Megacystis-microcolon-intestinal hypoperistalsis syndrome: evidence of intestinal myopathy.

We investigated small- and large-bowel specimens of three newborn infants presenting with the clinical and radiological symptoms of megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS). Conventional histological staining revealed marked thinning of the longitudinal muscle layer. Electron-microscopic investigations showed typical "central core" vacuolic degeneration of smooth-muscle-cells combined with proliferation of col lagen fibres. The expression of alpha-smooth-muscle actin was absent or markedly reduced in the circular and longitudinal muscle layers and muscularis mucosae compared to the normal controls. These findings suggest that the intestinal obstruction in MMIHS is due to an abnormality of the smooth-muscle cells.