Rivolta Carina M, Gil M Susana Mallea, Ballarino Carolina, Ridruejo M Carolina, Miguel Carlos M, Gimenez Silvia B, Bernacchi Silvia S, Targovnik Héctor M
Laboratory of Molecular Biology, Department of Genetic and Molecular Biology, School of Pharmacy and Biochemistry, University of Buenos Aires, Av. Córdoba 2351, 4to piso-sala 5, 1120, Buenos Aires, Argentina.
Mol Diagn. 2004 Sep;8(3):163-9. doi: 10.1007/BF03260060.
Resistance to the thyroid hormone (RTH) is an inherited syndrome of reduced tissue responsiveness to hormonal action caused by mutations located in the ligand-binding domain and adjacent hinge region of the thyroid hormone receptor β (TRβ) gene.
The patient in this study, a 42-year-old Caucasian male, came to medical attention because he experienced atrial fibrillation. Clinical evaluation showed a small and diffuse goiter and biochemical tests revealed markedly elevated concentrations of total T(4), total T(3), and free T(4), normal thyroid-stimulating hormone (TSH) values and slightly increased I(131) thyroid uptake at 24 hours. The thyroperoxidase, thyroglobulin, and TSH receptor antibodies were positive. He was treated with cabergoline plus methimazole. This treatment was stopped because of the inconsistent response, monotherapy with tri-iodothyroacetic acid (TRIAC) was then prescribed after molecular diagnosis confirmed RTH syndrome.
The exons 9 and 10 of the TRβ gene, including splicing signals and the flanking intronic regions of each intron, were amplified with PCR. DNA sequences from each amplified fragment were performed with the Taq polymerase-based chain terminator method and using the specific TRβ forward and reverse primers.
Direct sequence analysis of the exons 9 and 10 of the TRβ gene revealed an eight basepair deletion, 1297-1304delGCCTGCCA in exon 10. The mutation produces a frameshift at amino acid 433 and introduces a stop codon TGA at position 461, 85 nucleotides downstream from deletion. This alteration was not detected in either the father or mother of the patient, suggesting a de novo mutation that was confirmed by DNA fingerprint analysis.
In the present study we have identified a novel sporadic mutation corresponding to 1297-1304delGCCTGCCA deletion in the activating function 2 (AF-2) region of TRβ. To our knowledge, this is the first time that the presence of a partial deletion of eight nucleotides in the TRβ has been reported.
甲状腺激素抵抗（RTH）是一种遗传性综合征，由于甲状腺激素受体β（TRβ）基因的配体结合域及相邻铰链区发生突变，导致组织对激素作用的反应性降低。
本研究中的患者为一名42岁的白种男性，因房颤前来就医。临床评估显示有小而弥漫性的甲状腺肿，生化检查显示总T4、总T3和游离T4浓度显著升高，促甲状腺激素（TSH）值正常，24小时I(131)甲状腺摄取率略有增加。甲状腺过氧化物酶、甲状腺球蛋白和TSH受体抗体均为阳性。他接受了卡麦角林加甲巯咪唑治疗。由于反应不一致，该治疗被停止，在分子诊断确诊为RTH综合征后，随后开了三碘甲状腺乙酸（TRIAC）单药治疗。
用聚合酶链反应（PCR）扩增TRβ基因的外显子9和10，包括剪接信号和每个内含子的侧翼内含子区域。每个扩增片段的DNA序列采用基于Taq聚合酶的链终止法，使用特异性TRβ正向和反向引物进行测定。
TRβ基因外显子9和10的直接序列分析显示外显子10中有一个8个碱基对的缺失，即1297 - 1304delGCCTGCCA。该突变在氨基酸433处产生移码，并在缺失下游85个核苷酸的位置461处引入终止密码子TGA。在患者的父亲或母亲中均未检测到这种改变，提示为新发突变，DNA指纹分析证实了这一点。
在本研究中，我们在TRβ的激活功能2（AF - 2）区域鉴定出一种新的散发性突变，对应于1297 - 1304delGCCTGCCA缺失。据我们所知，这是首次报道TRβ中存在8个核苷酸的部分缺失。
