Methods: T-cell proliferation to mitogens performed by Mayo clinic. Antibody titers performed at St. Louis Children’s Hospital.
Results: A 15 month female with short stature was hospitalized with 3 months of failure to thrive and diagnosed with norovirus. Prior infectious history included norovirus 2 months prior, enterovirus at 10 and 12 months, RSV complicated by pneumonia at 9 months, one episode of thrush, and one otitis media. WBC count and total IgG/M normal. IgA undetectable. Lymphocyte subpopulations (cells/mm3) showed lymphopenia (728); CD4 (95), CD8 (7), and B cell (262) cytopenias; and normal NK cells. CD4 recent thymic emigrants (9.1%; RR=25.8-68%) and T-cell receptor excision circles (TREC) (500 copies; RR>4168) were reduced. T cell proliferation was normal to PWM (9.7%; RR>3.5%) and reduced to phytohemagglutinin (11.3%; RR>58.5%). Antibody titers to diphtheria, tetanus, H. influenzae type B, and S. pneumoniae were protective. Patient was diagnosed with SCID and underwent stem cell transplant. Genetic testing confirmed the diagnosis of CHH, a rare cause of SCID.
Conclusions: SCID due to CHH may present after the first year of life with atypical lab findings, including normal responses to vaccines and proliferation to mitogens. The low positive threshold used for T-cell response to PWM can be falsely reassuring.