Congenital Myotonic Dystrophy

Abstract

In the congenital form of myotonic dystrophy type 1, there is marked hypotonia at birth or in infancy, which is usually progressive in the following years. These children may remain mentally retarded and may present central nervous system involvement (i.e., hydrocephalus or other brain abnormalities).

In the severely affected cases, CTG triplet repeat expansions in the DMPK gene (Table 53.1) are more than 1000, and myotonia is not a common feature. Muscle biopsy in the congenital forms frequently shows striking similarities with myotubular myopathy; thus, DM1 should always be molecularly excluded if central nuclei are abundant in a biopsy from a neonate. The family history can be mute, since the mother could be pauci-symptomatic. The father usually does not transmit the disease because sperms with large CTG triplet expansions are not viable.