[Clinical features and care of patients with congenital and childhood-onset myotonic dystrophy].

Myotonic dystrophy type 1 (DM1) is an autosomal dominant disorder with variable expression. DM1 results from a trinucleotide expansion in the 3' untranslated region or the gene for myotonic dystrophy protein kinase (DMPK). Severity tends to increase and it shows a younger onset age with vertical transmission, a phenomenon known as anticipation. Congenital myotonic dystrophy (CDM) is classified as the most severe form of DM1, and its phenotype, with severe hypotonia, neonatal respiratory distress and feeding difficulties, is completely different from that of adult-onset type. Involvement of respiratory muscles may be the major cause of mortality in affected infants. Facial weakness with a tented upper lip is often recognized. If infants survive the neonatal period, muscle involvement symptoms gradually improve and most children do not require respiratory support or tube feeding. As CDM patients grow older, mental retardation or a developmental disorder becomes prominent. Furthermore, the main problems in childhood-onset DM, with an onset age under 10 years, are developmental disorders or learning disabilities, rather than muscle symptoms. Early meticulous support and cooperation with teachers are necessary. Medications such as methylphenidate may be helpful in DM1 children with attention deficit/hyperactivity disorder.