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This article is from BMC Proceedings , volume 8 . Abstract In this paper, we propose a novel mixed-effects model for longitudinal changes of systolic blood pressure (SBP) over time that can estimate the joint effect of multiple sequence variants on SBP after accounting for familial correlation and the time dependencies within individuals. First we carried out agenome-wide association study (GWAS) using chromosome 3 single-nucleotide polymorphisms(SNPs) to identify regions associated with SBP levels. In a second step, we examined the sequence data to fine-map additional variants in these regions. Four SNPs from two intergenic regions (PLXNA1-TPRA1, BPESC1-PISTR1) and one gene (NLGN1) were detected to be significantly associated with SBP after adjusting for multiple testing. These SNPs were used to capture the multilocus genotype diversity in the regions. The multilocus genotypes derived from these four variants were then treated as random effects in the mixed-effects model, and the corresponding confidence intervals (Cis) were built to assess the significance of the joint effect of the sequence variants on SBP. We found that multilocus genotypes (GG,TT,AG,GG), (GG,TT,GG,GG), and (GG,TT,AA,AG) are associated with higher SBPand (GG,CT,AA,AA), (AA,TT,AA,AA), and (AG,CT,AA,AG) are associated with lower SBP. The linear mixed-effects models provide a powerful tool for GWAS and the analysis of joint modeling of multilocus genotypes.