Cerebrotendinous xanthomatosis (CTX, OMIM #213700), is a rare autosomal recessive disorder of bile acid synthesis due to variants in the CYP27A1 gene resulting in deficiency of sterol 27-hydroxylase, a key enzyme producing chenodeoxycholic acid (CDCA), which is a primary bile acid [1, 2]. The gene discussed is CYP27A1; the disease is cerebrotendinous xanthomatosis.