Epidemiology of myotonic dystrophy in Italy: re-apprisal after genetic diagnosis

Expression levels of core spliceosomal proteins modulate the MBNL-mediated spliceopathy in DM1

Myotonic dystrophy type 1 (DM1) is a heterogeneous multisystemic disease caused by a CTG repeat expansion in DMPK. Transcription of the expanded allele produces toxic CUG repeat RNA that sequesters the MBNL family of alternative splicing (AS) regulators into ribonuclear foci, leading to pathogenic mis-splicing. To identify genetic modifiers of toxic CUG RNA levels and the spliceopathy, we performed a genome-scale siRNA screen using an established HeLa DM1 repeat-selective screening platform. We unexpectedly identified core spliceosomal proteins as a new class of modifiers that rescue the spliceopathy in DM1. Modest knockdown of one of our top hits, SNRPD2, in DM1 fibroblasts and myoblasts, significantly reduces DMPK expression and partially rescues MBNL-regulated AS dysfunction. While the focus on the DM1 spliceopathy has centered around the MBNL proteins, our work reveals an unappreciated role for MBNL:spliceosomal protein stoichiometry in modulating the spliceopathy, revealing new biological and therapeutic avenues for DM1.

Systemic Diseases and Heart Block

Systemic diseases can cause heart block owing to the involvement of the myocardium and thereby the conduction system. Younger patients (<60) with heart block should be evaluated for an underlying systemic disease. These disorders are classified into infiltrative, rheumatologic, endocrine, and hereditary neuromuscular degenerative diseases. Cardiac amyloidosis owing to amyloid fibrils and cardiac sarcoidosis owing to noncaseating granulomas can infiltrate the conduction system leading to heart block. Accelerated atherosclerosis, vasculitis, myocarditis, and interstitial inflammation contribute to heart block in rheumatologic disorders. Myotonic, Becker, and Duchenne muscular dystrophies are neuromuscular diseases involving the myocardium skeletal muscles and can cause heart block.

Hospital admissions from the emergency department of adult patients affected by myopathies

BACKGROUND AND PURPOSE

Myopathies are associated with classic signs and symptoms, but also with possible life-threatening complications that may require assistance in an emergency setting. This phenomenon is understudied in the literature. We aimed to assess the presentation, management, and outcomes of clinical manifestations potentially related to a muscle disorder requiring referral to the adult emergency department (ED) and hospitalization.

METHODS

Anonymized patient data retrieved using the International Classification of Diseases, Ninth Revision codes related to muscle disorders over 4 years were retrospectively analyzed. Medical reports were evaluated to extract demographic and clinical variables, along with outcomes. Two groups were defined based on the presence (known diagnosis [KD] group) or absence (unknown diagnosis [UD] group) of a diagnosed muscle disorder at arrival.

RESULTS

A total of 244 patients were included, 51% of whom were affected by a known myopathy, predominantly limb-girdle muscular dystrophies and myotonic dystrophies. The main reasons for ED visits in the KD group were respiratory issues, worsening of muscle weakness, and gastrointestinal problems. Heart complications were less prevalent. In the UD group, 27 patients received a new diagnosis of a specific primary muscle disorder after the ED access, mostly an inflammatory myopathy. Death during hospitalization was recorded in 26 patients, with a higher rate in the KD group and in patients affected by mitochondrial and inflammatory myopathies. Sepsis and dyspnea were associated with increased death risk.

CONCLUSIONS

Respiratory complications are the most common reason for myopathic patients accessing the ED, followed by gastrointestinal issues. Infections are severe threats and, once hospitalized, these patients have relatively high mortality.

Systemic Diseases and Heart Block

Systemic diseases can cause heart block owing to the involvement of the myocardium and thereby the conduction system. Younger patients (<60) with heart block should be evaluated for an underlying systemic disease. These disorders are classified into infiltrative, rheumatologic, endocrine, and hereditary neuromuscular degenerative diseases. Cardiac amyloidosis owing to amyloid fibrils and cardiac sarcoidosis owing to noncaseating granulomas can infiltrate the conduction system leading to heart block. Accelerated atherosclerosis, vasculitis, myocarditis, and interstitial inflammation contribute to heart block in rheumatologic disorders. Myotonic, Becker, and Duchenne muscular dystrophies are neuromuscular diseases involving the myocardium skeletal muscles and can cause heart block.

Application of Antisense Conjugates for the Treatment of Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is one of the most common muscular dystrophies and can be potentially treated with antisense therapy decreasing mutant DMPK, targeting miRNAs or their binding sites or via a blocking mechanism for MBNL1 displacement from the repeats. Unconjugated antisense molecules are able to correct the disease phenotype in mouse models, but they show poor muscle penetration upon systemic delivery in DM1 patients. In order to overcome this challenge, research has focused on the improvement of the therapeutic window and biodistribution of antisense therapy using bioconjugation to lipids, cell penetrating peptides or antibodies. Antisense conjugates are able to induce the long-lasting correction of DM1 pathology at both molecular and functional levels and also efficiently penetrate hard-to-reach tissues such as cardiac muscle. Delivery to the CNS at clinically relevant levels remains challenging and the use of alternative administration routes may be necessary to ameliorate some of the symptoms experienced by DM1 patients. With several antisense therapies currently in clinical trials, the outlook for achieving a clinically approved treatment for patients has never looked more promising.

