Resources » Syndrome Description

Overview

Macrocephaly-capillary malformation (M-CM), also known as megalencephaly-capillary malformation (MCAP) is a multiple malformation syndrome causing body and head overgrowth and abnormalities of the skin, vascular system, brain and limbs.  As of June 2012, the disorder has been attributed to mutations in a gene called PIK3CA.  M-CM / MCAP falls under an umbrella diagnosis of PIK3CA-related overgrowth spectrum (PROS).

The mutations in M-CM usually occur after cell division begins. This is called somatic mosaicism. Patients with somatic mosaicism do not inherit their condition. Individuals with this condition can have varying percentages of cells affected.  There are some patients with genetic test results that show all of their cells affected, which indicates a germline or constitutional mutation, but there are no known cases of inheritance.

A diagnosis of M-CM / MCAP can be made based on clinical observations but most patients are given genetic testing.  Though not every affected individual has all features, commonly found signs include macrocephaly, congenital macrosomia, extensive cutaneous capillary malformations, body asymmetry, extra or fused fingers or toes, lax joints, doughy skin, variable developmental delays and other neurologic problems such as seizures and low muscle tone. 

M-CM was first described in the medical literature in 1997.  At that time it was named macrocephaly-cutis marmorata telangiectatica congenita syndrome (M-CMTC).  The name was changed to macrocephaly-capillary malfromation (M-CM) in 2009. The name megalencephaly-capillary malformation (MCAP), was proposed in 2012. Some patients with clinical signs of M-CM / MCAP are given the umbrella diagnosis of PIK3CA-related overgrowth spectrum (PROS) only. 

The following is a detailed summary of M-CM / MCAP including an explanation of this condition, physical findings, medical issues and treatment options.  Not all patients will have every one of the described problems, and some issues prevalent in the patient community remain poorly characterized.