CTLA4 and autoimmune hemolytic anemia: The results of several studies, including those of a recent study that observed a single nucleotide polymorphism of the CTLA-4 gene (+49 A/G allele) at a significantly higher frequency in AHA patients compared with controls [36], indicate that CTLA-4 variants (CTLA-4 single nucleotide polymorphisms) might also be involved in the pathogenesis of AHA as well as that other genetic/environmental factors might contribute to the onset of AHA.