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MYO5B gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

MYO5B gene

The MYO5B gene provides instructions for making myosin Vb, a protein essential for maintaining cell polarity and recycling cell membrane components.

Normal Function

The MYO5B gene provides instructions for making a protein called myosin Vb. This protein is part of a group of myosins involved in cell movement and the transport of materials within and between cells. Myosin Vb helps determine the position of various components within cells, a process known as cell polarity. It also plays a role in moving components from the cell membrane to the interior of the cell for recycling.

Health Conditions Related to Genetic Changes

Microvillus inclusion disease

More than 40 mutations in the MYO5B gene have been found to cause microvillus inclusion disease, a condition characterized by chronic, life-threatening diarrhea beginning in infancy. The mutations 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 cell polarity. This leads to several issues:

  • Enterocytes cannot properly form microvilli, which are finger-like projections that absorb nutrients and fluids.
  • Small clumps of abnormal microvilli mix with misplaced digestive proteins inside the cells to form microvillus inclusions.
  • The intestine's ability to absorb nutrients and fluids is significantly reduced, leading to severe diarrhea, malnutrition, and dehydration.

Frequently Asked Questions

The MYO5B protein is essential for maintaining cell polarity in enterocytes, the cells lining the small intestine. When the gene is mutated, these cells lose their proper orientation and cannot form the finger-like projections called microvilli that are necessary for nutrient absorption. Instead, abnormal clumps of microvilli and misplaced digestive proteins form inside the cells, known as microvillus inclusions. This structural failure drastically reduces the surface area available for absorption, leading to the chronic diarrhea characteristic of the disease.
Treatment depends on the severity of the mutation. Some patients with partial loss of function may respond to medical therapies that reduce fluid loss, while others with complete loss of function may require a small bowel transplant. Long-term management often involves total parenteral nutrition (TPN), where nutrients are delivered directly into the bloodstream via a central line, bypassing the non-functional intestine. This requires careful monitoring for complications such as liver disease and line infections, and regular follow-up with a multidisciplinary team including gastroenterologists and transplant specialists.
The most critical early sign is severe, watery diarrhea that begins within the first few days of life and does not resolve with standard infant feeding. Because the intestine cannot absorb fluids or nutrients, infants are at high risk for rapid dehydration and electrolyte imbalances. Signs of emergency include sunken eyes, dry mouth, lack of tears when crying, lethargy, and significantly reduced urine output. Immediate medical intervention is required to provide intravenous fluids and prevent fatal dehydration.
Yes, parents can have future children, but there is a significant risk of recurrence. Since microvillus inclusion disease is typically inherited in an autosomal recessive pattern, both parents are likely carriers of a mutated copy of the MYO5B gene. There is a 25 percent chance with each pregnancy that the child will be affected. Genetic counseling is strongly recommended, and options such as preimplantation genetic testing (PGT) during IVF or prenatal diagnosis via chorionic villus sampling or amniocentesis can help identify affected embryos or fetuses before birth.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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