Automatic Text-Mining Approach to Identify Molecular Target Candidates Associated with Metabolic Processes for Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is an autosomal dominant hereditary disease caused by abnormal expansion of unstable CTG repeats in the 3' untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. This disease mainly affects skeletal muscle, resulting in myotonia, progressive distal muscle weakness, and atrophy, but also affects other tissues and systems, such as the heart and central nervous system. Despite some studies reporting therapeutic strategies for DM1, many issues remain unsolved, such as the contribution of metabolic and mitochondrial dysfunctions to DM1 pathogenesis. Therefore, it is crucial to identify molecular target candidates associated with metabolic processes for DM1. In this study, resorting to a bibliometric analysis, articles combining DM1, and metabolic/metabolism terms were identified and further analyzed using an unbiased strategy of automatic text mining with VOSviewer software. A list of candidate molecular targets for DM1 associated with metabolic/metabolism was generated and compared with genes previously associated with DM1 in the DisGeNET database. Furthermore, g:Profiler was used to perform a functional enrichment analysis using the Gene Ontology (GO) and REAC databases. Enriched signaling pathways were identified using integrated bioinformatics enrichment analyses. The results revealed that only 15 of the genes identified in the bibliometric analysis were previously associated with DM1 in the DisGeNET database. Of note, we identified 71 genes not previously associated with DM1, which are of particular interest and should be further explored. The functional enrichment analysis of these genes revealed that regulation of cellular metabolic and metabolic processes were the most associated biological processes. Additionally, a number of signaling pathways were found to be enriched, e.g., signaling by receptor tyrosine kinases, signaling by NRTK1 (TRKA), TRKA activation by NGF, PI3K-AKT activation, prolonged ERK activation events, and axon guidance. Overall, several valuable target candidates related to metabolic processes for DM1 were identified, such as NGF, NTRK1, RhoA, ROCK1, ROCK2, DAG, ACTA, ID1, ID2 MYOD, and MYOG. Therefore, our study strengthens the hypothesis that metabolic dysfunctions contribute to DM1 pathogenesis, and the exploitation of metabolic dysfunction targets is crucial for the development of future therapeutic interventions for DM1.

Intergenerational Influence of Gender and the DM1 Phenotype of the Transmitting Parent in Korean Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common autosomal-dominant disorder caused by the CTG repeat expansion of the DMPK, and it has been categorized into three phenotypes: mild, classic, and congenital DM1. Here, we reviewed the intergenerational influence of gender and phenotype of the transmitting parent on the occurrence of Korean DM1. A total of 44 parent–child pairs matched for the gender of the transmitting parent and the affected child and 29 parent–child pairs matched for the gender and DM1 phenotype of the transmitting parent were reviewed. The CTG repeat size of the DMPK in the affected child was found to be significantly greater when transmitted by a female parent to a female child (DM1-FF) (median, 1309 repeats; range, 400–2083) than when transmitted by a male parent to a male child (650; 160–1030; p = 0.038 and 0.048 using the Tukey HSD and the Bonferroni test) or by a male parent to a female child (480; 94–1140; p = 0.003). The difference in the CTG repeat size of the DMPK between the transmitting parent and the affected child was also lower when transmitted from a male parent with classic DM1 (−235; −280 to 0) compared to when it was transmitted from a female parent with mild DM1 (866; 612–905; p = 0.015 and 0.019) or from a female parent with classic DM1 (DM1-FC) (605; 10–1393; p = 0.005). This study highlights that gender and the DM1 phenotype of the transmitting parent had an impact on the CTG repeat size of the DMPK in the affected child, with greater increases being inherited from the DM1-FF or DM1-FC situations in Korean DM1.

Overview of Neuromuscular Disorder Molecular Diagnostic Experience for the Population of Latvia

Background and Objectives

Genetic testing has become an integral part of health care, allowing the confirmation of thousands of hereditary diseases, including neuromuscular disorders (NMDs). The reported average prevalence of individual inherited NMDs is 3.7–4.99 per 10,000. This number varies greatly in the selected populations after applying population-wide studies. The aim of this study was to evaluate the effect of genetic analysis as the first-tier test in patients with NMD and to calculate the disease prevalence and allelic frequencies for reoccurring genetic variants.

Methods

Patients with NMD from Latvia with molecular tests confirming their diagnosis in 2008–2020 were included in this retrospective study.

Results

Diagnosis was confirmed in 153 unique cases of all persons tested. Next-generation sequencing resulted in a detection rate of 37%. Two of the most common childhood-onset NMDs in our population were spinal muscular atrophy and dystrophinopathies, with a birth prevalence of 1.01 per 10,000 newborns and 2.08 per 10,000 (male newborn population), respectively. The calculated point prevalence was 0.079 per 10,000 for facioscapulohumeral muscular dystrophy type 1, 0.078 per 10,000 for limb-girdle muscular dystrophy, 0.073 per 10,000 for nondystrophic congenital myotonia, 0.052 per 10,000 for spinobulbar muscular atrophy, and 0.047 per 10,000 for type 1 myotonic dystrophy.

