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Recent Patents on DNA & Gene Sequences, 2012, 6, 216-223

Application of Genomics in the Prevention, Treatment and Management of Achilles Tendinopathy and Anterior Cruciate Ligament Ruptures A.V. September1, M. Posthumus1 and M. Collins2,1,* 1

UCT/MRC Research Unit for Exercise Science and Sports Medicine of the Department of Human Biology, Faculty of Health Sciences, University of Cape Town, South Africa; 2South African Medical Research Council, Cape Town, South Africa Received: April 05, 2012

Revised: July 03, 2012 Accepted: July 03, 2012

Abstract: Musculoskeletal soft tissue injuries such as Achilles tendinopathy and anterior cruciate ligament ruptures are common among elite athletes, recreational athletes and physically active individuals. The consequences of injury may be devastating and prevent the recreational or competitive athlete from reaching their potential or lead to a premature end to their careers. Although these injuries have been well described at a clinical level, the biological mechanisms causing these injuries are poorly understood. A further understanding of the biological mechanisms underlying the injury will assist the treatment and management of these injuries. In addition, understanding the biology is an important prerequisite in developing models that can be used to effectively identify risk, as well as, implement personalized prevention, treatment and rehabilitation programmes. Both intrinsic, including genetic variants, and extrinsic risk factors have nevertheless been implicated in the aetiology of these injuries. To date, several patents have been filed which involve the use of specific polymorphisms and regions within specific genes to be used in a genetic test for either tendon or ligament injury risk. The objective of this manuscript will be to review the evidence for the genetic predisposition to soft tissue injury, as well as the application of this data in the prevention, treatment and management of musculoskeletal soft tissue injuries.

Keywords: Tendon, Ligament, ACL, Achilles, Collagen genes, Matrix metalloproteinases, Extracellular matrix components, miRNA, Tenascin C, Growth differentiation factor 5, Caspase-8, Molecular markers, Patent, Genetic testing, COL1A1, COL5A1, COL12A1. IDENTIFICATION OF THE PROBLEM Participation in regular physical activity has numerous health benefits [1]. However, participating in physical activity, as well as training for and participation in both recreational and competitive sports increases the risk of musculoskeletal soft tissue injuries [2]. This review will focus on two of these injuries, namely chronic Achilles tendinopathy, a painful overuse injury, and anterior cruciate ligament (ACL) ruptures, an acute knee injury. The prevalence of Achilles tendinopathy appears to be steadily increasing throughout the world. There is a lifetime incidence of Achilles tendinopathy of approximately 10% and 50% within the general population and top-level male distance runners respectively [3, 4]. Achilles tendinopathy results in chronic pain, discomfort and impaired function, resulting not only in significant loss of sporting performance, but also decreased functional capacity at work and during exercise [2]. ACL ruptures are one of the most severe injuries sustained during participation [5, 6]. Athletes may loose up to 12 months of play as a result of rupturing their ACL [6]. This may result in the athlete not being able to participate for an entire season, long-term disability and a significant increased *Address correspondence to this author at the UCT/MRC Research Unit for Exercise Science and Sports Medicine, P.O. Box 115, Newlands 7725, South Africa; Tel: +27-21-650 4574; Fax: +27-21-686 7530; E-mail: [email protected]

2212-3431/12 $100.00+.00

risk of osteoarthritis of the knee [7]. The incidence of ACL rupture is relatively low in the general population [8, 9], however the high costs of surgical repair, rehabilitation and time loss has a significant impact on both the individual and society [10, 11]. CAUSES OF THE PROBLEM Under normal physiological conditions the matrix of both tendons and ligaments adapt in response to load [12]. However, a spectrum of loads ranging from high forces at low frequencies to low forces at high frequencies may result in maladaptation, culminating in a failed healing response or degeneration (Fig. 1) [12]. These effects may cause either acute or overuse injuries. Each athlete’s tolerable load is unique, thus resulting in a wide inter-individual variation in the response of these musculoskeletal soft tissues to load. This response is partially determined by the normal variation in the biochemical and mechanical properties of these tissues. Some athletes therefore intrinsically have an increased risk for tendon and ligament injuries. Predisposition to these injuries can negatively impact an athlete’s ability to train and compete optimally. Knowledge of the underlying biochemical and mechanical properties of musculoskeletal soft tissue injuries will assist clinicians and trainers in personalizing the optimal training load for the individual athlete, allowing them to reach optimal performance while reducing the risk of injury.

