Heterozygous germline loss-of-function variants in one of the three genes CCM1/KRIT1 (MIM 604214), CCM2/OSM/Malcavernin (MIM 607929), or CCM3/PDCD10 (MIM 609118) can be found in the vast majority of familial CCM cases (5). This evidence concerns the gene KRIT1 and cerebral cavernous malformation.