Cobalamin and folate deficiency: acquired and hereditary disorders in children.

This review highlights the features of cobalamin and folate deficiency and insufficiency that are particular to children. Maternal deficiency of cobalamin and insufficiency or deficiency of folate are the principal causes of deficiencies of these vitamins in the newborn. Maternal cobalamin deficiency can be caused by pernicious anemia or postgastrectomy, but most often results from a diet lacking in animal protein. The mothers are usually not anemic and failure to thrive and neurological deficits are more common in their infants than is megaloblastic anemia. Inborn errors of cobalamin transport and metabolism present with homocystinuria and methylmalonic aciduria, either alone or in combination. They share many of the clinical features of nutritional cobalamin deficiency. Maternal folate insufficiency results in neural tube defects, fetal loss, prematurity, and fetal growth retardation. Inborn errors of folate metabolism are rare, but polymorphisms affecting the gene for methylenetetrahydrofolate reductase (MTHFR) are common and may have significant health implications. Elevation of plasma methylmalonic acid (MMA) levels reflects a functional lack of cobalamin, whereas elevated total homocysteine levels are associated with a lack of either folate or cobalamin. The determination of these should be part of the investigation of failure to thrive, neurological disorders, and unexplained anemia or cytopenias in children.