Cerebrotendinous xanthomatosis (CTX), a rare neurodegenerative disorder caused by autosomal recessive mutations in the CYP27A1 gene, exhibits infantile-onset diarrhoea, juvenile-onset cataracts, young adult-onset tendon xanthomas, progressive neurological dysfunction and so on [116, 117]. The gene discussed is CYP27A1; the disease is cerebrotendinous xanthomatosis.