Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is a severe disorder affecting the muscles that line the bladder and intestines. It is characterized by impairment of the muscle contractions that move food through the digestive tract (peristalsis) and empty the bladder.

MMIHS can be caused by mutations in one of several genes, the most studied of which is ACTG2. The ACTG2 gene provides instructions for making a protein called gamma (γ)-2 actin. The γ-2 actin proteins organize into filaments that are important for the tensing of muscle fibers (muscle contraction), specifically contraction of smooth muscles of the urinary and intestinal tracts. These contractions empty urine from the bladder and move food through the intestines.

MMIHS is a rare disorder. More than 200 cases have been reported in the medical literature.

When caused by ACTG2 gene mutations, MMIHS follows an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. These cases result from new (de novo) mutations in the gene that occur during the formation of reproductive cells (eggs or sperm) or in early embryonic development. In these cases, affected individuals have no history of the disorder in their family.

Published Date: October 01, 2017
Published By: National Institutes of Health