The HHD of CCM2 binds the N-terminus of MEKK3, an upstream kinase in the p38 and ERK5 MAP kinase (MAPK) pathways and this interaction appears necessary to prevent hyperactive MEKK3–MEK5–ERK5 signalling which contributes to CCM pathogenesis [70–72]. This evidence concerns the gene CCM2 and cerebral cavernous malformation.