Genomic and clinical characterization of adult CVID patients: results from a single-centre turkish cohort.

Common Variable Immunodeficiency (CVID) is the most frequently encountered symptomatic primary immunodeficiency in clinical practice, presenting with heterogeneous clinical and genetic features. While traditionally considered polygenic, recent advances in genomic technologies have revealed monogenic causes in a significant subset of patients. This study aimed to investigate the genetic background of adult patients diagnosed with CVID or CVID-like phenotypes, using clinical exome sequencing (CES), focusing on atypical and syndromic presentations. Thirty adult patients fulfilling the ESID/PAGID criteria for CVID underwent CES. Genetic analysis targeted 451 immune-related genes, with variants interpreted according to ACMG guidelines. Pathogenicity was confirmed with Sanger sequencing. We detected potentially disease-related variants (TNFRSF13B, BTK, RAG1, SAMD9, NFKB2, PRKDC, CFTR, FCN3, IFIH1, ITGA3, and TNFRSF1A) in 12 of the 30 patients (40%). TNFRSF13B was the most frequently mutated gene among these patients. Deep phenotyping analyses revealed atypical findings included a hemizygous BTK variant mimicking CVID, a homozygous RAG1 variant consistent with leaky SCID, and a heterozygous SAMD9 variant not presenting with MIRAGE phenotype, and a homozygous ITGA3 insertion region variant that suggested a mild form of ILNED syndrome. Variants in CFTR, FCN3, and TNFRSF1A further expand the phenotypic spectrum, highlighting overlap between immunodeficiency and immune dysregulation syndromes in adulthood. A substantial proportion of adult patients with CVID-like phenotypes harbor variants in genes beyond the classical CVID-associated loci. Our findings support the utility of broad genetic screening in adult-onset antibody deficiency, particularly when non-infectious complications are present. Molecular diagnosis facilitates accurate classification, guides personalized treatment, and aids in genetic counseling.