© 2012 Bentham Science Publishers

Genomics and Risk for Musculoskeletal Soft Tissue Injuries

Recent Patents on DNA & Gene Sequences, 2012, Vol. 6, No. 3

Table 1. Tolerable Load Range

Force

Max Tolerable Load

Injury Region

No Injury Region

Min Tolerable Load Frequency

Fig. (1). A hypothetical curve illustrating the relationship between the magnitude (force) and frequency of the tolerable load, which will cause injury to a tendon or ligament. The tolerable load is unique for each individual. The maximum (max) and (min) tolerable loads within a population is indicated by the dashed lines, while the range in the tolerable range for the population is indicated in grey.

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Common non-modifiable and modifiable risk factors for chronic Achilles tendinopathy and/or anterior cruciate ligament ruptures

Non-Modifiable Risk Factors

Modifiable Risk Factors

1.

Age

1.

Physical activity

2.

Gender

2.

Training errors

3.

Previous Injury

3.

Footwear

4.

Anatomical factors

4.

Medication use

5.

Laxity and flexibility

5.

Smoking

6.

Systemic disease

6.

Nutrition

7.

Surfaces

7.

Occupation

8.

Environmental conditions

8.

Psychological factors

9.

Phase of menstrual cycle

9.

Body mass and size

10. Familial predisposition

10. Protective bracing

11. Genentic Polymorphisms

11. Biomechanical factors

Adapted from [14, 83].

Although there is debate within the scientific community with respect to the level of evidence, several risk factors have been suggested to be implicated in the etiology of Achilles tendon and ACL injuries (Table 1) [13, 14]. There is therefore no single cause for these injuries and they are considered multifactorial conditions caused by the complex interaction of several factors. Although the specific risk factors associated with these injuries are traditionally divided into intrinsic and extrinsic factors, they can also be divided into non-modifiable and modifiable risk factors. The practical application of the latter classification system will be addressed during this review. Recently, specific genetic sequence variants have been identified as non-modifiable risk factors for Achilles tendinopathy and ACL ruptures [15, 16]. Genetic risk factors should be included into multifactorial models aimed to reduce the risk, treat and rehabilitate tendon and ligament injuries. GENETIC RISK FACTORS Several genetic polymorphisms have been associated with altered risk for either ACL ruptures and/or chronic Achilles tendinopathy [15, 16]. These polymorphisms are located within the COL5A1, MIR608, COL1A1, COL12A1, TNC, GDF5, CASP8 and MMP12 genes and are discussed below. Several patents have been filed and are based on the application of these specific polymorphisms or sequence regions in a genetic test to either independently or collectively interact with each other or with other polymorphisms to modify the risk of either tendon or ligament injuries (Table 2). The genes implicated include COL5A1, TNC, COL27A1, MMP3, MIR608, CASP8, GDF5, IL6 and IL1 [17-22]. Additional research is required to identify the full spectrum of biological significant associated polymorphisms within other genes.

