Tendon involvement in inherited metabolic disorders is not limited to xanthomata in CTX and may also occur in familial hypercholesterolaemia type 3 (PCSK9), sitosterolemia (ABCG8), ataxia with vitamin E deficiency (TTPA), hyperlipoproteinemia type III (APOE), primary hypoalphalipoproteinemia type 2 (APOA1), Alagille syndrome (JAG1), and rarely in congenital hypophosphatasia, ochronosis and galactosemia (21). The gene discussed is PCSK9; the disease is sitosterolemia.