Influence of LRP5 polymorphisms on normal variation in BMD

Association between ADAMTS14_rs4747096 gene polymorphism and bone mineral density of Chinese Han population residing in fluorine exposed areas in ShanXi Province, China

This study aimed to investigate the effects of fluorine and ADAMTS14_rs4747096 on bone mineral density (BMD). The survey was explored in a cross-sectional case-control study conducted in Shanxi, China. The BMD was measured by an ultrasonic bone mineral density instrument. The urine fluoride concentration was detected using the fluoride ion electrode. ADAMTS14_rs4747096 polymorphism was examined by multiplex polymerase chain reaction (PCR) and sequencing. The multinomial logistic regressions found that the urine fluoride was a risk factor for osteopenia (OR = 1.379, 95% CI: 1.127-1.687, P = 0.0018), osteoporosis (OR = 1.480, 95% CI: 1.1138-1.926, P = 0.0035), and rs4747096 AG + GG genotype increased the risk of osteoporosis (OR = 2.017, 95% CI: 1.208-3.369, P = 0.0073). In addition, the interaction between urine fluoride and rs4747096 polymorphism on the risk of decreased BMD also was observed. The study suggests that fluoride exposure and mutation G allele in ADAMTS14_rs4747096 may be risk factors for the decrease of BMD. And there is an interaction between the two influencing factors.

LRP5 high bone mass (Worth-type autosomal dominant endosteal hyperostosis): case report and historical review of the literature

PURPOSE

LRP5 high bone mass (HBM) is an autosomal dominant endosteal hyperostosis caused by mutations of the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Alternative names included "autosomal dominant osteosclerosis" and "Worth disease." The aim of the paper is to provide an historical overview of a disorder whose literature is complicated and confusing due to the past use of several denominations and lack of reviews.

METHODS

We collected case reports of HBM with evidence of autosomal dominant transmission preceding the identification of the LRP5 mutations in 2002 (Worth-type endosteal hyperostosis) and cases of LRP5 HBM confirmed by genetic analysis since 2002. The prevalence of relevant clinical and laboratory findings was estimated. We described an affected woman with neurological manifestations.

RESULTS

A 44-year-old Caucasian woman with torus palatinus complained of headache, hypo-/anosmia, and complete mixed deafness. Dual-energy X-ray absorptiometry (DEXA) scan revealed elevated bone mass. The A242T mutation of the LRP5 gene was detected. Including the present case, 155 patients have been reported to date. Neurological involvement and increased serum alkaline phosphatase (ALP) were present in 19.4% and 3.7% of cases, respectively. Facial changes and torus palatinus were observed in 61% and 41% of cases, respectively.

CONCLUSIONS

We present the only historical review on Worth-type endosteal hyperostosis, now known as LRP5 HBM. Neurological manifestations, previously considered absent in the disease, affect 19.4% of the patients. Genetic analysis and appropriate denomination of LRP5 HBM are fundamental for diagnosis and to mitigate the confusion that has long characterized this disease.

Association between the LRP5 rs556442 gene polymorphism and the risks of NAFLD and CHD in a Chinese Han population

Background

Multiple studies have demonstrated the involvement of low-density lipoprotein receptor-related protein 5 (LRP5) in metabolism-related diseases. This study explored the relationship between the LRP5 rs556442 gene polymorphism and the risks of non-alcoholic fatty liver disease (NAFLD) and coronary heart disease (CHD) in a Chinese Han population.

Methods

This retrospective case–control study included 247 patients with NAFLD, 200 patients with CHD, 118 patients with both NAFLD and CHD, and 339 healthy controls from June 2018 to June 2019 at Qingdao Municipal Hospital. Basic information and clinical characteristics were collected for all subjects. The genotype and allele frequency of LRP5 rs556442 were determined.

Results

The genotype distributions of LRP5 rs556442 differed significantly between the CHD and NAFLD + CHD groups (P < 0.05). The LRP5 rs556442 GG genotype markedly promoted the risk of NAFLD in CHD patients [odds ratio (OR) = 2.857, 95% confidence interval (CI): 1.196–6.824, P = 0.018). After adjustment for sex, age, and body mass index (BMI), this association remained significant (OR = 3.252, 95% CI: 1.306–8.102, P = 0.011). In addition, the LRP5 rs556442 AA + AG genotype was associated with an increased BMI in obese NAFLD patients (OR = 1.526, 95% CI: 1.004–2.319, P = 0.048). However, after adjustment for sex and age, this association was no longer significant (OR = 1.504, 95% CI: 0.991–2.282, P = 0.055).

Conclusions

This study found that the LRP5 rs556442 GG genotype increased the risk of NAFLD in CHD patients and AA + AG genotype may be associated with an increased BMI in obese NAFLD patients among a Chinese Han population.

Trial registration ChiCTR, ChiCTR1800015426. Registered 28 March 2018—Retrospectively registered, http://www.chictr.org.cn/showproj.aspx?proj=26239.

Diagnostic yield of bone fragility gene panel sequencing in children and young adults referred for idiopathic primary osteoporosis at a single regional reference centre

Aim

To describe the presenting features, bone characteristics and molecular genetics in a large monocentric cohort of children and young adults with idiopathic primary osteoporosis.

Methods

Sixty-six patients (19 children, 47 adults; 28 males, 38 females; age at referral: 3.8 to 65 years) diagnosed with primary osteoporosis were included in this study; patients with features of osteogenesis imperfecta or other known syndromes associated with osteoporosis were excluded. For each patient, the following data were collected by retrospective chart review: family and personal history of fracture and osteoporosis, mineral homeostasis parameters and markers of bone formation and resorption, bone mineral density (BMD) of the lumbar spine (LS-BMD), the total body less head (TB-BMD), and total hip levels (TH-BMD) measured by DXA. As part of the initial assessment process, a bone fragility gene panel sequencing was performed in all of these patients.

Results

There was a higher predominance of males in the children (63%) and of females in the adults (66%) (p = 0.030). Compared to the adults, the children had a significantly lower frequency of vertebral fractures (26 vs 57%, p = 0.022) and a higher frequency of peripheral fractures (84 vs 53%; p = 0.019). Bone fragility gene panel sequencing allowed the identification of the heterozygous pathogenic variant in 27% of patients (most frequently in LRP5, WNT1 and COL1A1 or 2 genes) and the heterozygous p.(Val667Met) LRP5 variant in 11% of them. The frequency of pathogenic variants tended to be higher in the children compared to the adults without reaching statistical significance (42 vs 19%; p = 0.053). The frequency of the p.(Val667Met) LRP5 variant was similar in children and adults. No significant differences were found regarding the various clinical, biological and radiological characteristics of the patients according to genotype.

Conclusion

In this study, we reported the presenting features and bone characteristics in a large cohort of children and young adults with idiopathic primary osteoporosis. Bone fragility gene panel sequencing allowed the identification of genetic variants in a significant proportion of these patients. Molecular diagnosis in these patients is important in order to be able to offer genetic counselling and organise patient management.

The acute effects of different frequencies of whole-body vibration on arterial stiffness

Whole-body vibration (WBV) can decrease arterial stiffness, but the effects of low-frequency WBV on arterial stiffness are not known. The aim of this study was to clarify the acute effects on arterial stiffness of WBV by vibration frequency. This study involved 9 healthy men (age: 31 ± 7 years). Each WBV session involved 3 sets of 4 different vibrations (0 Hz [control], 12 Hz, 20 Hz, 30 Hz) lasting 60 s with a 60-s inter-session rest interval. During WBV, the participants adopted a static squat position with their knees bent. An automatic oscillometric device was used to measure brachial-ankle pulse wave velocity (baPWV) before (baseline) and 5, 15, and 30 min after WBV. There was a significant decrease in baPWV from baseline at 30 min (P = .02) after WBV at 30 Hz. However, there was no change in baPWV at any time points after WBV at 0 (control), 12, and 20 Hz. These results suggested that low-frequency WBV does not affect arterial stiffness.

