Megacystis-microcolon-intestinal hypoperistalsis syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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.

Some 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.

After 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.

The 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.

Another 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.

The life expectancy of people with MMIHS is shorter than normal, often due to malnutrition, overwhelming infection (sepsis), or the failure of multiple organs.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

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.

ACTG2 gene mutations lead to production of an altered γ-2 actin protein. These changes hinder the formation of actin filaments, which impairs the ability of smooth muscle in the bladder and intestines to contract. These problems with muscle contractions impair the release of urine and the movement of food through the intestines, leading to the key features of MMIHS.

Mutations in other genes have been found to cause rare cases of MMIHS. The proteins produced from these genes are also involved in smooth muscle contraction. Approximately 10 percent of people with MMIHS do not have a mutation in one of the identified genes. It is likely that additional genes that have not been identified are also involved in the disorder.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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.

When caused by mutations in other identified genes, MMIHS is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abdominal distention · Very frequent (99-80%)

Distention of the abdomen.

Hypoperistalsis · Very frequent (99-80%)

Reduced or inadequate peristalsis, with resultant slow passage of contents through the digestive tract.

Megacystis · Very frequent (99-80%)

Dilatation of the bladder postnatally.

Microcolon · Very frequent (99-80%)

A colon of abnormally small caliber.

Nausea and vomiting · Very frequent (99-80%)

Nausea is a commonly encountered symptom that has been defined as an unpleasant painless subjective feeling that one will imminently vomit. Vomiting has been defined as the forceful expulsion of the contents of the stomach, duodenum, or jejunum through the oral cavity. While nausea and vomiting are often thought to exist on a temporal continuum, this is not always the case. There are situations when severe nausea may be present without emesis and less frequently, when emesis may be present without preceding nausea.

Abnormality of the gastrointestinal tract · Frequent (79-30%)

An abnormality of the gastrointestinal tract.

Hydroureter · Frequent (79-30%)

The distention of the ureter with urine.

Intestinal malrotation · Frequent (79-30%)

An abnormality of the intestinal rotation and fixation that normally occurs during the development of the gut. This can lead to volvulus, or twisting of the intestine that causes obstruction and necrosis.

Other findings in the same source

From: Orphanet

Additional reported features include Multicystic kidney dysplasia (Frequent (79-30%)); Polyhydramnios (Frequent (79-30%)); Abnormal cardiovascular system morphology (Occasional (29-5%)); Cryptorchidism (Occasional (29-5%)); Death in infancy (Occasional (29-5%)); Neoplasm of the heart (Occasional (29-5%)); Omphalocele (Occasional (29-5%)); Sepsis (Occasional (29-5%)); Umbilical hernia (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Megacystis-microcolon-intestinal hypoperistalsis syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Megacystis-microcolon-intestinal hypoperistalsis syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.