Free cobalamin does not bind to the ileal receptor (IR), a specific receptor located on the brush border. Only the cobalamin/intrinsic-factor complex binds to IR and congenital deficiency of IR is a very rare cause of congenital megaloblastic anaemia known as Imerslund-Gräsbeck syndrome. In addition to megaloblastic anaemia this syndrome of malabsorption exhibits infections and neuropathy.

Synonym: Imerslund-Gräsbeck desease