Discussion

DNA diagnostics is a successful approach. The carrier frequencies of the common CAPN3, FKRP, SPG11, and HINT1 gene variants as well as that of the SMN1 gene exon 7 deletion in the population of Latvia are comparable with data from Europe. The carrier frequency of the CLCN1 gene variant c.2680C>T p.(Arg894Ter) is 2.11%, and consequently, congenital myotonia is the most frequent NMD in our population.

Systemic Diseases and Heart Block

Systemic diseases can cause heart block owing to the involvement of the myocardium and thereby the conduction system. Younger patients (<60) with heart block should be evaluated for an underlying systemic disease. These disorders are classified into infiltrative, rheumatologic, endocrine, and hereditary neuromuscular degenerative diseases. Cardiac amyloidosis owing to amyloid fibrils and cardiac sarcoidosis owing to noncaseating granulomas can infiltrate the conduction system leading to heart block. Accelerated atherosclerosis, vasculitis, myocarditis, and interstitial inflammation contribute to heart block in rheumatologic disorders. Myotonic, Becker, and Duchenne muscular dystrophies are neuromuscular diseases involving the myocardium skeletal muscles and can cause heart block.

Degradation of Toxic RNA in Myotonic Dystrophy Using Gapmer Antisense Oligonucleotides

Myotonic dystrophy (DM) types 1 (DM1) and 2 (DM2) are caused by autosomal dominant gain-of-function RNA which are, in turn, created by the expansion of repeat sequences in the DMPK and ZNF9 genes, respectively. The expansions are highly unstable and biased for further expansion in somatic cells and across generations. Despite the different genes involved, DM1 and DM2 share several clinical features due to having the similar underlying mechanism of repetitive RNA-mediated toxicity. Both disorders manifest as multisystemic conditions with features including myotonia, cataract development, and abnormalities in cardiac conduction. At present, there is no cure for DM and treatments mostly aim at symptom management. Among the therapeutics being developed, antisense therapy using gapmers is one of the most promising. Compared to other antisense oligonucleotides, gapmers maintain the ability to induce RNase H cleavage while having enhanced target binding affinity and nuclease resistance. This chapter will consolidate the different strategies studied thus far to develop a treatment for DM1 through the targeting of toxic repetitive RNA using gapmers.

Population-Based Prevalence of Myotonic Dystrophy Type 1 Using Genetic Analysis of Statewide Blood Screening Program

OBJECTIVE

To determine whether the genetic prevalence of the CTG expansion in the DMPK gene associated with myotonic dystrophy type 1 (DM1) in an unbiased cohort is higher than previously reported population estimates, ranging from 5 to 20 per 100,000 individuals.

METHODS

This study used a cross-sectional cohort of deidentified dried blood spots from the newborn screening program in the state of New York, taken from consecutive births from 2013 to 2014. Blood spots were screened for the CTG repeat expansion in the DMPK gene using triplet-repeat primed PCR and melt curve analysis. Melt curve morphology was assessed by 4 blinded reviewers to identify samples with possible CTG expansion. Expansion of the CTG repeat was validated by PCR fragment sizing using capillary electrophoresis for samples classified as positive or premutation to confirm the result. Prevalence was calculated as the number of samples with CTG repeat size ≥50 repeats compared to the overall cohort.

RESULTS

Of 50,382 consecutive births, there were 24 with a CTG repeat expansion ≥50, consistent with a diagnosis of DM1. This represents a significantly higher DM1 prevalence of 4.76 per 10,000 births (95% confidence interval 2.86-6.67) or 1 in every 2,100 births. There were an additional 96 samples (19.1 per 10,000 or 1 in 525 births) with a CTG expansion in the DMPK gene in the premutation range (CTG)_35-49.

CONCLUSION

The prevalence of individuals with CTG repeat expansions in DMPK is up to 5 times higher than previous reported estimates. This suggests that DM1, with multisystemic manifestations, is likely underdiagnosed in practice.

The Need for Establishing a Universal CTG Sizing Method in Myotonic Dystrophy Type 1

The number of cytosine-thymine-guanine (CTG) repeats (‘CTG expansion size’) in the 3′untranslated region (UTR) region of the dystrophia myotonica-protein kinase (DMPK) gene is a hallmark of myotonic dystrophy type 1 (DM1), which has been related to age of disease onset and clinical severity. However, accurate determination of CTG expansion size is challenging due to its characteristic instability. We compared five different approaches (heat pulse extension polymerase chain reaction [PCR], long PCR-Southern blot [with three different primers sets—1, 2 and 3] and small pool [SP]-PCR) to estimate CTG expansion size in the progenitor allele as well as the most abundant CTG expansion size, in 15 patients with DM1. Our results indicated variability between the methods (although we found no overall differences between long PCR 1 and 2 and SP-PCR, respectively). While keeping in mind the limited sample size of our patient cohort, SP-PCR appeared as the most suitable technique, with an inverse significant correlation found between CTG expansion size of the progenitor allele, as determined by this method, and age of disease onset (r = −0.734, p = 0.016). Yet, in light of the variability of the results obtained with the different methods, we propose that an international agreement is needed to determine which is the most suitable method for assessing CTG expansion size in DM1.

