Deficiency in CblC (cobalamin C) is an inborn metabolic disorder that causes combined methylmalonic acidemia and homocystinuria, with an impaired intracellular synthesis of the active forms of vitamin B12 (cobalamin), which results in increased levels of methylmalonic acid and homocysteine in the blood and urine [85]. The gene discussed is CBLC; the disease is Other metabolic disease.