Andreas Kindmark

A Meta‐Analysis of Trabecular Bone Score in Fracture Risk Prediction and Its Relationship to FRAX

Trabecular bone score (TBS) is a gray‐level textural index of bone microarchitecture derived from lumbar spine dual‐energy X‐ray absorptiometry (DXA) images. TBS is a bone mineral density (BMD)‐independent predictor of fracture risk. The objective of this meta‐analysis was to determine whether TBS predicted fracture risk independently of FRAX probability and to examine their combined performance by adjusting the FRAX probability for TBS. We utilized individual‐level data from 17,809 men and women in 14 prospective population‐based cohorts. Baseline evaluation included TBS and the FRAX risk variables, and outcomes during follow‐up (mean 6.7 years) comprised major osteoporotic fractures. The association between TBS, FRAX probabilities, and the risk of fracture was examined using an extension of the Poisson regression model in each cohort and for each sex and expressed as the gradient of risk (GR; hazard ratio per 1 SD change in risk variable in direction of increased risk). FRAX probabilities were adjusted for TBS using an adjustment factor derived from an independent cohort (the Manitoba Bone Density Cohort). Overall, the GR of TBS for major osteoporotic fracture was 1.44 (95% confidence interval [CI] 1.35–1.53) when adjusted for age and time since baseline and was similar in men and women (p > 0.10). When additionally adjusted for FRAX 10‐year probability of major osteoporotic fracture, TBS remained a significant, independent predictor for fracture (GR = 1.32, 95% CI 1.24–1.41). The adjustment of FRAX probability for TBS resulted in a small increase in the GR (1.76, 95% CI 1.65–1.87 versus 1.70, 95% CI 1.60–1.81). A smaller change in GR for hip fracture was observed (FRAX hip fracture probability GR 2.25 vs. 2.22). TBS is a significant predictor of fracture risk independently of FRAX. The findings support the use of TBS as a potential adjustment for FRAX probability, though the impact of the adjustment remains to be determined in the context of clinical assessment guidelines.

Feather pecking in chickens is genetically related to behavioural and developmental traits

Feather pecking (FP) is a detrimental behaviour in chickens, which is performed by only some individuals in a flock. FP was studied in 54 red junglefowl (ancestor of domestic chickens), 36 White Leghorn laying hens, and 762 birds from an F(2)-intercross between these two lines. From all F(2)-birds, growth and feed consumption were measured. Age at sexual maturity and egg production in females, and corticosterone levels in males were also measured. From 333 F(2)-birds of both sexes, and 20 parental birds, body composition with respect to bone mineral content, muscle and fat was obtained by post-mortem examinations using Dual X-Ray Absorptiometry (DXA). In femurs of the same birds, the bone density and structure were analysed using DXA and Peripheral Quantitative Computerized Tomography (pQCT), and a biomechanical analysis of bone strength was performed. Furthermore, plumage condition was determined in all birds as a measure of being exposed to feather pecking. Using 105 DNA-markers in all F(2)-birds, a genome-wide scan for Quantitative Trait Loci (QTL), associated with the behaviour in the F(2)-generation was performed. FP was at least as frequent in the red junglefowl as in the White Leghorn strain studied here, and significantly more common among females both in the parental strains and in the F(2)-generation. In the F(2)-birds, FP was phenotypically linked to early sexual maturation, fast growth, weak bones, and, in males, also high fat accumulation, indicating that feather peckers have a different resource allocation pattern. Behaviourally, F(2) feather peckers were more active in an open field test, in a novel food/novel object test, and in a restraint test, indicating that feather pecking might be genetically linked to a proactive coping strategy. Only one suggestive QTL with a low explanatory value was found on chromosome 3, showing that many genes, each with a small effect, are probably involved in the causation of feather pecking. There were significant effects of sire and dam on the risk of being a victim of feather pecking, and victims grew faster pre- and post-hatching, had lower corticosterone levels and were less active in a restraint test. Hence, a wide array of behavioural and developmental traits were genetically linked to FP.

Oestrogen receptor alpha gene haplotype and postmenopausal breast cancer risk: a case control study.

