Its mutations completely abrogate the development of T and B cells, causing typical SCID without immune leakiness [41]; however, mutations in gene-encoding components of the NHEJ pathway, such as prkdc, Ku70/80 and Ligase IV, result in a radiosensitive form of SCID with immune leakiness [42]. This evidence concerns the gene XRCC6 and severe combined immunodeficiency.