Bone mineral density, osteoporosis, and osteoporotic fractures: a genome-wide association study.

BACKGROUND: Osteoporosis is diagnosed by the measurement of bone mineral density, which is a highly heritable and multifactorial trait. We aimed to identify genetic loci that are associated with bone mineral density. METHODS: In this genome-wide association study, we identified the most promising of 314 075 single nucleotide polymorphisms (SNPs) in 2094 women in a UK study. We then tested these SNPs for replication in 6463 people from three other cohorts in western Europe. We also investigated allelic expression in lymphoblast cell lines. We tested the association between the replicated SNPs and osteoporotic fractures with data from two studies. FINDINGS: We identified genome-wide evidence for an association between bone mineral density and two SNPs (p<5x10(-8)). The SNPs were rs4355801, on chromosome 8, near to the TNFRSF11B (osteoprotegerin) gene, and rs3736228, on chromosome 11 in the LRP5 (lipoprotein-receptor-related protein) gene. A non-synonymous SNP in the LRP5 gene was associated with decreased bone mineral density (rs3736228, p=6.3x10(-12) for lumbar spine and p=1.9x10(-4) for femoral neck) and an increased risk of both osteoporotic fractures (odds ratio [OR] 1.3, 95% CI 1.09-1.52, p=0.002) and osteoporosis (OR 1.3, 1.08-1.63, p=0.008). Three SNPs near the TNFRSF11B gene were associated with decreased bone mineral density (top SNP, rs4355801: p=7.6x10(-10) for lumbar spine and p=3.3x10(-8) for femoral neck) and increased risk of osteoporosis (OR 1.2, 95% CI 1.01-1.42, p=0.038). For carriers of the risk allele at rs4355801, expression of TNFRSF11B in lymphoblast cell lines was halved (p=3.0x10(-6)). 1883 (22%) of 8557 people were at least heterozygous for these risk alleles, and these alleles had a cumulative association with bone mineral density (trend p=2.3x10(-17)). The presence of both risk alleles increased the risk of osteoporotic fractures (OR 1.3, 1.08-1.63, p=0.006) and this effect was independent of bone mineral density. INTERPRETATION: Two gene variants of key biological proteins increase the risk of osteoporosis and osteoporotic fracture. The combined effect of these risk alleles on fractures is similar to that of most well-replicated environmental risk factors, and they are present in more than one in five white people, suggesting a potential role in screening.

Association between KLOTHO gene and hand osteoarthritis in a female Caucasian population.

OBJECTIVE: Osteoarthritis (OA) is a common complex disease with strong heritable components. In this study, we investigated the association between four putatively functional genetic variants in KLOTHO gene, a strong ageing-related gene, and hand OA in a large female Caucasian population. METHODS: Subjects (n=1015, age range 33-74 years) were selected from the TwinsUK Registry. Radiographs of both hands were taken for each individual with standard posteroanterior view. The presence/absence of radiographic OA, osteophyte and joint space narrowing (JSN) was assessed using a standard atlas. Four putatively functional single nucleotide polymorphisms (SNPs) in KLOTHO gene were genotyped using allelic discrimination assay. Association was initially estimated using Pearson's chi(2) or Fisher's exact test at allelic and genotypic levels. The direction and magnitude of significant association were further investigated by robust logistic regression with age as a covariate. RESULTS: We found significant association between SNP G-395A and the presence/absence of radiographic hand OA and osteophyte, but not JSN. Allele G significantly increased the risk for radiographic hand OA and osteophytes with odds ratios (ORs) of 1.44 (P=0.008, 95% confidence interval (CI) 1.09-1.91) and 1.36 (P=0.006, 95% CI 1.09-1.70), respectively. From logistic regression modelling, genotype GG showed more than three-fold increased risk for both radiographic hand OA (OR=3.10, 95% CI 1.10-8.76) and osteophyte (OR=3.10, 95% CI 1.10-8.75) when compared to genotype AA. After adjustment for age, ORs for genotype GG further increased to 4.39 (P=0.006, 95% CI 1.51-12.74) for radiographic hand OA and to 4.47 (P=0.005, 95% CI 1.56-12.77) for osteophytes. CONCLUSIONS: Our results suggest that one variant in KLOTHO gene is associated with the susceptibility of hand OA and appears to act through osteophyte formation rather than cartilage damage.

Obesity is associated with genetic variants that alter dopamine availability.

Human and animal studies have implicated dopamine in appetite regulation, and family studies have shown that BMI has a strong genetic component. Dopamine availability is controlled largely by three enzymes: COMT, MAOA and MAOB, and by the dopamine transporter SLC6A3, and each gene has a well-characterized functional variant. Here we look at these four functional polymorphisms together, to investigate how heritable variation in dopamine levels influences the risk of obesity in a cohort of 1150, including 240 defined as obese (BMI > or = 30). The COMT and SLC6A3 polymorphisms showed no association with either weight, BMI or obesity risk. We found, however, that both MAOA and MAOB show an excess of the low-activity genotypes in obese individuals (MAOA:chi2= 15.45, p = 0.004; MAOB:chi2= 8.05, p = 0.018). Additionally, the MAOA genotype was significantly associated with both weight (p = 0.0005) and BMI (p = 0.001). When considered together, the 'at risk genotype'--low activity genotypes at both the MAOA and MAOB loci--shows a relative risk for obesity of 5.01. These results have not been replicated and, given the experience of complex trait genetics, warrant caution in interpretation. In implicating both the MAOA and MOAB variants, however, this study provides the first indication that dopamine availability (as opposed to other effects of MAOA) is involved in human obesity. It is therefore a priority to assess the associations in replication datasets.

