Myotonic Dystrophy

from other neurological departments in the city s hospitals. Every patient (and the "'healthy" relatives of MD subjects) underwent clinical and EMG re-examination, in order to confirm the initial diagnosis and to investigate the familial distribution of the diseases. The point prevalence rate was 0.9 (+0.6) • 10-s for MC and 2.1 (+_0.8) • 10-s for MD. During theperiod 1955-19 79 the mean annual incidence was O. 3 (+_0. 2) • 1 0-6 for MC and 0.7 (+_0.3) • 10-6for MD. The incidence-at-birth rate was 1.4 (+_1.2) • 10 -5 for MC and 2.9 (+_1.8) • 10-5 for MD. The modalities of inheritance and sex distribution of MC and MD were also studied. Knowledge of epidemiological features of these myopathies is of vital importance for genetic counselling.

A previous study in proximal myotonic myopathy (PROMM/DM-2) and myotonic dystrophy type 1 (DM-1) using brain positron emission tomography demonstrated a reduced cerebral blood flow in the frontal and temporal regions associated with cognitive impairment. The objective was to investigate further cognitive and behavioural aspects in a new series of patients with DM-1 and PROMM/DM-2. Nineteen patients with genetically determined PROMM/DM-2 and 21 patients with moderately severe DM-1 underwent neuropsychological testing and neuropsychiatric interviews. DM-1 and PROMM/DM-2 patients had significantly lower scores on tests of frontal lobe function compared to controls. Neuropsychiatric interviews demonstrated an avoidant trait personality disorder in both patient groups. Brain single photon emission computed tomography showed frontal and parieto-occipital hypoperfusion. The results suggest that there is a specific cognitive and behavioural profile in PROMM/DM-2 and in DM-1, and that this profile is associated with hypoperfusion in frontal and parieto-occipital regions of the brain. q

The study aims to develop and assess metric proprieties of the Portuguese version of the Hospital Anxiety and Depression Scale. A sequential sample includes 1322 participants diagnosed with cancer, stroke, epilepsy, coronary heart disease, diabetes, myotonic dystrophy, obstructive sleep apnoea, depression and a non-disease group, which completed the HADS. The first step includes translation, retroversion, inspection for lexical equivalence and content validity, and cognitive debriefing. Then we reproduce oblique exploratory factor analysis and use confirmatory factor analysis. We explore the sensibility of the questionnaire. The validation process of the Portuguese HADS version shows metric properties similar to those in international studies, suggesting that it measures the same constructs, in the same way, as the original HADS form.

Background: The era of genome-wide association studies (GWAS) has led to the identification of many inflammatory bowel disease (IBD)-associated single-nucleotide polymorphisms (SNPs) with unknown function. The next step would be to identify the functional consequences of these polymorphisms in order to target them efficiently for therapeutic purposes. One way to study this type of genetic variation is the use of cell line models. However, to characterize the functional effect of a SNP, it is important to know if the selected cell line model itself carries the studied genetic variation. Here, we genotyped 50 IBD markers across 32 susceptibility genes in 9 commonly used gastrointestinal cell lines.

In a randomized clinical trial the efficacy of strength training was studied in patients with myotonic dystrophy (n ϭ 33) and in patients with Charcot-Marie-Tooth disease (n ϭ 29). Measurements were performed at the start and after 8, 16 and 24 weeks of progressive resistance training. Surface electromyography (SEMG) of proximal leg muscles was recorded during isometric knee extension at maximum voluntary contraction (MVC) and at 20, 40, 60 and 80% of MVC. Changes in MVC, maximum electrical activity and torque-EMG ratios (TER) were calculated. Fatigue was studied by determining the changes in endurance and in the decline of the median frequency (F med ) of the SEMG during a sustained contraction at 80% MVC. These parameters showed no significant changes after the training in either of the diagnostic groups. Only the Charcot-Marie-Tooth training group showed a gradual significant increase in mean MVC over the whole training period (21%). After 24 weeks, the increase in mean RMS was similar (25%), but this was mainly due to a sharp rise during the first 8 weeks of training (20%). The findings indicate that the initial strength increase was due to a neural factor, while the subsequent increase was mainly due to muscle hypertrophy.

