CARASIL (Cerebral Autosomal Recessive Arteriopathy with Subcortical Infarcts and Leukoencephalopathy) is a rare genetic disorder caused by mutations in the HTRA1 gene. It is an autosomal recessive disorder, meaning that both parents must carry the mutated gene in order for their child to be affected. The HTRA1 gene is responsible for producing an enzyme that helps to break down proteins in the body. When this enzyme is not functioning properly, proteins can build up in the walls of the arteries, leading to narrowing and hardening of the arteries. This can cause a decrease in blood flow to the brain, leading to stroke-like symptoms. Other symptoms of CARASIL include cognitive decline, dementia, and movement disorders.