STAT2既是IFN-I信号通路的效应物，也是负调节因子。我们描述了一位患有I型干扰素病的患者中一种新型纯合错义STAT2替换的特征。采用全基因组测序(WGS)识别显示增强IFN-I信号通路特征的患者病因。在稳定的lentiviral重组STAT2-null人类纤维肉瘤U6A细胞体内，采用STAT2野生型或p.(A219V)进行定量聚合酶链反应、Western印迹、免疫荧光和共免疫沉淀等方法，对p.(A219V)变异体进行功能鉴定。 WGS鉴定出STAT2上一个罕见的同型纯合单核苷酸转换(c.656C>T)，导致p.(A219V)替换，该患者表现出发育迟缓、颅内钙化和血液中干扰素刺激基因(ISG)表达的上调。体外研究表明，STAT2 p.(A219V)变异体保持了传递IFN-I刺激的能力。值得注意的是，STAT2 p.(A219V)未能支持受体失敏化，导致持续的STAT2磷酸化和ISG的上调。机械上，STAT2 p.(A219V)显示出对泛素特异性蛋白酶18(USP18)的缺陷结合，为患者中慢性IFN-I通路激活提供了可能的解释。我们的数据表明，STAT2 p.(A219V)在IFN-I信号中发挥了受损的负调节作用，并且导致I型干扰素病状态的STAT2突变不仅限于先前报告的R148残基。实际上，结构建模强调至少还有3个关键残基对介导STAT2-USP18相互作用至关重要，这些突变可能导致IFN-I信号的缺陷负反馈调节。©2023年作者。

STAT2 is both an effector and negative regulator of type I interferon (IFN-I) signalling. We describe the characterization of a novel homozygous missense STAT2 substitution in a patient with a type I interferonopathy.Whole-genome sequencing (WGS) was used to identify the genetic basis of disease in a patient with features of enhanced IFN-I signalling. After stable lentiviral reconstitution of STAT2-null human fibrosarcoma U6A cells with STAT2 wild type or p.(A219V), we performed quantitative polymerase chain reaction, western blotting, immunofluorescence, and co-immunoprecipitation to functionally characterize the p.(A219V) variant.WGS identified a rare homozygous single nucleotide transition in STAT2 (c.656C > T), resulting in a p.(A219V) substitution, in a patient displaying developmental delay, intracranial calcification, and up-regulation of interferon-stimulated gene (ISG) expression in blood. In vitro studies revealed that the STAT2 p.(A219V) variant retained the ability to transduce an IFN-I stimulus. Notably, STAT2 p.(A219V) failed to support receptor desensitization, resulting in sustained STAT2 phosphorylation and ISG up-regulation. Mechanistically, STAT2 p.(A219V) showed defective binding to ubiquitin specific protease 18 (USP18), providing a possible explanation for the chronic IFN-I pathway activation seen in the patient.Our data indicate an impaired negative regulatory role of STAT2 p.(A219V) in IFN-I signalling and that mutations in STAT2 resulting in a type I interferonopathy state are not limited to the previously reported R148 residue. Indeed, structural modelling highlights at least 3 further residues critical to mediating a STAT2-USP18 interaction, in which mutations might be expected to result in defective negative feedback regulation of IFN-I signalling.© 2023. The Author(s).