RESUMO
PURPOSE: Thyroid hormones are essential for the normal function of almost all human tissues, and have critical roles in metabolism, differentiation and growth. Free triiodothyronine (fT3), free thyroxine (fT4) and thyroid-stimulating hormone (TSH) levels are under strong genetic influence; however, most of the heritability is yet unexplained. METHODS: In order to identify novel loci associated with fT3, fT4 and TSH serum levels we performed a genome-wide meta-analysis of 7 411 206 polymorphisms in up to 1731 euthyroid individuals from three Croatian cohorts from Dalmatia region: two genetically isolated island populations and one mainland population. Additionally, we also performed a bivariate analysis of fT3 and fT4 levels. RESULTS: The EPHB2 gene variant rs67142165 reached genome-wide significance for association with fT3 plasma levels (P = 9.27 × 10-9) and its significance was confirmed in bivariate analysis (P = 9.72 × 10-9). We also found a genome-wide significant association for variant rs13037502 upstream of the PTPN1 gene and TSH plasma levels (P = 1.67 × 10-8). CONCLUSION: We identified a first genome-wide significant variant associated with fT3 plasma levels, as well as a novel locus associated with TSH plasma levels. These findings are biologically relevant and enrich our knowledge about the genetic basis of pituitary-thyroid axis function.