Monogenic stroke was thought to be rare, with an estimated prevalence of CADASIL of 4 per 100 000 in the United Kingdom.3 However, recent studies have reported pathogenic variants are more prevalent in the general population,4 with typical NOTCH3 variants present in 1 in 452 individuals5 and HTRA1 variants in 1 in 275.6 This evidence concerns the gene NOTCH3 and CADASIL.