A Rare Haplotype in the Upstream Regulatory Region of COL1A1 Is Associated With Reduced Bone Quality and Hip Fracture

Three polymorphisms have been identified in the 5' regulatory region of the COL1A1 gene at positions -1997 (rs1107946), -1663 (rs2412298), and +1245G/T (rs1800012), which combine to form haplotypes that have been associated with BMD in several populations. These polymorphisms and haplotypes have not thus far been studied in relation to biomechanical properties of bone or fracture risk. Genotypes and haplotypes of the COL1A1 gene were related to the biomechanical properties of bone ex vivo in samples of bone tissue obtained from the femoral head of 98 consecutive patients undergoing surgery for low-trauma hip fractures. Genotype and haplotype frequencies in the hip fracture cases were compared with 341.8 population-based controls recruited from the same region. All three polymorphisms were associated with material density of the bone core, yield strength, and toughness. The association between -1663InsdelT and +1245G/ T alleles, yield strength, and toughness remained significant after adjusting for material density of the core and other confounding factors. A haplotype comprising the unfavorable allele at all three polymorphic sites (-1997T/-1663delT/+1245T) was also associated with yield strength, modulus, and toughness after adjusting for confounding factors. This haplotype was carried by 1.9/94 (20.2%) patients with hip fracture compared with only 2/3399 (0.06%) female controls drawn from the general population (p < 0.0001). In contrast, there was no significant difference between cases and controls in genotype distribution for the individual polymorphisms. This study shows that common genetic variants in the 5' regulatory region of COL1A1 are associated with biomechanical properties of bone and reduced bone quality by mechanisms independent of their effects on BMD. The biomechanically unfavorable allele at each polymorphic site defines a haplotype that is extremely rare in the general population but that is similar to 400-fold enriched in hip fracture patients. This haplotype may have clinical value as a genetic marker for susceptibility to hip fracture, and further studies to investigate this possibility would be of interest.