Abstract
Introduction
Achilles tendinopathy (AT) is a highly prevalent injury in athletes and non-athletes with an unknown aetiology. Genetic risk factors have been a recent focus of investigation. The aim of this systematic review was to determine which loci have been linked with mid-portion AT and could potentially be used as biomarkers in tendinopathy risk models or as preventative or therapeutic targets.
Materials and Methods
Eight electronic bibliographic databases were searched from inception to April 2015 for cross-sectional, prospective cohort and case-control studies that included empirical research investigating genes associated with mid-portion AT. Potential publications were assessed by two independent reviewers (AAC and PRJ) for inclusion and quality. Quality was evaluated using a validated scale.
Results
Twelve candidate gene studies and three pathway-based genetic association studies that investigated genetic risk factors for AT were identified. According to Ariëns's criteria, there was strong evidence for the COL5A1 gene. There was some evidence for 6 of the other genes investigated: COL5A3, TNC, CASP8, MIR608, GDF5, MMP3 and TIMP2 genes. There was inconclusive evidence for the following genes: COL3A1, COL5A2, COL11A1, COL11A2, COL12A1, COL1A1, COL27A1, COL14A1, COMP, THBS2, ADAMTS2, ADAMTS5, ADAMTS14, ADAM12, TGFβ1, IL-1β, IL-1RN, IL-6, NOS2 and NOS3. There was some evidence for combinations of functional variants of different genes and pseudohaplotypes constructed from many functional variants. The quality of included studies varied (3/9 to 7/9), and the average quality assessment score was 5.5/9 (61%).
Discussion
There are genetic differences between subjects with and without AT. To further elucidate these findings, prospective studies are needed to investigate the increased risk associated with specific genetic findings. Modifying training loads or preventative exercise may be used to mitigate increased risk, although it needs to be highlighted that a genetic association does not necessarily mean an individual will develop Achilles tendinopathy. Gene therapy may have a role in tendon healing, but further research is necessary to develop risk models and establish the most advantageous genes to transfer.
