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.