Vitamin B12 (FUT2, CUBN, TCN2)

FUT2 (rs602662, in strong linkage disequilibrium with the non-secretor mutation W143X) alters the B12 level via the gastrointestinal mucosa and the microbiota; in genome-wide studies this region was the strongest locus for plasma B12 (p ≈ 10⁻¹⁵ to 10⁻¹⁷; Hazra 2008, Hazra 2009). Cubilin (CUBN, rs1801222) mediates intrinsic-factor-B12 uptake in the ileum; the CUBN region was co-confirmed in the B12 meta-analysis. Transcobalamin II (TCN2, rs11254363) transports B12 in the blood to cells and alters transport capacity.

These markers are statistical associations from studies and do not explain an individual's laboratory result. Clinical assessment may use total B12 and, depending on the question and findings, other measures such as holotranscobalamin or methylmalonic acid. A genotype does not establish deficiency or indicate that a supplement should be taken. Secretor status is discussed on the FUT2 page.

The associations described here replace neither laboratory measurement nor clinical assessment. Genome displays the markers as technical information, not as a B12 status or treatment recommendation.