The CTG repeat size of the DMPK in the affected child was significantly greater when the DMPK repeats were transmitted from a female parent to a female child (DM1-FF) (median, 1309 repeats; range, 400–2083) than when they were transmitted from a male parent to a male child (DM1-MM) (650; 160–1030; p = 0.038 and 0.048 using the Tukey HSD and the Bonferroni test) or from a male parent to a female child (DM1-MF) (480; 94–1140; p = 0.003) (Figure 1a). Here, DMPK is linked to myotonic dystrophy type 1.