 Misalignments occurring during homologous recombinational repair, double-strand break repair or during other DNA repair processes likely contribute to trinucleotide repeat expansions in DM1.Paternal transmission of the congenital form is uncommon (13%), possibly due to selection pressures against sperm with expanded repeats, but juvenile or adult onset is equally transmitted from either parent.Anticipation tends to be less severe than in cases of maternal inheritance.