Megaloblastic Anemia and Immune Abnormalities in a Patient with Methionine Synthase Deficiency

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Abstract
We report a case of methionine synthase deficiency associated with cellular immune deficiency discovered in a 14‐year‐old boy. Principal findings were: developmental delay, recurrent upper and lower respiratory tract infections, megaloblastic anemia, discovered at 3 months of age, unresponsive to cyanocobalamin and poorly responsive to folinic acid. Biochemical studies showed: an abnormal deoxyuridine suppression test despite normal serum folate, cobalamin and transcobalamin levels; a normal intracellular uptake of these two coenzymes; and an absolute requirement of methionine for fibroblast growth, suggestive of defective methionine synthesis. An absence of methionine synthase activity in the patient's bone marrow and a profound depression of this activity in lymphocytes and liver were found. Hypergammaglobulinemia with variable lymphopenia, depressed lymphocyte transformation after lectin or recall‐antigen stimulation, defective delayed‐type hypersensitivity and decreased natural killer activity were noted as well. The patient died at the age of 14.