Association of the WNT16 Kozak sequence variant rs55710688 with BMD and fractures in Maltese postmenopausal women

Abstract

Osteoporosis is a skeletal disease characterised by a reduction in bone mass and microarchitectural deterioration of bone resulting in an increased fracture risk. The WNT16 protein encoded by the WNT16 gene is a ligand that activates canonical WNT signalling leading to increased bone formation. The WNT16 rs55710688 insertion variant (CCCA), located in the Kozak sequence of exon 1, elevates the translational efficiency of WNT16. The study aimed to determine if the WNT16 rs55710688 variant is associated with spine and hip BMD, and fracture risk at different anatomical sites in the Maltese population. Genotyping was performed in the MOFS case-control collection of 1,045 postmenopausal women using Competitive allele specific PCR. Genotype-phenotype associations were investigated using the Mann-Whitney and Kruskal-Wallis tests, whereas risk ratios were computed using logistic regression models providing odds ratios (ORs) with 95% confidence intervals (CI) adjusted for confounders. Genotyping was successful in 1,034 samples, with the reference and alternative allele frequencies detected at 75.8% and 24.2% respectively, which are in line with European populations. Genotype-phenotype associations showed that homozygosity for the alternative allele was associated with a higher lumbar spine (LS) BMD (p=0.04) and T-score (p=0.04) relative to homozygosity for the reference allele. Heterozygosity was associated with a higher total hip (TH) BMD (p=0.04) and T-score (p=0.04). A trend was also observed for femoral neck (FN) BMD in women with the homozygous alternative genotype having a higher BMD at this site. However, the association did not reach statistical significance (p=0.08). Risk ratios revealed that women with the homozygous alternative genotype exhibited a protective effect on LS BMD (age-adjusted OR: 0.4[95% CI 0.2-0.9], p=0.02) compared to women with the homozygous reference genotype. Additionally, homozygosity for the reference allele was associated with decreased risk of all-type of low-trauma fractures (age- & BMD- adjusted OR: 0.5[0.2-0.9], p=0.02). A weak association was observed with wrist fracture risk (age- & BMDadjusted OR: 0.4 [95% CI 0.1-1.1], p=0.07) possibly due to the low sample size. In conclusion, results indicate that the WNT16 rs55710688 variant exerts a protective effect on vertebral and hip BMD, highlighting its effect on trabecular and cortical bone. The results support the functional findings showcasing the increased transcriptional efficiency of WNT16 in the presence of the WNT16 rs55710688 alternative allele. Thus, the variant is a possible genetic variant underlying the complex genetics of osteoporosis and fracture risk in Malta.