The performance of a genome scan for serum lipid traits at 45 and 190 d in 5 half-sib families of Duroc pigs allowed us to detect several pig chromosomal regions with significant effects on these phenotypes. In the current work, we aimed to refine the position of 1 chromosome 4 (SSC4) genome-wide significant QTL for serum triglyceride concentration at 190 d. Genotyping of 4 additional microsatellites allowed reduction of the 90% confidence interval of this QTL to the genomic interval between markers SW2409 and SW839. Sequencing experiments were performed to characterize the variability of 2 lipid-related genes, the lipoprotein receptor-related protein 12 (LRP12) and tribbles homolog 1 (TRIB1) loci, that map to this region. In this way, 2 (c.771A > G and c.1101A > G) and 1 (c.*156_157del) polymorphisms were identified at the LRP12 coding region and TRIB1 3' untranslated region, respectively. Association analyses between LRP12 and TRIB1 genotypes did not reveal any significant effect on serum lipid concentrations, suggesting that variation of these two loci does not explain the segregation of the SSC4 QTL. However, highly significant associations were observed for gluteus medius saturated fatty acid content (LRP12 c.1101A > G, P = 0.0006; TRIB1 c.*156_157del, P = 0.0003). In the light of these and other findings, the potential involvement of LRP12 and TRIB1 in muscle lipid metabolism deserves to be further explored.