A variety of rare disorders may influence the selection and conduct of anesthesia (Table 23-1: Coexisting Diseases that Influence Anesthesia Management) (Dierdorf SF, Walton JS. Anesthesia for patients with rare coexisting diseases. In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Ortega R, Stock MC, eds.Clinical Anesthesia. Philadelphia: Lippincott Williams & Wilkins; 2013:612–640). Advances in molecular medicine continue to clarify disease mechanisms and provide the basis for new therapies.