Muscular dystrophies (MD) are a heterogeneous group of inherited neuromuscular disorders characterized by muscle necrosis and progressive muscle weakness. It is important for oral healthcare providers to be familiar with MD as special considerations are necessary to provide appropriate and safe dental care for these medically complex patients. This article briefly reviews the more common types of MD, namely, Duchenne MD, Becker MD, Emery-Dreifuss MD, facioscapulohumeral MD, limb-girdle MD, oculopharyngeal MD, and myotonic dystrophy. Aspects of their epidemiology, pathophysiology, clinical presentation, diagnosis, and medical management as well as oral health considerations are discussed.

We review the normal anatomy of the white matter (WM) tracts as they appear on directional diffusion tensor imaging (DTI) color maps, which will almost certainly be available to the general radiologist as part of a commercial DTI software package in the near future. Anatomic drawings and gross dissection pho- tographs are correlated with the directional DTI color maps to

Somatic mosaicism of repeat length is prominent in repeat expansion disorders such as Huntington disease and myotonic dystrophy. Somatic mosaicism is age-dependent, tissue-speci®c and expansion-biased, and likely contributes toward the tissue-speci®city and progressive nature of the symptoms. We propose that therapies targeted at somatic repeat expansion may have general utility in these disorders. Speci®cally, suppression of somatic expansion would be expected to be therapeutic, whilst reversion of the expanded mutant repeat to within the normal range would be predicted to be curative. However, the effects of genotoxic agents on the mutational properties of speci®c nuclear genes are notoriously dif®cult to de®ne. Nonetheless, we have determined that chronic exposure over a three month period to a number of genotoxic agents can alter the rate of triplet repeat expansion in whole populations of mammalian cells. Interestingly, high doses of caffeine increased the rate of expansion by~60%. More importantly, cytosine arabinoside, ethidium bromide, 5-azacytidine and aspirin all signi®cantly reduced the rate of expansion by from 35 to 75%. These data establish that drug induced suppression of somatic expansion is possible. These data also suggest that highly unstable expanded simple sequence repeats may act as sensitive reporters of genotoxic assault in the soma.

Transcripts containing expanded CNG repeats, which are found in several neuromuscular diseases, are not exported from the nucleus and aggregate as ribonuclear inclusions by an unknown mechanism. Using the MS2–GFP system, which tethers fluorescent proteins to a specific mRNA, we followed the dynamics of single CUG-repeat transcripts and RNA aggregation in living cells. Single transcripts with 145 CUG repeats from the dystrophia myotonica-protein kinase (DMPK) gene had reduced diffusion kinetics compared with transcripts containing only five CUG repeats. Fluorescence recovery after photobleaching (FRAP) experiments showed that CUG-repeat RNAs display a stochastic aggregation behaviour, because individual RNA foci formed at different rates and displayed different recoveries. Spontaneous clustering of CUG-repeat RNAs was also observed, confirming the stochastic aggregation revealed by FRAP. The splicing factor Mbnl1 colocalized with individual CUG-repeat transcripts and its aggregation ...

Myotonic dystrophy (DM1) is associated with expression of expanded CTG DNA repeats as RNA (CUG exp RNA). To test whether CUG exp RNA creates a global splicing defect, we compared skeletal muscle of two mouse DM1 models, one expressing a CTG exp transgene, and another homozygous for a defective Mbnl1 gene. Strong correlation in splicing changes for ~100 new Mbnl1-regulated exons indicates loss of Mbnl1 explains >80% of the splicing pathology due to CUG exp RNA. In contrast, only about half of mRNA level changes can be attributed to loss of Mbnl1, indicating CUG exp RNA has Mbnl1-independent effects, particularly on mRNAs for extracellular matrix (ECM) proteins. We propose that CUG exp RNA causes two separate effects: loss of Mbnl1 function, disrupting splicing, and loss of another function that disrupts ECM mRNA regulation, possibly mediated by MBNL2. These findings reveal unanticipated similarities between DM1 and other muscular dystrophies.

