Dysfunction in the PI3K pathway causes a spectrum of related megalencephaly syndromes.
A number of overgrowth syndromes affecting tissues of multiple lineages have been linked to specific mutations that can occur postzygotically and involve only diseased tissue. Investigators of two recent studies examined the overgrowth syndromes that affect the brain. Megalencephaly-capillary malformation (MCAP) is associated with skeletal overgrowth and vascular malformations that meet criteria for Klippel-Trenaunay syndrome; hemimegalencephaly (HME) is associated with hypomelanosis of Ito and Proteus syndrome.