Myotonic Dystrophies: A Genetic Overview.

Myotonic dystrophies (DM) are the most common muscular dystrophies in adults, which can affect other non-skeletal muscle organs such as the heart, brain and gastrointestinal system. There are two genetically distinct types of myotonic dystrophy: myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2), both dominantly inherited with significant overlap in clinical manifestations. DM1 results from CTG repeat expansions in the 3'-untranslated region (3'UTR) of the DMPK (dystrophia myotonica protein kinase) gene on chromosome 19, while DM2 is caused by CCTG repeat expansions in intron 1 of the CNBP (cellular nucleic acid-binding protein) gene on chromosome 3. Recent advances in genetics and molecular biology, especially in the field of RNA biology, have allowed better understanding of the potential pathomechanisms involved in DM. In this review article, core clinical features and genetics of DM are presented followed by a discussion on the current postulated pathomechanisms and therapeutic approaches used in DM, including the ones currently in human clinical trial phase.

In silico and in vitro effects of the I30T mutation on myelin protein zero instability in the cell membrane.

Charcot-Marie-Tooth (CMT) diseases are a heterogeneous group of genetic peripheral neuropathies caused by mutations in a variety of genes, which are involved in the development and maintenance of peripheral nerves. Myelin protein zero (MPZ) is expressed by Schwann cells, and MPZ mutations can lead to primarily demyelinating polyneuropathies including CMT type 1B. Different mutations demonstrate various forms of disease pathomechanisms, which may be beneficial in understanding the disease cellular pathology. Our molecular dynamics simulation study on the possible impacts of I30T mutation on the MPZ protein structure suggested a higher hydrophobicity and thus lower stability in the membranous structures. A study was also conducted to predict native/mutant MPZ interactions. To validate the results of the simulation study, the native and mutant forms of the MPZ protein were separately expressed in a cellular model, and the protein trafficking was chased down in a time course pattern. In vitro studies provided more evidence on the instability of the MPZ protein due to the mutation. In this study, qualitative and quantitative approaches were adopted to confirm the instability of mutant MPZ in cellular membranes.

Diagnostic challenges in POEMS syndrome presenting with polyneuropathy: A case series.

OBJECTIVE: To analyze the clinical characteristics of patients with POEMS presenting with polyneuropathy and discuss associated diagnostic challenges. METHOD: Retrospective analysis of 6 patients from 2 tertiary-care institutions. RESULTS: Six patients presented with progressive sensorimotor deficits predominantly or exclusively in the lower extremities and were diagnosed with POEMS syndrome. In 4 patients, a diagnosis of chronic inflammatory demyelinating polyradiculopathy (CIDP) was mistakenly made. Low concentration of serum paraprotein and elevated vascular endothelial growth factor (VEGF) were detected in all 6 patients. Initial serum immunofixation and skeletal survey were normal in 2 patients each. On nerve conduction studies, motor and sensory responses were absent in the lower extremity in all 6 patients. Conduction velocity slowing and F-wave latency prolongation appear slightly more pronounced than distal motor latency prolongation in the upper extremity. Spinal MRI showed diffuse lumbosacral nerve root enhancement in all. In 3 patients, targeted bone marrow biopsy was needed for confirming the POEMS diagnosis. Treatment with corticosteroids, chemotherapy agent, focal radiation and/or autologous stem cell transplantation led to significant improvement in 5 of 6 patients. CONCLUSION: Diagnosis of POEMS should be considered in patients with progressive polyneuropathies of mixed demyelinating and axon loss features, including CIDP patients not responding to standard treatment. A polyradiculoneuropathy rather than a pure polyneuropathy seems to exist in POEMS.

Intravascular T-cell lymphoma: A rare, poorly characterized entity with cytotoxic phenotype.

Intravascular T-cell lymphomas are rare, poorly characterized lesions. We discuss the clinical, radiologic and especially the laboratory characteristics of a lesion which presented in a 62-year-old woman with a history of progressive CNS abnormalities. Throughout the course of the disease, radiologic findings consisted mainly of multifocal mixed areas of ischemia and vasogenic edema involving cortical and subcortical regions. A brain biopsy identified an abnormal T-cell population confined to lumens of vessels. These T-cells were abnormal cytotoxic cells, positive for CD3, CD8, and negative for CD2, CD4, CD5, CD7 and CD30. While flow cytometry and immunohistochemistry failed to identify a similar population in the blood or bone marrow, molecular studies showed a clonal T-cell population in both the brain and the bone marrow. No other organs were involved. In spite of aggressive treatment, the patient's medical condition continued to progress and she passed away. In conclusion, this abnormal population of cytotoxic T-cells with intravascular localization probably represents a specific type of T-cell lymphoma with specific clinical, radiologic, molecular and immunophenotypic characteristics.

A mutation causes MuSK reduced sensitivity to agrin and congenital myasthenia.

Congenital myasthenic syndromes (CMSs) are a heterogeneous group of genetic disorders affecting neuromuscular transmission. The agrin/muscle-specific kinase (MuSK) pathway is critical for proper development and maintenance of the neuromuscular junction (NMJ). We report here an Iranian patient in whom CMS was diagnosed since he presented with congenital and fluctuating bilateral symmetric ptosis, upward gaze palsy and slowly progressive muscle weakness leading to loss of ambulation. Genetic analysis of the patient revealed a homozygous missense mutation c.2503A>G in the coding sequence of MUSK leading to the p.Met835Val substitution. The mutation was inherited from the two parents who were heterozygous according to the notion of consanguinity. Immunocytochemical and electron microscopy studies of biopsied deltoid muscle showed dramatic changes in pre- and post-synaptic elements of the NMJs. These changes induced a process of denervation/reinnervation in native NMJs and the formation, by an adaptive mechanism, of newly formed and ectopic NMJs. Aberrant axonal outgrowth, decreased nerve terminal ramification and nodal axonal sprouting were also noted. In vivo electroporation of the mutated MuSK in a mouse model showed disorganized NMJs and aberrant axonal growth reproducing a phenotype similar to that observed in the patient's biopsy specimen. In vitro experiments showed that the mutation alters agrin-dependent acetylcholine receptor aggregation, causes a constitutive activation of MuSK and a decrease in its agrin- and Dok-7-dependent phosphorylation.

