatal screening for alpha-fetoprotein
in maternal blood. In 1985, lawyers for the American
College of Obstetricians and Gynecologists noted that more
than 100,000 women in the United States had undergone
this type of testing and advised their membership that this
level of use suggested malpractice jeopardy if a clinician did
not offer testing (94). This legal alert was considered tantamount to making screening for alpha-fetoprotein in maternal blood standard of care in prenatal medicine (95).
The observation of an association between low levels of
alpha-fetoprotein in maternal blood and fetal trisomies such
as trisomy 21 (96) offered a second rationale for maternal
serum screening, as well as the opportunity to expand trisomy 21 screening to younger women. Alpha-fetoprotein in
maternal blood alone had only limited predictive value, but
further research identified a panel of maternal serum measures that provided reliable identification of pregnancies at
increased risk of trisomy 21. Current US obstetric practice
includes the offer of such screening in all pregnancies (97).
155
156 Burke et al.
prevalent in people of Ashkenazi descent (107). Both the
U.S. Preventive Services Task Force (108) and the American
College of Obstetricians and Gynecologists (109) recommend hematologic screening in early pregnancy to detect
beta-thalassemia, sickle cell disease, and other hemoglobinopathy carriers among patients at risk, as defined by race/
ethnicity (African American, African, Mediterranean, and
southeast Asian).
Recent additions to carrier screening
recommendations
Effect of reproductive genetic testing on disease
incidence
Reduction of disease incidence has been an explicit goal
of some carrier screening programs, including those for
Tay-Sachs disease and beta-thalassemia (85, 99). In current
practice guidelines, however, the emphasis is on offering
parents reproductive choices and on the voluntary nature of
testing (107–114). Nevertheless, population data on cystic
fibrosis and trisomy 21 suggest that an effect on incidence
can be seen even when it is not an explicit goal of screening
(Tables 6 and 7). Several studies have found reductions
in cystic fibrosis births associated with genetic screening
(Table 6) (116–121). One study observed a significant decrease in incidence of cystic fibrosis births in a region of
Italy where population-based carrier screening is offered,
but not in a contiguous region where carrier testing is more
limited (121). The decrease could not be fully explained by
documented instances of pregnancy termination and therefore could reflect other effects of knowledge about carrier
status, such as avoidance of pregnancy.
The story is more complicated for trisomy 21 (Table 7)
(122–130): while pregnancy termination has reduced
Effect of technology development
As with newborn screening, genome-scale tests are likely
to have important effects on reproductive genetic screening.
Prenatal array-based comparative genomic hybridization
(Table 2) is currently being used to evaluate abnormal fetal
ultrasound findings, and in some instances has been offered
to older pregnant women as a screening test (131, 132). The
test has higher sensitivity than previous chromosomal tests
but can also identify genetic changes of uncertain significance; for this reason, its use in prenatal screening is debated (133). A new technique, extraction of fetal DNA from
maternal serum (134), is also likely to cause debate because
it creates a noninvasive method to accomplish prenatal testing for a wide array of genetic conditions.
Genomic technology will also have an impact on carrier
testing: assessment of multiple carrier states will become
increasingly feasible, and, as tests become more comprehensive, tailoring testing to ethnicity will no longer be necessary (135). A prototype of a genome-scale carrier test has
been described, in which sequencing technology was used
to identify carrier states for 448 recessive childhood diseases (136). Although the test was successful in identifying
carriers, it also generated results that could not be fully
interpreted—for example, gene variants that could reflect
either a carrier state or normal variation. In addition, study
data indicated that 122 of 460 mutations identified as disease associated in previously published studies were in fact
normal variation. These findings indicate the need for a substantial research investment to generate accurate clinical
tests from emerging genomic technology.
As genome-scale tests become sufficiently accurate for
clinical use, preconception screening may become a more
viable component of reproductive genetics. Comprehensive
carrier assessment could involve a single test that could be
administered in a primary care setting. The test could also
combine carrier screening with other assessments of genetic
susceptibility—for example, tests for cancer or other common disease susceptibility—to guide prevention efforts.
This approach would blur the line between reproductive
genetics and the use of testing to predict risk or guide health
care in a way that parallels the call for expanded goals of
newborn screening (54).