COL5A1 and MIR608 The COL5A1 gene encodes the 1 chain of type V collagen. Type V collagen is involved in the assembly and lateral growth of the collagen fibril, the basic building block of tendons and ligaments [23]. Rare mutations within COL5A1 cause Ehlers-Danlos Syndrome (EDS), a disease characterized by generalized joint hypermobility [24]. This suggests that that there appears to be limited redundancy within collagen fibril biology. As illustrated in (Fig. 2), two functional copies of COL5A1 is essential for life [24], rare diseasecausing mutations within one copy of COL5A1 causes a classical Mendelian connective tissue disorder EDS [25] and we hypothesise that common polymorphisms within COL5A1 can, at least partially, modulate the risk for various musculoskeletal soft tissue injuries such as Achilles tendinopathy and ACL ruptures [26]. In support of this, the CC genotype of the COL5A1 rs12722 variant, within the 3’-untranslated region (UTR), was found to be associated with a reduce risk of chronic Achilles tendinopathy [27, 28] and ACL ruptures in females [29]. We have recently described two major functional forms of the COL5A1 3’-UTR, namely the C- and T-forms [30]. The T-form was predominately identified in chronic Achilles tendinopathic patients and associated with increased mRNA stability [30]. Furthermore, other variants within the 3’-UTR, which differentiated between the T- and C-functional forms have recently been shown to independently associate with chronic Achilles tendinopathy (Y Abrahams, Unpublished data). These include two short tandem repeat polymorphisms (STRPs), insAGGG (rs71746744) and delATCT (rs16399), as well as a single nucleotide polymorphism (SNP), A>T (rs1134170). The associated region of the COL5A1 3’-UTR contains, amoungst other elements, a functional miRNA binding site for Hsa-miR-608 [30]. SNP rs4919510 (C>G)

218 Recent Patents on DNA & Gene Sequences, 2012, Vol. 6, No. 3

Table 2.

September et al.

Selected patents which have to date been filed involving specific polymorphisms within specific genes for the genetic testing of tendon and ligament risk injury

Application Date

Region

Application Type

Application Number

Title

Inventors

COL5A1 TNC COL27A1

South Africa

National Phase

2008/05443

2011-05-03

South Africa

National Phase

ZAxPCTIB09/05489

[18]

2011-05-04

United States

National Phase

13/127,668

[19]

2011-05-13

Europe

National Phase

09824482.5

2011-05-19

Australia

National Phase

2009312451

South Africa

Provisional

Collins M et al.

Ref

2008-07-17

2011-11-04

Molecular Markers

Related Gene

Genetic risk factors for tendon and ligament injuries

Collins M et al.

COL5A1 MMP3

[17]

[20] [21]

Oligonucleotides and methods for determining a predisposition to soft tissue injuries

ZAPPAx2012/01

Collins M et al.

COL5A1 MIR608 CASP8 GDF5 IL6 IL1

[22]

COL5A1 Genetic Continuum 2 copies of mutated COL5A1 gene

1 copy of mutated COL5A1 gene

?

Allelic form of the COL5A1 gene

Lethal in utero

EDS

BJHS

Increased Injury Risk

Classical Monogenic Disorder Environmental Exposure NOT Required

Allelic form of the COL5A1 gene

Decreased Injury Risk

Environmental Exposure Interacting with Genetic Background

Fig. (2). The COL5A1 gene variant continuum. Two functional copies of COL5A1 is required for life. This is illustrated by observations that col5a1 -/- mice die in utero [24]. Furthermore, rare disease-causing mutations, which inactivate one copy of COL5A1 (haploinsufficiency), is a common cause of the Mendelian connective tissue disorder, types I and II Ehlers-Danlos syndrome (EDS) [25]. Since joint hypermobility is one of the clinical features of EDS, it has been suggested mutations or polymorphisms within COL5A1 cause the less serve benign joint hypermobility syndrome (BJHS) (82). We have suggested that common polymorphisms within COL5A1 can, at leastin part, together with appropriate exposure to various environmental factors affect the risk for chronic Achilles tendinopathy and ACL ruptures [26]. The heat bar and the shading of the boxes indicating the phenotypes indicate the severity of these different conditions. The black shading representing a lethal situation while the white shading the most favorable allelic form of COL5A1.

within the MIR608 gene was also associated with chronic Achilles tendinopathy (Y Abrahams, Unpublished data). Each of the MIR608 alleles encodes a distinct mature Hsa-miR-608. We have proposed that these functional forms of the COL5A1 3’-UTR results in altered type V collagen production [26]. The relative content of type V collagen in the Achilles tendon and other tissues may alter the biomechanical properties and thus influence susceptibility to musculoskeletal soft tissue injuries [26]. These studies [30] (Y Abrahams, Unpublished data) collectively provide evidence suggesting a functional significance to the COL5A1 3’UTR region initially implicated with increased risk of Achilles tendinopathy [27, 28] and anterior cruciate ligament ruptures [29].