A Rare Mutation in SMAD9 Associated With High Bone Mass Identifies the SMAD-Dependent BMP Signaling Pathway as a Potential Anabolic Target for Osteoporosis

Novel anabolic drug targets are needed to treat osteoporosis. Having established a large national cohort with unexplained high bone mass (HBM), we aimed to identify a novel monogenic cause of HBM and provide insight into a regulatory pathway potentially amenable to therapeutic intervention. We investigated a pedigree with unexplained HBM in whom previous sequencing had excluded known causes of monogenic HBM. Whole exome sequencing identified a rare (minor allele frequency 0.0023), highly evolutionarily conserved missense mutation in SMAD9 (c.65T>C, p.Leu22Pro) segregating with HBM in this autosomal dominant family. The same mutation was identified in another two unrelated individuals both with HBM. In silico protein modeling predicts the mutation severely disrupts the MH1 DNA-binding domain of SMAD9. Affected individuals have bone mineral density (BMD) Z-scores +3 to +5, mandible enlargement, a broad frame, torus palatinus/mandibularis, pes planus, increased shoe size, and a tendency to sink when swimming. Peripheral quantitative computed tomography (pQCT) measurement demonstrates increased trabecular volumetric BMD and increased cortical thickness conferring greater predicted bone strength; bone turnover markers are low/normal. Notably, fractures and nerve compression are not found. Both genome-wide and gene-based association testing involving estimated BMD measured at the heel in 362,924 white British subjects from the UK Biobank Study showed strong associations with SMAD9 (P_GWAS = 6 × 10^-16 ; P_GENE = 8 × 10^-17 ). Furthermore, we found Smad9 to be highly expressed in both murine cortical bone-derived osteocytes and skeletal elements of zebrafish larvae. Our findings support SMAD9 as a novel HBM gene and a potential novel osteoanabolic target for osteoporosis therapeutics. SMAD9 is thought to inhibit bone morphogenetic protein (BMP)-dependent target gene transcription to reduce osteoblast activity. Thus, we hypothesize SMAD9 c.65T>C is a loss-of-function mutation reducing BMP inhibition. Lowering SMAD9 as a potential novel anabolic mechanism for osteoporosis therapeutics warrants further investigation. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Association between polymorphisms in GGPS1 and RANKL genes and postmenopausal osteoporosis in Romanian women

Objectives: This study aimed to assess the relationship between bone mineral density, fragility fractures, fracture risk and polymorphisms of two osteoporosis-candidate genes (GGPS1 and RANKL) in Romanian women with postmenopausal osteoporosis. Methods: An analytical, prospective, transversal, observational, case-control study on 364 postmenopausal women, of which 228 were previously diagnosed with osteoporosis, was carried out between June 2016 and August 2017 in Cluj Napoca, Romania. Clinical data and blood samples were collected from all study participants. Polymorphisms in GGPS1 and RANKL genes were genotyped using TaqMan SNP Genotyping assays, run on a QuantStudio 3 real-time PCR machine. Results: The CT genotype in GGPS1 rs10925503 was associated with significant lower bone mineral density values at lumbar spine and femoral neck sites and a higher fracture risk compared to controls. No significant association was found between genotypes of RANKL rs2277439 with bone mineral density or fracture risk compared to the healthy controls. Conclusions: Our study showed a strong association between low bone mineral density and genotype CT of GGPS1 rs10925503 polymorphisms. No association was found for RANKL rs2277439 polymorphism.

The interactions of physical activity, exercise and genetics and their associations with bone mineral density: implications for injury risk in elite athletes

Low bone mineral density (BMD) is established as a primary predictor of osteoporotic risk and can also have substantial implications for athlete health and injury risk in the elite sporting environment. BMD is a highly multi-factorial phenotype influenced by diet, hormonal characteristics and physical activity. The interrelationships between such factors, and a strong genetic component, suggested to be around 50-85% at various anatomical sites, determine skeletal health throughout life. Genome-wide association studies and case-control designs have revealed many loci associated with variation in BMD. However, a number of the candidate genes identified at these loci have no known associated biological function or have yet to be replicated in subsequent investigations. Furthermore, few investigations have considered gene-environment interactions-in particular, whether specific genes may be sensitive to mechanical loading from physical activity and the outcome of such an interaction for BMD and potential injury risk. Therefore, this review considers the importance of physical activity on BMD, genetic associations with BMD and how subsequent investigation requires consideration of the interaction between these determinants. Future research using well-defined independent cohorts such as elite athletes, who experience much greater mechanical stress than most, to study such phenotypes, can provide a greater understanding of these factors as well as the biological underpinnings of such a physiologically "extreme" population. Subsequently, modification of training, exercise or rehabilitation programmes based on genetic characteristics could have substantial implications in both the sporting and public health domains once the fundamental research has been conducted successfully.

Low density lipoprotein receptor-related protein 5 gene polymorphisms and osteoporosis in Thai menopausal women

Background

Osteoporosis, characterized by low bone mineral density (BMD) and high bone fracture risk, is prevalent in Thai menopausal women. Genetic factors are known to play a key role in BMD. Low density lipoprotein receptor-related protein 5 (LRP5), a co-receptor in the Wnt/beta-catenin pathway, is involved in many aspects of bone biology. As coding single nucleotide polymorphisms (cSNPs) of LRP5, including A1330V (rs3736228), and Asian-related Q89R (rs41494349) and N740N (rs2306862), are associated with lowered BMD, this study aimed to determine the relationship between these LRP5 polymorphisms and BMD in 277 Thai menopausal women.

Results

Only rs3736228 deviated from the Hardy–Weinberg equilibrium of allele frequency (p = 0.022). The median, range and p value for the BMD related to each SNP parameter were compared (Mann–Whitney U test). Significant differences were observed between wild-type and risk alleles for both rs3736228 (total radial, p = 0.011; and radial 33, p = 0.001) and rs2306862 (radial 33: p = 0.015) SNPs, with no significant difference for rs41494349 SNP. Linkage disequilibrium was strong for both rs3736228 and rs2306862 SNPs. Haplotype analysis identified high CC frequency in both normal and osteopenia/osteoporosis groups, with a significant odds ratio for carrying the TT haplotype; however, this was non-significant after adjusting for age. Multivariate binary logistic regression analysis performed for rs3736228 showed that individuals with a body mass index <25 kg/m² had an increased risk of osteoporosis for each decade, but the polymorphism had no effect.

Conclusions

This study did not identify LRP5 polymorphisms as a risk factor for osteoporosis in Thai menopausal women. Further studies with larger sample sizes are needed to further clarify the role of LRP5 as a genetic determinant of osteoporosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12952-016-0059-7) contains supplementary material, which is available to authorized users.

Effects of Exercise on Low Density Lipoprotein Receptor Related Protein 5 Gene Expression in Patients With Postmenopausal Osteoporosis

Objectives

This study aims to investigate the effects of aerobic exercise on low density lipoprotein receptor related protein 5 (LRP5) gene messenger ribonucleic acid expression and evaluate the relationship between the clinical parameters and gene expression in patients with postmenopausal osteoporosis (OP).

Patients and methods

Seven patients with postmenopausal OP (mean age 60.0±5.3 years; range 51 to 66 years) were included in the study. An exercise protocol/program consisting of treadmill exercising for 30 minutes three days a week for six weeks was performed at a moderate intensity. LRP5 gene expression levels were evaluated before the onset of the exercise program and then four hours after the end of the first session and 12th (fourth week) and 18th (sixth week) sessions of exercise.

Results

Our results demonstrated variable changes in the LRP5 gene expression after the aerobic exercise sessions. Excluding one patient, the LRP5 gene expression levels showed a slight tendency to increase. In spite of this tendency, gene expression differences during the exercise sessions were not significant.

Conclusion

Our results suggest that interindividual variations of LRP5 gene expression exist after moderate intensity aerobic exercises in patients with postmenopausal OP. Despite of this variability, LRP5 gene expression levels increased slightly, except in peripheral blood in one patient. Future studies with larger sample sizes and different sampling time/tissues are required to shed more light on the impact of exercise at molecular level in OP.

