Foremost amongst these is phosphatase and tensin holog (PTEN), inactivating mutations of which cause increased head circumference, a core feature of all the PTEN-associated syndromes, such as Bannayan Riley Ruvalcaba syndrome (MIM 153480) and Cowden syndrome (MIM 158350) (9). The gene discussed is PTEN; the disease is Bannayan-Riley-Ruvalcaba syndrome.