Fetal Macrocephaly: A Novel Sonographic Finding in Congenital Myotonic Dystrophy

Objective  Sonographic clues to the diagnosis of congenital myotonic dystrophy (CDM) are limited, particularly in the absence of family history of myotonic dystrophy (DM). We reviewed cases of CDM for unique prenatal findings. Study Design  A single-center case series of fetuses with CMD with characteristic prenatal findings confirmed postnatally. Results  Four fetuses with pre- or postnatally diagnosed CDM presented with macrocephaly in utero. While head measurements were appropriate for gestational age until midgestation, third-trimester head circumference and biparietal diameter were both >2 standard deviation (SD) above the mean in all. Abdominal and femur measurements were otherwise appropriate for gestation. Postnatally, the occipitofrontal circumference was >2 SD above the mean in all, confirming the diagnosis of macrocephaly. Conclusion  CDM should be included in the differential diagnosis of third-trimester macrocephaly, especially in the presence of additional sonographic clues and when maternal medical history and physical examination are suggestive of DM.

Multisystemic Impairments in 93 Chinese Patients With Myotonic Dystrophy Type 1

Background: Myotonic dystrophy type 1 (DM1) is an autosomal dominant neuromuscular disease characterized by muscle weakness and multisystemic impairments, which significantly impact the quality of life. There is currently an increasing consensus on the necessity of a multidisciplinary assessment in patients with DM1, to improve the management of the disease.

Methods: To analyze the prevalence and pairwise relationships between various organs involved, we performed a retrospective study by reviewing demographic and clinical information of DM1 patients including age, disease duration, clinical history, muscular impairment rating scale score (MIRS), results of blood biochemistry, electrocardiogram, echocardiography, and ophthalmologic examination.

Results: Ninety three DM1 patients (60 males and 33 females), aged 34.7 ± 12.6 (mean ± standard deviation) years were recruited. Of which, two congenital cases were of maternal and paternal inheritance, respectively. In the other 91 patients, cataract was found in 44.1% of patients, followed by hypogonadism (40.8%), frontal balding (40.7%), and cardiac abnormalities (34.5%). Thyroid dysfunction and insulin insensitivity were relatively uncommon. Age (p < 0.001) is independently correlated with cataract, and MIRS correlates positively with cardiac abnormalities (p = 0.005) and frontal balding (p = 0.015). Male patients more frequently had frontal balding (Risk ratio, 3.98; 95% confidence interval, 1.493–10.611) compared with female patients. Male patients with cataract presented more frequent cardiac abnormalities (Risk ratio, 4.40; 95% confidence interval, 1.055–18.358) compared with non-cataract male patients. Hypogonadism in male patients was characterized as decreased testosterone level, accompanied by elevated levels of luteinizing hormone and follicle-stimulating hormone.

Conclusions: In Chinese patients with DM1, we conclude that (1) cataract, hypogonadism, frontal balding and cardiac abnormalities are frequently observed; (2) age is an independent indicator to cataract and MIRS is the only predictor for cardiac abnormalities and frontal balding; (3) a positive correlation between ophthalmologic and cardiac impairments in male patients is found; (4) endocrine abnormalities show diverse manifestations and hormone tests are recommended; (5) particular attention should be given to patients with older age and higher MIRS score.

The Added Value of Cardiac Magnetic Resonance in Muscular Dystrophies

Muscular dystrophies (MD) represent a heterogeneous group of rare genetic diseases that often lead to significant weakness due to progressive muscle degeneration. In many forms of MD, cardiac manifestations including heart failure, atrial and ventricular arrhythmias and conduction abnormalities can occur and may be a predominant feature of the disease. Cardiac magnetic resonance (CMR) can assess cardiac anatomy, global and regional ventricular function, volumes and mass as well as presence of myocardial inflammation, infiltration or fibrosis. The role for cardiac MRI has been well-established in a wide range of muscular dystrophies related cardiomyopathies. CMR is a more sensitive technique than echocardiography for early diagnosis of cardiac involvement. It has also great potential to improve the prediction of long-term outcome, particularly the development of heart failure and arrhythmic events; however it still has to be validated by longitudinal studies including large populations. This review will outline the utility of CMR in patients with muscular dystrophies for assessment of myocardial involvement, risk stratification, and in guiding therapeutic management.