Mutations in Known Monogenic High Bone Mass Loci Only Explain a Small Proportion of High Bone Mass Cases

High bone mass (HBM) can be an incidental clinical finding; however, monogenic HBM disorders (eg, LRP5 or SOST mutations) are rare. We aimed to determine to what extent HBM is explained by mutations in known HBM genes. A total of 258 unrelated HBM cases were identified from a review of 335,115 DXA scans from 13 UK centers. Cases were assessed clinically and underwent sequencing of known anabolic HBM loci: LRP5 (exons 2, 3, 4), LRP4 (exons 25, 26), SOST (exons 1, 2, and the van Buchem's disease [VBD] 52-kb intronic deletion 3'). Family members were assessed for HBM segregation with identified variants. Three-dimensional protein models were constructed for identified variants. Two novel missense LRP5 HBM mutations ([c.518C>T; p.Thr173Met], [c.796C>T; p.Arg266Cys]) were identified, plus three previously reported missense LRP5 mutations ([c.593A>G; p.Asn198Ser], [c.724G>A; p.Ala242Thr], [c.266A>G; p.Gln89Arg]), associated with HBM in 11 adults from seven families. Individuals with LRP5 HBM (∼prevalence 5/100,000) displayed a variable phenotype of skeletal dysplasia with increased trabecular BMD and cortical thickness on HRpQCT, and gynoid fat mass accumulation on DXA, compared with both non-LRP5 HBM and controls. One mostly asymptomatic woman carried a novel heterozygous nonsense SOST mutation (c.530C>A; p.Ser177X) predicted to prematurely truncate sclerostin. Protein modeling suggests the severity of the LRP5-HBM phenotype corresponds to the degree of protein disruption and the consequent effect on SOST-LRP5 binding. We predict p.Asn198Ser and p.Ala242Thr directly disrupt SOST binding; both correspond to severe HBM phenotypes (BMD Z-scores +3.1 to +12.2, inability to float). Less disruptive structural alterations predicted from p.Arg266Cys, p.Thr173Met, and p.Gln89Arg were associated with less severe phenotypes (Z-scores +2.4 to +6.2, ability to float). In conclusion, although mutations in known HBM loci may be asymptomatic, they only account for a very small proportion (∼3%) of HBM individuals, suggesting the great majority are explained by either unknown monogenic causes or polygenic inheritance.

The impact of LRP5 polymorphism (rs556442) on calcium homeostasis, bone mineral density, and body composition in Iranian children

Failure to achieve optimal bone mass in childhood is the primary cause of decreased adult bone mineral density (BMD) and increased bone fragility in later life. Activating and inactivating LRP5 gene mutations has been associated with extreme bone-related phenotypes. Our aim was to investigate the role of LRP5 polymorphism on BMD, mineral biochemical parameters, and body composition in Iranian children. This cross-sectional study was performed on 9-18 years old children (125 boys, 137 girls). The serum level of calcium, phosphorous, alkaline phosphatase, and vitamin D parameters were checked. The body composition and BMD variables were measured by the Hologic system DXA. The rs566442 (V1119V) coding polymorphism in exon 15 of LRP5 was performed using PCR-RFLP method. Linear regression analysis, with adjustment for age, gender, body size parameters, and pubertal status was used to determine the association between LRP5 polymorphism (rs556442) and bone and body composition parameters. The allele frequency of the rs566442 gene was 35.5 % A and 63.9 % G. Our study revealed that LRP5 (rs556442) has not any significant influence on serum calcium, phosphorus, 25OHvitD, and serum alkaline phosphatase (P > 0.05). Total lean mass was greater in GG genotype (P = 0.028). Total body less head area (P = 0.044), spine BMD (P = 0.04), and total femoral BMC (P = 0.049) were lower in AG heterozygote genotype. This study show LRP5 polymorphism may associate with body composition and BMD in Iranian children. However, further investigations should be done to evaluate the role of other polymorphism.

Atypical femoral fracture in osteoporosis pseudoglioma syndrome associated with two novel compound heterozygous mutations in LRP5

Osteoporosis pseudoglioma syndrome (OPPG) is a rare autosomal recessive condition of congenital blindness and severe childhood osteoporosis with skeletal fragility, caused by loss-of-function mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. We report the first case of atypical (subtrochanteric) femoral fracture (AFF) in OPPG, occurring in a 38-year-old man within the context of relatively low bone turnover and trabecular osteoporosis on bone histology. We identify two novel LRP5 mutations: R752W is associated with low bone mineral density (BMD), as demonstrated by the heterozygous carriage identified in his 57-year-old mother; however, the combination of this R752W mutation with another novel W79R mutation, causes a severe case of compound heterozygous OPPG. We undertake 3D homology modeling of the four extracellular YWTD β-propeller/EGF-like domains (E1-E4) of LRP5, and show that both novel mutations destabilize the β-propeller domains that are critical for protein and ligand binding to regulate Wnt signaling and osteoblast function. Although AFFs have been reported in other rare bone diseases, this is the first in a genetic condition of primary osteoblast dysfunction. The relatively low bone turnover observed, and knowledge of LRP5 function, implicates impaired bone remodeling in the pathogenesis of AFF.

The genetics of osteoporosis

INTRODUCTION

Osteoporosis is the commonest metabolic bone disease worldwide. The clinical hallmark of osteoporosis is low trauma fracture, with the most devastating being hip fracture, resulting in significant effects on both morbidity and mortality.

SOURCES OF DATA

Data for this review have been gathered from the published literature and from a range of web resources.

AREAS OF AGREEMENT

Genome-wide association studies in the field of osteoporosis have led to the identification of a number of loci associated with both bone mineral density and fracture risk and further increased our understanding of disease.

AREAS OF CONTROVERSY

The early strategies for mapping osteoporosis disease genes reported only isolated associations, with replication in independent cohorts proving difficult. Neither candidate gene or linkage studies showed association at genome-wide level of significance.

GROWING POINTS

The advent of massive parallel sequencing technologies has proved extremely successful in mapping monogenic diseases and thus leading to the utilization of this new technology in complex disease genetics.

AREAS TIMELY FOR DEVELOPING RESEARCH

The identification of novel genes and pathways will potentially lead to the identification of novel therapeutic options for patients with osteoporosis.

Recent genetic discoveries in osteoporosis, sarcopenia and obesity

Osteoporosis is a skeletal disorder characterized by low bone mineral density (BMD) and an increased susceptibility to fractures. Evidence from genetic studies indicates that BMD, a complex quantitative trait with a normal distribution, is genetically controlled. Genome-wide association studies (GWAS) as well as studies using candidate gene approaches have identified single-nucleotide polymorphisms (SNPs) that are associated with BMD, osteoporosis and osteoporotic fractures. These SNPs have been mapped close to or within genes including those encoding WNT/β-catenin signaling proteins. Understanding the genetics of osteoporosis will help to identify novel candidates for diagnostic and therapeutic targets. Genetic factors are also important for the development of sarcopenia, which is characterized by a loss of lean body mass, and obesity, which is characterized by high fat mass. Hence, in this review, we discuss the genetic factors, identified by genetic studies, which regulate the body components related to osteoporosis, sarcopenia, and obesity.

Wnts' fashion statement: from body stature to dysplasia

Bone is constantly being made and remodeled to maintain bone volume and calcium homeostasis. Even small changes in the dosage, location and duration of int/Wingless (Wnt) signaling affect skeletal development and homeostasis. Wnt/β-catenin signaling controls cell fate determination, proliferation and survival by affecting a balance between bone-forming osteoblast and bone-resorbing osteoclast cell differentiation. During early skeletal development, Wnt/β-catenin signaling is required in directing mesenchymal progenitor cells toward the osteoblast lineage. Later, Wnt/β-catenin in chondrocytes of the growth plate promotes chondrocyte survival, hypertrophic differentiation and endochondral ossification. Gain- or loss-of-function mutations in the Wnt signaling components are causally linked to high or low bone mass in mice and humans. Inactivation of Wnt/β-catenin signaling leads to imbalance between bone formation and resorption because of accelerated osteoclastogenesis due to decline in the levels of osteoprotegerin (OPG) secreted by osteoblasts or directly via Frizzled 8 (Fzd8). In this review, we provide a landscape of the Wnt pathway components in influencing progenitor cell differentiation toward osteoblasts or osteoclasts under physiological conditions as well as pathological disorders resulting in various skeletal dysplasia syndromes.

