CCM2 and cerebral cavernous malformation: Familial CCM lesions form as a consequence of mosaic complete inactivation of CCM1, -2, or -3. Here, we have used Cas9-CRISPR mutagenesis to create such a mosaicism for ccm2 in zebrafish and show that surviving adult ccm2 CRISPR animals develop brain and extracranial lesions that closely resemble those observed in humans with CCM.