| Background:Handgrip strength and motor function decline are common in the elderly.Both phenotypes reflect muscle strength levels.In addition to environmental factors,genetic factors also have an important influence on muscle strength.To the best of our knowledge,several studies have explored the heritability and genetic susceptibility locus of handgrip strength and lower limb motor function,but lack of relevant study in Chinese population.Considering that muscle strength varies widely among different ethnic,this present study aimed to investigate the heritability of handgrip strength and lower limb motor function,and to further investigate potential single nucleotide polymorphisms（SNPs）,genes,and pathways of those phenotypes using univariate genome-wide association study（GWAS）in northern Chinese population.Methods:Twin pairs from Qingdao Twin Registration System were selected for the present study.All subjects had provided written informed consent.Handgrip strength was measured using an electronic grip meter and lower limb motor function was assessed using five-times-sit-to-stand-test（FTSST）.Blood samples were taken from the subjects after an overnight fast,and the zygosity were further identified by sex,blood type,and microsatellite DNA scanning technique.Genotyping was performed using the Infinium Omni2.5 Ex OME-8v1.2 chip.Referring to the third phase data of the 1000Genome Project,genotype imputation was conducted using the IMPUTE2 software.The structural equation model constructed by Mx software was used evaluate genetic and environmental influence on handgrip strength or lower limb motor function,and age,sex,and body mass index（BMI）were adjusted.The best fitting model was selected to calculate the heritability of handgrip strength and lower limb motor function.In genome-wide association analysis,SNPs-based analysis was performed using genome-wide efficient Mixed Models analysis（GEMMA）to explore potential SNPs loci associated with handgrip strength or lower limb motor function.Quantile-quantile（Q-Q）plots were used to explore population stratification,with Manhattan plots showing significant SNPs loci.Haplo Reg V4.1 and website of the Gene Expression Organization（GTEx）project were used in Expression quantitative trait loci（eQTL）analysis to explore cis-eQTL in muscle-skeletal,adipose,and other potential tissues.Gene-based analysis was performed using Versatile Gene-Based Association Study-2（VEGAS2）software and pathway enrichment analysis was also performed.Results:A total of 369 twin pairs were included in the analysis for handgrip strength,with a median age（interquartile range）of 50（12）years,a median body mass index（interquartile range）of 23.9（4.3）kg/m2,and a median handgrip strength（interquartile range）of 32.4（16.5）kg.373 twin pairs were included in the study for lower limb motor function.The median time（interquartile range）for the five sit-to-stand test was 7.3（2.4）seconds.Both handgrip strength and lower limb motor function fit the AE model,and the heritability of handgrip strength and lower limb motor function were 57.77%and 53.36%,respectively.After the dizygotic twins were included in GWAS,the results were as follows:（1）In the SNPs-based study on handgrip strength,a total of 1,338,253 SNPs were included before interpolation.Although no single SNP reached the significant association level(P<1×10-5),19 SNPs reached suggestive association level,among which the lowest P value was rs78161270 located in the Dopa decarboxylase gene on chromosome 7(P=9.0×10-7).After genotype imputation,7,393,353 SNPs were included,and 162 SNPs reached the suggestive association level,among which the lowest P value was rs79287957(P=1.3×10-7).A total of 1,338,892 SNPs were included in the SNPs-based study on lower limb motor function before imputation.9 SNPs were found to be associated with lower limb motor function at the suggestive association level.A total of 7,400,336 SNPs were included after imputation,and 30 of them reached the suggestive association level.The lowest P value before and after imputation were rs201378641.（2）In genetic-based analysis,1,050 and 1,118 genes reached suggestive level for handgrip strength before and after the imputation.The top 5 genes with the lowest P value before imputation were WBP1L,TAF1B,LOC101927081,WDR20,and ATP6V0D1 and GTF2H2C,WBP1L,GTF2H2C＿2,UCKL1,TRIM43 after imputation,respectively.The number of genes nominally associated with lower limb motor function were 1,008 and1,084 before and after interpolation,respectively.The Top 5 genes were SFI1,HIPK2,CAND1.11,PNLIPRP2,TPD52L2,and CAND1.11,SFI1,MCPH1,CTAG2,SLC6A8,respectively.74 genes were associated with handgrip strength and lower limb motor function,including TECPR2,LDB1,and EFEMP2.（3）There were 626 biological pathways related to handgrip strength,including PPAR SIGNALING PATHWAY,STRIATED MUSCLE CONTRACTION,CYTOKINE-CYTOKINE RECEPTOR INTERACTION,STEROID HORMONES,and others.There are 699 biological pathways related to lower limb motor function,including AXON GUIDANCE,FIBROBLAST GROWTH FACTOR RECEPTOR SIGNALING,MYOSIN RELATED KINASE PATHWAY OF PLASMA MEMBRANE NEURTROPHIC,and NOTCH SIGNALING.Among which there are 230 common biological pathways.It includes STRIATED MUSCLE CONTRACTION,CYTOKINE-CYTOKINE RECEPTOR INTERACTION,STEROID HORMONES,etc.（4）eQTL analysis showed that 26 SNPs loci were cis-eQTL significantly related to handgrip strength in muscle-skeletal and adipose tissue.Among the top 20 genes,14 and17 genes harbored statistically significant cis-eQTL in at least one relevant tissue,respectively.Conclusion:This study indicated that handgrip strength and lower limb motor function is inherited at a moderate level in twin samples of Qingdao.We found multiple potential SNPs,genes,and pathways associated with handgrip strength and lower limb motor function.This provides clues for further understanding of the decline in muscle strength or motor function from a genetic perspective. |
