Androgen receptor CAG repeat size is associated with stress fracture risk: a pilot study

Musculoskeletal Injuries Among Females in the Military: A Scoping Review

INTRODUCTION

Musculoskeletal injuries (MSKi) are a common challenge for those in military careers. Compared to their male peers, reports indicate that female military members and recruits are at greater risk of suffering MSKi during training and deployment. The objectives of this study were to identify the types and causes of MSKi among female military personnel and to explore the various risk factors associated with MSKi.

MATERIALS AND METHODS

A scoping review was conducted over a 4-month time frame of English language, peer-reviewed studies published from 1946 to 2019. Search strategies for major biomedical databases (e.g., MEDLINE; Embase Classic + Embase; and the following EBM Reviews-Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, Health Technology Assessment, and the NHS Economic Evaluation Database) were developed by a senior medical information specialist and included 2,891 titles/abstracts. Study selection and data collection were designed according to the Population, Concept, and Context framework. Studies were included if the study population provided stratified data for females in a military context.

RESULTS

From a total of 2,287 citations captured from the literature searches, 168 peer-reviewed publications (144 unique studies) were eligible for inclusion. Studies were identified from across 10 countries and published between 1977 and 2019. Study designs were primarily prospective and retrospective cohorts. Most studies assessed both prevalence/incidence and risk factors for MSKi (62.50%), with few studies assessing cause (13.69%). For MSKi of female recruits compared to active female members, the prevalence was higher (19.7%-58.3% vs. 5.5%-56.6%), but the incidence (0.02%-57.7% vs. 13.5%-71.9%) was lower. The incidence of stress fractures was found to be much higher in female recruits than in active members (1.6%-23.9% vs. 2.7%). For anthropometric risk factors, increased body fat was a predictor of MSKi, but not stress fractures. For physiological risk factors for both female military groups, being less physically fit, later menarche, and having no/irregular menses were predictors of MSKi and stress fractures. For biomechanical risk factors, among female recruits, longer tibial length and femoral neck diameter increased the risk of stress fractures, and low foot arch increased risk of an ankle sprain. For female active military members, differences in shoulder rotation and bone strength were associated with risk of MSKi. For biological sex, being female compared to male was associated with an increased risk of MSKi, stress fractures, and general injuries. The consequences of experiencing MSKi for active military included limited duties, time off, and discharge. For recruits, these included missed training days, limited duty days, and release.

CONCLUSIONS

This scoping review provides insight into the current state of the evidence regarding the types and causes of MSKi, as well as the factors that influence MSKi among females in the military. Future research endeavors should focus on randomized controlled trials examining training paradigms to see if women are more susceptible. The data presented in the scoping review could potentially be used to develop training strategies to mitigate some of the identified barriers that negatively impact women from pursuing careers in the military.

The interactions of physical activity, exercise and genetics and their associations with bone mineral density: implications for injury risk in elite athletes

Low bone mineral density (BMD) is established as a primary predictor of osteoporotic risk and can also have substantial implications for athlete health and injury risk in the elite sporting environment. BMD is a highly multi-factorial phenotype influenced by diet, hormonal characteristics and physical activity. The interrelationships between such factors, and a strong genetic component, suggested to be around 50-85% at various anatomical sites, determine skeletal health throughout life. Genome-wide association studies and case-control designs have revealed many loci associated with variation in BMD. However, a number of the candidate genes identified at these loci have no known associated biological function or have yet to be replicated in subsequent investigations. Furthermore, few investigations have considered gene-environment interactions-in particular, whether specific genes may be sensitive to mechanical loading from physical activity and the outcome of such an interaction for BMD and potential injury risk. Therefore, this review considers the importance of physical activity on BMD, genetic associations with BMD and how subsequent investigation requires consideration of the interaction between these determinants. Future research using well-defined independent cohorts such as elite athletes, who experience much greater mechanical stress than most, to study such phenotypes, can provide a greater understanding of these factors as well as the biological underpinnings of such a physiologically "extreme" population. Subsequently, modification of training, exercise or rehabilitation programmes based on genetic characteristics could have substantial implications in both the sporting and public health domains once the fundamental research has been conducted successfully.

