Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL, OMIM 600142) is a hereditary cerebral small vessel disease (CSVD) caused by biallelic loss-of-function mutations in high-temperature requirement A serine peptidase 1 (HTRA1), which upregulates the transforming growth factor β1 (TGF-β1) signal (1). The gene discussed is HTRA1; the disease is CARASIL.