HLA-DR4-Ala74 beta is associated with risk and poor outcome of severe aplastic anemia.

ABSTRACT

Severe aplastic anemia (SAA) is a heterogeneous hematological disorder with a high mortality. Genetic predisposition has been shown to play a role in a considerable proportion of SAA cases. For instance, the human lymphocyte antigen HLA-DR2 has been repeatedly demonstrated to be over-represented in SAA patients. In this paper, we expand on the evidence for the contribution of HLA polymorphism in the susceptibility to SAA, which was obtained using the "high-resolution" technique of HLA-DRB1 subtyping. The DRB1*1501 allele appeared to be responsible for the predominance of DR2 specificity in SAA patients and was the most significant risk factor for this disease. It was observed in 23/44 (52.3%) patients versus 22/100 (22.0%) donors [odds ratio (OR) = 3.9; 95% confidence interval (CI) 1.8-8.3; P = 0.0005, corrected P (Pc) < 0.05]. In addition, DRB1*04 alleles also displayed non-random distribution in the SAA group. In particular, DRB1*04 variants coding for alanine at position 74 of the DR beta 1 chain (HLA-DR4-Ala74 beta subtype) were detected in all 13 DR4-positive SAA patients but only in 15/24 (62.5%) controls (OR = 16.6; 95% CI 0.9-312.0; P = 0.015). Multiple comparison analysis confirmed that the HLA-DR4-Ala74 beta subtype confers susceptibility to SAA independently from the DRB1*1501 allele. Finally, examination of the clinical records has shown that the HLA-DR4-Ala74 beta subtype is associated with poor outcome of SAA.