This pathway depicts the metabolism of cobalamin (also known as cbl or vitamin B12) and related diseases (for a full overview of the B12 metabolism, see [WP1533](https://www.wikipathways.org/index.php/Pathway:WP1533)).
Vit. B12 is derived from food sources and thereafter metabolised for 2 reasons; 1. to methylate homocysteine to methionine, and 2. to convert methylmalonyl-CoA to succinyl-CoA.
This pathway depicts 15 distinct diseases which are related to a malfunctioning in the absorption and transport section, or the intracellular processing of Cbl.
However, the exact function of some proteins which have been linked to these diseases, remains unclear.
Substitution of Vit. B12 is a therapeutic option for patients with absorption and transport related diseases, however does not perform so well for patient with intracellular processing defects.
This pathway was inspired by Chapter 13 of the book of Blau (ISBN 3642403360 (978-3642403361)).