LIG1 and myotonic dystrophy type 1: It is of interest that neither knockout of Lig1 nor the presence of the orthologous Lig1 R771W mutation that reduces ligase activity 20-fold had any impact on the somatic expansion of CAG/CTG repeats in mouse models of HD and myotonic dystrophy type 1 respectively, though the R771W mutation promoted maternal germline contractions (18, 42, 43).