TABLE 1.
Studies that assessed the concentration of one-carbon metabolism markers according to the TCN2 rs1801198 (c.776G>C) polymorphism1
| CC genotype |
CG genotype |
GG genotype |
||||||||
| Reference | STREGA score | Setting | Country (ethnicity) | Sample | n | Mean ± SD | n | Mean ± SD | n | Mean ± SD |
| Holotranscobalamin, pmol/L | ||||||||||
| Miller et al., 2002 (26) | 8 of 19 | Healthy older adults | United States (Caucasians) | Serum | 39 | 150 ± 812 | 63 | 113 ± 56 | 26 | 104 ± 83 |
| Födinger et al., 2003 (27) | 9 of 19 | End-stage renal disease | Austria (Caucasians) | Plasma | 47 | 132.2 ± 71.43 | 51 | 123 ± 56.5 | 22 | 132 ± 37.2 |
| Wans et al., 2003 (28) | 8 of 19 | Healthy older adults | Germany (Caucasians) | NR | 55 | 68 ± 28 | 77 | 67 ± 41 | 27 | 46 ± 21 |
| Zetterberg et al., 2003 (29) | 8 of 19 | Cognitive dysfunction | Sweden (Caucasians) | Plasma | 24 | 100.3 ± 39.63 | 34 | 83.5 ± 38.7 | 20 | 91.5 ± 56.3 |
| McCaddon et al., 2004 (30) | 9 of 19 | Alzheimer disease | United Kingdom (Caucasians) | Serum | 30 | 58 ± 14.73 | 51 | 45 ± 9.8 | 17 | 43.5 ± 9.8 |
| von Castel-Dunwoody et al., 2005 (31) | 11 of 19 | Healthy nonpregnant women | United States (mixed)4 | Serum | 103 | 87 ± 33 | 161 | 82 ± 26 | 80 | 74 ± 37 |
| Garrod et al., 2010 (32) | 9 of 19 | Community-dwelling older adult5 | United States (Latino) | Plasma | 229 | 80 ± 33 | 261 | 77 ± 33 | 64 | 70 ± 27 |
| Vitamin B-12, pmol/L | ||||||||||
| Miller et al., 2002 (26) | 8 of 19 | Healthy older adults | United States (Caucasians) | Serum | 39 | 319.6 ± 130.6 | 63 | 306.3 ± 124 | 26 | 282.7 ± 141 |
| Födinger et al., 2003 (27) | 9 of 19 | End-stage renal disease | Austria (Caucasians) | Plasma | 47 | 259 ± 141.53 | 51 | 253 ± 103 | 22 | 282.7 ± 161.7 |
| Wans et al., 2003 (28) | 8 of 19 | Healthy older adults | Germany (Caucasians) | NR | 55 | 293 ± 99 | 77 | 305 ± 143 | 27 | 289 ± 122 |
| Zetterberg et al., 2003 (29) | 8 of 19 | Cognitive dysfunction | Sweden (Caucasians) | Plasma | 24 | 419.8 ± 249.73 | 34 | 275.3 ± 72.5 | 20 | 335 ± 161.7 |
| McCaddon et al., 2004 (30) | 9 of 19 | Alzheimer disease | United Kingdom (Caucasians) | Serum | 30 | 251.7 ± 36.73 | 51 | 237.5 ± 28.3 | 17 | 307.8 ± 31.5 |
| Winkelmayer et al., 2004 (33) | 8 of 19 | Kidney-allograft recipients | Austria (Caucasians) | Plasma | 204 | 263 ± 197 | 383 | 253 ± 145 | 145 | 254 ± 116 |
| von Castel-Dunwoody et al., 2005 (31) | 11 of 19 | Healthy nonpregnant women | United States (mixed)4 | Plasma | 103 | 327 ± 144 | 161 | 320 ± 136 | 80 | 345 ± 144 |
