Resistance to thyroid hormone (RTH) is an inherited disease characterized by reduced tissue sensitivity to thyroid hormone. Approximately 90% of subjects with RTH have mutation in the thyroid hormone receptor β (TRβ) gene. Approximately 10% of subjects diagnosed as having RTH do not carry mutation in the TRβ gene. A possible linkage was reported with the retinoid X receptor-γ (RXR-γ) gene in two families. The aim of this study is to search for mutation within the RXR-γ gene in unrelated subjects with diagnosed RTH without mutations in the TRβ gene. Four subjects with RTH were studied, and sequence variants in the RXR-γ gene were searched by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP). Analysis of all the 10 exons of the RXR-γ gene, including intron-exon boundaries, promoter region and 3′ untranslated region (UTR) reveled two variant bands in subjects II and III. Sequencing of these variants showed two single nucleotide polymorphisms (SNPs): 447C > T in exon 3 for patients II and IVS9 + 6A > G for patient III. Both SNPs were also present at high frequency in a group of normal subjects and in nonaffected relatives of subject III. In conclusion, in patients with RTH we have found two SNPs in the RXR-γ gene; these SNPS are common in the general population, thus excluding a role for the RXR-γ gene in these patients.
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