Role of canonical WNT pathway genes in osteoporosis & fracture risk

Abstract

Osteoporosis is a multifactorial bone disease characterised by reduced bone mass and microarchitectural deterioration, leading to a high fracture risk. It has a strong genetic component, with several gene variants involved in the disease including those within WNT16, DKK1, and SOST, with all three encoded proteins having crucial roles in the WNT/β-catenin signalling pathway. Downstream to SOST is a distal enhancer element known as ECR5 required for SOST transcriptional activity. The study aimed to determine whether gene variants within WNT16, DKK1, and SOST, including SOST ECR5, alter osteoporosis and fracture risk in Malta. A total of eight carefully selected, BMD-associated variants were genotyped by quantitative real-time PCR (i.e., TaqMan® fluorogenic 5’ nuclease allelic discrimination assay or kompetitive allele specific PCR [KASPTM]) in 1,045 postmenopausal women from the MOFS collection to replicate findings from literature. The SOST ECR5 region was also sequenced using Sanger sequencing in a subset of the individuals with extreme bone phenotypes (i.e., normal to high bone mass, and low bone mass; n = 212) from the MOFS collection, which identified two variants that were subsequently tested in the entire collection. Genotype-phenotype associations were assessed using the Kruskal-Wallis and Mann-Whitney U tests, whereas exposure odds ratios were computed using logistic regression adjusted for confounders. Genotype and allele frequencies of all genotyped variants were in line with European non-Finnish population from gnomAD. Results showed that the homozygous alternative genotype for WNT16 rs142005327 exerted a protective effect on LS BMD (adj-OR: 0.3 [95% CI 0.2-0.7], p=0.003) FN BMD (adj-OR: 0.5 [95% CI 0.3-0.8], p=0.009), all type of low trauma fractures (adj-OR: 0.5 [95% CI 0.3-0.9], p=0.023), and wrist fractures (adj-OR: 0.4 [95% CI 0.1-0.9], p=0.036), together with higher sALP levels (adj-OR: 1.9 [95% CI 1.1-3.3], p=0.027). SOST rs4792909 exhibited a deleterious effect on FN BMD (sBMD GT p=0.012; T-score GT p=0.010), and TH BMD (sBMD GT p=0.021; T-score GT p=0.019), while SOST rs8064375 exhibited a deleterious effect on LS BMD (T-score GA p=0.045). To date, this is the first study linking SOST rs8064375 with BMD. Haplotypes for DKK1 variants were found associated with FN BMD, while WNT16 and SOST haplotypes were associated with LS and FN BMD, and fracture risk. The results showcase the potential role of these variants as genetic determinants of BMD and fractures in Malta, further highlighting the importance of the WNT/β-catenin pathway in bone and pathophysiology.