HLA-DRB1 and hematocrit: Some of these previous observations have been confirmed in a large group of UK Caucasian patients with HT; DRB1*04, DQB1*03:01, and DQA1*03:01 showed the most significant predisposing effect, while DQA1*01:02, DQA1*02:01, and DQB1*06 had the most significant protective effect.