Core Clinical Phenotypes in Myotonic Dystrophies

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) represent the most frequent multisystemic muscular dystrophies in adulthood. They are progressive, autosomal dominant diseases caused by an abnormal expansion of an unstable nucleotide repeat located in the non-coding region of their respective genes DMPK for DM1 and CNBP in DM2. Clinically, these multisystemic disorders are characterized by a high variability of muscular and extramuscular symptoms, often causing a delay in diagnosis. For both subtypes, many symptoms overlap, but some differences allow their clinical distinction. This article highlights the clinical core features of myotonic dystrophies, thus facilitating their early recognition and diagnosis. Particular attention will be given to signs and symptoms of muscular involvement, to issues related to respiratory impairment, and to the multiorgan involvement. This article is part of a Special Issue entitled “Beyond Borders: Myotonic Dystrophies—A European Perception.”

Prevalence of myotonic dystrophy type 1 in adults in western Sweden

Myotonic dystrophy type 1 (DM1) is the most common inherited muscle disorder in adults. The prevalence differs widely between countries, but a figure of 13/100.000 is most frequently cited. It is a multi-organ disorder classified into four categories: congenital, childhood, adult/classical and late-onset/mild. The purpose of this study was to estimate the total and age adjusted prevalence of DM1 in adults in western Sweden (the Västra Götaland Region, VGR) as well as in the city of Gothenburg and also in the VGR except Gothenburg. Patients with the diagnosis of DM1 in the VGR were traced by outpatient registers at the Neuromuscular Center, contacted by regular mail and thereafter telephone interviewed about organ manifestations in order to ascertain the age at onset and thus the disease category. Medical records were examined to obtain detail accuracy. We detected 230 adult DM1 patients in the VGR which gives a prevalence of 17.8/100.000. The prevalence of DM1 in Gothenburg was 14.1/100.000, which was significantly lower than in the remaining region which was 19.7/100.000. There was no gender difference. The age adjusted prevalence rates showed that DM1 is most prevalent in the age group 35-44 years (23.9/100.000) and 45-54 years (25.8/100.000). DM1 prevalence in the western Sweden thus seems to be somewhat higher than elsewhere in Europe, and is especially high in the less densely populated areas of the region. The disease burden in the community is larger than what was known previously.

A Systematic Review and Meta-analysis on the Epidemiology of the Muscular Dystrophies

Background: The muscular dystrophies are a heterogeneous group of genetic muscle diseases with variable distribution of weakness and mode of inheritance.Methods: We previously performed a systematic review of worldwide population-based studies on Duchenne and Becker muscular dystrophies; the current study focused on the epidemiology of other muscular dystrophies using Medline and EMBASE databases. Two reviewers independently reviewed all abstracts, full-text articles, and abstracted data from 1985 to 2011. Pooling of prevalence estimates was performed using random-effect models.Results: A total of 1104 abstracts and 167 full-text articles were reviewed. Thirty-one studies met all eligibility criteria and were included in the final analysis. The overall pooled prevalence of combined muscular dystrophies was 16.14 (confidence interval [CI], 11.21-23.23) per 100,000. The prevalence estimates per 100,000 were 8.26 (CI, 4.99-13.68) for myotonic dystrophy, 3.95 (CI, 2.89-5.40) for facioscapulohumeral dystrophy, 1.63 (CI, 0.94-2.81) for limb girdle muscular dystrophy, and 0.99 (CI, 0.62-1.57) for congenital muscular dystrophies.Conclusions: The studies differed widely in their approaches to case ascertainment, and substantial gaps remain in the global estimates of many other types of muscular dystrophies. Additional epidemiological studies using standardized diagnostic criteria as well as multiple sources of case ascertainment will help address the economic impact and health care burden of muscular dystrophies worldwide.

Prevalence of muscular dystrophies: a systematic literature review

BACKGROUND

Determining the prevalence of neuromuscular disorders for the general population is important to identify the scope of burden on society and enable comparisons with other health conditions. This systematic review aims to identify and collate the findings of studies published between 1960 and 2013 on the prevalence of all types of muscular dystrophies.

SUMMARY

Relevant articles were identified through electronic database searches and manual searches of reference lists. There were 38 articles from across 19 countries that met the inclusion criteria. The total combined prevalence for all muscular dystrophies for studies classified as having a low risk of bias ranged between 19.8 and 25.1 per 100,000 person-years. Myotonic dystrophy (0.5-18.1 per 100,000), Duchenne muscular dystrophy (1.7-4.2) and facioscapulohumeral muscular dystrophy (3.2-4.6 per 100,000) were found to be the most common types of disorder. There was wide variation in study methodology, case ascertainment, and verification procedures and populations studied, all of which may contribute to the wide prevalence range, in addition to the likely variation in prevalence by country. Key Messages: Greater consistency in the conduct and reporting of neuroepidemiological studies is urgently needed to enable comparisons to be made between studies, countries, and over time.

Myotonic dystrophy

Myotonic dystrophy (dystrophia myotonica, DM) is one of the most common lethal monogenic disorders in populations of European descent. DM type 1 was first described over a century ago. More recently, a second form of the disease, DM type 2 was recognized, which results from repeat expansion in a different gene. Both disorders have autosomal dominant inheritance and multisystem features, including myotonic myopathy, cataract, and cardiac conduction disease. This article reviews the clinical presentation and pathophysiology of DM and discusses current management and future potential for developing targeted therapies.

