Objective: Adenosine deaminase (ADA) deficiency is a rare inborn error of immunity caused by defects in purine metabolism and typically presents as severe combined immunodeficiency (ADA-SCID). The disease commonly manifests in early infancy with severe and recurrent infections. This study aimed to evaluate the clinical, immunological, biochemical, and genetic characteristics of patients diagnosed with ADA deficiency.Methods: This retrospective study included patients with confirmed ADA deficiency who were followed in the Pediatric Allergy and Immunology Clinic between 2020 and 2026. Demographic characteristics, clinical findings, laboratory data, immunological parameters, metabolite analyses, genetic test results, treatment approaches, and clinical outcomes were reviewed.Results: A total of six patients, including five males and one female, were included in the study. All patients were diagnosed within the first year of life, with a median age at diagnosis of 3.5 months (range, 1–7). Consanguinity was present in 83.3% of the patients. The most common presenting manifestation was recurrent pneumonia, observed in 66.7% of the patients. Oral candidiasis and chronic diarrhea were also frequently observed. Severe infectious complications occurred in 50% of the patients. Marked lymphopenia was present in all patients, with a median absolute lymphocyte count of 430/mm³ (range, 30–1570). Flow cytometric immunophenotyping demonstrated profound reductions in T-, B-, and NK-cell populations consistent with severe combined immunodeficiency. Biochemical analyses revealed markedly elevated dAXP levels in all patients, while adenosine levels were elevated in the majority of patients. Hematopoietic stem cell transplantation was performed in four patients, and five patients were alive at the last follow-up.Conclusion: ADA deficiency is a life-threatening inborn error of immunity that should be considered in infants presenting with severe recurrent infections and profound lymphopenia. Early recognition of warning signs, including consanguinity and sibling death history, is essential for prompt diagnosis and timely therapeutic intervention to improve outcomes.
Gül et al. (Fri,) studied this question.