BIOCHEMICAL AND CLINICAL-RESPONSE TO HYDROXOCOBALAMIN VERSUS CYANOCOBALAMIN TREATMENT IN PATIENTS WITH METHYLMALONIC ACIDEMIA AND HOMOCYSTINURIA (CBLC)

Objective: To compare the therapeutic effectiveness of hydroxocobalami n and cyanocobalamin in patients with combined methylmalonic acidemia and homocystinuria. Study design: Analysis of urine methylmalonic acid , plasma homocystine, and growth of two unrelated patients with cobala min C disease who were initially receiving cyanocobalamin and were sub sequently switched to hydroxocobalamin. Results: Each patient had a si gnificant decrease in urine methylmalonic acid excretion while receivi ng cyanocobalamin, but levels remained at least 10 times normal. Cyano cobalamin treatment resulted in a decrease of plasma homocystine to ne ar normal in one patient but had no effect on plasma homocystine in th e second patient. Each patient was switched to hydroxocobalamin and ur ine methylmalonic acid levels decreased to the limit of detection. Pla sma homocystine values while taking hydroxocobalamin remained < 5 nmol /ml in both patients. In patient 1, who continued to receive cyanocoba lamin therapy for more than 1 year, growth rates (height, weight, and head circumference) were very poor. After initiation of hydroxocobalam in, growth parameters normalized with growth rates above normal. Concl usion: Intramuscular cyanocobalamin treatment is inadequate in the tre atment of patients with cobalamin C disease. Appropriate management of cobalamin C disease should include only the hydroxocobalamin form of cobalamin.