RASGRP1 and lymphoproliferative syndrome: Studies have shown that deficiency of RASGRP1 (RAS guanyl nucleotide-releasing protein), a nucleotide exchange factor specific to T lymphocytes, leads to defective proliferation of the T lymphocytes required for an effective immune response to EBV, which may explain an inherited susceptibility to EBV-induced lymphoproliferative disorders such as NK/T cell lymphoma [11,12].