The ever-expanding conundrum of primary osteoporosis: aetiopathogenesis, diagnosis, and treatment

In recent years, as knowledge regarding the etiopathogenetic mechanisms of bone involvement characterizing many diseases has increased and diagnostic techniques evaluating bone health have progressively improved, the problem of low bone mass/quality in children and adolescents has attracted more and more attention, and the body evidence that there are groups of children who may be at risk of osteoporosis has grown. This interest is linked to an increased understanding that a higher peak bone mass (PBM) may be one of the most important determinants affecting the age of onset of osteoporosis in adulthood. This review provides an updated picture of bone pathophysiology and characteristics in children and adolescents with paediatric osteoporosis, taking into account the major causes of primary osteoporosis (PO) and evaluating the major aspects of bone densitometry in these patients. Finally, some options for the treatment of PO will be briefly discussed.

Association of LRP5 genotypes with osteoporosis in Tunisian post-menopausal women

Background

Osteoporosis is a highly heritable trait. Among the genes associated with bone mineral density (BMD), the low-density lipoprotein receptor-related protein 5 gene (LRP5) has been consistently identified in Caucasians. However LRP5 contribution to osteoporosis in populations of other ethnicities remains poorly known.

Methods

To determine whether LRP5 polymorphisms Ala1330Val and Val667Met are associated with BMD in North Africans, these genotypes were analyzed in 566 post-menopausal Tunisian women with mean age of 59.5 ± 7.7 years, of which 59.1% have low bone mass (T-score < −1 at spine or hip).

Results

In post-menopausal Tunisian women, 1330Val was weakly associated with reduced BMD T-score at lumbar spine (p = 0.047) but not femur neck. Moreover, the TT/TC genotypes tended to be more frequent in women with osteopenia and osteoporosis than in women with normal BMD (p = 0.066). Adjusting for body size and other potential confounders, LRP5 genotypes were no longer significantly associated with aBMD at any site.

Conclusions

The less common Val667Met polymorphism showed no association with osteoporosis. The Ala1330Val polymorphism is weakly associated with lower lumbar spine bone density and osteopenia/osteoporosis in postmenopausal Tunisian women. These observations expand our knowledge about the contribution of LRP5 genetic variation to osteoporosis risk in populations of diverse ethnic origin.

Pregnancy-associated osteoporosis with a heterozygous deactivating LDL receptor-related protein 5 (LRP5) mutation and a homozygous methylenetetrahydrofolate reductase (MTHFR) polymorphism

Pregnancy-associated osteoporosis (PAO) is a rare, idiopathic disorder that usually presents with vertebral compression fractures (VCFs) within 6 months of a first pregnancy and delivery. Spontaneous improvement is typical. There is no known genetic basis for PAO. A 26-year-old primagravida with a neonatal history of unilateral blindness attributable to hyperplastic primary vitreous sustained postpartum VCFs consistent with PAO. Her low bone mineral density (BMD) seemed to respond to vitamin D and calcium therapy, with no fractures after her next successful pregnancy. Investigation of subsequent fetal losses revealed homozygosity for the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism associated both with fetal loss and with osteoporosis (OP). Because her neonatal unilateral blindness and OP were suggestive of loss-of-function mutation(s) in the gene that encodes LDL receptor-related protein 5 (LRP5), LRP5 exon and splice site sequencing was also performed. This revealed a unique heterozygous 12-bp deletion in exon 21 (c.4454_4465del, p.1485_1488del SSSS) in the patient, her mother and sons, but not her father or brother. Her mother had a normal BMD, no history of fractures, PAO, ophthalmopathy, or fetal loss. Her two sons had no ophthalmopathy and no skeletal issues. Her osteoporotic father (with a family history of blindness) and brother had low BMDs first documented at ages ∼40 and 32 years, respectively. Serum biochemical and bone turnover studies were unremarkable in all subjects. We postulate that our patient's heterozygous LRP5 mutation together with her homozygous MTHFR polymorphism likely predisposed her to low peak BMD. However, OP did not cosegregate in her family with the LRP5 mutation, the homozygous MTHFR polymorphism, or even the combination of the two, implicating additional genetic or nongenetic factors in her PAO. Nevertheless, exploration for potential genetic contributions to PAO may explain part of the pathogenesis of this enigmatic disorder and identify some at-risk women.

Low bone mineral density is associated with dyslipidemia in South Korean men: the 2008-2010 Korean National Health and Nutrition Examination Survey

This study examined the relationship between bone mineral density (BMD) and dyslipidemia in South Korean men. Data from 6,300 men who participated in the Korean National Health and Nutrition Examination Survey from 2008 to 2010 were analyzed, including serum levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) after 8 hours of fasting and mean BMD measured at the lumbar spine (LS), total hip (TH), and femoral neck (FN). Dyslipidemia was defined according to the criteria of the National Cholesterol Education Program Adult Treatment Panel III. Other parameters of dyslipidemia were also calculated, such as TG/HDL-C, TC/HDL-C, non-HDL-C (NHDL-C), and LDL-C/HDL-C. Men with dyslipidemia and high levels of TG, TG/HDL-C, TC/HDL-C, NHDL-C, and LDL-C/HDL-C had lower BMD than men without dyslipidemia at the LS, TH, and FN after adjustment for age and body mass index (all p<0.01). On multivariable regression analysis, all odds ratios for high levels of TG, TG/HDL-C, TC/HDL-C, NHDL-C, and LDL-C/HDL-C with an increase in BMD (per standard deviation) were <1 at all 3 sites after adjustment for age and body mass index (model 1). After adjustment for all covariates, only odds ratios for high levels of TG, TG/HDL-C, TC/HDL-C, and NHDL-C were <1 at all 3 sites (model 2), but an increase in BMD was not associated with high LDL-C levels in models 1 and 2. In conclusion, BMD was inversely correlated with parameters of atherogenic dyslipidemia in South Korean men.

Association of LRP5 haplotypes with osteoporosis in Mexican women

Osteoporosis is a common health problem in Mexico, so it is essential to investigate the status of different gene polymorphisms that could serve as genetic susceptibility markers in the Mexican population. Genes with a role in bone metabolism are excellent candidates for association studies. In this study were determined the allelic and genotypic frequencies of four polymorphic markers (C/T rs3736228, G/A rs4988321, T/C rs627174 and T/C rs901824) in the low-density lipoprotein receptor-related protein 5 gene (LRP5) and their association with osteoporosis in 100 pos-menopausal osteoporotic Mexican women and their controls, using real time-PCR and TaqMan probes. Only the G/A polymorphism (rs4988321, Val667Met) showed significant differences (p = 0.039) when genotype frequencies were compared. However, when the haplotypes of these four polymorphisms were analyzed, interesting associations became evident. The CGTT haplotype showed significant association with low risk of osteoporosis (OR 0.629; p = 0.007; [95 % CI, 0.448-0.884]), whereas the TACT haplotype was significantly associated with a higher risk of osteoporosis (OR 7.965; p = 0.006; [95 % CI, 1.557-54.775]). Our results supported the association of LRP5 with osteoporosis and showed the potential value of LRP5 haplotypes to identify risk of osteoporosis in Mexican population.

Genetic predictors of skeletal outcomes in healthy fertile women: the Bonturno study

Skeletal traits as height (Ht) or bone mineral density (BMD) are strongly inherited. Low-density lipoprotein receptor-related protein 5 (LRP5) and farnesyl diphosphonate synthase (FDPS) are candidate genes for bone phenotypes. From Bonturno study, we genotyped 570 healthy Caucasian women aged 20 to 50 years (yrs) for LRP5 rs4988321 (A/G) and rs3736228 (C/T) and FDPS rs2297480 (A/C) single nucleotide polymorphisms. Serum C-telopeptide of type I collagen (CTX), osteocalcin (OC), and N-terminal propeptide of type I procollagen (P1NP) were measured in BMD-evaluated subjects at lumbar spine (LS), total hip (TH) and femoral neck (FN) sites. LRP5 rs4988321 locus correlated with FN-BMD (P = 0.0230), while LRP5 rs3736228 genotypes differed in LS-BMD (P = 0.0428). When clustered by age, lower FN-BMD was detected in LRP5 GG (P = 0.030) subjects of 41 to 50 years but not in younger. Both LRP5 GG and CC genotypes showed higher age-adjusted values of OC, CTX and P1NP. Increased CTX values were in LRP5 GGCC subjects than in those having at least one LRP5 A plus T alleles (P = 0.0190). LRP5 CC, GG or GGCC subjects with at least one FDPS C allele showed higher levels of CTX and OC in 31 to 40 yrs or older subjects. In conclusion, LRP5 and FDPS loci age-specifically affect skeletal traits in healthy fertile women.

