Translational Genetics and Genomics Section, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Md.
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md.
J Allergy Clin Immunol. 2024 Jan;153(1):230-242. doi: 10.1016/j.jaci.2023.08.036. Epub 2023 Sep 26.
Pathogenic variants of phospholipase C gamma 2 (PLCG2) cause 2 related forms of autosomal-dominant immune dysregulation (ID), PLCγ2-associated antibody deficiency and immune dysregulation (PLAID) and autoinflammatory PLAID (APLAID). Since describing these conditions, many PLCG2 variants of uncertain significance have been identified by clinical sequencing of patients with diverse features of ID.
We sought to functionally classify PLCG2 variants and explore known and novel genotype-function-phenotype relationships.
Clinical data from patients with PLCG2 variants were obtained via standardized questionnaire. PLCG2 variants were generated by mutagenesis of enhanced green fluorescent protein (EGFP)-PLCG2 plasmid, which was overexpressed in Plcg2-deficient DT-40 B cells. B-cell receptor-induced calcium flux and extracellular signal-regulated kinase phosphorylation were assayed by flow cytometry. In some cases, stimulation-induced calcium flux was also measured in primary patient cells.
Three-fourths of PLCG2 variants produced functional alteration of B-cell activation, in vitro. Thirteen variants led to gain of function (GOF); however, most functional variants defined a new class of PLCG2 mutation, monoallelic loss of function (LOF). Susceptibility to infection and autoinflammation were common with both GOF and LOF variants, whereas a new phenotypic cluster consisting of humoral immune deficiency, autoinflammation, susceptibility to herpesvirus infection, and natural killer cell dysfunction was observed in association with multiple heterozygous LOF variants detected in both familial and sporadic cases. In some cases, PLCG2 variants produced greater effects in natural killer cells than in B cells.
This work expands the genotypic and phenotypic associations with functional variation in PLCG2, including a novel form of ID in carriers of heterozygous loss of PLCG2 function. It also demonstrates the need for more diverse assays for assessing the impact of PLCG2 variants on human disease.
磷脂酶 C 伽马 2（PLCG2）的致病性变异导致 2 种相关的常染色体显性免疫失调（ID），即 PLCγ2 相关抗体缺陷和免疫失调（PLAID）和自身炎症性 PLAID（APLAID）。自描述这些病症以来，通过对具有 ID 不同特征的患者进行临床测序，已经鉴定出许多具有不确定意义的 PLCG2 变体。
我们试图对 PLCG2 变体进行功能分类，并探索已知和新的基因型-功能-表型关系。
通过标准化问卷获得具有 PLCG2 变体的患者的临床数据。通过对增强型绿色荧光蛋白（EGFP）-PLCG2 质粒进行突变生成 PLCG2 变体，该质粒在 Plcg2 缺陷的 DT-40 B 细胞中过表达。通过流式细胞术测定 B 细胞受体诱导的钙流和细胞外信号调节激酶磷酸化。在某些情况下，还在原代患者细胞中测量了刺激诱导的钙流。
PLCG2 变体中有四分之三在体外导致 B 细胞激活功能改变。有 13 种变体导致功能获得（GOF）；然而，大多数功能变体定义了 PLCG2 突变的一个新类别，即单等位基因功能丧失（LOF）。GOF 和 LOF 变体均易感染和自身炎症，而在家族性和散发性病例中检测到的多个杂合性 LOF 变体相关的新表型簇包括体液免疫缺陷、自身炎症、易感染疱疹病毒和自然杀伤细胞功能障碍。在某些情况下，PLCG2 变体对自然杀伤细胞的影响大于 B 细胞。
这项工作扩展了与 PLCG2 功能变异的基因型和表型关联，包括杂合性 PLCG2 功能丧失的携带者的新型 ID 形式。它还表明需要更具多样性的检测方法来评估 PLCG2 变体对人类疾病的影响。
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