Introduction: Severe combined immunodeficiency (SCID) refers to a heterogeneous group of disorders arising from a disturbance in the development and function of both T and B, and may also involve NK cells.
Case presentation: Male, 4 months old, originally from the State of Mexico, with no relevant family or personal history. The condition began at 19 days of life with a productive cough, exacerbated 24 hours ago, accompanied by cyanosis, respiratory distress and a fever of 38.6°C, as well as diaper rash, receiving multiple treatments, without improvement. Physical examination revealed white plaques on the buccal mucosa, chest auscultation with decreased breath sounds in the right basal hemithorax, and crackles, genital area with erythematous papules. Start management with supplemental oxygen, antipyretics, antibiotics, antifungal for community-acquired pneumonia. Complete blood count with neutrophilia and lymphopenia. Respiratory virus panel positive for respiratory syncytial virus B. Immunoglobulins with decreased IgM and IgG. Subpopulation of lymphocytes with immunophenotype LT (-) LB (-) NK (-) /ul. Mother’s HIV result non-reactive. SCID is diagnosed. Chest CT with perihilar consolidation, ground glass pattern. Intravenous immunoglobulin 1 g/kg/dose is administered, prophylaxis against opportunists. Sequencing with a pathogenic variant in the IL2RG gene, c.676C>T, giving rise to a missense change, p.Arg226Cys. Course with poor evolution. He died of respiratory failure due to pulmonary coinfection.
Discussion: X-linked SCID is caused by mutations of IL2RG, the gene encoding the interleukin common gamma chain of the cytokine receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Accounts with an estimated incidence of 1:130,000 births. Patients present during the first months of life with oral candidiasis, persistent diarrhea with failure to thrive, persistent respiratory viral infection and/or interstitial pneumonia often caused by P. jirovecii.
T-cell receptor excision circle (TREC) assay represents an important advance in the early diagnosis for a longer, healthier life.