Health and well-being management in the military: a systematic review of genetic studies

BACKGROUND

Genetic research may have therapeutic value for mental and physical disorders and could have an indicative or preventative capacity. Little is known about the extent, form and utility of military-specific genetic research.

METHOD

A systematic review was conducted to evaluate existing genetic well-being studies of service personnel. The review specifically aimed to ascertain the current state of knowledge and feasibility of using genetics to aid recruitment and health management within military populations. Databases searched included MEDLINE, Embase, PsycINFO and Web of Science for relevant studies. Papers were rated using a genetics-specific quality assessment framework.

RESULTS

Ten papers were included within the final review, with seven mental-health-focused and three physical-health-focused genetic studies found within military populations. Eight papers considered candidate genes, one gene expression and one study was an outline of a future study of significant interest. Genetic commonalties were derived to yield shared physiological pathways. The 10 reviewed papers revealed moderate quality based on quality assessment.

CONCLUSIONS

Current genetic research within military populations is limited. Further studies on genetics, cost effectiveness, ethics and continual monitoring need to be explored before considering any movement toward clinical translation.

Functional polymorphisms in the P2X7 receptor gene are associated with stress fracture injury

Military recruits and elite athletes are susceptible to stress fracture injuries. Genetic predisposition has been postulated to have a role in their development. The P2X7 receptor (P2X7R) gene, a key regulator of bone remodelling, is a genetic candidate that may contribute to stress fracture predisposition. The aim of this study is to evaluate the putative contribution of P2X7R to stress fracture injury in two separate cohorts, military personnel and elite athletes. In 210 Israeli Defense Forces (IDF) military conscripts, stress fracture injury was diagnosed (n = 43) based on symptoms and a positive bone scan. In a separate cohort of 518 elite athletes, self-reported medical imaging scan-certified stress fracture injuries were recorded (n = 125). Non-stress fracture controls were identified from these cohorts who had a normal bone scan or no history or symptoms of stress fracture injury. Study participants were genotyped for functional SNPs within the P2X7R gene using proprietary fluorescence-based competitive allele-specific PCR assay. Pearson's chi-squared (χ (2)) tests, corrected for multiple comparisons, were used to assess associations in genotype frequencies. The variant allele of P2X7R SNP rs3751143 (Glu496Ala-loss of function) was associated with stress fracture injury, whilst the variant allele of rs1718119 (Ala348Thr-gain of function) was associated with a reduced occurrence of stress fracture injury in military conscripts (P < 0.05). The association of the variant allele of rs3751143 with stress fractures was replicated in elite athletes (P < 0.05), whereas the variant allele of rs1718119 was also associated with reduced multiple stress fracture cases in elite athletes (P < 0.05). The association between independent P2X7R polymorphisms with stress fracture prevalence supports the role of a genetic predisposition in the development of stress fracture injury.

Novel candidate genes putatively involved in stress fracture predisposition detected by whole-exome sequencing

While genetic factors in all likelihood contribute to stress fracture (SF) pathogenesis, a few studies focusing on candidate genes have previously been reported. The objective of this study is to gain better understanding on the genetic basis of SF in a gene-naive manner. Exome sequence capture followed by massive parallel sequencing of two pooled DNA samples from Israeli combat soldiers was employed: cases with high grade SF and ethnically matched healthy controls. The resulting sequence variants were individually verified using the Sequenom™ platform and the contribution of the genetic alterations was validated in a second cohort of cases and controls. In the discovery set that included DNA pool of cases (n = 34) and controls (n = 60), a total of 1174 variants with >600 reads/variant/DNA pool were identified, and 146 (in 127 genes) of these exhibited statistically significant (P < 0·05) different rates between SF cases and controls after multiple comparisons correction. Subsequent validation of these 146 sequence variants individually in a total of 136 SF cases and 127 controls using the Sequenom™ platform validated 20/146 variants. Of these, three missense mutations (rs7426114, rs4073918, rs3752135 in the NEB, SLC6A18 and SIGLEC12 genes, respectively) and three synonymous mutations (rs2071856, rs2515941, rs716745 in the ELFN2, GRK4, LRRC55 genes) displayed significant different rates in SF cases compared with controls. Exome sequencing seemingly unravelled novel candidate genes as involved in SF pathogenesis and predisposition.

