What is M-CM?

M-CM stands for macrocephaly-capillary malformation. It is a rare genetic syndrome that causes irregular growth in parts of the body and the brain. Specific effects and severity vary from person to person, but common characteristics are brain overgrowth, hypotonia (low muscle tone), and developmental delays. Many patients also have vascular birthmarks and body asymmetry.

Genetic Cause

M-CM is caused by mutations in a gene called PIK3CA that increase the activity of the gene. In most cases, these mutations happen spontaneously after conception, so that the gene is changed in a percentage of the body's cells. There are currently no known cases of inheritance. M-CM is one of many conditions caused by changes in PIK3CA and is part of a group of conditions known as PIK3CA-related overgrowth spectrum or PROS.

Many Names

This condition was first defined in 1997 as M-CMTC for macrocephaly-cutis marmorata telangiectatica congenita. In 2007, M-CM for macrocephaly-capillary malformation was proposed to more accurately describe the vascular involvement. A newer name, MCAP for megalencephaly-capillary malformation was proposed in a 2012 paper that is now widely used in genetics literature. These names, along with other variations, all refer to the same condition.


cover of 2024 calendar with faces of many M-CM patients in a grid

2024 M-CM Network Wall Calendar

Our 2024 calendar is available for purchase from print-on-demand service Lulu.com. It is a beloved community project featuring photos from patient families all over the world. Get yours now »

picture of boxes of Vijoice for 250mg 125mg and 50mg doses

First FDA approved treatment for PROS conditions

The U.S. Food and Drug Administration granted accelerated approval for Novartis’ PI3K inhibitor Vijoice (alpelisib) for use in PIK3CA-related overgrowth spectrum (PROS), including M-CM / MCAP patients. Learn more »

photo of two t-shirts, a blue shirt says MIGHTY RARE and a grey shirt says I heart SOMEONE WITH M-CM

Wear That You Care

Visit our Bonfire storefront for a selection of t-shirts to spread awareness about rare disease and M-CM / MCAP. A portion of sales benefit the M-CM Network. Shop now »

Newly diagnosed?

Join our contact registry.

This lets us keep you informed of new discoveries and opportunities to participate in research and clinical trials. It also helps us to know how many M-CM patients there are, and where they are. Join now.

Connect with the community.

The online patient community is a rich source of support and information. Groups on Facebook include

Get involved.

Patients can advance research by contributing tissue samples and enrolling in research studies and clinical trials. Learn about ways to fundraise for the M-CM Network, or let us know how you would like to help.