Table 5.
Depression and CRP concentration according to genotypic combinations of the CRP gene at rs1130864 and rs1205 SNPs
| CCGG (n = 518) | CCGA (n = 889) | CCAA (n = 401) | CTGG (n = 771) | CTGA (n = 775) | CTAA (n = 2) | TTGG (n = 341) | TTGA (n = 3) | TTAA (n = 0) | |
|---|---|---|---|---|---|---|---|---|---|
| Depression, n (%) | 26 (5.0) | 45 (5.1) | 30 (7.5) | 33 (4.3) | 32 (4.1) | 0 | 16 (4.7) | 0 | – |
| CRP, geometric mean (SD), (mg/l) | 2.2 (2.8) | 1.8 (2.8) | 1.6 (2.6) | 2.4 (2.8) | 1.9 (2.9) | 2.7 (1.5) | 2.5 (2.8) | 4.1 (2.7) | – |
| CRP concentration, n (%) (mg/l) | |||||||||
| <1 | 108 (20.8) | 259 (29.1) | 131 (32.7) | 144 (18.7) | 206 (26.6) | 0 | 54 (15.8) | 0 | – |
| 1–2.9 | 220 (42.5) | 376 (42.3) | 175 (43.6) | 340 (44.1) | 343 (44.3) | 1 (50.0) | 153 (44.9) | 2 (66.7) | – |
| ≥3 | 190 (36.7) | 254 (28.6) | 95 (23.7) | 287 (37.2) | 226 (29.2) | 1 (50.0) | 134 (39.3) | 1 (33.3) | – |
The haplotype carrying both minor alleles is not observed in our sample. In other words, the haplotypes that exist are carrying one major (or common) allele and both combinations of haplotypes carrying one major and one minor allele. It is possible that this implies the T–A haplotype decreases the probability of survival into old age or that the SNPs are so close together that there have been almost no recombination events occurring between them over time (these SNPs are located 858 bp apart). This is reflected in the calculated linkage disequilibrium (LD) parameter D′ (D-prime) of 98.9% given these allele frequencies. Consequently, there is an exceedingly high LD between the common allele of one SNP and the rare allele of the other (and vice versa). If the common alleles at one locus had the same effect as the rare alleles in a locus in tight LD (e.g. difference of 90 vs 95%), then our study would most likely have been underpowered to demonstrate such a difference.