Homozygous myotonic dystrophy with craniosynostosis.

Myotonic dystrophy is considered a true dominant condition with no difference in the phenotype between heterozygous and homozygous cases. The homozygous state is very rare and only a few patients have been reported in the literature. We report a 2.5-year-old boy from a nonconsanguineous marriage, with a unique combination of clinical and radiological findings: hypotonia, motor and language developmental delay, ventriculomegaly, subcortical white matter lesions, and craniosynostosis. Mutation analysis revealed 2 copies of expansion mutation of 1260 and 60 cytosine-thymine-guanine repeats in the myotonic dystrophy protein kinase gene. Both the mildly symptomatic (434 repeats) mother and the asymptomatic (37 repeats) father are heterozygous. Craniosynostosis has not been reported previously in myotonic dystrophy. This homozygous case expands the clinical spectrum of myotonic dystrophy type 1 and provides support to the hypothesis that myotonic dystrophy type 1 pathophysiology could be, in part, due to the loss of normal function of the wild-type protein.