Vignette #4: Two Patients with Severe Combined Immunodeficiency (SCID)
A now 2-year-old Venezuelan male was found to have an abnormal newborn screen showing low T-cell receptor excision circles (TRECs), with family history significant for 2 siblings deceased as infants secondary to presumed sepsis. Workup revealed a novel mutation in the interleukin-2 receptor gamma (IL2RG) gene, causing a loss-of-function (LOF) mutation. LOF variants in IL2RG carry known pathogenicity, therefore this novel variant was classified as pathogenic and the patient was diagnosed with X-linked SCID. Testing of the patient’s father and brother were negative, while his sister was a heterozygous carrier of the pathogenic variant. We observed a second similar case of a 4-year-old male from the Dominican Republic found to have a homozygous pathogenic variant in the interleuken-7 receptor (IL7R) gene, similarly causing a novel LOF mutation predicted to be pathogenic.