| Fredriksen et al., 2007 (34) | 13 of 19 | Healthy population6 | Norway (Caucasians) | Serum | 3278 | 331.1 ± 247.33 | 4783 | 328 ± 235.2 | 2020 | 339.8 ± 226.1 |
| Garrod et al., 2010 (32) | 9 of 19 | Community-dwelling older adults5 | United States (Latino) | Plasma | 229 | 316 ± 142 | 261 | 312 ± 121 | 64 | 316 ± 107 |
| Stanisławska-Sachadyn et al., 2010 (35) | 12 of 19 | Male volunteers7 | Northern Ireland (Caucasians) | Serum | 190 | 253.1 ± 112.23 | 276 | 275.4 ± 97.6 | 131 | 281.7 ± 103.1 |
| Sawaengsri et al., 2016 (36) | 11 of 19 | Home-bound elderly participants8 | United States (mixed)9 | Plasma | 79 | 398 ± 30.5 | 61 | 336.5 ± 31.7 | 31 | 317 ± 33.9 |
| Homocysteine, μmol/L | ||||||||||
| Namour et al., 2001 (14) | 8 of 19 | Healthy older adults | France (Caucasians) | Plasma | 55 | 10.1 ± 0.4 | 76 | 11.7 ± 0.4 | 28 | 10.2 ± 0.8 |
| Miller et al., 2002 (26) | 8 of 19 | Healthy older adults | United States (Caucasians) | NR | 39 | 10.3 ± 2.6 | 63 | 10.7 ± 2.4 | 26 | 11.2 ± 2.8 |
| Födinger et al., 2003 (27) | 9 of 19 | End-stage renal disease | Austria Caucasians | Plasma | 47 | 25.1 ± 6.63 | 51 | 27.7 ± 7.8 | 22 | 26.9 ± 15.6 |
| Wans et al., 2003 (28) | 8 of 19 | Healthy older adults | Germany (Caucasians) | NR | 55 | 12.3 ± 4 | 77 | 12.2 ± 3.5 | 27 | 12.8 ± 3.4 |
| Zetterberg et al., 2003 (29) | 8 of 19 | Cognitive dysfunction | Sweden Caucasians | Plasma | 24 | 16 ± 6.43 | 34 | 16.3 ± 9 | 20 | 19 ± 6.3 |
| Winkelmayer et al., 2004 (33) | 8 of 19 | Kidney-allograft recipients | Austria Caucasians | Plasma | 204 | 16.8 ± 7.4 | 383 | 17 ± 9.8 | 145 | 17.8 ± 7.4 |
| von Castel-Dunwoody et al., 2005 (31) | 11 of 19 | Healthy nonpregnant women | United States (mixed)4 | Plasma | 103 | 6.2 ± 1 | 161 | 6.5 ± 1 | 80 | 6.3 ± 1 |
| Fredriksen et al., 2007 (34) | 13 of 19 | Healthy population6 | Norway (Caucasians) | Plasma | 3278 | 10.8 ± 4.43 | 4783 | 10.7 ± 4.2 | 2020 | 11 ± 4 |
| Garrod et al., 2010 (32) | 9 of 19 | Community-dwelling older adults5 | United States (Latino) | Plasma | 229 | 10.8 ± 9.1 | 261 | 10.2 ± 3.3 | 64 | 9.7 ± 3.3 |
| Stanisławska-Sachadyn et al., 2010 (35) | 12 of 19 | Male volunteers7 | Northern Ireland (Caucasians) | NR | 195 | 7.3 ± 2.33 | 286 | 7.1 ± 1.9 | 132 | 7.2 ± 2 |
| Sawaengsri et al., 2016 (36) | 11 of 19 | Home-bound elderly participants8 | United States (mixed)9 | Plasma | 79 | 9.9 ± 1.1 | 61 | 10.1 ± 1.1 | 31 | 10.7 ± 1.1 |
| Methylmalonic acid, nmol/L | ||||||||||
| Miller et al., 2002 (26) | 8 of 19 | Healthy older adults | United States (Caucasians) | NR | 39 | 208 ± 96 | 63 | 206 ± 80 | 26 | 264 ± 138 |