Primary osteoporosis without features of OI in children and adolescents: clinical and genetic characteristics

Our aim was to characterize clinical findings and familial associations, and to examine candidate genes for disease-causing mutations in a cohort of children suffering from primary osteoporosis without features of osteogenesis imperfecta. Patients with osteoporosis and their nuclear families were studied. Medical history was reviewed. Calcium homeostasis parameters were measured and spinal radiographs obtained. BMD was determined by DXA for patients, parents and siblings. LRP5, LRP6, and PTHLH genes were sequenced. Twenty-seven patients (14 males) from 24 families were recruited. Median age at presentation was 10.1 years (range 3.3-15.6 years). One-third of the children had at least one parent with a BMD below the expected range for age. LRP5, LRP6, and PTHLH showed no causative mutations. Four polymorphisms in LRP5 were overrepresented in patients; the minor allele frequency of Q89R, V667M, N740N, and A1330V was significantly higher than in controls. Age of onset, clinical severity, and inheritance patterns are variable in children with primary osteoporosis. Several patients had evidence suggestive of familial transmission. The underlying genetic factors remain to be elucidated.

Mutations in LRP5 cause primary osteoporosis without features of OI by reducing Wnt signaling activity

Background

Primary osteoporosis is a rare childhood-onset skeletal condition whose pathogenesis has been largely unknown. We have previously shown that primary osteoporosis can be caused by heterozygous missense mutations in the Low-density lipoprotein receptor-related protein 5 (LRP5) gene, and the role of LRP5 is further investigated here.

Methods

LRP5 was analyzed in 18 otherwise healthy children and adolescents who had evidence of osteoporosis (manifested as reduced bone mineral density i.e. BMD, recurrent peripheral fractures and/or vertebral compression fractures) but who lacked the clinical features of osteogenesis imperfecta (OI) or other known syndromes linked to low BMD. Also 51 controls were analyzed. Methods used in the genetic analyses included direct sequencing and multiplex ligation-dependent probe amplification (MLPA). In vitro studies were performed using luciferase assay and quantitative real-time polymerase chain reaction (qPCR) to examine the effect of two novel and three previously identified mutations on the activity of canonical Wnt signaling and on expression of tryptophan hydroxylase 1 (Tph1) and 5-hydroxytryptamine (5-Htr1b).

Results

Two novel LRP5 mutations (c.3446 T > A; p.L1149Q and c.3553 G > A; p.G1185R) were identified in two patients and their affected family members. In vitro analyses showed that one of these novel mutations together with two previously reported mutations (p.C913fs, p.R1036Q) significantly reduced the activity of the canonical Wnt signaling pathway. Such reductions may lead to decreased bone formation, and could explain the bone phenotype. Gut-derived Lrp5 has been shown to regulate serotonin synthesis by controlling the production of serotonin rate-limiting enzyme, Tph1. LRP5 mutations did not affect Tph1 expression, and only one mutant (p.L1149Q) reduced expression of serotonin receptor 5-Htr1b (p < 0.002).

Conclusions

Our results provide additional information on the role of LRP5 mutations and their effects on the development of juvenile-onset primary osteoporosis, and hence the pathogenesis of the disorder. The mutations causing primary osteoporosis reduce the signaling activity of the canonical Wnt signaling pathway and may therefore result in decreased bone formation. The specific mechanism affecting signaling activity remains to be resolved in future studies.

Genetic polymorphisms of the Wnt receptor LRP5 are differentially associated with trochanteric and cervical hip fractures

Epidemiological studies suggest that cervical and trochanteric hip fractures have different pathogenesis. We tested the hypothesis that genetic factors have different influences on both types of fractures. Ten polymorphisms of genes known to play an important role in skeletal homeostasis [estrogen receptor alpha (ESR1), aromatase (CYP19A1), type I collagen (COL1A1), and lipoprotein receptor-related protein 5 (LRP5)] were analyzed in 471 Spanish patients with fragility hip fractures. Two polymorphisms of the LRP5 gene (rs7116604 and rs3781600) were associated with the type of fracture (P = 0.0085 and 0.0047, respectively). The presence of rare alleles at each locus was associated with trochanteric fractures over cervical fractures (OR = 1.7 in individuals with at least one rare allele at rs7116604 or rs3781600 loci in comparison with the common homozygotes). Considering individuals bearing the four common alleles as reference, the OR for trochanteric fractures was 1.6 in those with one or two rare alleles and 7.5 in those with three or four rare alleles (P for trend = 0.0074), which is consistent with an allele-dosage effect. There were no significant differences in the frequency distributions of the ESR1, CYP19A1, and COL1A1 genotypes between trochanteric and cervical fractures in either the original group or an extended group of 818 patients. These results suggest that LRP5 alleles influence the type of hip fractures. They support the view that different genetic factors are involved in cervical and trochanteric fractures, which should be taken into consideration in future genetic association studies.

Update on Wnt signaling in bone cell biology and bone disease

For more than a decade, Wnt signaling pathways have been the focus of intense research activity in bone biology laboratories because of their importance in skeletal development, bone mass maintenance, and therapeutic potential for regenerative medicine. It is evident that even subtle alterations in the intensity, amplitude, location, and duration of Wnt signaling pathways affects skeletal development, as well as bone remodeling, regeneration, and repair during a lifespan. Here we review recent advances and discrepancies in how Wnt/Lrp5 signaling regulates osteoblasts and osteocytes, introduce new players in Wnt signaling pathways that have important roles in bone development, discuss emerging areas such as the role of Wnt signaling in osteoclastogenesis, and summarize progress made in translating basic studies to clinical therapeutics and diagnostics centered around inhibiting Wnt pathway antagonists, such as sclerostin, Dkk1 and Sfrp1. Emphasis is placed on the plethora of genetic studies in mouse models and genome wide association studies that reveal the requirement for and crucial roles of Wnt pathway components during skeletal development and disease.

Novel mutations affecting LRP5 splicing in patients with osteoporosis-pseudoglioma syndrome (OPPG)

Osteoporosis-pseudoglioma sydrome (OPPG) is an autosomal recessive disorder with early-onset severe osteoporosis and blindness, caused by biallelic loss-of-function mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Heterozygous carriers exhibit a milder bone phenotype. Only a few splice mutations in LRP5 have been published. We present clinical and genetic data for four patients with novel LRP5 mutations, three of which affect splicing. Patients were evaluated clinically and by radiography and bone densitometry. Genetic screening of LRP5 was performed on the basis of the clinical diagnosis of OPPG. Splice aberrances were confirmed by cDNA sequencing or exon trapping. The effect of one splice mutation on LRP5 protein function was studied. A novel splice-site mutation c.1584+4A>T abolished the donor splice site of exon 7 and activated a cryptic splice site, which led to an in-frame insertion of 21 amino acids (p.E528_V529ins21). Functional studies revealed severely impaired signal transduction presumably caused by defective intracellular transport of the mutated receptor. Exon trapping was used on two samples to confirm that splice-site mutations c.4112-2A>G and c.1015+1G>T caused splicing-out of exons 20 and 5, respectively. One patient carried a homozygous deletion of exon 4 causing the loss of exons 4 and 5, as demonstrated by cDNA analysis. Our results broaden the spectrum of mutations in LRP5 and provide the first functional data on splice aberrations.

