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

Whole Genome Sequencing Unravels New Genetic Determinants of Early-Onset Familial Osteoporosis and Low BMD in Malta

Background: Osteoporosis is a skeletal disease with a strong genetic background. The study aimed to identify the genetic determinants of early-onset familial osteoporosis and low bone mineral density (BMD) in a two-generation Maltese family. Methods: Fifteen relatives aged between 28–74 years were recruited. Whole genome sequencing was conducted on 12 relatives and shortlisted variants were genotyped in the Malta Osteoporotic Fracture Study (MOFS) for replication. Results: Sequential variant filtering following a dominant inheritance pattern identified rare missense variants within SELP, TGF-β2 and ADAMTS20, all of which were predicted to be likely pathogenic and participate in osteoimmunology. TGF-β2 c.1136C>T was identified in five individuals from the MOFS in heterozygosity, four of whom had osteopenia/osteoporosis at the lumbar spine and hip, and/or had sustained a low-trauma fracture. Heterozygosity for the ADAMTS20 c.4090A>T was accompanied by lower total hip BMD (p = 0.018) and lower total serum calcium levels in MOFS (p < 0.01), recapitulating the findings from the family. Women carrying at least one copy of the alternative allele (TC/CC) for SELP c.2177T>C exhibited a tendency for lower lumbar spine BMD and/or wrist fracture history relative to women with TT genotype. Conclusions: Our findings suggest that the identified variants, alone or in combination, could be causal factors of familial osteoporosis and low BMD, requiring replication in larger collections.

Wnt signaling: An attractive target for periodontitis treatment

Periodontitis is the most common chronic inflammatory disease, and a leading cause of tooth loss. Characterized by resorption of alveolar process and destruction of periodontal ligaments, periodontitis can impact not only periodontal tissues but also systemic diseases, such as diabetes, cardiovascular diseases, and respiratory infections. Currently, it is a hotspot to manage destruction and gain regeneration of periodontal tissues. Increasing evidence indicates that the Wnt signaling plays an important role in homeostasis of periodontal tissues, functions of periodontal derived cells, and progression of periodontitis. Its molecule expressions were abnormal in periodontitis. As such, modulators targeting the Wnt signaling may be an adjuvant therapy for periodontitis treatment. This review elucidates the role of Wnt signaling and its molecules, with a view to develop a potential application of drugs targeting the Wnt signaling for periodontitis treatment.

Comparative proteomics analysis of microvesicles in human serum for the evaluation of osteoporosis

Osteoporosis is an emerging health issue worldwide. Due to the decrease of bone mineral density and the deterioration of skeletal microarchitecture, osteoporosis could lead to increased bone fragility and higher fracture risk. Since lack of specific symptoms, novel serum proteomic indicators are urgently needed for the evaluation of osteoporosis. Microvesicles (MVs) are important messengers widely present in body fluids and have emerged as novel targets for the diagnosis of multiple diseases. In this study, MVs were successfully isolated from human serum and comprehensively characterized. Comparative proteomics analysis revealed differential MVs protein profiling in normal subjects, osteopenia patients, and osteoporosis patients. In total, about 200 proteins were identified and quantified from serum MVs, among which 19 proteins were upregulated (fold change >2) and five proteins were downregulated (fold change <0.5) in osteopenia group and osteoporosis group when compared with the normal group. Three protein candidates were selected for initial verification, including Vinculin, Filamin A, and Profilin 1. Profilin 1 was further pre-validated in an independent sample set, which could differentiate osteoporosis group from osteopenia group and normal group (p < 0.05). Our data collectively demonstrate that serum MVs proteome can be valuable indicators for the evaluation and diagnostics of bone loss disease.

Assessing the Genetic Correlations Between Blood Plasma Proteins and Osteoporosis: A Polygenic Risk Score Analysis