GENETIC SCREENING AS A COMPONENT OF
PRIMARY CARE
No DNA-based tests are routinely incorporated into primary care practice. However, screening for genetic risk is
widely recommended in the form of family history assessment. An initiative of the US Surgeon General, supported
by the Centers for Disease Control and Prevention and
many professional organizations, urges individuals to learn
their family history and discuss it with their health care
providers: ‘‘Tracing the illnesses suffered by your parents,
Epidemiol Rev 2011;33:148–164
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Carrier screening is currently recommended for 2 additional conditions: cystic fibrosis and spinal muscular atrophy
(110–114). Screening for cystic fibrosis carriers is based on
a small subset of mutations in the cystic fibrosis transmembrane conductance regulator gene, CFTR, from more than
1,000 so far documented that are the most common in the
population (111–113). In 2001, the American College of
Obstetricians and Gynecologists and the American College
of Medical Genetics (110–112) recommended that cystic
fibrosis carrier screening be ‘‘offered’’ to non-Hispanic
European Americans, for whom carrier detection is greater
than 85%, and ‘‘made available’’ to patients of other ethnicities. This recommendation reflected the higher prevalence
of cystic fibrosis in people of northern European descent
and the limited sensitivity of the screening panel in most
other ethnic groups. However, the recommendation posed
difficulties for health care providers; an American College
of Obstetricians and Gynecologists survey found that few of
its members used ethnicity in deciding whether to offer cystic
fibrosis carrier testing (115). In a 2005 update, the American
College of Obstetricians and Gynecologists endorsed offering screening to all couples regardless of race or ethnicity
(112). Carrier screening for spinal muscular atrophy (Table 1)
is also recommended for all racial and ethnic groups (113).
trisomy 21 births in many regions, a trend toward increasing
maternal age has also been observed. Because trisomy 21
increases with maternal age, the net effect on trisomy 21
incidence has been variable.
Genetic Screening
157
Table 6. Genetic Screening and the Incidence of Cystic Fibrosisa
Location, Years, and Population
(Reference No.)
Genetic Screening Context
Sources
Findings
Newborn screening for cystic
fibrosis in place throughout the
study period; recommendations for
population-based cystic fibrosis
carrier screening introduced in 2001
Data from newborn screening
records
Incidence of cystic fibrosis
births lower in 2003–2006
compared with 1999–2002
(P < 0.005)
Brittany, France, 1990–2005,
newborns and women
receiving prenatal genetic
testing in Brittany (117)
Newborn screening for cystic fibrosis
in place throughout the study
period; prenatal testing for cystic
fibrosis available to at-risk couples
Data from newborn screening
records and specialty center
records
Stable cystic fibrosis birth
incidence (1/3,153 in 1990–
2000, 1/3,188 in 2000–2005);
163 cystic fibrosis
pregnancies terminated;
estimated 30% lower cystic
fibrosis birth incidence as a
result of pregnancy
termination
Victoria, Australia, 1979–2006,
newborns and women
receiving prenatal genetic
testing in Victoria (118)
Newborn screening for cystic
fibrosis introduced in 1989;
increased availability of prenatal
testing for cystic fibrosis for
at-risk couples after 1989
Data from 3 cystic fibrosis
specialty centers, newborn
screening records, and
specialty center records
Cystic fibrosis livebirths: 3.96/
10,000 in 1979–1988 and
3.28/10,000 in 1980–2006
(reduction of 17%, P ¼ 0.025);
number of prenatal tests for
cystic fibrosis: 10 in 1979–
1988 (3 cystic fibrosis
pregnancies, all terminated),
304 in 1980–2006 (76 cystic
fibrosis pregnancies, 70
terminated)
Canada, 1971–2000, people
with cystic fibrosis in
Canada (119)
Prenatal testing for cystic fibrosis
available in 1989
Nonparametric model of cystic
fibrosis birth rates, from
Canadian Cystic Fibrosis
Foundation data registry and
Canadian vital statistics
Estimated cystic fibrosis birth
rates stable at 1/2,714 from
1971 to 1988; subsequently,
birth rates followed a linear
decline to 1/3,608 in 2000
The Netherlands, 1961–1965,
1975–1994, people with
cystic fibrosis in the
Netherlands (120)
Prenatal testing available starting
in 1990
Survey of all living cystic
fibrosis patients; additional
data from cystic fibrosis
mortality statistics and birth
records
Birth prevalence: 1961–1965:
1/3,600, 1974–1994: 1/4,750;
% of infants with 1 nonWestern parent increased
from 1% in 1972 to 16% in
2000
Northeast Italy, 1993–2007,
newborns in northeast Italy
(121)
Newborn screening for cystic fibrosis
in place throughout the study
period; population-based cystic
fibrosis carrier and prenatal testing
available in the eastern region of
northeast Italy; these services
provided for only at-risk parents
and assisted reproduction in the
western region
Data from newborn screening
records and specialty center
records
A mean annual decrease in
cystic fibrosis births of 0.16/
10,000 observed; reduction
significantly greater in the
eastern than in the western
region and inversely related
to the number of carrier tests
performed
a
Relevant articles were identified in 3 searches of the PubMed database using the terms ‘‘cystic fibrosis,’’ ‘‘incidence,’’ and ‘‘screening’’ in
combination with ‘‘newborn,’’ ‘‘carrier,’’ or ‘‘genetic*’’; the searches were limited to articles published in English from 2000 to 2010. Articles were
selected if they provided data on cystic fibrosis birth incidence and use of genetic screening, provided data on time trends in cystic fibrosis birth
incidence, and derived data from a defined geographic location or health care system. A total of 132 articles were identified; 7 met inclusion criteria.
