Microvillus inclusion disease

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Microvillus inclusion disease is a condition characterized by chronic, watery, life-threatening diarrhea typically beginning in the first hours to days of life. Rarely, the diarrhea starts around age 3 or 4 months. Food intake increases the frequency of diarrhea.

Microvillus inclusion disease prevents the absorption of nutrients from food during digestion, resulting in malnutrition and dehydration. Affected infants often have difficulty gaining weight and growing at the expected rate (faltering weight), developmental delay, liver and kidney problems, and thinning of the bones (osteoporosis). Some affected individuals develop cholestasis, which is a reduced ability to produce and release a digestive fluid called bile. Cholestasis leads to irreversible liver disease (cirrhosis).

In individuals with microvillus inclusion disease, lifelong nutritional support is needed and given through intravenous feedings (parenteral nutrition).

A variant of microvillus inclusion disease with milder diarrhea often does not require full-time parenteral nutrition. Individuals with the variant type frequently live past childhood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the MYO5B gene cause microvillus inclusion disease. The MYO5B gene provides instructions for making a protein called myosin Vb. This protein helps to determine the position of various components within cells (cell polarity). Myosin Vb also plays a role in moving components from the cell membrane to the interior of the cell for recycling.

MYO5B gene mutations that cause microvillus inclusion disease result in a decrease or absence of myosin Vb function. In cells that line the small intestine (enterocytes), a lack of myosin Vb function changes the cell polarity. As a result, enterocytes cannot properly form structures called microvilli, which normally project like small fingers from the surface of the cells and absorb nutrients and fluids from food as it passes through the intestine. Inside affected enterocytes, small clumps of abnormal microvilli mix with misplaced digestive proteins to form microvillus inclusions, which contribute to the dysfunction of enterocytes. Disorganized enterocytes with poorly formed microvilli reduce the intestine's ability to take in nutrients. The inability to absorb nutrients and fluids during digestion leads to recurrent diarrhea, malnutrition, and dehydration in individuals with microvillus inclusion disease.

Some people with the signs and symptoms of microvillus inclusion disease do not have mutations in the MYO5B gene. These cases may be variants of microvillus inclusion disease. Studies suggest that mutations in other genes can cause these cases, but the causes are usually unknown.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition 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

The prevalence of microvillus inclusion disease is unknown. At least 200 cases have been reported in Europe, although this condition occurs worldwide.

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 · Frequent (79-30%)

Distention of the abdomen.

Abnormal renal physiology · Frequent (79-30%)

An abnormal functionality of the kidney.

Diarrhea · Frequent (79-30%)

Abnormally increased frequency (usually defined as three or more) loose or watery bowel movements a day.

Global developmental delay · Frequent (79-30%)

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Hypovolemia · Frequent (79-30%)

An decrease in the amount of intravascular fluid, particularly in the volume of the circulating blood.

Metabolic acidosis · Frequent (79-30%)

Metabolic acidosis (MA) is characterized by a fall in blood pH due to a reduction of serum bicarbonate concentration. This can occur as a result of either the accumulation of acids (high anion gap MA) or the loss of bicarbonate from the gastrointestinal tract or the kidney (hyperchloremic MA). By definition, MA is not due to a respirary cause.

Nephrocalcinosis · Frequent (79-30%)

Nephrocalcinosis is the deposition of calcium salts in renal parenchyma.

Pruritus · Frequent (79-30%)

Pruritus is an itch or a sensation that makes a person want to scratch. This term refers to an abnormally increased disposition to experience pruritus.

Other findings in the same source

From: Orphanet

Additional reported features include Villous atrophy (Frequent (79-30%)); Abnormality of small intestinal villus morphology (Frequent (79-30%)); Dehydration (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Microvillus inclusion disease is Gastroenterology, with a gastroenterologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

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.

• Which digestive symptoms or nutritional changes matter most?
• What question would an endoscopy, scan or laboratory test answer if one is proposed?
• How should persistent pain, bleeding or difficulty eating be followed up?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Microvillus inclusion disease. 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.

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.