Severe Combined Immunodeficiency (SCID), characterized by a profound decrease in both the number and function of T cells, is related to more than 20 different mutations. Recombination-activating gene (RAG) 1 and 2 seem to be two of the most common forms presenting with various manifestations, including typical SCID, Omenn syndrome (OS), atypical SCID (AS), or delayed onset combined immunodeficiency with granulomas. One interesting manifestation in RAG mutation is the change in the immunophenotype over time, even after hematopoietic stem cell transplantation (HSCT). As bone marrow transplantation (BMT) is the only curative treatment of SCID, it is necessary to differentiate between SCID and OS due to the different conditioning regimens (CR). We present a novel case of atypical SCID (SCID manifestations with more than 300 CD3+T cells) caused by RAG 2 gene mutation whose immunophenotype changed to atypical Omenn syndrome (all Omenn syndrome manifestations except rash, eosinophilia, and elevated IgE) over time.Differentiation of leaky SCID, SCID and Omenn syndrome in RAG mutation genes and overlap manifestations is important in treatment plan and prognosis.