description
Vitamins are essential nutrients, required in small amounts from the diet for the normal growth and development of a multicellular organism. Where there is vitamin deficiency, either by poor diet or a defect in metabolic conversion, diseases called Avitaminoses occur. Currently, cobalamin (Cbl, vitamin B12) metabolic defects are described below (Chapter 155 in The Metabolic and Molecular Bases of Inherited Disease, 8th ed, Scriver et al. 2001

external resources
NCBI:1268959
REACTOME:R-HSA-3296482

genes
ACACA , GIF , MTR , MTRR , MUT , PC , PCCA , PCCB , TCN2 , CUBN , MMACHC , MMADHC , CD320 , MCCC1 , MCCC2 , AMN , MMAA ,