Objective-Before the advanced evaluation of deglutition and selection of a treatment method, objective screening methods are necessary for patients with dysphagia. In this study a new electroclinical test was established to evaluate patients with dysphagia. Methods-This test is based on determining piecemeal deglutition; which is a physiological phenomenon occurring when a bolus of a large volume is divided into two or more parts which are swallowed successively. The combined electrophysiological and mechanical method used to record laryngeal movements detected by a piezoelectric transducer, and activities of the related submental integrated EMG (SM-EMG)-and sometimes the cricopharyngeal muscle of the upper oesophageal sphincter (CP-EMG)-were performed during swallowing. Thirty normal subjects and 66 patients with overt dysphagia of neurogenic origin were investigated after detailed clinical evaluation. Twenty patients with a potential risk of dysphagia, but who were normal clinically at the time of investigation, were also evaluated to determine the specificity of the test. All subjects were instructed to swallow doses of water, gradually increasing in quantity from 1 ml to 20 ml, and any recurrence of the signals related to swallowing within the eight seconds was accepted as a sign of dysphagia limit. Results-In normal subjects as well as in the patients without dysphagia, piecemeal deglutition was never seen with less than 20 ml water. This volume was therefore accepted as the lower limit of piecemeal deglutition. In patients with dysphagia, dysphagia limits were significantly lower than those of normal subjects. Conclusion-The method is a highly specific and sensitive test for the objective evaluation of oropharyngeal dysphagia even in patients with suspected dysphagia of neurogenic origin. It can also be safely and simply applied in any EMG laboratory.

Brain function is compromised in myotonic dystrophy type 1 (DM1), but the underlying mechanisms are not fully understood. To gain insight into the cellular and molecular pathways primarily affected, we studied a mouse model of DM1 and brains of adult patients. We found pronounced RNA toxicity in the Bergmann glia of the cerebellum, in association with abnormal Purkinje cell firing and fine motor incoordination in DM1 mice. A global proteomics approach revealed downregulation of the GLT1 glutamate transporter in DM1 mice and human patients, which we found to be the result of MBNL1 inactivation. GLT1 downregulation in DM1 astrocytes increases glutamate neurotoxicity and is detrimental to neurons. Finally, we demonstrated that the upregulation of GLT1 corrected Purkinje cell firing and motor incoordination in DM1 mice. Our findings show that glial defects are critical in DM1 brain pathophysiology and open promising therapeutic perspectives through the modulation of glutamate levels.

Atrial Preference Pacing (APP) is a pacemaker (PM) algorithm that works by increasing the atrial pacing rate to achieve continuous suppression of a spontaneous atrial rhythm and prevent supraventricular tachyarrhythmias. We have previously shown that atrial preference pacing may significantly reduce the number and the duration of AF episodes in myotonic dystrophy type 1 (DM1) patients who are paced for standard indications.However, the role that APP therapies play in the prevention of AF in a long-term period remains still unclear. Aim of the present prospective study was to evaluate whether this beneficial effect is maintained for 24-months follow-up period.To this aim, 50 patients with Myotonic Dystrophy type 1 who underwent dual-chamber PM implantation for first- and second- degree atrioventricular block, were consecutively enrolled and followed for 2 years. One month later the stabilization period, after the implantation, they were randomized to APP algorithm programmed OFF or ON for 6 months each, using a cross-over design, and remained in the same program for the second year. The results showed that while the number of AF episodes during active treatment (APP ON phases) was lower than that registered during no treatment (APP OFF phases), no statistically significant difference was found in AF episodes duration between the two phases. Furthermore, during the APP OFF and APP ON phases, the percentage of atrial pacing was 0 and 99%, respectively, while the percentage of ventricular pacing did not show differences statistically significant (11 vs. 9%, P = 0.2). Atrial premature beats were significantly higher during APP OFF phases than during APP ON phases. Lead parameters remained stable over time and there were no lead-related complications. Based on these 24-months follow-up data, we can conclude that, in DM1 patients who underwent dual-chamber PM implantation, APP is an efficacy algorithm for preventing paroxysmal AF even in long term periods.

In hospitalized patients with chronic medical and surgical conditions, many factors can negatively affect food intake, including psychological factors and anorexia. Appetite disturbance is a common occurrence in patients presenting with complicated medical illnesses. Poor appetite may be a primary symptom directly related to the illness, or it could be attributed to a number of causes comprising fatigue, poor motivation, depression, or all of the above. There is limited research reporting on the association between depression, poor motivation, and lack of appetite contributing to malnutrition. Following is a case report on the management of a severely malnourished 17-year-old man admitted to the hospital with myotonic dystrophy, depression, and inflammatory bowel disease. The psychiatry consultation service was consulted to address psychological factors contributing to malnutrition. The patient's history, laboratory data, the management and hospitalization course of the patient are addressed in this study. Case Report 4. Reinhardt GF, Myscofski JW, Wilkens DG, Dobrin PB, Mangan JE, Stannard RT. Incidence and mortality of hypoalbuminemic patients in hospitalized veterans.

