Segmental overgrowth disorders due to of somatic mutations in phosphatidylinositol-4,5-bisphospate 3-kinase, catalytic subunit alpha (PIK3CA), are designated as the PIK3CA-related overgrowth spectrum (PROS), named as a spectrum because of their clinical diversity. Over the past 10 years, there have been a tremendous number of reports of various segmental overgrowth disorders. Recently, somatic activating mutations in the phosphatidylinositol-3-kinase (PI3K)/Protein Kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway have been reported in several of these segmental overgrowth conditions. Whereas AKT3 is expressed most strongly in the nervous system, the other genes implicated in these syndromes including AKT1, PIK3CA, and mTOR have widespread expression and, therefore, more widespread organ involvement. These genes function in the mTOR signaling pathway to control cell growth and metabolism.