Regarding genetic predisposition, SS and HT patients may carry some polymorphic variants of genes belonging to the human leukocyte antigen (HLA) locus, such as the alleles HLA-DR3, HLA-DRB1*04:05, HLA-DR8, HLA-DR11, HLA-DRB4*01:01, HLA-DQA1*05:01 and HLA-DQB1*02:01 [12,13,14,15]. Here, HLA-DRB1 is linked to hematocrit.