RANK/RANKL/OPG pathway: genetic associations with stress fracture period prevalence in elite athletes

CONTEXT

The RANK/RANKL/OPG signalling pathway is important in the regulation of bone turnover, with single nucleotide polymorphisms (SNPs) in genes within this pathway associated with bone phenotypic adaptations.

OBJECTIVE

To determine whether four SNPs associated with genes in the RANK/RANKL/OPG signalling pathway were associated with stress fracture injury in elite athletes.

DESIGN, PARTICIPANTS, AND METHODS

Radiologically confirmed stress fracture history was reported in 518 elite athletes, forming the Stress Fracture Elite Athlete (SFEA) cohort. Data were analysed for the whole group and were sub-stratified into male and cases of multiple stress fracture groups. Genotypes were determined using proprietary fluorescence-based competitive allele-specific PCR assays.

RESULTS

SNPs rs3018362 (RANK) and rs1021188 (RANKL) were associated with stress fracture injury (P<0.05). 8.1% of the stress fracture group and 2.8% of the non-stress fracture group were homozygote for the rare allele of rs1021188. Allele frequency, heterozygotes and homozygotes for the rare allele of rs3018362 were associated with stress fracture period prevalence (P<0.05). Analysis of the male only group showed 8.2% of rs1021188 rare allele homozygotes had suffered a stress fracture whilst 2.5% of the non-stress fracture group were homozygous. In cases of multiple stress fractures, homozygotes for the rare allele of rs1021188 and individuals possessing at least one copy of the rare allele of rs4355801 (OPG) were shown to be associated with stress fracture injury (P<0.05).

CONCLUSIONS

The data support an association between SNPs in the RANK/RANKL/OPG signalling pathway and the development of stress fracture injury. The association of rs3018362 (RANK) and rs1021188 (RANKL) with stress fracture injury susceptibility supports their role in the maintenance of bone health and offers potential targets for therapeutic interventions.

The genetic profile of bone repair

Bone repair following a fracture is a complex, well orchestrated, physiological process in response to injury. Even though the exact number of the genes and expressed proteins involved in fracture healing remains unknown, the molecular complexity of the repair process has been demonstrated, and it involves numerous genes and molecules, such as extracellular matrix genes, growth and differentiation factors, matrix metalloproteinases, angiogenic factors and others. Discrepancies in fracture healing responses and final outcome seen in the clinical practice may be attributed among other factors to biological variations between patients and different genetic "profiles", resulting in "altered" signalling pathways that regulate the bone repair process. Preliminary human studies support a "genetic" component in the pathophysiology of impaired bone repair seen in atrophic non-unions by correlating genetic variations of specific molecules regulating fracture healing with non-union. However, the role of the genetic "profile" of each individual in fracture healing and final outcome, and its possible interaction with other exogenous factors remains a topic of extensive research.

Genetic predisposition to non-union: evidence today

Atrophic non-union represents a complex clinical condition and research is ongoing in an effort to elucidate its pathophysiology and to offer new and more efficient treatment modalities. Differences seen in fracture healing responses and final outcome may be attributed among other factors to biological variations between patients resulting in a "disturbed" signalling pathway and an "inert or deficient local biology with reduced potentials for bone regeneration". The genetic contribution with or without the interaction of other exogenous factors in cases of impaired fracture healing, is yet to be elucidated. However, preliminary animal and human studies demonstrate the molecular basis of fracture non-unions and correlate genetic variants of the molecules regulating fracture healing and their expression patterns with impaired bone healing and fracture non-union. Further research is needed to clarify the genetic component and its role and interaction with other risk factors that may result in increased susceptibility of a patient to develop this complication.