The association of polymorphism rs3736228 within the LRP5 gene with Bone Mineral Density in a Cohort of Caucasian Young Adults

INTRODUCTION: Osteoporosis is a significant burden for our aging population. Developing a better understanding of the genetic underpinnings of poor bone quality may assist in the future development of prevention strategies. Correa-Rodriguez et al. have identified a group of single nucleotide polymorphisms (SNPs) that were associated with bone mineral density (BMD) in a population of Spanish Caucasians. In particular, they found that SNP rs3736228 in the low-density lipoprotein receptor related protein 5 (LRP5) gene had an influence on BMD. While the role of LRP5 in the Wnt canonical pathway has been fairly well characterized, its association with phenotypic BMD and osteoporosis has only been explored in a limited fashion. The aim of this study is to expand on this, and to replicate the findings of previous studies in a cohort of healthy young adults. METHODS: Cohort: The University of Calgary cohort from the Assessing Inherited Metabolic Syndrome Markers in the Young (UC AIMMY) study. Participants included consist of 168 healthy, predominantly Caucasian young adults. Phenotypes: height, weight, BMI, and total BMD. Genotyping: Allelic discrimination was determined. Statistical Analysis: After being tested for Hardy-Weinberg equilibrium (HWE), the data was run through analysis of covariance (ANCOVA). RESULTS: Using a dominant model, we found that females with one or more copies of the risk T allele of SNP rs3736228 had a significant negative association with total BMD (p = 0.0347). However, a similar association was not seen in males in this cohort. We did not find a significant association for this polymorphism and height, weight, or BMI. DISCUSSION: Polymorphisms in rs3736228 alter the codon in position 1330, downregulating the LRP5 cell surface receptor function. The LRP5 gene has now been shown in multiple studies to be associated with bone quality measures like calcaneal Qualitative Ultrasound (QUS) and BMD. Our study suggests that SNP rs3736228 also influences BMD in healthy young females. This supports the work of Correa-Rodriguez et al that found that when stratifying by sex, females only showed a trend towards significance (p = 0.092) in QUS measures. SIGNIFICANCE: This study expands our understanding of the importance of LRP5 rs3736228 polymorphisms in BMD by extending its relationship to a cohort of predominantly Caucasian college students. While the development of BMD is polygenic, this work broadened the role of SNP rs3736228 across the age span, and the sexual dimorphism seen in musculoskeletal traits

Association of recently described RANK and OPG polymorphisms and measures of bone quality in young adults

Background: Increased fracture susceptibility is correlated with suboptimal bone quality measures, which are thought to be highly influenced by genetic factors. Previous studies have determined that specific receptor activator of nuclear factor-kappaB (RANK), RANK ligand (RANKL), and osteoprotegerin (OPG) single nucleotide polymorphisms (SNPs) are associated with bone mineral density (BMD) and bone geometry parameters in older men. The RANK, RANKL, and OPG systems play a vital role in the regulation of osteoclasts and bone resorption. Further investigation into genetic variation within these genes is essential in order to identify those at risk for future fragility fractures. Objective: Our study sought to determine whether RANKL/RANK/OPG SNPs rs3018362, rs17665435, rs6567276, and rs10505348 influence bone quality measures in younger populations. Methods: The Assessing Inherited Markers of Metabolic Syndrome in the Young (AIMMY) study comprised healthy, young adults (18-35yrs) from the University of Calgary (UC) sub-cohort (n=209). The Bone Health study comprised healthy African-American children (5-9yrs, n=97). The Functional Single Nucleotide Polymorphism Associated with Human Muscle Size and Strength (FAMuSS) study comprised healthy, young adults (18-40yrs, n=891). The bone quality phenotypes analyzed included total body BMD in AIMMY and total BMD adjusted for height in the Bone Health study measured by dual energy x-ray absorptiometry (DEXA). Three SNPs for RANK (rs3018362, rs17665435, rs6567276) and one SNP for OPG (rs10505348) were genotyped in the AIMMY sub-cohort using ThermoFisher’s Applied Biosystems Taqman SNP genotyping assays. Alleles were determined through allelic discrimination assays using real-time PCR (qPCR). SNPs were genotyped in the FAMuSS cohort using Illumina Multi-Ethnic Genotyping Array (MEGA). Hardy-Weinberg equilibrium was tested for the allelic frequency of each SNP and analysis of covariance (ANCOVA) was used to test for associations. Results and Discussion: Our results did not support those of previous studies and suggest that the SNPs rs3018362, rs17665435, rs6567276, and rs10505348 are not associated with BMD or other bone quality measures in young adults. The only association that approached significance was rs3018362 and height-adjusted BMD in males of the Bone Health cohort (p=0.07). We suspect that the lack of association in our study indicates that these SNPs may not play a role in the development of peak bone mass despite being important in determining bone quality in seniors. To further characterize the effect of RANKL/RANK/OPG variations on the multifactorial regulation of bone quality phenotypes, future studies should evaluate the relationship between these variants and bone phenotypes in cohorts of varying ages and ethnicities