Genome-wide Association Study Of Low Back Pain

Background:Low back pain（LBP）is a common musculoskeletal condition and reason for seeking health care and it has been the leading cause of global burden measured with years lived with disability.For more than 90%of LBP with unknown etiologies so far,precise and effective treatments are scarce.LBP is a complicated trait with considerable genetic contributions,and its heritability was estimated to be larger than 30%in twin studies.Elucidating genetic basis and prioritizing candidate genes paves the way for the exploration of molecular intervention targets and identification of risk factors for LBP,and hence is of great scientific value.Genome-wide association study（GWAS）is a powerful tool to study the genetics of complex traits with the advent of the post-genomic era.Here,we aimed to reveal genetic underpinnings of LBP with GWAS and follow-up bioinformatic analyses.Methods:Firstly,we performed a GWAS to identify risk loci and candidate genes for LBP.We obtained 18601 cases with LBP and 520453controls from European biobanks.Cases were ascertained by the International Classification of Diseases（ICD-10,M54.5）.The GWAS meta-analysis yielded summary statistics of LBP and significant single nucleotide polymorphisms（SNPs）.Then we conducted the integrated annotation by physical mapping,quantitative trait loci（QTLs）of gene expression,high-throughput chromosome conformation capture datasets,and gene-based association analysis.Secondly,we prioritized candidate genes for LBP by integrating multi-tissue and multi-omics data.The summary-data based Mendelian randomization（MR）analysis was implemented using expression QTL data of whole blood,adipose,muscle,neural and skin tissues.We identified expression cis-QTLs and target genes in association with LBP risks.We further validated the relationship between molecular traits and LBP risks using DNA methylome and proteome datasets.Lastly,we investigated effects of sarcopenia-related traits on LBP.We obtained GWAS summary statistics of handgrip strength,sarcopenic muscle weakness,appendicular lean mass,site-specific fat-free mass.We performed the linkage disequilibrium regression analysis to assess genetic correlations.We selected genetic instrumental SNPs to implement the inverse-variance MR and multiple sensitivity analyses.Results:We found three loci at suggestive threshold(P<1×10^-6),3p12.3（rs141968060）,5q34（rs140484435）and 19p13.3（rs4807174）.Here rs4807174 was a cis-expression QTL of BTBD2 in multiple tissues and in vitro validation implicated BTBD2 in myogenesis.Overall,the first part identified BTBD2 as a candidate gene for LBP.We found one shared gene WFIKKN1 whose expressions in multiple tissues were inversely associated with LBP risks.Furthermore,increased methylation levels at three sites of the WFIKKN1 promoter（cg05351750,cg05932139 and cg19227170）were associated with higher LBP risks.However,there was no evidence for the relationship between serum levels of WFIKKN and risks of LBP.Previous studies revealed WFIKKN1 as an antagonist of MSTN,and hence WFIKKN1 would facilitate myogenesis.Overall,the second part identified WFIKKN1 as a functional candidate gene for LBP.Lastly,we found that sarcopenic muscle weakness was associated with higher LBP risks,whereas increased body fat-free mass had protective effects.Overall,the last part demonstrated that sarcopenia was a risk factor for LBP.Conclusion:the study identified two novel risk genes for LBP,BTBD2and WFIKKN1,which were possibly involved in myogenesis and affected the onset of LBP.We further validated decreased muscle mass and strength as risk factors for LBP.This study provided theoretical basis for the role of muscular factors in LBP and brought hints to further research on the molecular mechanism and precise treatment and prevention of LBP.