Semidominant inheritance has been documented in other human disease traits, such as achondroplasia (ACH; point mutation of FGFR3; MIM: 100800) and Huntington disease (HTT triplet-repat polyglutamine expansion; MIM: 143100), and in gene duplication traits such as that resulting from CMT1A duplication.58 This evidence concerns the gene FGFR3 and juvenile Huntington disease.