IntroductionOestrogen receptor α, which mediates the effect of oestrogen in target tissues, is genetically polymorphic. Because breast cancer development is dependent on oestrogenic influence, we have investigated whether polymorphisms in the oestrogen receptor α gene (ESR1) are associated with breast cancer risk.MethodsWe genotyped breast cancer cases and age-matched population controls for one microsatellite marker and four single-nucleotide polymorphisms (SNPs) in ESR1. The numbers of genotyped cases and controls for each marker were as follows: TAn, 1514 cases and 1514 controls; c.454-397C → T, 1557 cases and 1512 controls; c.454-351A → G, 1556 cases and 1512 controls; c.729C → T, 1562 cases and 1513 controls; c.975C → G, 1562 cases and 1513 controls. Using logistic regression models, we calculated odds ratios (ORs) and 95% confidence intervals (CIs). Haplotype effects were estimated in an exploratory analysis, using expectation-maximisation algorithms for case-control study data.ResultsThere were no compelling associations between single polymorphic loci and breast cancer risk. In haplotype analyses, a common haplotype of the c.454-351A → G or c.454-397C → T and c.975C → G SNPs appeared to be associated with an increased risk for ductal breast cancer: one copy of the c.454-351A → G and c.975C → G haplotype entailed an OR of 1.19 (95% CI 1.06–1.33) and two copies with an OR of 1.42 (95% CI 1.15–1.77), compared with no copies, under a model of multiplicative penetrance. The association with the c.454-397C → T and c.975C → G haplotypes was similar. Our data indicated that these haplotypes were more influential in women with a high body mass index. Adjustment for multiple comparisons rendered the associations statistically non-significant.ConclusionWe found suggestions of an association between common haplotypes in ESR1 and the risk for ductal breast cancer that is stronger in heavy women.

COL1 C-propeptide cleavage site mutations cause high bone mass osteogenesis imperfecta

Osteogenesis imperfecta (OI) is most often caused by mutations in the type I procollagen genes (COL1A1/COL1A2). We identified two children with substitutions in the type I procollagen C‐propeptide cleavage site, which disrupt a unique processing step in collagen maturation and define a novel phenotype within OI. The patients have mild OI caused by mutations in COL1A1 (Patient 1: p.Asp1219Asn) or COL1A2 (Patient 2: p.Ala1119Thr), respectively. Patient 1 L1–L4 DXA Z‐score was +3.9 and pQCT vBMD was+3.1; Patient 2 had L1–L4 DXA Z‐score of 0.0 and pQCT vBMD of −1.8. Patient BMD contrasts with radiographic osteopenia and histomorphometry without osteosclerosis. Mutant procollagen processing is impaired in pericellular and in vitro assays. Patient dermal collagen fibrils have irregular borders. Incorporation of pC‐collagen into matrix leads to increased bone mineralization. FTIR imaging confirms elevated mineral/matrix ratios in both patients, along with increased collagen maturation in trabecular bone, compared to normal or OI controls. Bone mineralization density distribution revealed a marked shift toward increased mineralization density for both patients. Patient 1 has areas of higher and lower bone mineralization than controls; Patient 2s bone matrix has a mineral content exceeding even classical OI bone. These patients define a new phenotype of high BMD OI and demonstrate that procollagen C‐propeptide cleavage is crucial to normal bone mineralization. Hum Mutat 32:1–12, 2011.

Population genomics in a disease targeted primary cell model

The common genetic variants associated with complex traits typically lie in noncoding DNA and may alter gene regulation in a cell type-specific manner. Consequently, the choice of tissue or cell model in the dissection of disease associations is important. We carried out an expression quantitative trait loci (eQTL) study of primary human osteoblasts (HOb) derived from 95 unrelated donors of Swedish origin, each represented by two independently derived primary lines to provide biological replication. We combined our data with publicly available information from a genome-wide association study (GWAS) of bone mineral density (BMD). The top 2000 BMD-associated SNPs (P < approximately 10(-3)) were tested for cis-association of gene expression in HObs and in lymphoblastoid cell lines (LCLs) using publicly available data and showed that HObs have a significantly greater enrichment (threefold) of converging cis-eQTLs as compared to LCLs. The top 10 BMD loci with SNPs showing strong cis-effects on gene expression in HObs (P = 6 x 10(-10) - 7 x 10(-16)) were selected for further validation using a staged design in two cohorts of Caucasian male subjects. All 10 variants were tested in the Swedish MrOS Cohort (n = 3014), providing evidence for two novel BMD loci (SRR and MSH3). These variants were then tested in the Rotterdam Study (n = 2090), yielding converging evidence for BMD association at the 17p13.3 SRR locus (P(combined) = 5.6 x 10(-5)). The cis-regulatory effect was further fine-mapped to the proximal promoter of the SRR gene (rs3744270, r(2) = 0.5, P = 2.6 x 10(-15)). Our results suggest that primary cells relevant to disease phenotypes complement traditional approaches for prioritization and validation of GWAS hits for follow-up studies.