Two articles presented data from the same region (Brittany); the article with more complete incidence data was used.
grandparents, and other blood relatives can help your doctor
predict the disorders to which you may be at risk and take
action to keep you and your family healthy’’ (137). This
initiative is in keeping with long-standing practice standards
that define family history as an essential component of a full
patient evaluation.
The scientific basis for using family history as a risk assessment tool is weak, however. Although family history has
been documented as a risk factor for numerous diseases, a
National Institutes of Health State of the Science evaluation
found limited evidence to guide its use in clinical practice,
particularly to prevent common complex diseases (138).
The evaluation panel concluded that research is needed to
define systematic methods for obtaining family history,
Epidemiol Rev 2011;33:148–164
evaluate the use of family history to guide interventions,
and assess outcomes.
Despite these cautions, family history is already incorporated in numerous practice guidelines. For example, the U.S.
Preventive Services Task Force recommends that family
history of breast and ovarian cancer be used to identify
women who are appropriate candidates for breast cancer
gene (BRCA) testing (139). Similarly, guidelines for colorectal cancer screening utilize family history in identifying
candidates for genetic testing and determining the appropriate age to begin screening (140), and family history is used
as a factor in the initiation of cholesterol-lowering therapies
(141). These examples build on decades of epidemiologic
observation (142).
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Massachusetts, 1999–2006,
newborns in Massachusetts
(116)
158 Burke et al.
Table 7. Genetic Screening and the Incidence of Trisomy 21a
Location, Years, and Population
(Reference No.)
Genetic Screening Context
Sources
Findings
Maternal serum screening introduced
in 1992; prior to that time, prenatal
testing for trisomy 21 offered to
pregnant women >34 years of age
Data from public health
databases (pregnancy
outcomes, pregnancy
terminations, birth defects
registry) and from hospital
records
During the study period, trisomy
21 births decreased from 1.05
to 0.42/1,000 livebirths; use of
prenatal testing for trisomy 21
increased from 5.8% in 1991
to 10.1% in 1996.
Denmark, 2000–2007,
pregnant women and
children born during the
study period in 19 Danish
departments (123)
First-trimester trisomy 21 screening
introduced in 2004–2006,
combining assessment of maternal
serum markers, ultrasound findings,
and maternal age
Data from public health
databases (birth data,
cytogenetics registry)
Trisomy 21 births decreased
from 55–65/year in 2004–
2005 to 31/year in 2005
and 32 in 2006.
Atlanta, Georgia, 1990–1999,
pregnant women and
children born during the
study period in the Atlanta
metropolitan region (124)
Both prenatal testing for pregnant
women >34 years of age and
maternal serum screening
available during the study period
Data from hospital sources
only (1990–1993) or
hospital and perinatal
offices (1994–1999)
Trisomy 21 incidence in 1990–
1993: 8.4/10,000 livebirths
when terminations were
excluded and 8.8/10,000
livebirths when terminations
were included; incidence in
1994–1999: 10.1/10,000
livebirths when terminations
were excluded and 15.3/
10,000 livebirths when
terminations were included.
Paris, France, 1981–2000,
pregnant women, and
children born during the
study period (125)
Start of reimbursement for prenatal
testing following abnormal ultrasound
in 1989; start of widespread serum
screening for trisomy 21 in 1996
Data from the Paris Registry
of Congenital Anomalies,
state birth records
Incidence of trisomy 21 births
decreased 3%/year despite
increasing average maternal
age during the time period.
Eastern Switzerland, 1980–
1996, pregnant women,
and children born during
the study period (126)
Prenatal testing for trisomy 21
available during the study period
Data from cytogenetic
laboratories for women
residing in eastern
Switzerland, state birth
records
During the study period, trisomy
21 births remained constant,
average maternal age
increased, and prenatal
detection of trisomy 21
increased.
