Betaine treatment of cystathionine β-synthase-deficient homocystinuria; does it work and can it be improved?

Kenneth N MacleanDepartment of Pediatrics, University of Colorado School of Medicine, Aurora, CO, USAAbstract: Inactivating mutations in cystathionine β-synthase result in classical homocystinuria (HCU) and are typically accompanied by severe elevations of plasma and tissue homocysteine, methionine, S-adenosylmethionine, S-adenosylhomocysteine and significantly decreased cysteine. HCU is usually accompanied by marfanoid skeletal abnormalities, osteoporosis, ectopia lentis and/or severe myopia, cognitive impairment, and a dramatically increased incidence of atherosclerosis and thromboembolic complications of variable presentation. If untreated, HCU is a serious life-threatening disease. Betaine (N,N,N-trimethylglycine) is a zwitterionic quaternary ammonium compound that can lower homocysteine, S-adenosylmethionine, S-adenosylhomocysteine, and increase cysteine in HCU by serving as a methyl donor for the remethylation of homocysteine in a reaction catalyzed by betaine–homocysteine S-methyltransferase. This review considers the clinical efficacy and safety of betaine treatment of HCU. Possible strategies by which the efficacy of this treatment might be improved are discussed.Keywords: homocystinuria, homocysteine, betaine, cystathionine beta-synthase, betaine–homocysteine S-methyltransferas