Myotonic Dystrophy Type 1 or Steinert’s Disease

Abstract

Myotonic Dystrophy Type 1 (DM1) is the most common worldwide autosomal dominant muscular dystrophy due to polynucleotide [CTG] _n triplet expansion located on the 3′UTR of chromosome 19q13.3. A toxic gain-of-function of abnormally stored RNA in the nuclei of affected cells is assumed to be responsible for several clinical features of the disease. It plays a basic role in deregulating RNA binding protein levels and in several mRNA splicing processes of several genes, thus leading to the multisystemic features typical of DM1. In DM1, the musculoskeletal apparatus, heart, brain, eye, endocrine, respiratory and gastroenteric systems are involved with variable levels of severity. DM1 onset can be congenital, juvenile, adult or late. DM1 can be diagnosed on the grounds of clinical presentation (distal muscular atrophy and weakness, grip and percussion myotonia, ptosis, hatchet face, slurred speech, rhinolalia), EMG myotonic pattern, EKG (such as AV-blocks) or routine blood test abnormalities (such as increased CK values or hypogamma-globulinemia) and history of cataract. Its confirmation can come by DNA analysis. At present, only symptomatic therapy is possible and is addressed at correcting hormonal and glycemic balance, removing cataract, preventing respiratory failure and, above all, major cardiac disturbances. Efficacious therapies targeted at the pathogenic mechanism of DM1 are not yet available, while studies that seek to block toxic RNA intranuclear storage with specific molecules are still ongoing.