A definitive diagnosis of CADASIL is established through genetic testing that identifies mutations in the NOTCH3 gene, resulting in an abnormal number of cysteine residues (typically five or seven) in one of the EGFr domains of the NOTCH3 protein, which is particularly prominent in the vascular smooth muscle cells in the brain, confirming the consensus on CADASIL diagnosis [5]. This evidence concerns the gene NOTCH3 and CADASIL.