High-density polymorphisms analysis of 23 candidate genes for association with bone mineral density

Osteoporosis is a bone disease characterized by low bone mineral density (BMD), a highly heritable and polygenic trait. Women are more prone than men to develop osteoporosis due to a lower peak bone mass and accelerated bone loss at menopause. Peak bone mass has been convincingly shown to be due to genetic factors with heritability up to 80%. Menopausal bone loss has been shown to have around 38% to 49% heritability depending on the site studied. To have more statistical power to detect small genetic effects we focused on premenopausal women. We studied 23 candidate genes, some involved in calcium and vitamin-D regulation and others because estrogens strongly induced their gene expression in mice where it was correlated with humerus trabecular bone density. High-density polymorphisms were selected to cover the entire gene variability and 231 polymorphisms were genotyped in a first sample of 709 premenopausal women. Positive associations were retested in a second, independent, sample of 673 premenopausal women. Ten polymorphisms remained associated with BMD in the combined samples and one was further associated in a large sample of postmenopausal women (1401 women). This associated polymorphism was located in the gene CSF3R (granulocyte colony stimulating factor receptor) that had never been associated with BMD before. The results reported in this study suggest a role for CSF3R in the determination of bone density in women.

Clinical review 2: Genetic determinants of bone density and fracture risk--state of the art and future directions

CONTEXT

Osteoporosis is a common, highly heritable condition that causes substantial morbidity and mortality, the etiopathogenesis of which is poorly understood. Genetic studies are making increasingly rapid progress in identifying the genes involved.

EVIDENCE ACQUISITION AND SYNTHESIS

In this review, we will summarize the current understanding of the genetics of osteoporosis based on publications from PubMed from the year 1987 onward.

CONCLUSIONS

Most genes involved in osteoporosis identified to date encode components of known pathways involved in bone synthesis or resorption, but as the field progresses, new pathways are being identified. Only a small proportion of the total genetic variation involved in osteoporosis has been identified, and new approaches will be required to identify most of the remaining genes.

Replication study of candidate genes/loci associated with osteoporosis based on genome-wide screening

Osteoporosis is a major public health problem characterized by low bone mineral density (BMD). This replication study confirmed 38 single-nucleotide polymorphisms (SNPs) out of 139 SNPs previously reported in three recent genome-wide association studies (GWASs) in an independent US white sample. Ten SNPs achieved combined p < 3.6 x 10(-4).

INTRODUCTION

BMD is under strong genetic control. This study aims to verify the potential associations between BMD and candidate genes/loci reported by GWAS of FHS100K, Icelandic deCODE, and UK-NL.

METHODS

Eight promising (at the genome-wide significant level after Bonferroni correction) and 131 available sub-promising (at the most stringent p value, p < 5.5 x 10(-5) in the three GWASs reports) SNPs were selected. By using genotypic information from Affymetrix 500 K SNP arrays, we tested their associations with BMD in 1,000 unrelated US whites. Fisher's combined probability method was used to quantify the overall evidence of association. BMD was measured by dual energy X-ray absorptiometry.

RESULTS

Two promising SNPs, rs3762397 and rs3736228, were replicated in the current study with p < 0.05. Besides, 36 sub-promising SNPs were replicated at the same significant level. Ten SNPs achieved significant combined p < 3.6 x 10(-4) (0.05/139 SNPs, corrected for multiple testing).

CONCLUSIONS

Osteoporosis susceptibility of 38 SNPs was replicated in 1,000 unrelated US whites. This study showed promise for replication of some initial genome-wide association signals.

Mapping genes for osteoporosis--old dogs and new tricks

In stark contrast to its horticultural origins, modern genetics is an extremely technology-driven field. Almost all the major advances in the field over the past 20 years have followed technological developments that have permitted change in study designs. The development of PCR in the 1980s led to RFLP mapping of monogenic diseases. The development of fluorescent-tagged genotyping methods led to linkage mapping approaches for common diseases that dominated the 1990s. The development of microarray SNP genotyping has led to the genome-wide association study era of the new millennium. And now the development of next-generation sequencing technologies is about to open up a new era of gene-mapping, enabling many potential new study designs. This review aims to present the strengths and weaknesses of the current approaches, and present some new ideas about gene-mapping approaches that are likely to advance our knowledge of the genes involved in heritable bone traits such as bone mineral density (BMD) and fracture.

Various types of LRP5 mutations in four patients with osteoporosis-pseudoglioma syndrome: identification of a 7.2-kb microdeletion using oligonucleotide tiling microarray

Osteoporosis-pseudoglioma syndrome (OPS; OMIM 259770) is an autosomal-recessive genetic disorder characterized by severe osteoporosis and visual disturbance from childhood. Biallelic mutations in the low-density lipoprotein receptor-related protein 5 gene (LRP5) have been frequently detected, while a subset of patients had only one or no detectable mutation. We report on the clinical and molecular findings of four unrelated Japanese patients with the syndrome. The four patients had typical skeletal and ocular phenotypes of OPS, namely severe juvenile osteoporosis and early-onset visual disturbance, with or without mental retardation. We undertook standard PCR-based sequencing for LRP5 and found four missense mutations (p.L145F, p.T244M, p.P382L, and p.T552M), one nonsense mutation (p.R1534X), and one splice site mutation (c.1584+1G>A) among four OPS patients. Although three patients had two heterozygous mutations, one had only one heterozygous splice site mutation. In this patient, RT-PCR from lymphocytic RNA demonstrated splice error resulting in 63-bp insertion between exons 7 and 8. Furthermore, the patient was found to have only mutated RT-PCR fragment, implying that a seemingly normal allele did not express LRP5 mRNA. We then conducted custom- designed oligonucleotide tiling microarray analyses targeted to a 600-kb genome region harboring LRP5 and discovered a 7.2-kb microdeletion encompassing exons 22 and 23 of LRP5. We found various types of LRP5 mutations, including an exon-level deletion that is undetectable by standard PCR-based mutation screening. Oligonucleotide tiling microarray seems to be a powerful tool in identifying cryptic structural mutations.

The role of cigarette smoking and statins in the development of postmenopausal osteoporosis: a pilot study utilizing the Marshfield Clinic Personalized Medicine Cohort

SUMMARY

A cohort of postmenopausal osteoporotic females and controls with normal bone mineral density, the interleukin 6 (IL6) -634G > C (rs1800796) C allele of the promoter region showed association with osteoporosis. The lipoprotein receptor-related protein 5 (LRP5) gene showed association between C135242T C/T alleles and osteoporosis only in smokers, suggesting a role for environmental interaction.

INTRODUCTION

A nested case-control study within a population-based cohort was undertaken to assess the relative impact of cigarette smoking, statin use, genetic polymorphisms, and one-way interaction of these factors on development of osteoporosis in postmenopausal women.

METHODS

Genotyping of 14 single-nucleotide polymorphisms (SNPs) corresponding to vitamin D receptor gene, estrogen receptor 1, collagen type 1 alpha 1, IL6, transcription growth factor beta, apolipoprotein E, and LRP5 genes was performed in cases (n = 309) with osteoporosis and controls (n = 293) with normal bone mineral density drawn from a homogeneous Caucasian population. SNPs were chosen based on known functional consequences or prior evidence for association and genotyped using matrix-assisted laser desorption ionization time-of-flight technology.

RESULTS

Cases differed from controls relative to body mass index, age, and smoking but not statin use. After adjusting for age, the IL6 -634G > C (rs1800796) allele showed association with osteoporosis (odds ratio (OR) for CC + CG = 2.51, p = 0.0047)), independent of statin use or smoking status. On stratification for smoking, association with LRP5 C135242T (rs545382) and osteoporosis emerged (OR 2.8 in smokers for CT alleles, p = 0.03)), suggestive of potential environmental interaction.

CONCLUSION

Evidence suggested a role for genetic variation in IL6 and LRP5 in conferring risk for osteoporosis in Caucasian women, with the latter manifest only in smokers.

Association of single nucleotide polymorphisms in secreted frizzled-related protein 1 gene with bone mineral density in Japanese women

AIM

Recent studies have demonstrated that the Wnt signaling pathway plays an important role in bone metabolism. The purpose of this study was to examine whether the gene of secreted frizzled-related protein 1 (SFRP1), a Wnt antagonist, is involved in the etiology of osteoporosis using association study.

METHODS

Seven single nucleotide polymorphisms (SNP) in the SFRP1 gene were genotyped and analyzed for association with bone mineral density (BMD) in 931 Japanese women (63.5 +/- 6.7 years old, mean +/- standard deviation).