Osteoporosis is a common metabolic bone disease. The impact of global blood plasma proteins on the risk of osteoporosis remains elusive now. We performed a large-scale polygenic risk score (PRS) analysis to evaluate the potential effects of blood plasma proteins on the development of osteoporosis in 2286 Caucasians, including 558 males and 1728 females. Bone mineral density (BMD) and bone areas at ulna & radius, hip, and spine were measured using Hologic 4500W DXA. BMD/bone areas values were adjusted for age, sex, height, and weight as covariates. Genome-wide SNP genotyping of 2286 Caucasian subjects was performed using Affymetrix Human SNP Array 6.0. The 267 blood plasma proteins-associated SNP loci and their genetic effects were obtained from recently published genome-wide association study (GWAS) using a highly multiplexed aptamer-based affinity proteomics platform. The polygenetic risk score (PRS) of study subjects for each blood plasma protein was calculated from the genotypes data of the 2286 Caucasian subjects by PLINK software. Pearson correlation analysis of individual PRS values and BMD/bone area value was performed using R. Additionally, gender-specific analysis also was performed by Pearson correlation analysis. 267 blood plasma proteins were analyzed in this study. For BMD, we observed association signals between 41 proteins and BMD, mainly including whole body total BMD versus Factor H (p value = 9.00 × 10^-3), whole body total BMD versus BGH3 (p value = 1.40 × 10^-2), spine total BMD versus IGF-I (p value = 2.15 × 10^-2), and spine total BMD versus SAP (p value = 3.90 × 10^-2). As for bone areas, association evidence was observed between 45 blood plasma proteins and bone areas, such as ferritin versus spine area (p value = 1.90 × 10^-2), C4 versus hip area (p value = 1.25 × 10^-2), and hemoglobin versus right ulna and radius area (p value = 2.70 × 10^-2). Our study results suggest the modest impact of blood plasma proteins on the variations of BMD/bone areas, and identify several candidate blood plasma proteins for osteoporosis.

Association of vitamin D receptor ApaI gene polymorphism with osteoporosis susceptibility in postmenopausal Han Chinese women in Xinjiang

Osteoporosis is a polygenic disorder and has been demonstrated to be associated with ~30 candidate genes, the majority of which have also been implicated in the regulation of bone mineral density (BMD). Vitamin D receptor (VDR) is the candidate gene that has been most extensively studied. Certain studies have reported that the VDR single nucleotide polymorphism ApaI is associated with the risk of osteoporosis in Caucasian and African women. However, this association has not yet been studied in postmenopausal Han Chinese women in the Xinjiang area. In the present study, ApaI polymorphisms of VDR were defined by polymerase chain reaction-restriction fragment length polymorphism, in order to analyze the distribution of ApaI polymorphisms in postmenopausal Han Chinese women from Xinjiang. BMD was measured by dual energy X-ray absorptiometry at the lumbar spine (L2-4), Ward's triangle, great trochanter and femoral shaft. A total of 336 women were included in this study. The genotype distribution of ApaI was consistent with the Hardy-Weinberg equilibrium (all P>0.05). There were no significant differences in ApaI genotype frequencies between the 90 cases in the osteoporosis group and 246 cases in the non-osteoporosis group (P=0.946). Meanwhile, it was identified that BMD values of the tested locations were negatively correlated with age (P<0.05) and positively correlated with body mass index (BMI; P<0.05). On further attribution risk analysis, BMD was identified as a risk factor [odds ratio (OR): 0.464, 95% confidence interval (CI): 0.372-0.580, P=0.001] and BMI a protective factor (OR: 1.502, 95% CI: 1.008-2.240, P=0.032) in osteoporosis. When BMD was adjusted for confounding factors including age and BMI, it was observed that the ApaI polymorphism was not associated with BMD at the sites tested (P>0.05). In conclusion, the present study identified no significant association of the common VDR polymorphism ApaI with BMD at several skeletal sites in postmenopausal Han Chinese women in the Xinjiang area. Age was negatively correlated with BMD at different sites and identified as a risk factor; while BMI was positively correlated with BMD and identified as a protective factor.

Osteoporosis-Pseudoglioma in a Mauritanian Child due to a Novel Mutation in LRP5

Osteoporosis-pseudoglioma (OPPG) syndrome is a very rare autosomal recessive disorder, caused by mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. It manifests by severe juvenile osteoporosis with congenital or infancy-onset visual loss. We describe a case of OPPG due to novel mutation in LRP5 gene, occurring in a female Mauritanian child. This 10-year-old female child was born blind, and after then multiple fragility fractures appeared. PCR amplification and sequencing revealed a novel homozygous nonsense mutation in exon 10 of the LRP5 gene (c.2270G>A; pTrP757^⁎); this mutation leads to the production of a truncated protein containing 757 amino acids instead of 1615, located in the third β-propeller domain of the LRP5 protein. Both parents were heterozygous for the mutation. This is the first case of the OPPG described in black Africans, which broadens the spectrum of LRP5 gene mutations in OPPG.