The alpha-synuclein gene in multiple system atrophy.

BACKGROUND: The formation of alpha-synuclein aggregates may be a critical event in the pathogenesis of multiple system atrophy (MSA). However, the role of this gene in the aetiology of MSA is unknown and untested. METHOD: The linkage disequilibrium (LD) structure of the alpha-synuclein gene was established and LD patterns were used to identify a set of tagging single nucleotide polymorphisms (SNPs) that represent 95% of the haplotype diversity across the entire gene. The effect of polymorphisms on the pathological expression of MSA in pathologically confirmed cases was also evaluated. RESULTS AND CONCLUSION: In 253 Gilman probable or definite MSA patients, 457 possible, probable, and definite MSA cases and 1472 controls, a frequency difference for the individual tagging SNPs or tag-defined haplotypes was not detected. No effect was observed of polymorphisms on the pathological expression of MSA in pathologically confirmed cases.

Novel association suggests multiple independent QTLs within chromosome 5q21-33 region control variation in total humans IgE levels.

Asthma is a common, heterogeneous, complex disease accompanied by raised total and specific immunoglobulin-E (IgE) antibody levels. Despite numerous previous reports of linkage and association of asthma, atopy and serum IgE levels to genes within the 5q21-33 region, definitive, replicable results are still not available. We used the classical twin design to (i) estimate the relative contributions of genes and environment to variation in total IgE levels, (ii) assess genetic linkage, and (iii) examine allelic association of 11 microsatellite markers spanning the 5q21-33 region to total IgE. Variation in total IgE level was shown to be highly heritable (65%). Although evidence for linkage of the 11 microsatellites to IgE was not observed, the omnibus test of association, not confounded by population substructure, showed positive association of D5S393 and D5S673 to IgE. Genes in the vicinity of D5S673 include hepatitis A virus receptor (HAVCR-1) and IL-12B. Recently, the mouse orthologue of HAVCR-1, the T-cell membrane family of proteins, have been shown to be in strong association with expression of airway hyperactivity in a mouse model of human asthma and atopy. IL-12B subserves many proinflammatory functions and also induces B cells proliferation.

Genetic determinism in the relationship between human CD4+ and CD8+ T lymphocyte populations?

The adaptive immune system in mammals acts in a coordinated manner to eliminate environmentally derived pathogens. Humans, mice and rats show within species variation in the levels and ratios of their peripheral CD4+ and CD8+ T cells and to a significant degree this variation is under the control of polymorphic genes. Whether genes act separately to specify CD4+ and CD8+ subpopulation levels or whether CD8+ variation is controlled through gene and environmental action on CD4+ cells or vice versa, is not known. We use a quantitative modelling approach in identical and non-identical female human twins to delineate the lines of control which act upon and between CD4+ and CD8+ subsets. The major findings of the study are: (1) genetic variation controls CD8+ T cell levels through two major routes-the first is via an effect on CD4+ T cells which accounts for the observed co-variation between CD4+ and CD8+ T cells, the second is through direct action on CD8+ T cell levels. (2) No evidence of a gene effect from CD8+ T cells on CD4+ cells is observed. Our findings have implications for the evolution of the complex defence system of which CD4+ and CD8+ T cells are a crucial part and encourage further work towards locating common pleiotropic quantitative trait loci responsible for variation in numbers of T cells.

Genetic influence on peripheral blood T lymphocyte levels.

T lymphocytes are a major component of the adaptive immune system. CD4 positive T cell subpopulations regulate B cell and macrophage effector function while CD8 positive T cells are largely responsible for anti-viral cytotoxic activity. The degree of natural variation in the levels and ratios of the various T cell subpopulations is a possible risk factor for the development of autoimmune disease, infectious disease and cancer. There is some evidence from studies of inbred strains of mice and humans which suggests that variation in T cell subpopulations is genetically influenced. However, family studies alone cannot distinguish between common environmental and shared genetic influences and provide less robust estimates of the heritability than twin studies. To comprehensively examine genetic influences on a selection of important T cell phenotypes, we investigated variation in levels of total lymphocytes, CD3+, CD4+, CD8+, CD3+CD4+, CD3+CD8+ lymphocytes and in CD4:CD8 ratio as a proportion of lymphocytes and of T cells using the classical twin model approach. Healthy female twin pairs were sampled from the St. Thomas' UK Adult Twin Registry. A maximum of 103 monozygotic (MZ) and 186 dizygotic (DZ) twins aged 18-80 years participated in the study. Whole blood samples were analysed for T cell subsets by flow cytometry. The relative genetic contribution to these phenotypes was estimated using a variance components model-fitting approach. Heritability estimates were calculated of 65% for CD4:CD8 T cell and lymphocyte ratios, around 50% for absolute lymphocyte, CD3+ and CD4+ counts, and 56% for CD8+ numbers. Unique (rather than shared) familial environment explains the remainder of the variance. Genetic factors have a major influence on the variation in peripheral T cell subset numbers. Polymorphism dictating such variation should be taken into account when assessing risk factors for T cell immune-mediated disease with a genetic background.