RESULTS

One SNP (rs16890444) located in intron and another (rs3242) located in the 3'-untranslated region of the sFRP1 gene were significantly associated with the lumbar spine BMD value, and BMD values for both the femoral neck and the total hip, respectively. Women with the T/T genotype of the former SNP had a lower BMD value of the lumbar spine (L2-L4) compared with those with C/C or C/T (BMD value adjusted for age, duration after menopause, and body mass index: 0.781 vs 0.830, P = 0.037), while women with the T/T genotype of the latter SNP had higher BMD values of femoral neck and total hip compared with those with C/C or C/T (adjusted BMD value: femoral neck, 0.721 vs 0.633, P = 0.025; total hip, 0.834 vs 0.737, P = 0.027).

CONCLUSION

These results suggest that the SFRP1 may be a candidate gene for a BMD determinant, but further studies need to consolidate the present findings.

Genetics of osteoporosis: accelerating pace in gene identification and validation

Osteoporosis is characterized by low bone mineral density and structural deterioration of bone tissue, leading to an increased risk of fractures. It is the most common metabolic bone disorder worldwide, affecting one in three women and one in eight men over the age of 50. In the past 15 years, a large number of genes have been reported as being associated with osteoporosis. However, only in the past 4 years we have witnessed an accelerated pace in identifying and validating osteoporosis susceptibility loci. This increase in pace is mostly due to large-scale association studies, meta-analyses, and genome-wide association studies of both single nucleotide polymorphisms and copy number variations. A comprehensive review of these developments revealed that, to date, at least 15 genes (VDR, ESR1, ESR2, LRP5, LRP4, SOST, GRP177, OPG, RANK, RANKL, COLIA1, SPP1, ITGA1, SP7, and SOX6) can be reasonably assigned as confirmed osteoporosis susceptibility genes, whereas, another >30 genes are promising candidate genes. Notably, confirmed and promising genes are clustered in three biological pathways, the estrogen endocrine pathway, the Wnt/beta-catenin signaling pathway, and the RANKL/RANK/OPG pathway. New biological pathways will certainly emerge when more osteoporosis genes are identified and validated. These genetic findings may provide new routes toward improved therapeutic and preventive interventions of this complex disease.

Analysis of association of LRP5, LRP6, SOST, DKK1, and CTNNB1 genes with bone mineral density in a Slovenian population

The Wnt pathway has a bifunctional role in bone mass regulation, influencing osteoblasts and osteoclasts. The Wnt pathway genes are therefore candidate genes for susceptibility to osteoporosis. In our study, we focused on the effects of polymorphisms in selected Wnt pathway genes: low-density lipoprotein receptor-related proteins 5 and 6 (LRP5 and LRP6), Dickkopf1 (DKK1), sclerostin (SOST), and beta-catenin (CTNNB1). We genotyped 652 subjects for the following polymorphisms: A1330V in LRP5; I1062V in LRP6; E232K in DKK1; D32Y, G34V, and N287S in CTNNB1; and -1397_-1396insGGA in SOST. Bone mineral density (BMD) was also measured. The allele frequencies were as follows: for A1330V C:T = 87%:13%, for I1062V C:T = 20%:80%, and for -1397_-1396insGGA-:GGA = 64%:36%. The studied nucleotide changes in the DKK1 and CTNNB1 genes were shown not to be polymorphic. In a Slovenian population, no association was shown between lumbar spine and femoral neck BMD in A1330V (P = 0.151 and 0.243) and in I1062V (P = 0.209 and 0.405). We observed a difference between SOST genotypes, corresponding to an allele dose effect, which was borderline significant for lumbar spine and femoral neck BMD (P = 0.047 and 0.085); but this did not survive the adjustment for multiple testing. These results indicate that a larger sample size would be necessary to detect these subtle effects. Our results suggest that A1330V in LRP5, I1062V in LRP6, and -1397_-1396insGGA in SOST are not associated with BMD in the Slovenian population.

Body composition and bone mineral density in children with premature adrenarche and the association of LRP5 gene polymorphisms with bone mineral density

CONTEXT

Precocious increase in adrenal androgen production is the hallmark of premature adrenarche (PA). Adrenal androgens have anabolic properties.

OBJECTIVE

The objective of the study was to test whether body composition and bone mineral density (BMD) are altered in PA and study whether genetic variation in low-density lipoprotein receptor-related protein 5 (LRP5) affects BMD in PA.

DESIGN

This was a cross-sectional study.

SETTING

The study was conducted at a university hospital.

SUBJECTS AND MEASURES

The study included 126 prepubertal children (64 with PA, 10 boys; 62 non-PA controls, 10 boys). Femoral neck and lumbar spine areal and calculated volumetric BMD (dual energy X-ray absorptiometry), body composition (bioimpedance), serum 25-hydroxyvitamin D, and markers of bone turnover and calcium homeostasis were compared between the PA and control groups. Single-nucleotide polymorphisms of LRP5 were determined and associated with BMD.

RESULTS

Children with PA had higher femoral neck and lumbar spine BMD(areal) than the controls (Z-score 0.56 vs. -0.09, P < 0.001, and 0.20 vs. -0.31, P = 0.009, respectively). However, the mean BMDs did not differ significantly between the groups when adjusted for height or bone size. BMD(areal) correlated strongly with height sd score in both groups. Among the PA children, LRP5 single-nucleotide polymorphism E644E minor variant was associated with lower and F549F minor variant with higher BMD. Total body fat mass, fat percent, serum PTH, and alkaline phosphatase concentrations were higher and 25-hydroxyvitamin D lower in the PA group.

CONCLUSIONS

Prepubertal children with PA had higher BMD(areal) compared with healthy controls. This was mainly explained by their increased height. LRP5 polymorphisms may contribute to bone mass accrual in prepubertal PA children.

LRP5 sequence and polymorphisms in the baboon

BACKGROUND

LRP5 is known to have an important relationship with bone density and a variety of other biological processes. Mapping to human chromosome 11q13.2, LRP5 shows considerable evolutionary conservation. Orthologs of this gene exist in many species, although comparison of human LRP5 with other non-human primates has not been performed until now.

METHODS

We reported the complementary DNA (cDNA) sequence and deduced amino acid sequence for baboon LRP5, and compared the baboon and human sequences. cDNA sequences for 21 baboons were examined to identify single-nucleotide polymorphisms (SNPs).

RESULTS

Sequences of coding regions in human and baboon LRP5 showed 97- 99% homology. Twenty-five SNPs were identified in the coding region of baboon LRP5.

CONCLUSION

The observed degree of coding sequence homology in LRP5 led us to expect that the baboon may serve as a useful model for future research into the role(s) of this gene in primate metabolic diseases.

LRP5 in premature adrenarche and in metabolic characteristics of prepubertal children

OBJECTIVE

Premature adrenarche (PA) is associated with unfavourable metabolic characteristics. We hypothesized that genetic variation in low density lipoprotein (LDL) receptor-related protein 5 (LRP5), which is involved in Wnt signalling in the adrenal cortex and in cholesterol metabolism, plays a role in the pathogenesis of PA.

DESIGN AND PATIENTS

We performed a cross-sectional association study in 73 Finnish children with PA and 97 age- and gender-matched healthy controls.

MEASUREMENTS

LRP5 genotypes were determined by direct sequencing. Single-marker associations with clinical-metabolic characteristics, including adrenocortical function, glucose tolerance and lipid profile, were examined with age and gender as covariates.

RESULTS

Nineteen single nucleotide polymorphisms (SNPs) in LRP5 were found in the 170 children. No significant differences in the genotype distributions were observed between the PA and control groups. SNPs A1330V and N740N were associated with higher serum dehydroepiandrosterone sulphate (DHEAS) levels in the control subjects (A/A vs. A/a; mean 0.8 vs. 1.4 micromol/l, P = 0.01). They were also associated with higher plasma levels of total (4.2 vs. 4.7 mmol/l, P = 0.02) and LDL cholesterol (2.4 vs. 2.9 mmol/l, P = 0.02) in the control group, as was SNP V1119V (P = 0.04 and P = 0.03, respectively). SNPs F549F and V1119V were associated with higher systolic blood pressure (P = 0.04 and P = 0.02, respectively). There were no differences in the parameters of glucose metabolism between the genotype groups.

