ACTG2 and familial visceral myopathy: Visceral myopathy (MIM# 155310) due to ACTG2 pathogenic variants causes gut dysmotility due to smooth muscle dysfunction with phenotypes ranging from cases predominantly affecting the GI tract with typical CIPO features to the megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS), which is characterized by severely disabling defects, such as dysfunctional bowels, reduced intrauterine colon growth (microcolon), and bladder-emptying defects requiring catheterization [43].