Epstein-Barr virus infections in the X-linked recessive lymphoproliferative syndrome.

Prospective studies demonstrated variable phenotypic expression of the X-linked recessive lymphoproliferative syndrome (X.L.R.L.S.) in three brothers: (1) hypogammaglobulinaemia and subclinical Epstein-Barr-virus (E.B.V.) infection with antibody response to E.B.V.; (2) E.B.V. infection with defective immune response to E.B.V., fatal infectious mononucleosis (I.M.), and immunoblastic lymphoma; and (3) histiocytic lymphoma. Hypogammaglobulinaemia and measles pneumonitis had preceded infection with E.B.V. The diverse phenotypic expressions probably resulted from the varied immune response to E.B.V. Recombination of X chromosomes was documented by Xg-blood-group studies in a survivor. E.B.V. can induce fatal I.M. and malignant lymphoma in X.L.R.L.S., but an immune response to E.B.V. can be protective.