Background and PurposeDystrophia myotonica or myotonic dystrophy is a progressive neuromuscular disorder in which patients demonstrate an irregular respiratory pattern and are particularly subject to cardiopulmonary compromise. The aim of the present study was to investigate the effects of both proprioceptive neuromuscular facilitation (PNF) and staged basal expansion (SBE) breathing exercises in subjects with myotonic dystrophy in two different positions: high support sitting and left side-lying.Dystrophia myotonica or myotonic dystrophy is a progressive neuromuscular disorder in which patients demonstrate an irregular respiratory pattern and are particularly subject to cardiopulmonary compromise. The aim of the present study was to investigate the effects of both proprioceptive neuromuscular facilitation (PNF) and staged basal expansion (SBE) breathing exercises in subjects with myotonic dystrophy in two different positions: high support sitting and left side-lying.MethodA randomized, double-blind study design was used. Seven non-congenital myotonic dystrophy subjects took part in the study. Six ‘treatment’ levels were applied to each subject: resting in high support sitting; resting in left side-lying; PNF of deep breathing in high support sitting; PNF of deep breathing in left side-lying; SBE in high support sitting and SBE in left side-lying. The outcome measures employed were arterial oxygen saturation (SpO2) and heart rate, as measured by oximetry and thoraco-abdominal motion (TAM), and respiratory rate, as measured by a pneumograph.A randomized, double-blind study design was used. Seven non-congenital myotonic dystrophy subjects took part in the study. Six ‘treatment’ levels were applied to each subject: resting in high support sitting; resting in left side-lying; PNF of deep breathing in high support sitting; PNF of deep breathing in left side-lying; SBE in high support sitting and SBE in left side-lying. The outcome measures employed were arterial oxygen saturation (SpO2) and heart rate, as measured by oximetry and thoraco-abdominal motion (TAM), and respiratory rate, as measured by a pneumograph.ResultsThe PNF technique was found to be the main contributor to improvement in SpO2 for subjects with myotonic dystrophy, where a 2.2% increase was found in the high support sitting position and a 2.6% increase was found in the left side-lying position. There was an increase of between 377% and 556% in TAM during application of both treatment techniques, in either the high support sitting or left side-lying positions. Respiratory rate declined between 15% and 30% immediately after treatment application and heart rate dropped slightly by between 0.2% and 4.1%.The PNF technique was found to be the main contributor to improvement in SpO2 for subjects with myotonic dystrophy, where a 2.2% increase was found in the high support sitting position and a 2.6% increase was found in the left side-lying position. There was an increase of between 377% and 556% in TAM during application of both treatment techniques, in either the high support sitting or left side-lying positions. Respiratory rate declined between 15% and 30% immediately after treatment application and heart rate dropped slightly by between 0.2% and 4.1%.ConclusionThe present study provides objective evidence that application of these respiratory physiotherapy interventions elicits an improvement in respiratory function in subjects with myotonic dystrophy. Further research into the physiological effects of these techniques could explore the mechanisms responsible for improvement in respiratory indices. Copyright © 2002 Whurr Publishers Ltd.The present study provides objective evidence that application of these respiratory physiotherapy interventions elicits an improvement in respiratory function in subjects with myotonic dystrophy. Further research into the physiological effects of these techniques could explore the mechanisms responsible for improvement in respiratory indices. Copyright © 2002 Whurr Publishers Ltd.

LEGENDS TO THE VIDEO Segment 1. The patient has a mild resting tremor of the left hand, which had a frequency of 4-5 Hz. In addition, a postural tremor of the right hand was observed when the arms were outstretched and during drawing a spiral.

An RNA gain-of-function of expanded transcripts is the most accredited molecular mechanism for myotonic dystrophy type 1 (DM1) and 2 (DM2). To disclose molecular parallels and divergences in pathogenesis of both disorders, we compared the expression profile of muscle biopsies from DM1 and DM2 patients to controls. DM muscle tissues showed a reduction in the major skeletal muscle chloride channel (CLCNl) and transcription factor Sp1 transcript levels and an abnormal processing of the CLCN1 and insulin receptor (IR) pre-mRNAs. No essential differences were observed in the muscle blind-like gene (MBNL1) and CUG binding protein 1 (CUGBP1) transcript levels as well as in the splicing pattern of the myotubularin-related 1 (MTMR1) gene. Macroarray analysis of 96 neuroscience-related genes revealed a considerable similar expression profile between the DM samples, reflective of a common muscle pathology origin. Using a twofold threshold, we found six misregulated genes important in calcium and potassium metabolism and in mitochondrial functions. Our results indicate that the DM1 and DM2 overlapping clinical phenotypes may derive from a common trans acting mechanism that traps and influences shared genes and proteins.

