Walsh & Hoyt: Hereditary Muscular Dystrophies

Myotonic dystrophy, a relatively common autosomal dominant disorder with a prevalence of 1 in 20,000, is characterized by progressive myopathy, cataracts, cardiomyopathy with conduction defects, and diabetes mellitus. Other classic findings include frontal balding, bifacial weakness, ptosis, and cognitive and psychiatric dysfunction. Less common ophthalmologic manifestations can include ocular hypotonia, external ophthalmoplegia, pigmentary retinopathy, and optic atrophy. Most patients with myotonic dystrophy have an expansion of an unstable CTG repeat in a protein kinase gene on chromosome 19q13.3, although variants of the disease are genetically heterogeneous.