Myotonic muscular dystrophy (neonatal)

Jean K Mah MD (Dr. Mah of the University of Calgary has no relevant financial relationships to disclose.)
Harvey B Sarnat MD FRCPC MS, editor. (Dr. Sarnat of the University of Calgary has no relevant financial relationships to disclose.)
Originally released April 2, 2002; last updated May 4, 2017; expires May 4, 2020

This article includes discussion of myotonic muscular dystrophy (neonatal), congenital myotonic dystrophy, dystrophia myotonica of the newborn, and infantile myotonic dystrophy. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Congenital myotonic dystrophy is a severe multisystem disorder characterized by hypotonia, generalized muscle weakness, and joint contractures in affected infants. It is usually transmitted via mothers with type 1 myotonic dystrophy (DM1) due to abnormal CTG repeat expansion of the DMPK gene on chromosome 19q13. Barbé and colleagues proposed that higher levels of methylation flanking the CTG repeat may account for the maternal bias in transmission as well as earlier age at onset of the disease (Barbé et al 2017). In this article, the author reviews the clinical features of children with congenital DM1. The extramuscular manifestations, including cardiac arrhythmias, cognitive impairment, communication problems, and maladaptive behaviors, are important challenges for the affected individuals and their caregivers. Early diagnosis and ongoing supportive care are required to ensure optimal outcomes.

Key points

 

• Myotonic dystrophy type 1 (DM1) is an autosomal dominant disorder due to abnormal expansion of trinucleotide repeats in the DMPK gene on chromosome 19q13.3.

 

• The severe neonatal form of DM1 is usually associated with 2000 or more CTG repeats, with the mother being the affected parent in the majority of cases.

 

• Infants with the severe neonatal form of DM1 present with hypotonia, generalized weakness, respiratory insufficiency, and feeding difficulties at birth.

 

• Other potential long-term complications include developmental delay, learning disabilities, behavioral problems, and mental retardation.

 

• A multidisciplinary team approach is needed to address the supportive needs of affected children and their families.

Historical note and terminology

In 1901 a rare, severe neonatal form of the already recognized disease of myotonic muscular dystrophy was first described by Gardiner (Gardiner 1901). The clinical presentation was better defined in the 1960s and 1970s by several authors and was distinguished from the more common, slowly progressive disease of the older child and adult, though occurring in the same families (Vanier 1960; Dodge et al 1965; Pruzanski 1966; Watters and Williams 1967; Bell 1972; Dyken and Harper 1973; Bossen et al 1974; Harper 1975; Swift et al 1975; Sarnat et al 1976). Harper pointed out that in 94% of affected neonates of both sexes, the mother was the transmitting parent despite autosomal dominant inheritance that theoretically should not be gender-specific. Additional genetic studies in the early 1990s clarified the reason as a large number of trinucleotide repeats in the defective gene of type 1 myotonic dystrophy.

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