Interleukin-2 receptor common gamma chain (IL2RG) defects present a diagnostic challenge

Background: The protein encoded by interleukin-2 receptor common gamma chain (IL2RG) is an important signaling component of many interleukin receptors, including those of interleukin-2, -4, -7, and -21, known as the common gamma chain. Mutations in the gene encoding the common gamma chain of the interleukin-2 receptor cause X-linked severe combined immunodeficiency (SCID). In this report, we present an unknown genetic defect of a patient diagnosed with SCID whose genetic analysis was performed 2 decades later. Methods: Whole genome sequencing and Sanger confirmation were used to identify a novel frameshift mutation in IL2RG. Massively parallel sequencing of genes associated with SCID were performed on the patient’s mother and sister. Results: Next generation sequencing techniques identified a heterozygous frame-shift deletion in the gene encoding the common gamma chain of IL2RG in our patient. The patient’s mother had a low level mosaicism for the same deletion. The sister had no detectable deletion. Conclusion: We have identified a novel mutation in IL2RG resulting in an X-linked SCID phenotype. The genetic analysis of the patient’s mother revealed a mosaicism which was not passed on to his sister. The importance of genetic analysis in family members and SCID patients with an unknown genetic defect should be emphasized for family planning and subsequent genetic counseling. Statement of novelty: Genetic testing is an extremely important component in evaluating severe combined immunodeficiency as it impacts treatment course and prognosis, and allows for genetic analysis and counselling of family members.