Institute for Immunodeficiency, Center for Chronic Immunodeficiency (CCI), Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Institute for Transfusion Medicine, University of Ulm, Ulm, Germany.
J Allergy Clin Immunol. 2024 Jan;153(1):297-308.e12. doi: 10.1016/j.jaci.2023.11.006. Epub 2023 Nov 17.
Elevated TCRαβCD4CD8 double-negative T cells (DNT) and serum biomarkers help identify FAS mutant patients with autoimmune lymphoproliferative syndrome (ALPS). However, in some patients with clinical features and biomarkers consistent with ALPS, germline or somatic FAS mutations cannot be identified on standard exon sequencing (ALPS-undetermined: ALPS-U).
We sought to explore whether complex genetic alterations in the FAS gene escaping standard sequencing or mutations in other FAS pathway-related genes could explain these cases.
Genetic analysis included whole FAS gene sequencing, copy number variation analysis, and sequencing of FAS cDNA and other FAS pathway-related genes. It was guided by FAS expression analysis on CD57DNT, which can predict somatic loss of heterozygosity (sLOH).
Nine of 16 patients with ALPS-U lacked FAS expression on CD57DNT predicting heterozygous "loss-of-expression" FAS mutations plus acquired somatic second hits in the FAS gene, enriched in DNT. Indeed, 7 of 9 analyzed patients carried deep intronic mutations or large deletions in the FAS gene combined with sLOH detectable in DNT; 1 patient showed a FAS exon duplication. Three patients had reduced FAS expression, and 2 of them harbored mutations in the FAS promoter, which reduced FAS expression in reporter assays. Three of the 4 ALPS-U patients with normal FAS expression carried heterozygous FADD mutations with sLOH.
A combination of serum biomarkers and DNT phenotyping is an accurate means to identify patients with ALPS who are missed by routine exome sequencing.
升高的 TCRαβCD4CD8 双阴性 T 细胞（DNT）和血清生物标志物有助于鉴定具有自身免疫性淋巴增生综合征（ALPS）的 FAS 突变患者。然而，在一些具有与 ALPS 一致的临床特征和生物标志物的患者中，标准外显子测序不能识别种系或体细胞 FAS 突变（未确定的 ALPS：ALPS-U）。
我们试图探讨 FAS 基因中的复杂遗传改变是否能解释这些病例，这些改变逃避了标准测序或其他 FAS 途径相关基因的突变。
遗传分析包括全 FAS 基因测序、拷贝数变异分析以及 FAS cDNA 和其他 FAS 途径相关基因的测序。它由 CD57DNT 上的 FAS 表达分析指导，该分析可预测体细胞杂合性丢失（sLOH）。
16 例 ALPS-U 患者中有 9 例缺乏 CD57DNT 上的 FAS 表达，预测杂合“表达丧失”FAS 突变加上 FAS 基因中的获得性体细胞二次打击，在 DNT 中富集。事实上，在 9 例分析的患者中，有 7 例携带 FAS 基因的深内含子突变或大片段缺失，与 DNT 中可检测到的 sLOH 相结合；1 例患者表现为 FAS 外显子重复。3 例患者 FAS 表达减少，其中 2 例患者 FAS 启动子突变，降低了报告基因检测中的 FAS 表达。4 例 ALPS-U 患者中有 3 例正常 FAS 表达，携带 sLOH 的杂合性 FADD 突变。
血清生物标志物和 DNT 表型结合是准确识别常规外显子测序遗漏的 ALPS 患者的方法。