Singapore, 1993–1998,
pregnant women, and
children born during the
study period (127)
Prenatal testing for trisomy 21
available during the study period
Data from public health
databases (registry of
births and deaths) and
hospital, clinic, and
laboratory records
Trisomy births decreased from
1.17 to 0.89/1,000 livebirths
during the study period;
decrease could be accounted
for by increased prenatal
detection and pregnancy
termination.
South Belgium, 1984–1989
and 1993–1998, pregnant
women receiving prenatal
genetic testing (128)
Maternal serum screening introduced
in 1990–1991; all prenatal testing
performed at centralized genetic
centers
Data on prenatal testing and
pregnancy outcome from
genetic center records
In 1984–1989, 244 trisomy 21
cases were detected (1/876
pregnancies), 17% prenatally;
in 1993–1998, 294 trisomy 21
cases were detected (1/704),
56% prenatally; more than
90% of prenatal trisomy 21
cases were terminated, for an
estimated shift in birth incidence from 1/794 to 1/1,606.
Czech Republic, 1996–2007,
children born during the
study period (129)
First-trimester screening for trisomy 21
implemented during the study period
Data from national registry
of congenital anomalies
Trisomy 21 births/10,000 births
decreased from 5.42 in 1996
to 3.66 in 2007, with a
corresponding increase in
first-trimester prenatal testing.
Croatia, 1996–2005,
pregnant women, and
children born in the
Primorsko-goranska
region (130)
Maternal serum screening and prenatal
testing for women >34 years of age
available during the study period
Data from public health
databases and regional
specialty centers
The trisomy 21 birth incidence
was 1.4 per 1,000 livebirths
for the study period; a
decreasing trend was
observed over the study
period but was not significant;
34% of pregnant women had
maternal serum screening,
and 12% of women >34
years of age had prenatal
trisomy 21 testing.
a
Relevant articles were identified in 2 searches of the PubMed database using the terms ‘‘trisomy 21’’ or ‘‘Down syndrome’’ in combination with
‘‘incidence’’ and ‘‘prenatal.’’ The searches were limited to articles published in English from 2000 to 2010. Articles were selected if they provided data
on trisomy 21 birth incidence and use of genetic screening, included data on time trends in birth incidence of trisomy 21, and derived data from
a defined geographic location or health care system. A total of 361 articles were identified; 9 met inclusion criteria. An additional article was identified
from references of the selected articles. Two articles provided data from the same region (Victoria, Australia); the more recent article was used.
Epidemiol Rev 2011;33:148–164
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South Australia, 1982–1996,
women who gave birth or
terminated pregnancy with
trisomy 21 (122)
Genetic Screening
159
Table 8. Binning Information From Genome-scale Tests
Bin
Example
1. Medically actionable conditions or risks
Identification of cancer susceptibility or increased risk of adverse
reaction to a specific drug
2. Gene variants associated with clinical outcome,
not medically actionable
Identification of small increased risk in common disease
susceptibility that does not change general prevention
recommendation (e.g., small increased risk of diabetes)
3. Gene variants with only reproductive implications
(no health risks for carrier)
Identification of carrier status for severe genetic disease
4. Gene variants that provide potentially sensitive
information, not medically actionable
Identification of increased risk of dementia or mental illness
5. Gene variants of unproven, unknown, or unclear
clinical significance
Most data derived from whole exome sequencing, whole genome sequencing,
and current analysis of single nucleotide polymorphism microarray
THE FUTURE OF GENETIC SCREENING: GENOMESCALE TESTING
Different genome-scale tests have specific strengths and
limitations (Table 2), but all provide information about multiple genetic risks and carry the potential for discovering
information that is confusing and difficult to interpret. Effective use of these tests in clinical care will require substantially more data correlating genetic variation with health
outcomes, but, as the clinical implications of genomic data
are understood, these technologies offer mechanisms for
universal screening. Early prototypes of this approach are
already being reported (136, 145); they point to important
challenges that have been foreshadowed by newborn screening and carrier screening.
Making sense of complex data
Extensive sequencing procedures—such as whole exome
sequencing and whole genome sequencing (Table 2)—are
intrinsically broad in scope, identifying gene variants associated with both severe and mild, treatable and untreatable
conditions. They also provide much information that is ambiguous or uninterpretable. Over time, some of the ambiguity will lessen as more is learned about associations between
Epidemiol Rev 2011;33:148–164
genetic variation and disease. However, most genetic contributors to health and disease are part of a complex etiology
involving environmental exposure and social determinants;
genomic prediction will always be incomplete.
