CTLA4 and autoimmune lymphoproliferative syndrome due to CTLA4 haploinsufficiency: Not surprisingly, deleterious heterozygous mutations in the CTLA4 gene cause an autosomal dominant disorder called CTLA-4 Haploinsufficiency with Autoimmune Infiltration (CHAI) (or simply CTLA4 deficiency) which has similar symptoms (14, 15).