Efflux transporters in ulcerative colitis: decreased expression of BCRP (ABCG2) and Pgp (ABCB1).

Background Efflux transport proteins are important components of the intestinal barrier against bacterial toxins, carcinogens, and drugs. This investigation was conducted to determine the expression of Breast Cancer Resistance Protein (BCRP/ABCG2), P‐glycoprotein (Pgp/MDR1/ABCB1), and Multidrug Resistance Protein 2 (MRP2/ABCC2) in the gut mucosa of patients with ulcerative colitis (UC). Methods Patients were thoroughly diagnosed according to well‐established clinical, endoscopic, and histologic criteria to be included in the group of patients with active UC (n = 16) or UC in remission (n = 17). Colonic and rectal mucosa from patients with UC were compared with tissues from control subjects (n = 15). The mRNA expression (TaqMan) of the efflux transporters and the proinflammatory cytokines interleukin (IL)‐1&bgr; and IL‐6 was determined. Western blot was used in the analysis of protein expression and the tissue localization of BCRP was determined with confocal microscopy. Results BCRP and Pgp expression was strongly reduced in individuals with active inflammation compared with controls and was negatively correlated with the levels of IL‐6 mRNA. The BCRP staining of colonic epithelium seen in healthy mucosa was diminished in inflamed tissues, with concurrent disruption of epithelial F‐actin structure. Conclusions Two of the efflux transporters of importance for the barrier function of the gut mucosa, Pgp and BCRP, are expressed at strongly reduced levels during active inflammation in patients with UC. Investigations are warranted to determine whether the low levels of efflux transporters during active UC contribute to altered transport and tissue exposure of carcinogens, bacterial toxins, and drugs. (Inflamm Bowel Dis 2007)

A single nucleotide polymorphism in the promoter region of the human gene for osteoprotegerin is related to vascular morphology and function

Osteoprotegerin (OPG) is a secreted member of the tumor necrosis factor receptor family, and has previously been shown to regulate bone mass by inhibiting osteoclast differentiation and activation. Recent evidence indicates that OPG also plays a role in the vascular system, since ablation of the OPG gene in mice results in calcification of the aorta and renal arteries, and association has been found between serum levels of OPG and cardiovascular mortality. This study presents a novel single nucleotide polymorphism, a T/C transition located 129 bp upstream the TATA-box of the human OPG gene, detected by sequence analysis. The OPG genotype was determined by restriction fragment length polymorphism in a cohort consisting of 59 healthy subjects. The intima-media thickness (IMT) in the common carotid artery and maximal post-ischemic forearm blood flow (FBF) were investigated. Subjects with the CC genotype showed a significantly increased IMT (p<0.05) and a concommitantly reduced maximal FBF (p<0.01) as compared to those with the T allele. Thus, our results show that the polymorphism in the promoter region of OPG is associated with both vascular morphology and function in apparently healthy subjects.

Global analysis of the impact of environmental perturbation on cis-regulation of gene expression.