Population frequency of myotonic dystrophy: higher than expected frequency of myotonic dystrophy type 2 (DM2) mutation in Finland

Myotonic dystrophy (DM) is the most common adult-onset muscular dystrophy with an estimated prevalence of 1/8000. There are two genetically distinct types, DM1 and DM2. DM2 is generally milder with more phenotypic variability than the classic DM1. Our previous data on co-segregation of heterozygous recessive CLCN1 mutations in DM2 patients indicated a higher than expected DM2 prevalence. The aim of this study was to determine the DM2 and DM1 frequency in the general population, and to explore whether the DM2 mutation functions as a modifier in other neuromuscular diseases (NMD) to account for unexplained phenotypic variability. We genotyped 5535 Finnish individuals: 4532 normal blood donors, 606 patients with various non-myotonic NMD, 221 tibial muscular dystrophy patients and their 176 healthy relatives for the DM2 and DM1 mutations. We also genotyped an Italian idiopathic non-myotonic proximal myopathy cohort (n = 93) for the DM2 mutation. In 5496 samples analyzed for DM2, we found three DM2 mutations and two premutations. In 5511 samples analyzed for DM1, we found two DM1 mutations and two premutations. In the Italian cohort, we identified one patient with a DM2 mutation. We conclude that the DM2 mutation frequency is significantly higher in the general population (1/1830; P-value = 0.0326) than previously estimated. The identification of DM2 mutations in NMD patients with clinical phenotypes not previously associated with DM2 is of particular interest and is in accord with the high overall prevalence. On the basis of our results, DM2 appears more frequent than DM1, with most DM2 patients currently undiagnosed with symptoms frequently occurring in the elderly population.

Retrospective study on PET-SPECT imaging in a large cohort of myotonic dystrophy type 1 patients

The aim was to study brain involvement in myotonic dystrophy type 1 by single photon emission tomography (SPECT) and positron emission tomography (PET). 58 DM1 patients were subjected to SPECT; 17 to both SPECT and PET. SPECT patients were grouped as 'normally perfused' and 'abnormally perfused'; PET patients as 'normal performers' and 'abnormal performers'. To quantify hypoperfusion and/or hypometabolism, we used a semi-quantitative scale. To localize focal hypoperfusion/hypometabolism, nine cerebral areas of involvement were identified. The Chi-square, Wilcoxon, McNemar tests were used for statistics. SPECT showed abnormalities in 52/58 patients. PET showed an abnormal glucidic uptake in 15/17. Hypoperfusion was mild/moderate in 50/58 patients, mostly involving the left supratentorial areas. Abnormal glucidic uptake was mainly observed in the left frontal lobe. Abnormalities in blood perfusion and/or glucose metabolism are frequent in DM1. These abnormalities involve the left more often than the right hemisphere, the frontal lobe more than other lobes. Such abnormalities are more often cortical than subcortical.

Myotonic dystrophy type I combined with X-linked dominant Charcot-Marie-Tooth neuropathy

Both the myotonic dystrophy type 1 (DM1) and the X-linked dominant Charcot-Marie-Tooth disease (CMTX1) are well-established inherited neuromuscular disorders characterized by progressive weakness and atrophy of the distal limb muscles. The underlying causes of the DM1 and CMTX1 are mutations in the DMPK and GJB1 gene, respectively. A patient with both DM1 and CMTX1 inherited these from his father and mother, respectively. Histopathological and electrodiagnostic studies revealed both chronic neuropathic and myopathic features. Physical disabilities were more severe than seen with either DM1 or CMTX1 alone. In addition, the present case reveals an asymmetric atrophy (22%) of the right calf muscle compared to the left side.

Brain involvement in myotonic dystrophies: neuroimaging and neuropsychological comparative study in DM1 and DM2

The objective of this study was to determine the degree of brain involvement in a cohort of myotonic dystrophy type 1 and type 2 (DM1, DM2) patients by brain studies and functional tests and to compare the results of the two groups. DM1, DM2 are multisystemic disorders due to polynucleotide expansions. Previous studies on brain involvement by neuroimaging and functional methods have led to contradictory results. Fifty molecularly defined DM1 patients and 14 DM2 patients, were recruited for the study. Age at recruitment, age at disease onset, disease duration and educational level were recorded. Neuromuscular assessment was done by MIRS. An extensive neuropsychological battery was performed in 48/50 DM1 and in a control group of 44 healthy matched subjects. Forty six of 50 DM1 and 12/14 DM2 underwent brain MRI; 21/50 DM1 and 9/14 DM2 underwent brain perfusion SPECT, with semiquantitative analysis of the results. MRI images were classified by ARWMC (age-related white matter changes) score, in order to quantify recurrence, localization and patterns of distribution of white matter hyperintense lesions (WMHLs) in our two cohorts. MRI results were matched to SPECT and to neuropsychological results. Thirty-seven of 46 DM1 and 10/12 DM2 had abnormal MRI imaging, showing scattered supratentorial, bilateral, symmetrical focal or diffuse WMHLs. A typical temporo-insular diffuse subcortical pattern was seen in DM1 subjects only, with no correlation with cognitive involvement. Major cognitive involvement was seen in the case of diffuse frontal lesions. A relationship with CTG expansion size was documented for DM1 subjects. SPECT showed minimal hypoperfusion in the posterior cortex planes in DM1 and, to a lesser extent, in DM2. Very mild degrees of involvement in the DM2 cohort were seen. Neuroimaging and functional investigations confirmed a more severe involvement of the brain in DM1 compared to DM2. A temporo-insular diffuse lesional pattern, specific for DM1, was found on MRI. This confirms greater expansion size as a risk factor for more extensive brain involvement in DM1.

