FYN and X-linked lymphoproliferative disease: However, only development of iNKT cells, but not other hematopoietic cells, is absent in patients with X-linked lymphoproliferative disease (SAP defect) [17] and SAP-deficient mice [16,17] or reduced in NOD [19-22], SLAMF1/SLAMF6 double mutant chimeras [27] and in Fyn deficient mice [32,33].