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.

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.

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.