Megalencephaly-capillary malformation syndrome (MCAP) is a disorder characterized by overgrowth of several tissues in the body. Its primary features are a large brain (megalencephaly) and abnormalities of small blood vessels in the skin called capillaries (capillary malformations).

MCAP is caused by mutations in the PIK3CA gene, which provides instructions for making the p110 alpha (p110α) protein. This protein is one piece (subunit) of an enzyme called phosphatidylinositol 3-kinase (PI3K), which plays a role in chemical signaling within cells. PI3K signaling is important for many cell activities, including cell growth and division (proliferation), movement (migration) of cells, and cell survival. These functions make PI3K important for the development of tissues throughout the body, including the brain and blood vessels.

The prevalence of MCAP is unknown. At least 150 affected individuals have been reported in the medical literature. Because the condition is often thought to be misdiagnosed or underdiagnosed, it may be more common than reported.

MCAP is not inherited from a parent and does not run in families. In people with MCAP, a PIK3CA gene mutation arises randomly in one cell during the early stages of development before birth. As cells continue to divide, some cells will have the mutation and other cells will not. This mixture of cells with and without a genetic mutation is known as mosaicism.

Published Date: June 01, 2017
Published By: National Institutes of Health