Dystrophie myotonique de type 2

The group of myotonic dystrophies encompasses two distinct autosomal dominant genetic entities: the myotonic dystrophy type 1 (Steinert disease or DM1) and the myotonic dystrophy type 2 (PROMM or DM2). They share similar clinical core features: muscle weakness, myotonia and cataracts. Both are multiorgan disorders. An important distinction is the lack of congenital form in the DM2. The clinical diagnosis of DM2 is more complex than that of DM1. Muscle biopsy may be useful to the diagnosis. Myotonic dystrophy type 2 is caused by a (CCTG) n expansion in intron 1 of the gene encoding the zinc-finger protein (ZFN9) at locus 3q21.3. Non conventional molecular genetics methods are needed for mutation detection due to the extremely large size and somatic instability of the expansion mutation. The multisystemic features might be explained by CCUG expansion expressed at the RNA level.