COL1A1 Type I collagen, which constitutes up to 80% of the dry mass of tendons and ligaments, is a heterotrimer consisting of 2 1(I) chains and 1 2(I) chain [31]. The 1(I) and 2(I) chains are encoded by the COL1A1 and COL1A2 genes respectively. The functional Sp1 binding site polymorphism has been associated with several complex disorders of connective tissue, including, myocardial infarction [32], lumbar disc disease [33], stress urinary incontinence [34], and most notably, osteoporosis [35]. In addition, mutations within the COL1A1 gene cause classical Mendelian conditions such as Osteogenesis imperfecta and EDS [36]. Similarly to COL5A1, this suggests the importance and limited redundancy within collagen fibril biology.



A recent study investigating the molecular mechanism of the functional COL1A1 Sp1 binding site polymorphism reported that the T allele had an increased binding affinity for the transcription factor Sp1 [37]. The increased transcriptional binding was accompanied by an increase in COL1A1 mRNA, and thus altered production of the 1(I) chain relative to the 2(I) chain [37]. It is proposed that this change may lead to 1(I)3 homotrimer formation and thus altered tissue mechanical properties. The mechanism whereby this altered protein ratio results in reduced bone quality and strength does however remain unknown. Although the TT genotype have previously been shown to be a risk factor for the complex connective tissue disorders mentioned above, it has been shown that this genotype is protective against acute musculoskeletal soft tissue injuries [38-40]. The TT genotype was shown to be underrepresented within individuals with ACL ruptures and/or acute shoulder dislocation within two independent studies in a South African and Swedish cohort [38, 40]. In addition, there have also been trends that this genotype was underrepresent within individuals with Achilles tendon ruptures [39]. Further work is required to determine the presence of the 1(I)3 homotrimer and its effect on the mechannical properties of tendon and ligament tissues.

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rs970547) was associated with ACL ruptures in females [44]. This polymorphism was however not associated with chronic Achilles tendinopathy [45]. The AluI RFLP is a nonsynonymous coding variant within exon 65, which changes the amino acid at position 3058 from a serine to a glycine. The wild-type serine amino acid is a neutral polar amino acid with a larger side chain than the substitute non-polar neutral glycine amino acid. This non-synonymous SNP is predicted to potentially have a functional consequence, although not proven as yet [46]. Further research is required to confirm if and how this polymorphism potentially may affect the mechanical properties of musculoskeletal soft tissue. TNC

COL12A1

The TNC gene codes for the glycoprotein tenascin C, found abundantly in tissues subjected to high tensile and compressive stress such as tendons and ligaments [47]. Tenascin-C binds to components of the extracellular matrix and cell receptors thereby playing an important role in the regulation of cell-matrix interactions [48]. Expression of tenacin-C has also been shown to increase in response to mechanical stress in tendons and ligaments [48, 49], It isreasonable to hypothesize that tenascin-C may play a role in the adaptation of tendon tissue during the initial reactive and to a lesser extent, the tendon disrepair phases of tendinopathy.

Type XII collagen is a homotrimer consisting of 3 1(XII) chains. It is a member of the Fibril Associated Collagens with Interrupted Triple helices (FACITs) [41]. The 1(XII) chains are encoded by the COL12A1 gene. Type XII collagen, is also believed to regulate microfibril diameter (fibrillogenesis) [42, 43]. We have shown that the COL12A1 Alu Irestriction fragment length polymorphism (RFLP, SNP

Interestingly, a GT dinucleotide repeat polymorphism (a microsatellite) within the TNC gene was associated with risk of Achilles tendinopathy and rupture [50]. The functional effect of this microsatellite remains unknown. Further work is required to identify the functional variant within the TNC or flanking genes, which predisposes individual to Achilles tendinopathy.

