The MYO5B gene provides instructions for making a protein called myosin Vb. This protein is one of a group of proteins with similar structures called myosins, which are involved in cell movement and the transport of materials within and between cells. Myosin Vb 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.
More than 40 mutations in the MYO5B gene have been found to cause microvillus inclusion disease. This condition is characterized by chronic, life-threatening diarrhea beginning in infancy. The MYO5B gene mutations that cause this condition 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 and fluids. The inability to absorb nutrients and fluids during digestion leads to severe diarrhea, malnutrition, and dehydration in individuals with microvillus inclusion disease.
- MYO5B variant protein
- unconventional myosin-Vb