The NMR structure of an RNA with a copy of the 5′CUG/3′GUC motif found in the triplet repeating disorder myotonic dystrophy type 1 (DM1) is disclosed. The lowest energy conformation of the UU pair is a single hydrogen bonded structure; however, the UU protons undergo exchange indicating structural dynamics. Molecular dynamics simulations show that the single hydrogen bonded structure is the most populated one but the UU pair interconverts between 0, 1, and 2 hydrogen bonded pairs. These studies have implications for the recognition of the DM1 RNA by small molecules and proteins. RNA plays essential roles in many biological processes and is thus an important therapeutic target.(1) In particular, recent studies have shown that an RNA gain of function causes myotonic dystrophy types 1 and 2 (DM1 and DM2,1 respectively).(2,3) DM1 is caused by a trinucleotide CTG repeat in the 3′UTR of the DMPK gene. Once transcribed, expanded CUG repeats fold into an RNA hairpin with repeating 5′CUG/3′GUC motifs and binds CUG binding protein and the RNA splicing regulator muscleblind-like protein 1 (MBNL-1). The downstream effect of these interactions is mis-splicing of the main muscle chloride channel (clc1) and insulin receptor transcripts, for example.(4,5) Oligonucleotides (6) and the small molecule pentamidine (7) target the DM1 CUG repeats and correct pre-mRNA splicing defects in animal models of disease. Other small molecules targeting DM1 RNAs have been developed, including triazine-acridine conjugates (8) and compounds selected via dynamic diversity screening strategy.(9) In addition, rational, modular assembly strategies have been developed to provide nanomolar in vitro inhibitors. (10-13). In order to gain insights into how small molecules and proteins bind DM1 RNAs, † This work was funded by the National Institutes of Health (3R01GM079235-02S1 and 1R01GM079235-01A2) and Research Corporation. MDD is a Dreyfus New Faculty Awardee, a Dreyfus Teacher-Scholar, and a Cottrell Scholar.

To study the effect of DM1-associated CTG repeats on neuronal function, we developed a PC12 cellbased model that constitutively expresses the DMPK gene 3 0untranslated region with 90 CTG repeats (CTG90 cells). As CTG90 cells exhibit impaired neurite outgrowth and as microtubule-associated proteins (MAPs) are crucial for microtubule stability, we analyzed whether MAPs are a target of CTG repeats. NGF induces mRNA expression of Map2, Map1a and Map6 in control cells (PC12 cells transfected with the empty vector), but this induction is abolished for Map2 and Map1a in CTG90 cells. MAP2 and MAP6/ STOP proteins decrease in NGF-treated CTG90 cells, whereas MAP1A increases. Data suggest that CTG repeats might alter somehow the expression of MAPs, which appears to be related with CTG90 cell-deficient neurite outgrowth. Decreased MAP2 levels found in the hippocampus of a DM1 mouse model indicates that targeting of MAPs expression by CTG repeats might be relevant to DM1.

Myotonic dystrophy type 1 Myotonic dystrophy type 2 Clinical finding Muscle biopsy Molecular mechanism Pathology Myotonic dystrophy (DM) is the most common adult muscular dystrophy, characterized by autosomal dominant progressive myopathy, myotonia and multiorgan involvement. To date two distinct forms caused by similar mutations have been identified. Myotonic dystrophy type 1 (DM1, Steinert's disease) is caused by a (CTG)n expansion in DMPK, while myotonic dystrophy type 2 (DM2) is caused by a (CCTG)n expansion in ZNF9/CNBP. When transcribed into CUG/CCUG-containing RNA, mutant transcripts aggregate as nuclear foci that sequester RNA-binding proteins, resulting in spliceopathy of downstream effector genes. However, it is now clear that additional pathogenic mechanism like changes in gene expression, protein translation and micro-RNA metabolism may also contribute to disease pathology. Despite clinical and genetic similarities, DM1 and DM2 are distinct disorders requiring different diagnostic and management strategies. This review is an update on the recent advances in the understanding of the molecular mechanisms behind myotonic dystrophies. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis, guest edited by V. Askanas and K. Engel.