Population of Athletes 1.  History   Medical   Injury   Physical Activity 2.  Clinical Examination 3.  Genotyping

High Risk

Intermediate Risk

Low Risk

Reduce Injury Risk:1.  Personalized Training Programmes 2.  Alter Exposure to Other Modifiable Risk Factors

Fig. (3). Schematic diagram illustrating the use of traditional examinations and specialized investigations together with the aid of the athletes genetic profile (testing of multiple genetic variants) to stratify a population of athletes into those at high, intermediate and low risk for musculoskeletal soft tissue injuries, such as chronic Achilles tendinoapthy and ACL ruptures. The risk of injury can therefore be reduced in the high-risk athletes by personalizing their training programmes and/or exposure to other modifiable risk factors.


GDF5 The GDF5 gene encodes the growth and differentiation factor 5 (GDF-5). This protein is also known as bone morphogenic protein 14, BMP-14, or cartilage-derived morphogenic protein 1 or CDMP-1. GDF-5 is involved in several processes including the maintenance, development and repair of bones, cartilage and other musculoskeletal soft tissues, including tendons [51, 52]. Disease-causing mutations within the GDF5 gene have been implicated in several inherited developmental disorders such as brachydactyly type C, Grebe and Hunter-Thompsonforms of acromesomelic skeletal dysplasias, and DuPan syndrome [53, 54]. A possible biological role of GDF-5 in tendons and ligaments was first gleaned from the study in which ectopic administration of GDF-5 resulted in neotendon formation [55]. Further investigation of mutant GDF-5 deficient mice revealed more insight into the ultrastructural, compositional, and mechanical characteristics of their Achilles tendons. These tendons were significantly weaker and contained approximately 40% less collagen [56]. A functional SNP (rs143383; T>C) within the GDF5 promoter was previously associated with multifactorial phenotypes including osteoarthritis [57], congenital hip dysplasia [58], height, hip axis length and fracture risk [59]. Interestingly, the T allele of the GDF5 rs143383 polymorphism was correlated with reduced expression of the GDF5 gene within a wide range of soft tissues [60]. This polymorphism was recently associated with both Achilles tendinopathy and rupture [61]. CASP8 The CASP8 gene codes for caspase-8, a component of the pathway that regulates apoptosis of tendon fibroblasts. The normal tendon healing process involves the removal of damaged fibroblasts by cytokine-mediated apoptosis. This process is critical in regulating the balance between ECM synthesis and degradation and thereby assisting in maintaining homeostasis of the components of the extracellular matrix [62]. Excessive apoptosis, which has been observed in tendinopathy, may therefore compromise the ability of the tendon to regulate repair processes. The expression of CASP8 was found to be elevated in tendinopathy. It is has been proposed that repetitive loading may change the extracellular matrix composition and cause excessive fibroblast apoptosis [63, 64]. Two polymorphisms CASP8 -652 6N del (rs3834129) and CASP8 Asp302His (rs1045485) have previously been associated with reduced risk of other multifactorial conditions [65]. The functional CASP8 -652 6N delpolymorphism is a six nucleotide deletion (CTTACT) within the promoter of the CASP8 gene. The del allele destroys a Sp1 binding element which results in decreased caspase-8 expression [66]. The CASP8 51423G>C polymorphism results in an Asp302His substitution of which the functional significance still remains unknown. However, it is proposed that this nonsynonymous substitution on the surface of the caspase-8 protein may interfere with the processing of procaspase-8 and which may affect subsequent interactions with anti-apoptosis molecules [67].

September et al.

