SCID: Severe combined immunodeficiency; T: T lymphocytes; B: B lymphocytes; NK: Natural killer cells; IL2R: Interleukin 2 receptor; ADA: Adenosine deaminase; RAG: Recombination activating gene; IL7R: Interleukin 7 receptor; CD: Cluster differentiation; PTPRC: Protein tyrosine phosphatase type C; NHEJ: Non homologous end joining factor; PKCS: Protein kinase catalytic subunit; PRKDC: Protein kinase DNA activated catalytic subunit; JAK: Janus kinase; LAT: Linker for activation of T cells; AK: Adenylate kinase; +: high count; -: low count. The gene discussed is ADK; the disease is severe combined immunodeficiency.