HTT and Huntington disease: However, the consistency between the trinucleotide repeat instability in patients’ tissues and those in iPSCs is still not clear in other triplet repeat diseases, such as Huntington disease (HD), caused by CAG repeat expansion in the Huntingtin (HTT) gene, and myotonic dystrophy (DM1), caused by CTG repeat expansion in the 3′ UTR of the DMPK gene, both of which exhibit somatic instability of the repeats, and significant anticipation [30].