Myotonic Dystrophy 1; Dm1

Description

Myotonic dystrophy is an autosomal dominant disorder characterized mainly by myotonia, muscular dystrophy, cataracts, hypogonadism, frontal balding, and ECG changes. The genetic defect in DM1 results from an amplified trinucleotide repeat in the 3-prime untranslated region of a protein kinase gene. Disease severity varies with the number of repeats: normal individuals have 5 to 37 repeats, mildly affected persons have 50 to 150 repeats, patients with classic DM have 100 to 1,000 repeats, and those with congenital onset can have more than 2,000 repeats. The disorder shows genetic anticipation, with expansion of the repeat number dependent on the sex of the transmitting parent. Alleles of 40 to 80 repeats are usually expanded when transmitted by males, whereas only alleles longer than 80 repeats tend to expand in maternal transmissions. Repeat contraction events occur 4.2 to 6.4% of the time (Musova et al., 2009). Genetic Heterogeneity of Myotonic DystrophySee also myotonic dystrophy-2 (DM2 ), which is caused by mutation in the ZNF9 gene (OMIM ) on chromosome 3q21.

Clinical Features

• Intellectual disability
• Seizures
• Generalized hypotonia
• Muscle weakness
• Muscular hypotonia
• Pain
• Cataract
• Ptosis
• Cognitive impairment
• Delayed speech and language development

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