Trinucleotide repeat disorders (TRDs) are a set of genetic disorders caused by trinucleotide repeat expansion in certain genes that exceed the normal, stable threshold, which varies from gene to gene. A dynamic mutation in a healthy gene may increase the repeat count and result in a defective gene. At present there are 14 pathogenic trinucleotide repeat disorders that are known to affect humans. The occurrence of these "triplet repeat diseases" within populations ranges from fairly common (Fragile X syndrome and Myotonic dystrophy type 1) to rare (Dentatorubral-pallidoluysian atrophy). In the present study we report a detailed scenario of TRDs in India mostly in respect to the 9 most common disorders namely; Fragile X syndrome, Myotonic dystrophy type 1, Spinocerebellar ataxia (type 1, 2, 3, 6 and 7), Friedreich Ataxia and Huntington Disease.

While transfer of a protein encoded by a single nucleus to nearby nuclei in multinucleated cells has been known for almost 25 years, the biological consequences for gain-of-function diseases have not been considered. Here, we have investigated nuclear protein spreading and its potential consequences in two of the three most prevalent neuromuscular diseases. By performing co-cultures between diseased or control human myoblasts and murine C2C12 myoblasts, we demonstrate that in facioscapulohumeral dystrophy, although the transcription of the toxic protein DUX4 occurs in only a limited number of nuclei, the resulting protein diffuses into nearby nuclei within the myotubes, thus spreading aberrant gene expression. In myotonic dystrophy type 1, we observed that in human-mouse heterokaryons, the expression of a mutated DMPK from human nuclei titrates splicing factors produced by neighboring nuclei, inducing the mis-splicing of several pre-mRNAs in murine nuclei. In both cases, the spreading of the pathological phenotypes from one nucleus to another is observed, highlighting an additional mechanism that contributes to the dissemination and worsening of the muscle pathogenesis. These results indicate that nuclear protein spreading may be an important component of pathophysiology of gain of function muscular diseases which should be taken into consideration in the design of new therapeutic approaches.

Drosophila Muscleblind (Mbl) proteins control terminal muscle and neural differentiation, but their molecular function has not been experimentally addressed. Such an analysis is relevant as the human Muscleblind-like homologs (MBNL1-3) are implicated in the pathogenesis of the inherited muscular developmental and degenerative disease myotonic dystrophy. The Drosophila muscleblind gene expresses four protein coding splice forms (mblA to mblD) that are differentially expressed during the Drosophila life cycle, and which vary markedly in their ability to rescue the embryonic lethal phenotype of muscleblind mutant flies. Analysis of muscleblind mutant embryos reveals misregulated alternative splicing of the transcripts encoding Z-band component alpha-Actinin, which can be replicated in human cells expressing a Drosophilaalpha-actinin minigene and epitope-tagged Muscleblind isoforms. MblC appreciably altered alpha-actinin splicing in this assay, whereas other isoforms had only a marginal or no effect, demonstrating functional specialization among Muscleblind proteins. To further analyze the molecular basis of these differences, we studied the subcellular localization of Muscleblind isoforms. Consistent with the splicing assay results, MblB and MblC were enriched in the nucleus while MblA was predominantly cytoplasmic. In myotonic dystrophy, transcripts bearing expanded non-coding CUG or CCUG repeats interfere with the function of human MBNL proteins. Co-expression of CUG repeat RNA with the alpha-actinin minigene altered splicing compared with that seen in muscleblind mutant embryos, indicating that CUG repeat expansion RNA also interferes with Drosophila muscleblind function. Moreover MblA, B, and C co-localize with CUG repeat RNA in nuclear foci in cell culture. Our observations indicate that Muscleblind isoforms perform different functions in vivo, that MblC controls muscleblind-dependent alternative splicing events, and establish the functional conservation between Muscleblind and MBNL proteins both over a physiological target (alpha-actinin) and a pathogenic one (CUG repeats).

