MVID is caused by loss of function changes (mutations) in myosin Vb (Myo5b) gene, a molecular motor gene that is responsible for traffic of proteins into the brush border of epithelial cells. Most cases of MVID are caused by mutations in Myo5b. However, some patients with MVID with late presentation and milder disease have been reported to have mutations in syntaxin 3, a gene for a SNARE protein that is responsible for vesicle fusion with the membrane.
MVID follows an autosomal recessive pattern of inheritance. Recessive genetic disorders occur when an individual inherits a non-working gene from each parent. If an individual receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the non-working gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier, like the parents, is 50% with each pregnancy. The chance for a child to receive working genes from both parents is 25%. The risk is the same for males and females.
All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder. MVID has been reported in consanguineous families.