Congenital myotonic dystrophy is a multisystem disorder characterized by hypotonia, generalized muscle weakness, respiratory intolerance, feeding issues, and joint contractures in the neonatal period. Most cases are maternally transmitted due to an abnormal trinucleotide (CTG) repeat expansion of the DMPK gene. In this article, the author reviews the clinical features of children with congenital myotonic dystrophy. The extramuscular manifestations, including cardiac arrhythmias, cognitive impairment, , and maladaptive behaviors, are important challenges for these children. Despite the severe disease phenotype, affected individuals who survive beyond the infancy period generally experience an improvement in their motor function during childhood. Recent natural history data and early results from clinical trials have provided evidence of trial-readiness to examine potential disease-modifying therapies for congenital myotonic dystrophy.
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• Myotonic dystrophy type 1 is an autosomal dominant disorder due to abnormal expansion of trinucleotide repeats in the DMPK gene on chromosome 19q13.3.
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• The severe neonatal form of myotonic dystrophy type 1 is usually associated with 1000 or more CTG repeats, with the mother being the affected parent in the majority of cases.
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• Infants with the severe neonatal form of myotonic dystrophy type 1 present with hypotonia, generalized weakness, respiratory insufficiency, and feeding difficulties at birth.
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• Other potential long-term complications include developmental delay, learning disabilities, behavioral problems, and intellectual disability.
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• 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 (31). 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 (77; 19; 61; 80; 07; 21; 09; 33; 71; 67). 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.