Among these genes, 7 are linked with Τ−Β+SCID (IL2RG, JAK3, IL7R, PTPRC, CD3D, CD3E and CD247), 9 are involved in Τ−Β−SCID (RAG1, RAG2, DCLRE1C, PRKDC, NHEJ1, LIG4, ADA, AK2 and RAC2) and 14 (ZAP70, TAP1, TAP2, TAPBP, B2M, CIITA, RFXANK, RFX5, RFXAP, DOCK2, CD3G, MALT1, CARD11 and BCL10) are associated with combined immunodeficiency, generally less profound than SCID. This evidence concerns the gene B2M and severe combined immunodeficiency.