Genetic determinants of fibro-osseous lesions in aged inbred mice

Fibro-osseous lesions in mice are progressive aging changes in which the bone marrow is replaced to various degrees by fibrovascular stroma and bony trabeculae in a wide variety of bones. The frequency and severity varied greatly among 28 different inbred mouse stains, predominantly affecting females, ranging from 0% for 10 strains to 100% for KK/HlJ and NZW/LacJ female mice. Few lesions were observed in male mice and for 23 of the strains, no lesions were observed in males for any of the cohorts. There were no significant correlations between strain-specific severities of fibro-osseous lesions and ovarian (r=0.11; P=0.57) or endometrial (r=0.03; P=0.89) cyst formation frequency or abnormalities in parathyroid glands. Frequency of fibro-osseous lesions was most strongly associated (P<10(-6)) with genome variations on chromosome (Chr) 8 at 90.6 and 90.8Mb (rs33108071, rs33500669; P=5.0·10(-10), 1.3·10(-6)), Chr 15 at 23.6 and 23.8Mb (rs32087871, rs45770368; P=7.3·10(-7), 2.7·10(-6)), and Chr 19 at 33.2, 33.4, and 33.6Mb (rs311004232, rs30524929, rs30448815; P=2.8·10(-6), 2.8·10(-6), 2.8·10(-6)) in genome-wide association studies (GWAS). The relatively large number of candidate genes identified in the GWAS analyses suggests that this may be an extremely complex polygenic disease. These results indicate that fibro-osseous lesions are surprisingly common in many inbred strains of laboratory mice as they age. While this presents little problem in most studies that utilize young animals, it may complicate aging studies, particularly those focused on bone.

LRP receptor family member associated bone disease

A dozen years ago the identification of causal mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene involved in two rare bone disorders propelled research in the bone field in totally new directions. Since then, there have been an explosion in the number of reports that highlight the role of the Wnt/β-catenin pathway in the regulation of bone homeostasis. In this review we discuss some of the most recent reports (in the past 2 years) highlighting the involvement of the members of the LRP family (LRP5, LRP6, LRP4, and more recently LRP8) in the maintenance of bone and their implications in bone diseases. These reports include records of new single nucleotides polymorphisms (SNPs) and haplotypes that suggest variants in these genes can contribute to subtle variation in bone traits to mutations that give rise to extreme bone phenotypes. All of these serve to further support and reinforce the importance of this tightly regulated pathway in bone. Furthermore, we discuss provocative reports suggesting novel approaches through inhibitors of this pathway to treat rarer diseases such as Osteoporosis-Pseudoglioma Syndrome (OPPG), Osteogenesis Imperfecta (OI), and Sclerosteosis/Van Buchem disease. It is hoped that by understanding the role of each component of the pathway and their involvement in bone diseases that this knowledge will allow us to develop new, more effective therapeutic approaches for more common diseases such as post-menopausal osteoporosis, osteoarthritis, and rheumatoid arthritis as well as these rarer bone diseases.

Polymorphisms in VDR gene in Tunisian postmenopausal women are associated with osteopenia phenotype

OBJECTIVES

Osteopenia is characterized by intermediate values of bone mineral density (BMD) as compared to normal and osteoporotic subjects. BMD, a surrogate phenotype for osteoporosis, is influenced in part by genetic factors. Among the genes associated with BMD, the vitamin D receptor (VDR) was the first gene studied as a potential candidate associated with BMD in adult and postmenopausal bone loss. However, results are controversial.

METHODS

To determine whether VDR polymorphisms ApaI and TaqI are associated with BMD, osteopenia, osteoporosis and low-impact fracture risk in North Africans, these genotypes were analyzed in 566 postmenopausal Tunisian women.

RESULTS

In postmenopausal Tunisian women, the GT ApaI genotype seems to be protective against osteoporosis development (p = 0.02; odds ratio = 0.54). Moreover, the presence of the combined GT/TT genotype of ApaI and TaqI polymorphisms is more frequent in normal BMD women than in osteoporotic women (p = 0.00; odds ratio = 0.41). Interestingly, the GG ApaI genotype is associated with osteopenia development (p = 0.02; odds ratio = 1.86) and also the TT TaqI polymorphism (p = 0.02; odds ratio = 1.53). The GG ApaI genotype is associated with a three times risk of vertebral fracture.

CONCLUSIONS

The ApaI polymorphism showed an association with osteopenia and low-impact vertebral fracture incidence but not with osteoporosis. The TaqI polymorphism is associated specifically with the osteopenia phenotype. The presence of the two polymorphisms increases the risk to develop osteopenia in postmenopausal Tunisian women. Osteopenia seems to be genetically determined. However, osteoporosis is the result of interaction between genetic and environmental factors.