COL4A1 and CADASIL: Different monogenic cerebral SVD were discovered (Table 1), including cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) [27], cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) [28,29], cathepsin A–related arteriopathy with strokes and leukoencephalopathy (CARASAL) [30], hereditary diffuse leukoencephalopathy with spheroids (HDLS) [31], COL4A1/2-related cerebral SVD [27,32,33], autosomal-dominant retinal vasculopathy with cerebral leukodystrophy, and Fabry disease.