Rare Diseases Functional Genomics, Kids Research, The Children's Hospital at Westmead and Children's Medical Research Institute, Westmead, NSW, Australia.
School of Science, STEM (Science, Technology, Engineering, and Mathematics) College, Royal Melbourne Institute of Technology (RMIT), Bundoora, VIC, Australia.
Blood Adv. 2022 Jun 28;6(12):3779-3791. doi: 10.1182/bloodadvances.2022007029.
Telomere biology disorders (TBDs) are a spectrum of multisystem inherited disorders characterized by bone marrow failure, resulting from mutations in the genes encoding telomerase or other proteins involved in maintaining telomere length and integrity. Pathogenicity of variants in these genes can be hard to evaluate, because TBD mutations show highly variable penetrance and genetic anticipation related to inheritance of shorter telomeres with each generation. Thus, detailed functional analysis of newly identified variants is often essential. Herein, we describe a patient with compound heterozygous variants in the TERT gene, which encodes the catalytic subunit of telomerase, hTERT. This patient had the extremely severe Hoyeraal-Hreidarsson form of TBD, although his heterozygous parents were clinically unaffected. Molecular dynamic modeling and detailed biochemical analyses demonstrate that one allele (L557P) affects association of hTERT with its cognate RNA component hTR, whereas the other (K1050E) affects the binding of telomerase to its DNA substrate and enzyme processivity. Unexpectedly, the data demonstrate a functional interaction between the proteins encoded by the two alleles, with wild-type hTERT rescuing the effect of K1050E on processivity, whereas L557P hTERT does not. These data contribute to the mechanistic understanding of telomerase, indicating that RNA binding in one hTERT molecule affects the processivity of telomere addition by the other molecule. This work emphasizes the importance of functional characterization of TERT variants to reach a definitive molecular diagnosis for patients with TBD, and, in particular, it illustrates the importance of analyzing the effects of compound heterozygous variants in combination, to reveal interallelic effects.
端粒生物学障碍（TBDs）是一组多系统遗传性疾病，其特征为骨髓衰竭，是由于编码端粒酶或其他参与维持端粒长度和完整性的蛋白质的基因突变所致。这些基因中的变体的致病性很难评估，因为 TBD 突变的外显率和遗传预期高度可变，与每一代较短的端粒遗传有关。因此，通常需要对新鉴定的变体进行详细的功能分析。在这里，我们描述了一名 TERT 基因复合杂合变体的患者，该基因编码端粒酶的催化亚基 hTERT。尽管其杂合父母在临床上未受影响，但该患者患有极其严重的 Hoyeraal-Hreidarsson 型 TBD。分子动力学建模和详细的生化分析表明，一个等位基因（L557P）影响 hTERT 与其同源 RNA 成分 hTR 的结合，而另一个等位基因（K1050E）影响端粒酶与其 DNA 底物的结合和酶的进程。出乎意料的是，数据表明两个等位基因所编码的蛋白质之间存在功能相互作用，野生型 hTERT 可挽救 K1050E 对进程性的影响，而 L557P hTERT 则不能。这些数据有助于对端粒酶的机制理解，表明一个 hTERT 分子中的 RNA 结合会影响另一个分子的端粒添加进程性。这项工作强调了对 TERT 变体进行功能特征分析以对 TBD 患者进行明确分子诊断的重要性，特别是说明了分析复合杂合变体组合的影响以揭示等位基因间效应的重要性。
