Background:
Transcobalamin ii is a serum protein that transports vitamin b12 from the intestine to the tissues. this complex, holo-transcobalamin ii, may reflect vitamin b12 availability in the body. conflicting data exist with regard to the effect of a polymorphism in the gene coding for transcobalamin ii, tcn2 776c>g, on transcobalamin ii levels in the general population, which in turn may affect holo-transcobalamin ii, vitamin b12, as well as total homocysteine (thcy) plasma levels. the effect of tcn2 776c>g on vitamin b12 cellular availability in dialysis patients is unknown.
Methods:
We examined the effect of tcn2 776c>g on holo-transcobalamin ii, vitamin b12, and thcy plasma concentrations in 120 dialysis patients.
Results:
Holo-transcobalamin ii levels were normal or supranormal in all patients and showed a linear association with albumin (r = 0.205, p = 0.025) and with vitamin b12 (r = 0.778, p = 0.001), but not with age, creatinine, body mass index, thcy, ln-thcy, vitamin b6, plasma folate, and red blood cell folate concentration. tcn2 776c>g showed no effect on holo-transcobalamin ii, vitamin b12, and thcy concentration [one-way analysis of variance (anova), post-hoc scheffe test]. multiple linear regression analyses showed that albumin and b12 are independently associated with holo-transcobalamin ii, whereas tcn2 776c>g and mthfr 677c>t had no effect. independent predictors of ln-thcy included creatinine, red blood cell folate, and the mthfr 677tt genotype. there was also an effect of the tcn2 776cc genotype on ln-thcy levels in this multivariate analysis, however, that deserves cautious interpretation because there was no effect of tcn2 genotypes by anova and scheffe test [median ln-thcy concentrations according to tcn2 genotypes (micromol/l): cc, 3.22; cg, 3.30; gg, 3.23].
Conclusion:
Tcn2 776c>g does not influence holo-transcobalamin ii or vitamin b12 levels, and has no major effect on thcy concentrations of end-stage renal disease patients.