Haploinsufficiency of, or impaired ligand binding to, CTLA4 result in a rareautosomal dominant immune dysregulation syndrome with incomplete penetrancenamed autoimmune lymphoproliferative syndrome type V (ALPS5 or CHAI; OMIM#616100). This evidence concerns the gene CTLA4 and autoimmune lymphoproliferative syndrome due to CTLA4 haploinsufficiency.