Founder effects are largely responsible for changes in frequency profiles of genetic variants in local populations or isolates. They are often recognized by elevated incidence of certain hereditary disorders as observed in regions of Charlevoix and Saguenay-Lac-Saint-Jean (SLSJ) in Northeastern Quebec. Dominantly transmitted myotonic dystrophy (DM1) is highly prevalent in SLSJ where its carrier rate reaches 1/550, compared with 1/5,000 to 1/50,000 elsewhere. To shed light on the origin of DM1 in this region, we have screened 50 nuclear DM1 families from SLSJ and studied the genetic variation in a 2.05 Mb (2.9 cM) segment spanning the site of the expansion mutation. The markers analyzed included 22 biallelic SNPs and two microsatellites. Among 50 independent DM1 chromosomes, we distinguished ten DM1-associated haplotypes and grouped them into three haplotype families, A, B and C, based on the relevant extent of allele sharing between them. To test whether the data were consistent with a single entry of the mutation into SLSJ, we evaluated the age of the founder effect from the proportion of recombinant haplotypes. Taking the prevalent haplotype A1_21 (58%) as ancestral to all the disease-associated haplotypes in this study, the estimated age of the founder effect was 19 generations, long predating the colonization of Nouvelle-France. In contrast, considering A1_21 as ancestral to the haplotype family A only, yielded the estimated founder age of nine generations, consistent with the settlement of Charlevoix at the turn of 17th century and subsequent colonization of SLSJ. We conclude that it was the carrier of haplotype A (present day carrier rate of 1/730) that was a ''driver'' of the founder effect, while minor haplotypes B and C, with corresponding carrier rates of 1/3,000 and 1/10,000, respectively, contribute DM1 to the incidence level known in other populations. Other studies confirm that this might be a general scenario in which a major ''driver'' mutation/haplotype issued from a founder effect is found accompanied by distinct minor mutations/haplotypes occurring at background population frequencies.

Triplet and tetranucleotide repeats a b s t r a c t Non-B DNA conformations adopted by certain types of DNA sequences promote genetic instabilities, especially gross rearrangements including translocations. We conclude the following: (a) slipped (hairpin) structures, cruciforms, triplexes, tetraplexes and i-motifs, and left-handed Z-DNA are formed in chromosomes and elicit profound genetic consequences via recombination-repair, (b) repeating sequences, probably in their non-B conformations, cause gross genomic rearrangements (translocations, deletions, insertions, inversions, and duplications), and (c) these rearrangements are the genetic basis for numerous human diseases including polycystic kidney disease, adrenoleukodystrophy, follicular lymphomas, and spermatogenic failure.

The expansions of long repeating tracts of CTG⅐CAG, CCTG⅐CAGG, and GAA⅐TTC are integral to the etiology of myotonic dystrophy type 1 (DM1), myotonic dystrophy type 2 (DM2), and Friedreich's ataxia (FRDA). Essentially all studies on the molecular mechanisms of this expansion process invoke an important role for non-B DNA conformations which may be adopted by these repeat sequences. We have directly evaluated the role(s) of the repeating sequences per se, or of the non-B DNA conformations formed by these sequences, in the mutagenic process. Studies in Escherichia coli and three types of mammalian (COS-7, CV-1, and HEK-293) fibroblast-like cells revealed that conditions which promoted the formation of the non-B DNA structures enhanced the genetic instabilities, both within the repeat sequences and in the flanking sequences of up to ϳ4 kbp. The three strategies utilized included: the in vivo modulation of global negative supercoil density using topA and gyrB mutant E. coli strains; the in vivo cleavage of hairpin loops, which are an obligate consequence of slipped-strand structures, cruciforms, and intramolecular triplexes, by inactivation of the SbcC protein; and by genetic instability studies with plasmids containing long repeating sequence inserts that do, and do not, adopt non-B DNA structures in vitro. Hence, non-B DNA conformations are critical for these mutagenesis mechanisms.

Myotonic dystrophy (DM) and facioscapulohumeral muscular dystrophy (FSHD) are the two most common adult muscular dystrophies and have progressive and often disabling manifestations. Higher levels of medication adherence lead to better health outcomes, especially important to patients with DM and FSHD because of their multisystem manifestations and complexity of care. However, medication adherence has not previously been studied in a large cohort of DM type 1 (DM1), DM type 2 (DM2), and FSHD patients. The purpose of our study was to survey medication adherence and disease manifestations in patients enrolled in the NIH-supported National DM and FSHD Registry. The study was completed by 110 DM1, 49 DM2, and 193 FSHD patients. Notable comorbidities were hypertension in FSHD (44 %) and DM2 (37 %), gastroesophageal reflux disease in DM1 (24 %) and DM2 (31 %) and arrhythmias (29 %) and thyroid disease (20 %) in DM1. Each group reported high levels of adherence based on regimen complexity, ...