CTLA-4 Insufficiency due to a Novel CTLA-4 Deletion, Identified through Copy Number Variation Analysis

Background: The diagnostic yield of next-generation sequencing (NGS) technologies in the diagnosis of monogenic inborn errors of immunity (IEI) remains limited, rarely exceeding 30%. Monoallelic pathogenic germline variants in cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) result in variable immunodeficiency and immune dysregulation. The genetic diagnosis of CTLA-4 insufficiency can affect follow-up procedures and may lead to consideration of treatment with CTLA-4-Ig. Objectives: The aim of the study was to identify the genetic cause of familial immunodeficiency and immune dysregulation in cases where single nucleotide variant analysis of short-read NGS data yielded no diagnostic result. Methods: Analysis of copy number variants (CNVs) was applied on short-read NGS data. Results: We identified a novel monoallelic deletion-insertion variant in CTLA-4 (c.445_568-544delinsTTTGCGATTG) resulting in familial autoimmunity. This is the second larger scale variant in CTLA-4, which despite consistently reduced expression of CTLA-4 displayed variable expressivity, ranging from typical juvenile idiopathic arthritis to common variable immunodeficiency-like immunodeficiency. Conclusions: Our report suggests the significance of integration of CNV analysis in routine evaluation of NGS, which may increase its diagnostic yield in IEI.