Mungan syndrome (MGS) is characterized by chronic intestinal pseudoobstruction (CIPO), megaduodenum, long-segment Barrett esophagus, and cardiac abnormalities of variable severity (summary by Bonora et al., 2015).

Smooth muscle dysfunction syndrome (SMDYS) presents with a recognizable pattern of complications, including congenital mydriasis, patent ductus arteriosus (PDA), pulmonary artery hypertension, aortic and other arterial aneurysms, moyamoya-like cerebrovascular disease, intestinal hypoperistalsis and malrotation, and hypotonic bladder. It is caused by heterozygous mutations of the ACTA2 gene altering the arginine-179 codon (summary by Regalado et al., 2018).

Megacystis-microcolon-intestinal hypoperistalsis syndrome-4 (MMIHS4) is a severe early-onset disorder characterized by impaired smooth muscle contractility in the bladder and intestines (Kandler et al., 2020). For a discussion of genetic heterogeneity of MMIHS, see 249210.