We have shown that both the CASP8 -652 6N del polymorphism and the CASP851423G>C polymorphism associate with risk of Achilles tendinopathy [68]. These results further highlight the apoptosis signaling cascade as one of the biological pathways involved in the development of Achilles tendinopathy. MMP3 and MMP12 Matrix metalloproteinases (MMPs) are the main physiological mediators of extracellular matrix degradation and remodeling [69]. The MMPs comprise of a family of 25 related, yet distinct, zinc-containing enzymes known to catalytically degrade components of the ECM, including the regulations of other MMPs [70]. Several MMP genes, which include, MMP10, MMP1, MMP3 and MMP12 have been mapped to human chromosome 11q22.3 [71]. Genetic sequence variants within this locus have previously been associated with several complex phenotypes such as rheumatoid arthritis [72], osteoarthritis [73], lumber disk degeneration [74], idiopathic scoliosis [75] and aseptic prosthetic loosening [76]. Three polymorphisms, in high linkage disequilibrium with each other, within MMP3 have recently been implicated with risk of chronic Achilles tendinopathy in a South African Caucasian population [77]. One of these polymorphisms, rs679620 (G>A), results in the substitution of a glutamate to a lysine residue at the amino acid position 45 of pro-MMP3. The functional significance of this substitution remains unknown. The association of polymorphisms within the other MMP genes within this genomic cluster with chronic Achilles tendinopathy still remains to be explored. To the contrary, four functional polymorphisms within the neighboring MMP10, MMP1, MMP3 and MMP12 genes within this cluster have been investigated with risk of ACL ruptures [78]. The functional MMP12 rs2276109 polymorphism was independently associated with risk of ACL ruptures in both males and females. In addition, a haplotype consisting of all four variants was further implicated with risk of ACL ruptures [78]. The functionally significant MMP12 rs2276109 polymorphism was previously shown to increase the binding affinity of activator protein-1 (AP-1), a transcription factor which results in increase MMP12 promoter activity [79]. APPLICATION None of the identified genetic and non-genetic intrinsic risk factors independently cause Achilles tendon or ACL injuries. They merely modulate or contribute to the risk for these injuries. Predisposed individual need to be exposed to appropriate environmental factors in order for the tissue to become injured. Any genetic test for Achilles tendon or ACL injuries can therefore never be diagnostic in nature. They can only be used in conjunction with other intrinsic and extrinsic factors to determine risk for a specific injury (Fig. 3). As previously mentioned genetic polymorphisms are nonmodifiable risk factors. However since injuries results from an interaction between the non-modifiable and modifiable risk factors, the inclusion of the non-modifiable risk factors, such as genetic polymorphisms, in any injury risk assessment model is essential. Once at risk athletes have been


identified using non-modifiable (an example being genetic factors) and modifiable risk factors (an example being training factors), athletes, coaches and clinicians can potentially alter the modifiable risk factors in an attempt to reduce the overall risk of injury. With these advancements in molecular biology, personalized medicine to prevent and treat exercise related medical conditions such as Chronic Achilles tendinopathy and ACL ruptures is becoming a reality. PERSONALIZED MEDICINE Personalized medicine (PM) is a model, which proposes tailor made clinical management of a patient based on their genetic and non-genetic medical profile [16]. This model has the potential to improve the quality of medical care through more comprehensive diagnostics, improved treatment intervention and management. The success of this model is therefore dictated by the (i) effectiveness of a genetic test to identify patients who can benefit from targeted therapies and (ii) the ability of the clinician to easily and meaningfully interpret the panel of test. Healthcare costs are soaring worldwide and it is therefore a real threat that PM costs may be yet another burden to an already unsustainable healthcare. However, there are several examples within other parallel research areas, such as cancer genomics, that have demonstrated that these genetic tests may result in improved care at lower costs [80, 81]. Traditionally, genetic tests have only been available through healthcare professionals, who order the appropriate test and interpret the test results together with the appropriate additional clinical data. Direct-to-consumer (DTC) genetic testing, on the other hand, refers to genetic tests that are available directly to the individual without the need to go through a health care professional. There are several companies who are marketing genetic platforms designed from peer reviewed scientific literature and/ or public domains. DTC companies like Athleticode, for example, makes the following claims on their webpage “DNA Testing to Prevent Injuries & Improve Performance”, “Athleticode provides individualized, science-based reports that will change the way you train” (http://athleticode.com/ accessed on 2 April 2012). This and other DTC tests are available directly to the individual without the need to go through a health care professional. Perhaps one of the main benefits of DTC genetic testing is its accessibility to the public, its implicit promotion and emphasis on proactive healthcare. However, more importantly the possible main risks include (i) the potential over interpretation of the genetic tests by the consumer, (ii) the validity of the tests and (iii) the privacy or ownership of the genetic information. There are important differences between the companies which offer DTC genetic testing compared to companies using traditional genetic testing methods or tertiary institutions who are offering similar testing which need to be considered. There is no regulation over DTC genetic testing. In addition, the staff involved in developing the tests conducted by academic institutions, or companies with links to academic institutions, have many years of research experience and are usually recognised internationally as experts in the clinical conditions being tested. More


