Pathological effects of vitamin B12 deficiency

Vitamin B12 (cobalamin (Cbl)) acts on many organs and systems of the human body. Because of Cbl systemic action, a Cbl-deficient (Cbl-D) status recurs as numerous symptoms, more or less serious, at the level of the whole body. Conventionally, symptoms are different between inherited disorders in which Cbl deficiency occurs at birth or juvenile age and acquired disorders that affect adults. Deserve a special mention also the effects of a Cbl-D status when it develops during fetal development of the individual (i.e., in Cbl-D pregnant mothers). For this reason, this chapter has been divided in subchapters describing the effects of deficiency during development, in children and adults, dividing the latter in the principal affected targets (nervous system, blood, heart, gastric system and immune system). The role of Cbl in cancer is another important topic of this chapter. As a dietary methyl group donor, Cbl can partecipate in human cancerogenesis modulating epigenetic mechanisms: DNA methylation is, in fact, crucial for altering gene expression of oncogenes and oncosuppressors.