Intrinsic factor - lack of
Intrinsic factor is a natural substance normally present in the stomach. It is essential to the digestion of vitamin B-12. Lack of intrinsic factor leads to pernicious anemia and vitamin B-12 deficiency.
Babies that are born without intrinsic factor cannot properly absorb vitamin B-12 starting around 6 months of age, while the juvenile type tends to manifest itself at an age greater than 10 years.
by Harutyun Medina, M.D.