| Wans et al., 2003 (28) | 8 of 19 | Healthy older adults | Germany (Caucasians) | NR | 55 | 375.5 ± 274.93 | 77 | 315.5 ± 217.1 | 27 | 243 ± 107.4 |
| Fredriksen et al., 2007 (34) | 13 of 19 | Healthy population6 | Norway (Caucasians) | Plasma | 3278 | 177 ± 8.83 | 4783 | 181 ± 8.8 | 2020 | 187 ± 8 |
| Garrod et al., 2010 (32) | 9 of 19 | Community-dwelling older adults5 | United States (Latino) | Plasma | 229 | 286 ± 841 | 261 | 204 ± 182 | 64 | 207 ± 134 |
| Folate, nmol/L | ||||||||||
| Födinger et al., 2003 (27) | 9 of 19 | End-stage renal disease | Austria (Caucasians) | Plasma | 47 | 16.9 ± 7.73 | 51 | 16 ± 7.3 | 22 | 17.7 ± 6 |
| Wans et al., 2003 (28) | 8 of 19 | Healthy older adults | Germany (Caucasians) | NR | 55 | 19.1 ± 93 | 77 | 37.2 ± 29.7 | 27 | 23.7 ± 14.9 |
| Winkelmayer et al., 2004 (33) | 8 of 19 | Kidney-allograft recipients | Austria (Caucasians) | Plasma | 204 | 15.2 ± 17.2 | 383 | 14.8 ± 11.5 | 145 | 14.5 ± 6.9 |
| Fredriksen et al., 2007 (34) | 13 of 19 | Healthy population6 | Norway (Caucasians) | Serum | 3278 | 17.2 ± 13.33 | 4783 | 17.3 ± 12.7 | 2020 | 16.7 ± 12.3 |
| Sawaengsri et al., 2016 (36) | 11 of 19 | Home-bound elderly participants8 | United States (mixed)9 | Plasma | 79 | 31 ± 18.8 | 61 | 31.5 ± 21.1 | 31 | 34.4 ± 20.2 |
| Folate, red blood cells, nmol/L | ||||||||||
| Miller et al., 2002 (26) | 8 of 19 | Healthy older adults | United States (Caucasians) | Whole blood | 39 | 822.6 ± 219.8 | 63 | 856.6 ± 240.2 | 26 | 901.9 ± 240.2 |
| Födinger et al., 2003 (27) | 9 of 19 | End-stage renal disease | Austria (Caucasians) | Whole blood | 47 | 1345.7 ± 589.63 | 51 | 1162 ± 427.2 | 22 | 1272.3 ± 368.5 |
| Zetterberg et al., 2003 (29) | 8 of 19 | Cognitive dysfunction | Sweden (Caucasians) | Whole blood | 24 | 209.5 ± 61.23 | 34 | 277 ± 164 | 20 | 366.8 ± 250.9 |
| Garrod et al., 2010 (32) | 9 of 19 | Community-dwelling older adults5 | United States (Latino) | Whole blood | 229 | 1144.3 ± 346.7 | 261 | 1162.5 ± 362.6 | 64 | 1153.4 ± 358 |
1
NR, not reported; STREGA, Strengthening the Reporting of Genetic Association Studies; TCN2, transcobalamin 2.
2
Concentration is expressed as pg/mL.
3
Value was calculated on the basis of the median and IQR or the median and range according to the validated method described by Wan et al. (18).
4
White: 81%; African: 9%; Hispanic: 4%; Asian: 2%; other: 4%.
5
Sacramento Area Latino Study on Aging.
6
Norwegian Colorectal Cancer Prevention study.
7
Belfast-based industrial workforce.
8
Nutrition, Aging, and Memory in Elders study.
9
Non-Hispanic white: 61.4%; non-Hispanic African: 33.9%; Asian: 1.8%; Native American or Alaskan Native: 1.8%; Hispanic: 1.2%.