JOURNAL OF SPORTS SCIENCE & MEDICINE
CANDIDATE GENE ANALYSIS IN ISRAELI SOLDIERS WITH STRESS FRACTURES
Ran Yanovich1, Eitan Friedman2,4, Roni Milgrom2, Bernice Oberman3, Laurence Freedman3 and Daniel S. Moran1,5
1Heller Institute of Medical Research, 2Susanne Levy Gertner Oncogenetics Unit, and 3Biostatistics Unit Gertner Institute of Epidemiology and Health Policy Research, Sheba Medical Center, Tel-Hashomer, Israel; 4Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel, 5Ariel University Center of Samaria, Israel.
© Journal of Sports Science and Medicine (2012) 11, 147 - 155
|To investigate the association of polymorphisms within candidate
genes which we hypothesized may contribute to stress fracture predisposition,
a case-control, cross- sectional study design was employed. Genotyping 268
Single Nucleotide Polymorphisms- SNPs within 17 genes in 385 Israeli young
male and female recruits (182 with and 203 without stress fractures). Twenty-five
polymorphisms within 9 genes (NR3C1, ANKH, VDR, ROR2, CALCR, IL6, COL1A2,
CBG, and LRP4) showed statistically significant differences (p < 0.05)
in the distribution between stress fracture cases and non stress fracture
controls. Seventeen genetic variants were associated with an increased stress
fracture risk, and eight variants with a decreased stress fracture risk.
None of the SNP associations remained significant after correcting for multiple
comparisons (false discovery rate- FDR). Our findings suggest that genes
may be involved in stress fracture pathogenesis. Specifically, the CALCR
and the VDR genes are intriguing candidates. The putative involvement of
these genes in stress fracture predisposition requires analysis of more
cases and controls and sequencing the relevant genomic regions, in order
to define the specific gene mutations.
Key words: Stress fractures; Bone remodeling; genetic variance; SNPs; inherited predisposition.
Stress fracture (SF) is a prevalent overuse injury that usually
affects bones of the lower extremities in physically active individuals,
especially amongst athletes and military recruits of combat units during
basic training (Hod et al., 2006;
Murray et al., 2006).
While the precise underlying mechanisms operative in SF pathogenesis remain
elusive, the current paradigm stipulates that repeated, cyclical, weight-bearing
activity leads to a change in the bone's remodeling processes- osteoclast
mediated bone resorption and osteoblast driven bone formation (Romani
et al., 2002).
When this process is unbalanced, microscopic, and subsequent macroscopic
bone fissures are encountered that are collectively referred to as SF
(Orava and Hulkko, 1984).
study was approved by the IDF IRB and the Ministry of Health's IRB for
genetic studies ethic committees for human studies. All participants were
active duty soldiers and were recruited from among combat soldiers referred
to the Institute of Nuclear Medicine at the Medical Services and Supply
Center of the IDF's Medical Corps with clinical symptoms compatible with
SF from January 2007 to December 2009. Each participant, after signing
a written informed consent, filled a questionnaire that detailed demographic
data, personal and family history of SF and bone diseases, engagement
in sports and smoking and alcohol history, and additional data relevant
to SF risk.
hundred and three soldiers (162 males and 41 females) ranging between
18-32 years, mean age: 20.2 ± 1.3 years, were classified as having no
evidence of SF and were assigned "control" status (C group),
and 182 soldiers (165 males and 17 females) ranging between 18-30 years,
mean age: 20.1 ± 1.7 years, with grade 3-4 SF or multiple grade 2 SF were
assigned "case" status (SF group). Both cases and controls were
for the most part soldiers in basic training with 79% among SF cases and
73% among controls within 4 months of recruitment and initiation of their
basic training. The compliance rate was low: the overall number of seemingly
eligible individuals for both cases and controls over the time of recruitment
was 3208 IDF soldiers, most of these being controls. There was a 12% compliance
respect to the bone scan results, 110 participants from the SF group (71.4%)
were diagnosed with multiple SFs, while 53.4% (59 /110) suffered from
bilateral tibia fractures, 17.3% (19/110) had bilateral femoral fractures.
Among the 28.6% (44/154) of participants who sustained single SF, 48.2%
had tibial SF, 39.3% had femoral SF, and 12.5% had SF in the fibula.
In this pilot study the association of SF with 25 sequence variants
within the following 9 genes: NRC31, ANKH, VDR, ROR2, CALCR, IL6, COL1A2,
CBG, and LRP4 were assessed. Specifically sequence variants within two
genes CALCR and VDR emerged from the current study as seemingly associated
with stress fracture. Recently, six CALCR polymorphisms were reportedly
associated (p < 0.005) with lower lumbar spine BMD (rs10488551, rs2283002,
and rs6976450) and lower hip BMD (rs2214213, rs7790825, and rs972978)
among 709 pre menopausal Canadian females (average age: 44.5 ± 7.2 years)
(Giroux et al., 2010).
In the present study, one of these 6 SNP's (rs12154667) was associated
with lower SF risk, another (rs1548456) with an increased SF risk and
two haplotypes- with an increased stress fracture risk. Since Calcitonin
is one of the hormones involved in regulating osteoclast activity and
calcium secretion (Bijvoet et al., 1971;
Bussolati and Pearse, 1967),
it seems plausible that these intronic polymorphisms affect intracellular
molecular pathways eventually manifesting as SF.
|This study suggests that there may be genetic factors that contribute to SF pathogenesis and has indicated some of the genes that may underlie SF predisposition in young military recruits. Specifically the CALCR and the VDR genes are intriguing candidates to be involved in stress fracture pathogenesis. Obviously, these results need to be replicated, confirmed and extended by analyzing more cases and controls, before any conclusions can be drawn.|
|This study was funded by a grant from TATRC (W81XWH-09-2-0054) to Eitan Friedman and Daniel S. Moran and was performed in part as a prerequisite for the graduate degree (PhD) for Ran Yanovich at the Sackler School of medicine, Tel -Aviv University, Tel-Aviv. We wish to thank Dr. Marina Bogomolov for her advice and input in the false discovery rate analysis.|
Employment: The deputy director of the military physiology unit, Heller Institute of Research, Sheba Medical Centerin Israel.
Employment: Head of the Oncogenetics unit, Sheba Medical Center, Tel Hashomer, A full professor at the Department of Internal Medicine, SacklerMedical School, Tel-Aviv University.
Degree: MD, PhD
Research interests: The genetic basis of common disorders and inherited predisposition to cancer
Employment: Doctoral candidate at the Weitzman Institute of Science, Rechovot, Israel.
Employment: The biostatistics unit, at the Gertner Institute of Epidemiology and Health Policy Research teaches at the Tel-Aviv University
Employment: Professor, Bar Ilan University, Israel< and the head of the Biostatistics Unit, Gertner Institute of Epidemiology and Health Policy Research, Sheba Medical Center.
Daniel S. MORAN
Employment: Professor, Ariel University Center of Samaria, and Senior researcher at the Heller Institute of Research, Sheba Medical Center.
Research interests: Adaptation to stress and extreme conditions encountered during military service, including stress fractures.