Background
Gender differences in the prevalence of chronic back pain (cBP) have been recorded, but not fully explained. Suggesting gene-by-sex interaction as a possible reason, we explored sex-specific genetic loci for cBP using the UK Biobank. 
Material and methods 
A total of 200,948 males and 236,412 females of European ancestry have been analysed. The phenotype was “Back pain for 3+months”. GWAS were carried out examining males and females separately adjusting for age and technical covariates, followed by a comparisons of SNP effect sizes (regression estimates) between the sexes. 
Results
The prevalence of cBP was 17.7% and 18.2% and the mean age (SD) was 57.5 (8.1) and 57.1 (7.9) in males and females, respectively. Four and 8 non-overlapping genome-wide significant loci were identified for males and females. SNP-explained heritability was higher in females (0.079 vs 0.067, p = 0.006). There was a high genetic correlation between the sexes (r = 0.84, p = 1.7e-94). GWAS comparing the effect size between sexes revealed three significant loci: on chromosomes 4 (rs62327819, SLC10A7), 6 (rs556434841, MEI4), and 8 (rs184345217, CSMD1) (Figure). We found differences in genetic correlations between sexes for four traits: “Neck and shoulder pain”, “Serious illness, injury or assault to yourself”, “Dorsalgia”, and “Self-reported disc problems” (Table).
Conclusions
The results suggest modest differences in the genetic component of cBP in males and females. Their impact of cBP epidemiology are to be explored. 
The study was performed using the UK Biobank data (project # 18219).

SEX-SPECIFIC EFFECTS IN THE GENETICS OF CHRONIC BACK PAIN