TIMP2 and GDF-5 gene variants and achilles tendon pathology: replication study in a British case-control population

Introduction: Achilles tendon pathology (ATP) encompasses a range of tendon overuse injuries that can be sub-classified into separate pathologies [Weinfeld, 2014]. To date, a number of single nucleotide polymorphisms (SNPs) have been associated with ATP [Raleigh and Collins, 2012] but, with the exception of the COL5A1 rs12722 variant, limited work has been published on attempting to replicate these findings in cohorts other than those recruited from either South Africa or Australia. We selected variants within the TIMP2 (rs4789932) and GDF-5 (rs143383) genes, that have previously been shown to associate with ATP [El Khoury et al, 2013 and Posthumus et al, 2010], and attempted to replicate previous associations in a newly recruited British-based, case-control, Caucasian cohort. Methods: We recruited 133 ATP Caucasian patients from the County Clinic in Northampton along with 131 physically active controls from various sports clubs within the East Midlands region. DNA samples were collected from saliva (DNA genotek Ltd) and Taqman technology, using allele specific probes and primers, was used to genotype all DNA samples. Reactions were run on a StepOne Plus real-time PCR instrument (ABI). Genotypes were called according to post run cluster profiles and data were analysed using Chi-squared (c2) analysis or Fisher’s exact test. Significance was accepted at p < 0.05. All procedures were approved by the University of Northampton Research Ethics Committee. Results: For the TIMP2 rs4789932 variant we found no association between genotype and case or control status in the entire cohort (p = 0.279). However, in sex specific analysis we did find that the CC genotype was associated (p = 0.043) with male ATP cases compared to controls (Table 1). For the GDF-5 rs143383 variant, we found no association between genotype and case or control status in the entire cohort (p = 0.538) or in either male (p = 0.319) or female (p = 0.737) specific analysis (data not shown). Genotypes did not associate with any other potential confounding variables. Conclusions: The TIMP2 rs478992 CC genotype was associated with male cases of ATP. Although this locus was previously associated with ATP in cohorts recruited from the Southern Hemisphere it was the CT genotype that was the risk factor and the association was not sex specific [El Khoury et al, 2013]. This result might be related to differences in unknown environmental exposures between the cohorts investigated that may modify the effect of the genotype. We found no evidence of an association between ATP and the GDF-5 variant. These data should be viewed as preliminary findings and will need to be repeated in a larger cohort.