Late-onset autosomal dominant limb girdle muscular dystrophy and Paget's disease of bone unlinked to the VCP gene locus

The broadwide spectrum of differential diagnoses of autosomal dominant muscular dystrophies in adults can be specified by additional features. The combination of late-onset muscular dystrophy, rimmed vacuoles and inclusion bodies in the muscle biopsy, and Paget's disease of bone suggests a mutation in the Valosin-containing protein gene (VCP, p97 or CDC48) even without dementia. We report on a German family with late-onset autosomal dominant muscular dystrophy starting in the pelvic girdle about age 40years, a subsequent rapidly-progressing course, high alkaline phosphatase and Paget's disease of bone. Clinical examination revealed no cognitive impairment. Histology showed myopathic changes with rimmed vacuoles and inclusion bodies on muscle biopsy. Mutations in VCP, filamin C, desmin, alphaB-crystallin, ZASP and myosin heavy chains 2 and 7 as well as the genes for facioscapulohumeral muscular dystrophy, Myotonic Dystrophy I and II, and LGMD1A-G were excluded by a combination of linkage analysis and direct sequencing. The family presented here suggests that a yet-unknown genetic defect can give rise to an autosomal dominant myopathy with Paget's disease but without dementia.

Hereditary channelopathies in neurology

Ion channelopathies are caused by malfunction or altered regulation of ion channel proteins due to hereditary or acquired protein changes. In neurology, main phenotypes include certain forms of epilepsy, ataxia, migraine, neuropathic pain, myotonia, and muscle weakness including myasthenia and periodic paralyses. The total prevalence of monogenic channelopathies in neurology is about 35:100,000. Susceptibility-related mutations further increase the relevance of channel genes in medicine considerably. As many disease mechanisms have been elucidated by functional characterization on the molecular level, the channelopathies are regarded as model disorders for pathogenesis and treatment of non-monogenic forms of epilepsy and migraine. As more than 35% of marketed drugs target ion channels, there is a high chance to identify compounds that counteract the effects of the mutations.

Facioscapulohumeral muscular dystrophy: epidemiological and molecular study in a north-east Italian population sample

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disease associated with a partial deletion on chromosome 4q35. Few relevant investigations have been reported on its epidemiology and were essentially based on clinical diagnosis, having been performed before recognition of the molecular mutation. We report an epidemiological survey on FSHD patients, in which the diagnosis was obtained by combined clinical and molecular evaluation. The survey concerned the north-east Italian province of Padova, an area of 871,190 inhabitants (1 January 2004). We identified 40 patients affected by FSHD based on clinical diagnosis. In 33 of them, the EcoRI fragment size in the 4q35 region ranged from 14 to 35 kb. Four other patients belonging to the same family harbored a 38-kb fragment. In these four cases, the relationship between the borderline deletion with the mild FSHD phenotype was corroborated by additional haplotype reconstruction and segregation analysis. Interestingly, the same mild facial-sparing clinical pattern was apparent only in one other patient with an EcoRI fragment of 32 kb, suggesting that this unusual FSHD phenotype may be due to very small 4q35 deletions. On the whole, estimating a prevalence rate of 44 x 10(-6), our survey confirmed FSHD as one of the most frequent neuromuscular disorders in Western populations.

Myotonic dystrophy in a female with myasthenia gravis

The likelihood of coexistence in the same patient of myasthenia gravis and myotonic dystrophy has been estimated at 1 in 40 million. The case of a patient in whom both diagnoses were made is reported here. A 13-year-old girl was diagnosed with myasthenia gravis because of weakness, fluctuating fatigability, and mild difficulty with chewing and swallowing. She had ptosis, with weakness predominantly of her face, arms, and neck. Serum antibodies against acetylcholine receptors were 9.9 nmol/L. She was started on pyridostigmine, with significant clinical improvement, reassuming normal daily activities. Two years later, generalized weakness reappeared and reappraisal of her symptomatology disclosed tongue percussion and hand action myotonia. Molecular genetic analysis disclosed 550 repeats of cytosine-thymidine-guanosine triplets on the DMPK gene. Undiagnosed relatives had expansions ranging from 110 to 1000 repeats. Myotonic dystrophy is considered the most common muscular dystrophy, with highly variable clinical manifestations; mildly affected individuals may escape clinical detection. Myasthenia gravis has an estimated prevalence of 15 per 100,000. No studies on the epidemiology of these diseases have been done in Chile. Although both diseases have specific clinical and laboratory presentations, they share some features in the mode of presentation that may generate difficulty in diagnosis of both entities in the same patient.

