CTSA and Leukoencephalopathy: Monogenic CSVD has been proven to be caused by specific genetic mutations, including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) (14, 15), cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) (15), COL4A1/2-related CSVD (16–18), Fabry's disease (19), retinal vasculopathy with cerebral leukodystrophy (RVCL) (14), and cathepsin A–related arteriopathy with strokes and leukoencephalopathy (CARASAL) (20).