Myotonic Dystrophy and the Heart A Review
Myotonic Dystrophy (Dystrophia Myotonica, DM) is the most frequently inherited neuromuscular disease of adult life. DM is a multisystem disease with major cardiac involvement. Core features of myotonic dystrophy are myotonia, muscle weakness, cataract, and cardiac conduction abnormalities. Classical DM (first described by Steinert and called Steinert’s disease or DM1) has been identified as an autosomal dominant disorder associated with the presence of an abnormal expansion of a CTG tri nucleotide repeat on chromosome 19q13.3 (the DM 1 locus). DM1 is inherited in an autosomal dominant pattern. And the underlying mutation is an unstable expansion of CTG repeats in the 3′ untranslated region (3′UTR) of the dystrophia myotonica protein kinase gene (DMPK, MIM* 605377) and in the promoter of the downstream SIX homeobox 5 gene (SIX5, MIM* 600963).Based on the nature of the causing mutation, DM1 belongs to “disorders of unstable repeat expansion”. Being the first disease described with an RNA gain-of-function mutation effect, DM1 is now the paradigm for RNA toxicity model of the disease pathogenesis, as reviewed elsewhere.