Monoallelic cysteine-altering NOTCH3 (NOTCH3cys) variants cause the adult-onset small vessel disease cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and biallelic NOTCH3 loss-of-function (NOTCH3lof) variants cause a rare, childhood-onset small vessel disease. The gene discussed is NOTCH3; the disease is Childhood onset.