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Association between Single Nucleotide Polymorphisms of SMAD3 and BMP5 with the Risk of Knee Osteoarthritis.

INTRODUCTION
The role of genetic factors influencing osteoarthritis (OA) susceptibility is well documented and several candidate genes have been identified to be associated with it. Among these genes are Bone Morphogenetic Protein 5 (BMP5) and Smad family member 3 (SMAD3), all involved in Transforming Growth Factor (TGF) signaling pathway. The knee is the commonly affected joint, and knee OA has an especially high prevalence in Asian population.


AIM
To investigate associations between Single Nucleotide Polymorphisms (SNPs) rs12901499 in SMAD3 and rs921126 in the BMP5 gene with knee OA susceptibility in and around Lucknow, Uttar Pradesh, India.


MATERIALS AND METHODS
SNPs rs12901499 in SMAD3 and rs921126 in BMP5 were genotyped in patients with knee OA and age- sex matched OA-free controls from our population. A total of 450 patients with knee OA and 458 controls were enrolled in the study. Venous blood samples were obtained from all cases as well as controls for PCR-RFLP (Polymerase Chain Reaction- Restriction Fragment Length Polymorphism). Data was collected and entered in excel sheets. Statistical analyses of the data were performed using statistical software package SPSS version 16.0. Chi-square, Student's t-test and logistic regression tests were used to analyse the data.


RESULTS
GA and GG genotypes of both SNPs (rs12901499 and rs921126), and variant G, were associated with a significantly increased risk of knee OA. A significantly increased risk of knee OA was associated with the genotype GG and GA of rs12901499 (p < 0.03 and p <0.004 respectively) and rs921126 (p< 0.0001 and p<0.001 respectively) compared with the AA genotype. In addition, those bearing at least one G allele (GG + GA) had a significantly increased risk of knee OA compared with those without the G allele (AA) in rs921126 (p< 0.0001). However, in rs12901499, significant association with the risk of knee OA was not found (p<0.4). On age and gender based stratification, the association between the risk of OA and rs921126 GG mutant compared with AA homozygotes was strong in both gender (adjusted OR= 2.93 for male and 2.25 for female) and in those aged >55 years (adjusted OR= 3.4), similarly in rs12901499, GG mutant compared with AA homozygote was strong in female (adjusted OR= 1.5) and in those aged >55 years (adjusted OR= 1.5).


CONCLUSION
The results showed that both in SMAD3 rs12901499 and BMP5 921126, G allele is significantly associated with knee OA. A to G change and variant G genotype may contribute to knee OA risk in our study population of Lucknow.