CYP27A1 and cerebrotendinous xanthomatosis: Cerebrotendinous xanthomatosis (CTX) is an autosomal recessive disorder of lipid metabolism caused by pathogenic variants in theCYP27A1gene (OMIM 213700).66This results in reduced activity of sterol 27-hydroxylase, leading to the accumulation of lipids in tissues, particularly in the brain, eye lenses, and tendons.67, 68The estimated prevalence of CTX is ∼ 1 in 50,000 individuals.67