Servicio de Endocrinologia, Hospital de Pediatria Garrahan, Buenos Aires C1245AAM, Argentina.
J Clin Endocrinol Metab. 2010 Sep;95(9):E98-103. doi: 10.1210/jc.2010-0223. Epub 2010 Jun 9.
Patients with TSH-beta subunit defects and congenital hypothyroidism are missed by TSH-based neonatal screening.
Our objective was to report the molecular consequences of a novel splice-junction mutation and a novel missense mutation in the TSH-beta subunit gene found in two patients with congenital central hypothyroidism and conventional treatment-resistant anemia.
Patient 1 had a homozygous G to A nucleotide change at the 5' donor splice site of exon/intron 2. This resulted in a silent change at codon 34 of the mature protein. In vitro splicing assays showed that the mutant minigene dramatically affected pre-mRNA processing, causing exon 2 to be completely skipped. The putative product from a new out-of-frame translational start point in exon 3 is expected to yield a nonsense 25-amino-acid peptide. In patient 2, sequence analysis revealed a compound heterozygosis for the already reported 313delT (C105Vfs114X) mutation and for a second novel mutation in exon 3, substituting G for A at cDNA nucleotide position 323, resulting in a C88Y change. This cysteine residue is conserved among all dimeric pituitary and placental glycoprotein hormone-beta subunits. Data from in silico analysis confirmed that the C88Y mutation would affect subunit conformation. Indeed, two different bioinformatics approaches, PolyPhen and SIFT analysis, predicted C88Y to be a damaging substitution.
In isolated TSH deficiency, the exact molecular diagnosis is mandatory for diagnosis of isolated pituitary deficiency, delineation of prognosis, and genetic counseling. Moreover, diagnosis of central hypothyroidism should be considered in the face of severe infant anemia of uncertain etiology.
促甲状腺激素-β亚基缺陷和先天性甲状腺功能减退症患者会被基于 TSH 的新生儿筛查遗漏。
我们的目的是报告两个患有先天性中枢性甲状腺功能减退症和常规治疗抵抗性贫血的患者中 TSH-β亚基基因的一种新剪接突变和一种新错义突变的分子后果。
患者 1 在 2 号外显子/内含子 5'供体位点发生 G 到 A 的核苷酸变化，导致成熟蛋白的密码子 34 发生无义变化。体外剪接分析表明，突变的 minigene 显著影响前体 mRNA 加工，导致外显子 2 完全缺失。外显子 3 中新的无义翻译起始点的假定产物预计会产生一个无意义的 25 个氨基酸肽。在患者 2 中，序列分析显示已报道的 313delT（C105Vfs114X）突变和 3 号外显子的第二个新突变的复合杂合性，导致 cDNA 核苷酸位置 323 的 G 突变为 A，导致 C88Y 变化。这个半胱氨酸残基在所有二聚体垂体和胎盘糖蛋白激素-β亚基中都是保守的。来自计算机分析的数据证实，C88Y 突变会影响亚基构象。实际上，两种不同的生物信息学方法，即 PolyPhen 和 SIFT 分析，预测 C88Y 是一种有害的取代。
在孤立性 TSH 缺乏症中，明确的分子诊断对于孤立性垂体缺乏症的诊断、预后的划定和遗传咨询是必需的。此外，在面对原因不明的严重婴儿贫血时，应考虑中枢性甲状腺功能减退症的诊断。
