Enhancing Primary Immunodeficiency Diagnosis: Findings From Targeted Genetic Testing in a Turkish Cohort.

Primary immunodeficiency disorders (PIDDs) comprise a heterogeneous group of genetic conditions characterised by recurrent infections, immune dysregulation and increased susceptibility to malignancies. While clinical evaluation remains essential for diagnosis, genetic testing plays a pivotal role in confirming the diagnosis and guiding management. This cross-sectional study evaluates the diagnostic yield and clinical utility of targeted gene panel testing in patients with a strong clinical suspicion of PIDDs, within the framework of the Jeffrey Modell Foundation's 'Jeffrey's Insights' programme. Between 2022 and 2024, 104 patients without a prior genetic diagnosis were evaluated at the Department of Paediatric Allergy and Clinical Immunology, Başakşehir Çam and Sakura City Hospital, Türkiye. In 72 of 104 patients, the identified variants were consistent with clinical phenotypes. Pathogenic or likely pathogenic variants were identified in 41.3% of patients, increasing to 57.7% when including variants of uncertain significance (VUS) with high CADD scores. Genetic findings prompted reclassification of International Union of Immunological Societies (IUIS) categories in 25% of cases. Autosomal recessive inheritance and parental consanguinity were notable, reflecting regional genetic patterns. Failure to thrive and low switched memory B cell percentages were significantly associated with confirmed genetic diagnoses, while food allergy, viral skin infections and eczema were more common in genetically undiagnosed patients. These findings support the clinical value of targeted gene panels as an effective, accessible and informative tool in the diagnosis and classification of PIDDs, enhancing precision in patient care and enabling tailored therapeutic strategies.