These rare anaemias are produced by defects in the absorption, transport or cell metabolism of vitamin B12 and folic acid. The best known congenital megaloblastic anaemia is due to congenital deficiency of Transcobalamin II (TC II). Other relatively well known causes of congenital megaloblastic anaemia are the hereditary deficiency in folate conjugase and the congenital deficiency in ileal receptor (Imerslund-Gräsbeck disease). 

Synonym: Transcobalamin II congenital deficiency