Genetic variants altering cis-regulation of normal gene expression (cis-eQTLs) have been extensively mapped in human cells and tissues, but the extent by which controlled, environmental perturbation influences cis-eQTLs is unclear. We carried out large-scale induction experiments using primary human bone cells derived from unrelated donors of Swedish origin treated with 18 different stimuli (7 treatments and 2 controls, each assessed at 2 time points). The treatments with the largest impact on the transcriptome, verified on two independent expression arrays, included BMP-2 (t = 2h), dexamethasone (DEX) (t = 24h), and PGE2 (t = 24h). Using these treatments and control, we performed expression profiling for 18,144 RefSeq transcripts on biological replicates of the complete study cohort of 113 individuals (ntotal = 782) and combined it with genome-wide SNP-genotyping data in order to map treatment-specific cis-eQTLs (defined as SNPs located within the gene ±250 kb). We found that 93% of cis-eQTLs at 1% FDR were observed in at least one additional treatment, and in fact, on average, only 1.4% of the cis-eQTLs were considered as treatment-specific at high confidence. The relative invariability of cis-regulation following perturbation was reiterated independently by genome-wide allelic expression tests where only a small proportion of variance could be attributed to treatment. Treatment-specific cis-regulatory effects were, however, 2- to 6-fold more abundant among differently expressed genes upon treatment. We further followed-up and validated the DEX–specific cis-regulation of the MYO6 and TNC loci and found top cis-regulatory variants located 180 kb and 250 kb upstream of the transcription start sites, respectively. Our results suggest that, as opposed to tissue-specificity of cis-eQTLs, the interactions between cellular environment and cis-variants are relatively rare (∼1.5%), but that detection of such specific interactions can be achieved by a combination of functional genomic approaches as described here.

The genetic architecture of a female sexual ornament

Abstract Understanding the evolution of sexual ornaments, and particularly that of female sexual ornaments, is an enduring challenge in evolutionary biology. Key to this challenge are establishing the relationship between ornament expression and female reproductive investment, and determining the genetic basis underpinning such relationship. Advances in genomics provide unprecedented opportunities to study the genetic architecture of sexual ornaments in model species. Here, we present a quantitative trait locus (QTL) analysis of a female sexual ornament, the comb of the fowl, Gallus gallus, using a large-scale intercross between red junglefowl and a domestic line, selected for egg production. First, we demonstrate that female somatic investment in comb reflects female reproductive investment. Despite a trade-off between reproductive and skeletal investment mediated by the mobilization of skeletal minerals for egg production, females with proportionally large combs also had relatively high skeletal investment. Second, we identify a major QTL for bisexual expression of comb mass and several QTL specific to female comb mass. Importantly, QTL for comb mass were nonrandomly clustered with QTL for female reproductive and skeletal investment on chromosomes one and three. Together, these results shed light onto the physiological and genetic architecture of a female ornament.

Polymorphisms in the CYP19 and AR genes--relation to bone mass and longitudinal bone changes in postmenopausal women with or without hormone replacement therapy: The Danish Osteoporosis Prevention Study.

Polymorphisms in the androgen receptor (AR) gene and genes encoding enzymes involved in synthesis of sex steroids (e.g., the CYP19 gene encoding aromatase) have recently received attention in osteoporosis research. In the Danish Osteoporosis Prevention Study, recent postmenopausal women were allocated to either hormone replacement therapy (HRT) or no treatment. We genotyped 1792 women for the CYP19 (TTTA)n repeat [short (TTTA)n ≤ 7 or long (TTTA)n > 7] the CYP19 C1558-T, and the AR (CAG)n repeat polymorphism [short (CAG)n < 22, long (CAG)n ≥ 22], and investigated associations with bone mineral density (BMD) and 5-year change in BMD. The CYP19 polymorphisms were in strong linkage disequilibrium. Perimenopausal bone mass or bone loss in untreated women was not associated with the CYP19 polymorphisms. In hormone-treated women, BMD increase in the femoral neck was highest (+0.3%/year) for long CYP19 alleles, lowest (−0.09%/year) for short alleles, and intermediate (−0.002%/year) in heterozygous women, P = 0.015. Differences were also significant in the lumbar spine, total hip, and ultradistal forearm. The C1558-T T-allele was associated with a more pronounced response to HRT (P = 0.04, total hip). AR genotype was not related to BMD, but a modifying effect of sex hormone-binding globulin (SHBG) was present. In the highest SHBG quartile (SHBG > 95 nmol/1, n = 222), AR genotype was associated with baseline BMD (femoral neck: P < 0.001, total hip: P = 0.008), but without a clear gene dosage effect. We have demonstrated that polymorphisms in the CYP19 gene are associated with the magnitude of bone gain in response to HRT and that the (CAG)n repeat polymorphism in the AR gene is associated with bone mass in women with high levels of SHBG. These findings emphasize the complexity of the genetics of bone mass and bone loss.