Notably, while all cases affected by clinical and neuroradiological signs of CCM disease were confirmed to be heterozygous carriers for the KRIT1 c.1664C>T variant, an adult male of 42 y (III.3) and a male child of 20 y (IV.2) were found to be carriers but they currently had no clinical symptoms and showed a normal MRI, thus confirming the incomplete penetrance of pathogenic germline mutations in KRIT1. The gene discussed is KRIT1; the disease is cerebral cavernous malformation.