Genome-scale tests therefore raise critical questions
about how tests are offered and results reported. A recent
report of clinical counseling following whole genome sequencing performed in a research study (145) illustrates
the complexity of interpreting and communicating whole
genome sequencing findings. An individual underwent
whole genome sequencing as part of a research study and
subsequently worked with a team of colleagues to determine
the health implications of the results. A key—and expected—
finding was the large volume of information: 2.6 million
single nucleotide polymorphisms and 752 copy number variants were identified (145). The team decided to focus its
analysis on genes associated with inherited disease, novel
gene variants, variants known to be associated with drug
response, and variants known to be associated with common
disease risk. Consultation with multiple databases and the
published literature was required. The team developed an
innovative, but resource-intensive, approach for estimating
common disease risk, in which pretest risk was assessed using
conventional risk factors, to determine the degree to which
risk changed as a result of whole genome sequencing.
This extensive analytic effort yielded a variety of findings: gene variants of high and limited penetrance, carrier
status for several autosomal recessive diseases, more than 60
gene variants associated with drug response, and altered risk
for 8 of 55 common diseases. Despite this wealth of information, much of the data remained uninterpretable (136).
Making use of whole genome sequencing data:
the binning concept
One approach to the diversity of information provided
by whole exome sequencing or whole genome sequencing
would be to define ‘‘bins’’ for different types of information; a potential schema for doing so is shown in Table 8.
From a traditional screening perspective, only a subset of
bin 1 findings would be considered for inclusion in a screening test—those for which medical action is effective at an
early, asymptomatic stage. The history of genetic screening suggests that there would also be strong interest in
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Cascade genetic screening offers an adjunct to familybased risk assessment. This term refers to screening of family members after an individual is diagnosed with genetic
disease. For example, screening family members after an
initial diagnosis of inherited colorectal cancer syndrome
substantially increases the benefit of the initial diagnosis
(143). This approach offers a means to increase detection
of rare conditions when universal screening is not feasible or
economically viable (144).
The association between family history and disease risk
undoubtedly captures the effects of both heredity and shared
environment and of complex gene-environment interactions. It is likely, however, that family history often functions as a rough proxy for genome-scale tests, identifying
genetic susceptibilities via a positive family history. Advocates for expansion of genetic screening anticipate that DNAbased tests may offer better ways to identify actionable risks
(12, 16).
160 Burke et al.
Policy implications
From the perspective of screening policy, the most challenging effect of burgeoning genomic technology is the way
in which it has led some to question the traditional goals of
screening. Similar to the introduction of tandem mass spectrometry in newborn screening, but on a much larger scale,
genome-scale tests may increasingly be used to justify a different approach to screening—one that seeks to inform individuals about all their genetic traits and susceptibilities.
Many will likely view this technology as offering a new
way to think about the screening process—as a source of
valued information with many different potential purposes,
not limited to the purpose of early detection to improve health
outcome. Some commentaries already suggest that whole
genome sequencing and other genome-scale tests might be
used as a fundamental measurement tool, more akin to a physical examination than a screening test (12, 15, 16, 145).
Whether this approach is desirable will require both
research and considered judgment. In particular, empiric
research is needed to define the harms associated with overdiagnosis, false-positive and false-negative results, and the
other incidental findings that will inevitably accompany
screening by genome-scale tests (146). As the benefits and
harms are clarified, there will also be a need for careful
deliberation about the use of genome-scale screening on
the part of all concerned, including genomic researchers,
clinicians, public health officials, health care payers, and,
most importantly, potential recipients of this novel screening approach.
ACKNOWLEDGMENTS
Author affiliations: Department of Bioethics and Humanities, University of Washington, Seattle, Washington (Wylie
Burke); Department of Pediatrics, University of Michigan,
Ann Arbor, Michigan (Beth Tarini); School of Nursing,
Oregon Health and Science University, Portland, Oregon
(Nancy A. Press); Department of Public Health and Preventive Medicine, School of Medicine, Oregon Health and
Science University, Portland, Oregon (Nancy A. Press); Department of Genetics, University of North Carolina, Chapel
Hill, North Carolina (James P. Evans); and Department of
Medicine, University of North Carolina, Chapel Hill, North
Carolina (James P. Evans).
This work was partially supported by the Center for
Genomics and Healthcare Equality (grant P50 HG 3374
from the National Human Genome Research Institute) and
by a K23 Mentored Patient-Oriented Research Career Development Award to B. T. from the Eunice Kennedy Shriver
National Institute of Child Health and Human Development
(K23HD057994).
Conflict of interest: none declared.
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