An autosomal recessive condition caused by mutation(s) in the MTRR gene, encoding methionine synthase reductase. It is characterized by homocystinuria and megaloblastic anemia. The disease is MONDO_0009354 (methylcobalamin deficiency type cblE). Also known as: functional methionine synthase deficiency type cblE, homocystinuria-megaloblastic anemia, cbl e type.