One of the most debilitating aspects of CCM is haemorrhagic stroke caused by chronic or acute blood leakage from lesions.2 Our previous work indicated that inhibition of VEGF signalling in KRIT1 hemizygous cells and animals could acutely restore permeability to control levels.14 We hypothesized that the loss of both alleles of Krit1 in Krit1ieKO animals would have a more profound impact on vascular permeability, which could be reversed by inhibition of VEGF signalling. This evidence concerns the gene KRIT1 and hemorrhagic stroke.