BACKGROUND: Megacystis microcolon hypoperistalsis syndrome (MMIHS) is a rare condition with high morbidity and mortality. It is characterized by megacystis, microcolon, and intestinal hypoperistalsis leading to various grades of bladder and bowel obstruction.
METHODS: This report describes a pregnant woman with a history of bowel obstruction, urine retention, and heavy postpartum bleeding where ultrasound findings of fetal megacystis during pregnancy led to genetic testing in the family. The fetus, the pregnant woman, and four female family members were heterozygous for a pathogenic variant detected in the ACTG2 gene. The fetus was treated successfully for hydronephrosis using vesicoamniotic shunting.
CONCLUSIONS: Early diagnosis of a fetus with MMIHS is important to secure multidisciplinary prenatal and neonatal treatment. Furthermore, gene testing must be considered when a woman presents a history of pseudo-obstruction and urine retention to prevent complications during pregnancy and labor. Finally, recurrent familial postpartum bleeding should lead to referral to genetic evaluation.

BACKGROUND: Dominant gamma-smooth muscle actin gene (ACTG2) variants cause clinically diverse forms of visceral myopathy. Many patients undergo intestinal resection or biopsy before identification of their genetic defect. The pathology of ACTG2-variant visceral myopathy has not been evaluated systematically.
METHODS: Glass slides, ultrastructural images, molecular genetic reports, and clinical records from 16 patients with pathogenic (15) or likely pathogenic (1) ACTG2 variants were reviewed and compared with surgical specimens from controls (no evidence of a primary myopathy or pseudo-obstruction due to Hirschsprung disease) and published descriptions.
RESULTS: The variable clinical manifestations in our cohort matched those in the literature. Only non-specific light and electron microscopic findings observed in non-myopathic controls were encountered in 13 of 16 patients. The remaining 3 patients harbored hyalinized cytoplasmic inclusions in smooth muscle cells and 1 of them had polyglucosan bodies in the muscularis propria.
CONCLUSIONS: Apart from hyalinized inclusions, which were only observed in 3/16 patients, intestinal pathology in the majority of patients with ACTG2 variants is not indicative of an underlying visceral myopathy. Molecular testing should be considered even when no diagnostic intestinal pathology is identified.