Table 2.
Subgroup analysis for the MTHFR C677T polymorphism.
| Number of studies | Number of participants in case/control | Summary effect estimate | 95% CI | Tests for heterogeneity | |||
|---|---|---|---|---|---|---|---|
| CC genotype | Comparator genotype | ||||||
| Subgroup by sex | |||||||
|
| |||||||
| Pooled studies for sex | I 2 (%) | ||||||
| CT versus CC | 11 | 1,650/1,833 | 1,420/1,523 | 1.04 | 0.94–1.16 | χ² = 14.28, df = 10 (P = 0.16) | 30 |
| TT versus CC | 11 | 1,650/1,833 | 326/425 | 0.87 | 0.75–1.01 | χ² = 14.01, df = 10 (P = 0.17) | 29 |
| Men | |||||||
| CT versus CC | 9 | 1,257/1,436§ | 1,081/1,199§ | 1.12 | 0.94–1.34 | χ² = 18.68, df = 8 (P = 0.02) | 57 |
| TT versus CC | 9 | 1,257/1,436§ | 271/346§ | 0.87 | 0.74–1.02 | χ² = 8.36, df = 8 (P = 0.40) | 4 |
| Women | |||||||
| CT versus CC | 8 | 755/897§ | 627/773§ | 0.98 | 0.85–1.12 | χ² = 7.63, df = 7 (P = 0.37) | 8 |
| TT versus CC | 8 | 755/897§ | 162/217§ | 0.92 | 0.65–1.31 | χ² = 20.74, df = 7 (P = 0.004) | 66 |
|
| |||||||
| Subgroup by cancer type | |||||||
|
| |||||||
| Pooled studies | |||||||
| CT versus CC | 27 | 3,735/6,767 | 3,403/6,307 | 1.01 | 0.95–1.08 | χ² = 23.65, df = 26 (P = 0.60) | 0 |
| TT versus CC | 24* | 3,735/6,767 | 886/2,117 | 0.80 | 0.71–0.89 | χ² = 31.45, df = 23 (P = 0.11) | 27 |
| Colon cancer studies | |||||||
| CT versus CC | 16 | 2,096/4,463 | 1,933/4,090 | 1.01 | 0.93–1.10 | χ² = 11.23, df = 15 (P = 0.74) | 0 |
| TT versus CC | 14** | 2,096/4,463 | 452/1,352 | 0.76 | 0.64–0.91 | χ² = 22.79, df = 13 (P = 0.04) | 43 |
| Rectal cancer studies | |||||||
| CT versus CC | 11 | 1,639/3,291 | 1,470/2,996 | 1.10 | 0.92–1.31 | χ² = 27.95, df = 10 (P = 0.002) | 64 |
| TT versus CC | 10 | 1,639/3,291 | 386/1,020 | 0.82 | 0.72–0.94 | χ² = 8.38, df = 9 (P = 0.50) | 0 |
|
| |||||||
| Subgroup by location | |||||||
|
| |||||||
| Asian countries | |||||||
| CT versus CC | 22 | 2,640/3,401 | 2,985/3,903 | 0.98 | 0.89–1.06 | χ² = 23.98, df = 21 (P = 0.29) | 12 |
| TT versus CC | 20** | 2,640/3,401 | 1,001/1,565 | 0.83 | 0.69–1.01 | χ² = 49.66, df = 19 (P = 0.0001) | 62 |
| European countries | |||||||
| CT versus CC | 22 | 5,480/6,960 | 5,374/6,857 | 1.00 | 0.87–1.13 | χ² = 109.92, df = 21 (P < 0.00001) | 81 |
| TT versus CC | 22 | 5,480/6,960 | 1,294/1,793 | 0.92 | 0.80–1.06 | χ² = 43.74, df = 21 (P = 0.003) | 52 |
| USA | |||||||
| CT versus CC | 8 | 2,011/3,355 | 1,932/2,997 | 0.98 | 0.90–1.07 | χ² = 6.07, df = 7 (P = 0.53) | 0 |
| TT versus CC | 8 | 2,011/3,355 | 436/1,055 | 0.73 | 0.63–0.84 | χ² = 1.91, df = 7 (P = 0.96) | 0 |
| Middle Eastern countries | |||||||
| CT versus CC | 5 | 277/374 | 274/302 | 1.46 | 0.62–3.46 | χ² = 45.30, df = 4 (P < 0.00001) | 91 |
| TT versus CC | 5 | 277/374 | 72/105 | 0.69 | 0.42–1.13 | χ² = 5.56, df = 4 (P = 0.23) | 28 |
|
| |||||||
| Subgroup by control | |||||||
|
| |||||||
| Healthy person controls | |||||||
| CT versus CC | 45 | 8,706/12,958 | 8,043/12,044 | 1.02 | 0.94–1.11 | χ² = 154.26, df = 44 (P < 0.00001) | 71 |
| TT versus CC | 43** | 8,706/12,958 | 2,136/3,636 | 0.90 | 0.81–1.00 | χ² = 88.37, df = 42 (P = 0.0001) | 52 |
| Hospital patient controls | |||||||
| CT versus CC | 16 | 2,418/2,863 | 2,932/3,619 | 0.93 | 0.83–1.05 | χ² = 27.35, df = 15 (P = 0.03) | 45 |
| TT versus CC | 16 | 2,418/2,863 | 939/1,254 | 0.82 | 0.68–1.00 | χ² = 36.07, df = 15 (P = 0.002) | 58 |
§Not all studies reported both case and control numbers.
*There were two studies without TT genotype information, one study with rectal cancer data, and two studies with colon cancer data.
**There were two studies that had 0 people for the TT genotype.
CRC: colorectal cancer.