Congenital myotonic dystrophy transmitted from an asymptomatic father with a DM-specific gene

We present the first report of paternal transmission of congenital myotonic dystrophy (DM). The patients had typical congenital DM and showed unstable CTG repeats on Southern blot analysis. The mother had no expansion of the DM gene, but the asymptomatic father had minimal expansion of the CTG repeats.