X-Linked Severe Combined Immunodeficiency (XSCID) is a severe combined immunodeficiency disorder that typically has a lymphocyte profile of T?, B+, NK?, with a prevalence of about 1 in 50,000 to 1 in 100,000 live births. XSCID usually manifests in affected males between three and six months of age. The clinical presentation during the first year of life almost universally includes failure to thrive, oral/diaper candidiasis, recurrent infections, absent tonsils and lymph nodes, persistent infections and infections with opportunistic organisms. Other features that may be noted are disseminating infections, recurrent bacterial meningitis and transplacental transfer of maternal lymphocytes to the infant, resulting is graft-vs-host disease with erythematous skin rashes, hepatomegaly and lymphadenopathy. Atypical XSCID occurs in a small subset of patients whose IL2RG gene produces a small amount of protein with residual activity. These individuals have an atypical presentation that is T+B+NK?. These patients may display immune disregulation and autoimmunity presenting with rashes, splenomegaly, gastrointestinal malabsorption, other autoimmune conditions, and short stature.