Collectively known as PIK3CA-related overgrowth spectrum (PROS), these disorders differ from PHTS in important respects: PTEN mutations in PHTS are usually found in all cells, most commonly due to germline transmission, while PIK3CA mutations in PROS occur in mosaic form, are disproportionately found in some tissues, and appear not to be compatible with germline transmission. This evidence concerns the gene PIK3CA and PTEN hamartoma tumor syndrome.