Epidemiology of myotonic dystrophy type 1 (Steinert disease) in Belgrade (Serbia)

The aim of this study was to estimate the incidence and prevalence of myotonic dystrophy type 1 (DM1) in Belgrade during the period 1983-2002. The patients who had DM1 were ascertained through hospital records from all neurological departments in Belgrade during 1983-2002. The molecular genetic analysis was performed in all patents included in the study. We identified 101 DM1 patients (52 males and 49 females). The average annual incidence rate of DM1 in Belgrade for the period observed was 2.0/1,000,000 (95% confidence interval (CI), 0.3-8.3), 2.1/1,000,000 (95% CI, 0.3-8.3) for males and 2.0/1,000,000 (95% CI, 0.3-8.3) for females. The highest age-specific DM1 incidence was registered in the age group 20-49: 3.4/1,000,000 (95% CI, 0.5-7.6), 4.0/1,000,000 (95% CI, 1.1-10.2) in males and 2.5/1,000,000 (95% CI, 0.5-7.6) in females. In the population of Belgrade, a cumulative probability of acquiring DM1 was 1 per 8621 for men and 1 per 9259 for women (1 per 8940 of the population for both sexes). The prevalence of DM1 in Belgrade on 31 December 2002 was 5.3/100,000 (95% CI, 4.2-6.6).

Derivation of human embryonic stem cell lines from embryos obtained after IVF and after PGD for monogenic disorders

BACKGROUND

Human embryonic stem (hES) cells are pluripotent cells usually derived from the inner cell mass (ICM) of blastocysts. Because of their ability to differentiate into all three embryonic germ layers, hES cells represent an important material for studying developmental biology and cell replacement therapy. hES cell lines derived from blastocysts diagnosed as carrying a genetic disorder after PGD represent in vitro disease models.

METHODS

ICMs isolated by immunosurgery from human blastocysts donated for research after IVF cycles and after PGD were plated in serum-free medium (except VUB01) on mouse feeder layers.

RESULTS

Five hES cell lines were isolated, two from IVF embryos and three from PGD embryos. All lines behave similarly in culture and present a normal karyotype. The lines express all the markers considered characteristic of undifferentiated hES cells and were proven to be pluripotent both in vitro and in vivo (ongoing for VUB05_HD).

CONCLUSIONS

We report here on the derivation of two hES cell lines presumed to be genetically normal (VUB01 and VUB02) and three hES cell lines carrying mutations for myotonic dystrophy type 1 (VUB03_DM1), cystic fibrosis (VUB04_CF) and Huntington disease (VUB05_HD).

A neonatal form of Steinert's myotonic dystrophy in twins after in vitro fertilization

OBJECTIVE

To report a case of nonidentical twins affected with a congenital form of Steinert's myotonic dystrophy (DM1), conceived by IVF owing to parental sterility, in which the mother presented a paucisymptomatic form of DM1 which was diagnosed as a result of the condition inherited by the twins.

DESIGN

Case report.

SETTING

Neonatal intensive care unit of a tertiary hospital.

PATIENT(S)

Newborn twins affected with the congenital form of DM1 and a 35-year-old nulliparous mother.

INTERVENTION(S)

In vitro fertilization.

MAIN OUTCOME MEASURE(S)

Molecular study of the CTG triplet expansion related with DM1.

RESULT(S)

Molecular study evidenced a pathologic expansion in both twins as well as in their mother.

CONCLUSION(S)

This case should serve as a reminder to practitioners that assisted reproductive techniques have opened the possibility that asymptomatic or paucisymptomatic carriers of a genetic syndrome can inadvertently conceive fetuses affected with more serious forms of the illness.

[Epidemiology of myotonic dystrophy type 1 in the population of central Serbia]

The objective of this epidemiological survey was to estimate the frequency and distribution of Myotonic dystrophy type 1 (MD1) (Steinert's disease) in central Serbia, during the period 1983-2002. The data on the number of diagnosed MD1 patients were obtained using the analysis of hospital records, which were examined in all the relevant neurological institutions in central Serbia in the mentioned period. Incidence rate and prevalence were used for the data analysis. In the study period in central Serbia, 154 patients (78 males and 76 females) with MD1 were identified. The average annual incidence rate of MD1 was 1.3 (95% CI-confidence interval 0.1-7.2) per 1,000,000 population, 1.4/1,000,000 (95% CI 0.1-7.2) for males, 1.3/1,000,000 (95% CI 0.1-7.2) for females. The trend of MD1 incidence rates in the observed period in central Serbia had a tendency of the statistically significant decrease, according to the linear model, in both male (y = 0.205 - 0.0066x, p = 0.021) and female populations (y = 0.1788 - 0.0048x, p = 0.032). The prevalence of MD1 on December 31, 2002 in central Serbia was 3.8/100,000 (95% IP 3.2-4.6), 3.7/100,000 (95% IP 3.3 - 4.8) for males, 3.3/100,000 (95% IP 3.0 - 4.4) for females.