Genetic studies conducted over the last 20 years have demonstrated that the hereditary form of CCM is caused by germline heterozygous loss-of-function mutations in one of three known genes: KRIT1 (CCM1), CCM2 and PDCD10 (CCM3) [8,9,10,11,12,13]. The gene discussed is KRIT1; the disease is cerebral cavernous malformation.