ACTG2 and megacystis-microcolon-intestinal hypoperistalsis syndrome 1: The etiology of MMIHS is heterozygous, and most cases are autosomal-dominant sporadic and caused by de novo heterozygous variants in the ACTG2 (actin, gamma 2) gene, which encodes actin gamma as a component of the cytoskeleton and a mediator of internal cell motility [7].