The plasma level of vitamin B12 is a modifiable quantitative trait associated with many diseases (Hazra et al., 2008). Vitamin B12 found in meat and milk products is composed of corrin and cobalt rings and is necessary for the formation of red blood cells, DNA synthesis during cell division, and maintenance of the myelin nerve sheath, among other functions. Deficiency in vitamin B12, clinically associated with pernicious anemia, cardiovascular disease, cancer, and neurodegenerative disorders, is often related to poor intestinal B12 absorption rather than direct dietary deficiency. [from OMIM]