CONCLUSIONS

Genetic variation in LRP5 did not predispose to PA but was associated with metabolic characteristics, especially lipid profile, in healthy prepubertal children.

No association between hip geometry and four common polymorphisms associated with fracture: the Danish osteoporosis prevention study

Both osteoporosis and hip geometry are independently associated with fracture risk. There is a significant genetic contribution to the risk of osteoporosis, and evidence provided by twin studies has suggested that hip geometry may also in part be genetically programmed. Polymorphisms in a number of genes, including those coding for methylene-tetrahydrofolate reductase (MTHFR c.677C > T), the purinergic P2X(7) receptor (Glu496Ala and Ile568Asn), and the low-density lipoprotein receptor-related protein 5 (LRP5 exon 9 [c.266A > G]), have been associated with an increased fracture incidence and/or reduced bone mineral density (BMD). The aim of the present study was to test whether these polymorphisms influence hip structural geometry in perimenopausal women. The four polymorphisms were genotyped in 800 healthy recently perimenopausal women never using hormone replacement therapy. BMD of the femoral neck was measured using a Hologic QDR-2000 densitometer and femoral neck axis length, neck width, neck shaft angle, and femoral head diameter were measured from the screen images. Genotype frequencies were compatible with Hardy-Weinberg equilibrium. No significant differences between homozygotes for the minor allele and carriers of the common allele regarding parameters of hip geometry were demonstrated. According to the anthropometric characteristics of the subjects, only body height in the MTHFR TT genotype group was significantly different from the combined CT/CC genotype group (P < 0.05). The geometric dimensions of the proximal femur in perimenopausal women are not associated with the MTHFR c.677C > T, P2X(7) (Glu496Ala), P2X(7) (Ile568Asn), and LRP5 exon 9 (c.266A > G) polymorphisms.

Quantitative trait loci, genes, and polymorphisms that regulate bone mineral density in mouse

This is an in silico analysis of data available from genome-wide scans. Through analysis of QTL, genes and polymorphisms that regulate BMD, we identified 82 BMD QTL, 191 BMD-associated (BMDA) genes, and 83 genes containing known BMD-associated polymorphisms (BMDAP). The catalogue of all BMDA/BMDAP genes and relevant literatures are provided. In total, there are substantially more BMDA/BMDAP genes in regions of the genome where QTL have been identified than in non-QTL regions. Among 191 BMDA genes and 83 BMDAP genes, 133 and 58 are localized in QTL regions, respectively. The difference was still noticeable for the chromosome distribution of these genes between QTL and non-QTL regions. These results have allowed us to generate an integrative profile of QTL, genes, polymorphisms that determine BMD. These data could facilitate more rapid and comprehensive identification of causal genes underlying the determination of BMD in mouse and provide new insights into how BMD is regulated in humans.

Replication of associations between LRP5 and ESRRA variants and bone density in premenopausal women

Replication is a critical step to validate positive genetic associations. In this study, we tested two previously reported positive associations. The low density lipoprotein receptor-related protein 5 (LRP5) Val667Met and lumbar spine bone density are replicated. This result is in line with results from large consortiums such as Genomos. However, the estrogen-related receptor alpha (ESRRA) repeat in the promoter is not replicated although the polymorphism studied was functional and could have been a causative variant.

INTRODUCTION

We sought to validate associations previously reported between LRP5 V667M polymorphism and lumbar spine (LS, p = 0.013) and femoral neck (FN, p = 0.0002) bone mineral density (BMD), and between ESRRA 23 base pair repeat polymorphism and LS BMD (p = 0.0036) in a sample of premenopausal Caucasian women using an independent sample.

METHODS

For the replication sample, we recruited 673 premenopausal women from the Toronto metropolitan area. All women were Caucasian and had BMD measured. LRP5 V667M was genotyped by allele-specific PCR and ESRRA repeats by sizing of PCR products on agarose gels.

RESULTS

We reproduced the same association as we reported previously between LRP5 V667M and LS BMD (p = 0.015) but not with FN BMD (p = 0.254). The combined data from the two populations indicate an effect size of 0.28SD for LS BMD (p = 0.00048) and an effect size of 0.26 SD for FN BMD (p = 0.00037). In contrast, the association we reported earlier between ESRRA repeats and LS BMD was not replicated in the sample from Toronto (p = 0.645).

CONCLUSIONS

The association between LRP5 V667M and LS BMD is confirmed but not that between ESRRA repeats and LS BMD. This result indicates that it is imperative to validate any positive association in an independent sample.

Association between the A1330V polymorphism of the low-density lipoprotein receptor-related protein 5 gene and bone mineral density: a meta-analysis

The association between the A1330V polymorphism of the low-density lipoprotein receptor-related protein 5 gene (LRP5) with bone mineral density (BMD) has been studied, but results have been mixed. Accordingly, the authors performed a meta-analysis on studies on the association between the A1330V LRP5 polymorphism and BMD. Appropriate studies were identified using MEDLINE and by manual searching. A total of 7 separate comparisons were considered in this meta-analysis. Individuals with the AA genotype showed significantly higher lumbar BMD than those with the AV/VV or VV genotype. Weighted mean differences (WMDs) were 0.147 g/cm(2) (95% confidence interval [CI] 0.069-0.224, P < 0.001) and 0.182 g/cm(2) (95% CI 0.024-0.340, P = 0.024) without between-study heterogeneity for AA versus AV/VV and AA versus VV, respectively. Six studies analyzed femur neck (FN) BMD. Individuals with the AA genotype had a significantly higher FN BMD than those with the AV/VV genotype (WMD = 0.165 g/cm(2), 95% CI = 0.087-0.215, P < 0.001), without between-study heterogeneity. Trochanter BMD was measured in three studies. Results showed that subjects with the AA genotype tended to have higher BMD than patients with the AV or VV genotype (WMD = 0.136 g/cm(2), 95% CI = -0.002 to 0.274, P = 0.053). In conclusion, this meta-analysis shows that the LRP5 A1330V polymorphism is associated with BMD, and that individuals with the AA genotype have a higher BMD than those with the AV/VV or VV genotype.

Radiographic osteoarthritis at three joint sites and FRZB, LRP5, and LRP6 polymorphisms in two population-based cohorts

OBJECTIVE

To examine the association of genetic variation in key players in the Wnt signaling pathway with aspects of osteoarthritis (OA) in two population-based cohort studies: the Rotterdam Study and the Chingford Study.

METHODS

Radiographic OA (ROA) was defined as a Kellgren/Lawrence score (K/L) score > or = 2 for the knee and hip. Total hip replacement (THR) was scored. Hand OA was defined as presence of ROA (K/L > or = 2) in two out of three hand joint groups [distal interphalangeal (DIPs), proximal interphalangeal (PIPs), first carpometacarpal (CMC1)/trapezio-scaphoid joint (TS)] of each hand. The concentration of urinary C-terminal cross-linked telopeptide of type II collagen (CTX-II) was standardized to the total urine creatinine. Genotypes for the amino acid variants, Arg200Trp and Arg324Gly of Frizzled-Related protein gene (FRZB), Ala1330Val of Low-density lipoprotein receptor-related protein 5 (LRP5) and Ile1062Val of Low-density lipoprotein receptor-related protein 6 (LRP6), were obtained using the Taqman allelic discrimination assay. A meta-analysis was performed for the FRZB Arg324Gly polymorphism and hip- and knee-OA using RevMan version 4.3.

RESULTS

No consistent associations were observed between the FRZB, LRP5 and LRP6 amino acid variants and radiographic hip-, knee-, or hand-OA or THR, in either study population. While power was limited for most studies to date, a meta-analysis of all published studies regarding the FRZB Arg324Gly polymorphism was performed for hip- and knee-OA separately. This showed no significant associations between the Gly324 allele and risk for hip- or knee OA, although there was large heterogeneity between studies for hip OA in females.

CONCLUSION

No association was seen between FRZB, LRP5 and LRP6 variants with radiographic osteoarthritic outcomes in two population-based cohorts. In future studies, increased power and standardization of OA-phenotypes are highly recommended for replication studies and to allow meta-analysis.