Nonsense mutation-associated Becker muscular dystrophy: interplay between exon definition and splicing regulatory elements within the DMD gene.

Nonsense mutations are usually predicted to function as null alleles due to premature termination of protein translation. However, nonsense mutations in the DMD gene, encoding the dystrophin protein, have been associated with both the severe Duchenne Muscular Dystrophy (DMD) and milder Becker Muscular Dystrophy (BMD) phenotypes. In a large survey, we identified 243 unique nonsense mutations in the DMD gene, and for 210 of these we could establish definitive phenotypes. We analyzed the reading frame predicted by exons flanking those in which nonsense mutations were found, and present evidence that nonsense mutations resulting in BMD likely do so by inducing exon skipping, confirming that exonic point mutations affecting exon definition have played a significant role in determining phenotype. We present a new model based on the combination of exon definition and intronic splicing regulatory elements for the selective association of BMD nonsense mutations with a subset of DMD exons prone to mutation-induced exon skipping.

Clinical and genetic characterization of manifesting carriers of DMD mutations.

Manifesting carriers of DMD gene mutations may present diagnostic challenges, particularly in the absence of a family history of dystrophinopathy. We review the clinical and genetic features in 15 manifesting carriers identified among 860 subjects within the United Dystrophinopathy Project, a large clinical dystrophinopathy cohort whose members undergo comprehensive DMD mutation analysis. We defined manifesting carriers as females with significant weakness, excluding those with only myalgias/cramps. DNA extracted from peripheral blood was used to study X-chromosome inactivation patterns. Among these manifesting carriers, age at symptom onset ranged from 2 to 47 years. Seven had no family history and eight had male relatives with Duchenne muscular dystrophy (DMD). Clinical severity among the manifesting carriers varied from a DMD-like progression to a very mild Becker muscular dystrophy-like phenotype. Eight had exonic deletions or duplications and six had point mutations. One patient had two mutations (an exonic deletion and a splice site mutation), consistent with a heterozygous compound state. The X-chromosome inactivation pattern was skewed toward non-random in four out of seven informative deletions or duplications but was random in all cases with nonsense mutations. We present the results of DMD mutation analysis in this manifesting carrier cohort, including the first example of a presumably compound heterozygous DMD mutation. Our results demonstrate that improved molecular diagnostic methods facilitate the identification of DMD mutations in manifesting carriers, and confirm the heterogeneity of mutational mechanisms as well as the wide spectrum of phenotypes.

Mutational spectrum of DMD mutations in dystrophinopathy patients: application of modern diagnostic techniques to a large cohort.

Mutations in the DMD gene, encoding the dystrophin protein, are responsible for the dystrophinopathies Duchenne Muscular Dystrophy (DMD), Becker Muscular Dystrophy (BMD), and X-linked Dilated Cardiomyopathy (XLDC). Mutation analysis has traditionally been challenging, due to the large gene size (79 exons over 2.2 Mb of genomic DNA). We report a very large aggregate data set comprised of DMD mutations detected in samples from patients enrolled in the United Dystrophinopathy Project, a multicenter research consortium, and in referral samples submitted for mutation analysis with a diagnosis of dystrophinopathy. We report 1,111 mutations in the DMD gene, including 891 mutations with associated phenotypes. These results encompass 506 point mutations (including 294 nonsense mutations) and significantly expand the number of mutations associated with the dystrophinopathies, highlighting the utility of modern diagnostic techniques. Our data supports the uniform hypermutability of CGA>TGA mutations, establishes the frequency of polymorphic muscle (Dp427m) protein isoforms and reveals unique genomic haplotypes associated with "private" mutations. We note that 60% of these patients would be predicted to benefit from skipping of a single DMD exon using antisense oligonucleotide therapy, and 62% would be predicted to benefit from an inclusive multiexonskipping approach directed toward exons 45 through 55.

Wilson's disease: a great masquerader.

BACKGROUND: Wilson's disease (WD) is a treatable autosomal recessive metabolic disorder which could lead to protean hepatic or neurologic manifestations. WD could mimic many neurologic disorders and is often diagnosed with a long delay. This study describes central nervous system manifestations of a group of Iranian patients with neurologic WD. METHODS: Data from case records of patients with neurologic WD presenting at a referral university hospital and a private clinic in Tehran from 1984 to 2004 were analyzed. RESULTS: Fifty patients from 44 unrelated families with WD were identified, whose mean duration of follow-up was 51.8 (+/-58.5) months. The median age of onset of neurologic symptoms in 37 patients with primary neurologic or simultaneous hepatic-neurologic presentation was 16 (10-38) years, whereas in 13 patients with prior hepatic damage, this was 18.5 (11-34) years. The 6 most common manifestations were dysarthria (80%), drooling (48%), tremor in limbs (44%), abnormal gait (44%), psychiatric and/or sleep symptoms (44%), and dystonia in limbs (42%). CONCLUSION: Neurologic WD has heterogeneous manifestations and should be considered in young patients presenting with dysarthria, drooling, any kind of movement disorders or psychiatric symptoms.