Congenital megabladder (MGBL) is characterized by a massively dilated bladder with disrupted smooth muscle in the bladder wall. MGBL is a sex-limited trait with 95% male predominance, likely the result of differences in urethra and bladder development and length differences in urethra between males and females (Houweling et al., 2019).

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.\n\nSome of the major features of MMIHS can be recognized before birth using ultrasound imaging. Affected fetuses have an enlarged bladder (megacystis) because it does not empty. In addition, the large intestine (colon) is abnormally narrow (microcolon) because of a shortage of functional muscle lining it. Intestinal and bladder problems persist throughout life.\n\nAfter birth, the continued impairment of peristalsis (hypoperistalsis) often causes a digestive condition called intestinal pseudo-obstruction. This condition, which mimics a physical blockage (obstruction) of the intestines but without an actual blockage, leads to a buildup of partially digested food in the intestines. This buildup can cause abdominal swelling (distention) and pain, nausea, and vomiting. The vomit usually contains a green or yellow digestive fluid called bile. Because digestion is impeded and the body does not get the nutrients from food, nutritional support is usually needed, which is given through intravenous feedings (parenteral nutrition). While some affected individuals rely solely on intravenous feedings, others require it only on occasion. Long-term use of parenteral nutrition can lead to liver problems.\n\nThe reduced ability to pass urine also contributes to painful distention of the abdomen. Many people with MMIHS require placement of a tube (urinary catheter) to remove urine from the bladder.\n\nAnother abnormality in some people with MMIHS is intestinal malrotation, in which the intestines do not fold properly. Instead, they twist abnormally, often causing a blockage. Individuals with MMIHS can also develop problems with the kidneys or the ureters, which are the ducts that carry urine from the kidneys to the bladder.\n\nThe life expectancy of people with MMIHS is shorter than normal, often due to malnutrition, overwhelming infection (sepsis), or the failure of multiple organs.

Megacystis-microcolon-intestinal hypoperistalsis syndrome-2 (MMIHS2) is characterized by prenatal bladder enlargement, neonatal functional gastrointestinal obstruction, and chronic dependence on total parenteral nutrition and urinary catheterization. The majority of cases have a fatal outcome due to malnutrition and sepsis, followed by multiorgan failure (summary by Wang et al., 2019). For a discussion of genetic heterogeneity of MMIHS, see 249210.

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a rare congenital defect of visceral smooth muscle, primarily affecting females who present at birth with functional obstruction of the intestine, microcolon, dilation of the bladder, and secondary hydronephrosis. Total parenteral nutrition, adequate intermittent catheterization of bladder, and surgical corrections for intestinal malrotation are frequent modes of treatment for this disease without which rapid death ensues. In some instances, multivisceral organ transplantation has been undertaken with some success. Despite these clinical interventions, MMIHS often leads to premature death due to complications of therapy (summary by Halim et al., 2017). For a discussion of genetic heterogeneity of MMIHS, see 249210.