Effect of TCN2 776C>G on vitamin B12 cellular availability in end-stage renal disease patients.
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].


CONCLUSIONS
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.
Födinger
Manuela
M
Institute of Medical and Chemical Laboratory Diagnostics and Dialysis, Department of Medicine III, University of Vienna, Austria.
Veitl
Mario
M
Skoupy
Sonja
S
Wojcik
Jadwiga
J
Röhrer
Claudia
C
Hagen
Wolfgang
W
Puttinger
Heidi
H
Hauser
Anna-Christine
AC
Vychytil
Andreas
A
Sunder-Plassmann
Gere
G
D000328:Adult; D000368:Aged; D001682:Biological Availability; D003430:Cross-Sectional Studies; D003596:Cytosine; D005260:Female; D005838:Genotype; D006147:Guanine; D006710:Homocysteine / Q000097:blood; D006801:Humans; D007676:Kidney Failure, Chronic / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics; D008875:Middle Aged; D009994:Osmolar Concentration; D014155:Transcobalamins / Q000235:genetics* / Q000378:metabolism; D014805:Vitamin B 12 / Q000097:blood*
D014155:Transcobalamins; D006710:Homocysteine; D006147:Guanine; D003596:Cytosine; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D014805:Vitamin B 12