An Unbalanced Rearrangement of Chromosomes 4:20 is Associated with Childhood Osteoporosis and Reduced Caspase-3 Levels.

The purpose of this study was to investigate the association of a chromosome 4:20 imbalance with osteoporosis in three related children. Bone biochemistry, bone turnover markers, and dual-energy X-ray absorptiometry (DXA) scanning were performed in all three cases and bone biopsy and histomorphometry in one. The chromosome imbalance was delineated by array comparative genomic hybridization (aCGH) and analyzed for candidate genes. A potential candidate gene within the deleted region is caspase-3, previously linked to low bone mineral density (BMD) in heterozygous mice thus caspase-3 activity was measured in cases and controls. Routine bone biochemistry and markers of bone turnover did not reveal any abnormality. DXA showed reduced total and lumbar spine bone mineral content. aCGH showed an 8 megabase (Mb) deletion of terminal chromosome 4q incorporating a region previously linked to low BMD and a 15 Mb duplication of terminal chromosome 20p. Bone biopsy showed a high bone turnover state, trabecularisation of cortical bone and numerous small osteoclasts coupled with normal bone formation. Basal serum caspase-3 activity was lower in cases compared with controls. We conclude that the early-onset osteoporosis with low basal levels of caspase-3 and abnormal osteoclasts is a feature of this chromosomal translocation. Further investigation of the role of the deleted and duplicated genes and especially caspase-3 is required.

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 3418 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 19/94 (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 approximately 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.