Megacystis–microcolon–intestinal hypoperistalsis syndrome (MMIHS) due to a de novo ACTG2 mutation: A neonatal case report

Background Megacystis–microcolon–intestinal hypoperistalsis syndrome (MMIHS) is a rare congenital visceral myopathy characterized by severe gastrointestinal dysmotility and bladder dysfunction, most commonly associated with ACTG2- mutations. Case report We report a preterm neonate with prenatally detected megacystis and a de novo heterozygous ACTG2 variant (c.593G>T; p.Gly198Val). Postnatally, the patient developed progressive abdominal distension and feeding intolerance. Imaging demonstrated dilated bowel loops and microcolon. Exploratory laparotomy on day 5 confirmed dilated ileum, microcolon, and massive megacystis without mechanical obstruction. Gastrostomy and ileostomy were performed. The patient required parenteral nutrition followed by gradual enteral feeding with stool recirculation. Clean intermittent catheterization and antibiotic prophylaxis were initiated. Conclusion MMIHS should be suspected in cases of fetal megacystis. Early genetic diagnosis and multidisciplinary management, including intestinal failure rehabilitation and urological care, are essential to improve outcomes.