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important, these individuals have an in depth knowledge of the current biological mechanisms underpinning these phenotypes. It is not enough to extrapolate data from the public domain and design a genetic test as the in-depth biology supporting the test also needs to be understood and the knowledge has to be current. The test results need to be interpreted in relation to the phenotype being a complex multifactorial clinical condition. It is therefore imperative that genetic testing not be offered directly to the public but rather be used as a clinical tool requested by a referring health care professional. There is a significant delay in the publication of new knowledge within the public domain with regard to the genetic basis of Achilles tendinopathy and ACL ruptures. This lag period therefore would significantly impact the commercialisation of the most appropriate biologically significant genetic tests by DTCs. For this reason,it should be emphasised that the implementation of genetic testing for tendon and ligamant injuries should be done in collaboration with researchers actively involved in this rapidly growing area of research. With the growing emphasis on personalised medicine and health promotion it is perhaps a reality that DTC genetic testing in the marketplace is going to expand. For this reason, it is perhaps a responsibility of the healthcare professional to become more familiar with the testing platforms on offer to the general public and the need for them to caution their patients about the limitations of these tests; to possibly guide them to which of the available tests are the most informative and which are the most clinically relevant tests based on biological functional data. An individual’s unique genetic information potentially has the greatest medical benefit when it is interpreted within the context of all previous medical history, family history and all previous and existing environmental profile or exposure. All this individual patient data needs to be collectively synthesised by the health professional for improved diagnoses, treatment intervention and management. CURRENT AND FUTURE DEVELOPMENT Chronic Achilles tendinopathy and ACL ruptures are major medical concerns affecting all levels of athletes and physically active individuals. The consequences of these injuries may be devastating and can result in either preventing the individual from reaching their full potential or the premature end to an athletic career. Both non-modifiable, including specific genetic sequence variants, and modifiable risk factors have been implicated in the aetiology of these complex injuries. It is therefore imperative that these associations be explored in independent populations and that the functional significance and biological relevance of these loci be further explored. In addition, it is vital that all risk factors (genetic and non-genetic) be incorporated into a multifactorial model to predict risk for Achilles tendinopathy and ACL ruptures. However there are still several limitations to the application of genomic research data in musculoskeletal soft tissue injury which include (i) the validity of the injury associated polymorphisms in other populations (ii) the collective contribution of several associated polymorphisms to injury risk (iii) the dynamic relationship between a genetic profile


and an environmental profile in modulating injury susceptibility (iv) the successfulness of intervention strategies given a specific genetic and environmental profile, (v) the epigenetic environment on modifying any one of the intricate relationships between the genetic and environmental profiles to contribute to an individual’s injury risk profile, and (vi) the identification of all other polymorphisms which modulate injury risk. Further research should explore these limitations. The lessons learnt from such exploration will undoubtedly increase our understanding of musculoskeletal soft tissue injury risk. Although beyond the scope of this review, the unique ethical issues related to the testing of professional athletes needs to be debated at many levels. Genetic testing for these injuries, however, can therefore never be diagnostic and can only be used to assist in determining risk. It is critical that the results from genetic tests are correctly interpreted by the healthcare professional as part of a multifactorial model in the risk management of the individual athlete. A multidisciplinary approach needs to be followed to increase our understanding of the pathogenesis of complex multifactorial musculoskeletal soft tissue injuries such as Achilles tendinopathy and ACL ruptures. ACKNOWLEDGEMENTS This study was supported in part by funds from the National Research Foundation (NRF) of South Africa, University of Cape Town (UCT), and the South African Medical Research Council (MRC). MP was supported by the Thembakazi Trust.

September et al. [10] [11]

[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]

CONFLICT OF INTEREST The authors declare no conflict of interest. PATIENT CONSENT

[25] [26]

Declared none. [27]

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