Impact of Human Leukocyte Antigen on the Risk of Stroke in Patients with Sickle Cell Disease
Authors: Al-Harrasi Huda , Al-Khabori Murtadha , Al-Kindi Salam , Wali Yasser Ahmed Mohamed Soliman , Al Huneini Mohamed , Al-Riyami Hamad 
Published: November 2019

Objectives: Sickle Cell Disease (SCD) is an inherited hemoglobinopathy with multiple complications including stroke. It is observed that siblings with SCD have an increased risk of stroke if there was a sibling in the family with SCD and stroke (Driscoll M C, Blood, 2003). Human Leukocyte Antigen (HLA) is extremely variable among individuals and certain HLA alleles have previously been associated with a number of diseases. It has been shown that HLA-DRB1*0301, HLA-DRB1*0302 and HLA-DQB1*0201 increase the risk of stroke and HLA-DRB1*1501 and HLA-DQB1*0602 lower the risk of stroke in patients with SCD (Styles L, Blood, 2000). These alleles are not common in all populations. We therefore planned to assess the impact of other HLA alleles on the risk of stroke in patients with SCD.
Methods: This is a retrospective case-control study conducted at Sultan Qaboos University Hospital. We included all adult and pediatric patients with SCD and diagnosed with stroke using CT/MRI of the brain. The study included patients diagnosed during the period of 1995 to 2015. HLA typing was performed using molecular techniques. HLA alleles with a frequency of at least 5% were selected for analysis. Association studies were performed using Fisher Exact test. All statistical tests were performed using R program (version 3.1.2).
Results: A total of 244 patients were included (66 patients with SCD and stroke [cases] and 178 patients with SCD with no stroke. The median age was 26 years (Interquartile Range [IQR]: 19-32) and 23 (IQR: 17-29 ) for cases and controls respectively. The median hemoglobin, mean corpuscular volume, hemoglobin S level and lactate dehydrogenase level was 9 g/dL, 70 fL, 70% and 400 U/L respectively for the cases, and 9 g/dL, 60 fL, 70% and 400 U/L respectively for the control. The most frequent HLA-A allele was HLA-A*02 (24%) which did not impact the risk of stroke (Odds Ratio [OR]: 1.59, 95% Confidence Interval [CI]: 0.84-3.02) as were the other tested HLA-A alleles (all CIs crossed OR of 1.00). The most frequent HLA-B allele was HLA-B*51 (15%) which did not impact the risk of stroke (OR: 0.89, 95% CI: 0.43-1.85) as were the other tested HLA-B alleles (all CIs crossed OR of 1.00). The most frequent HLA-C allele was HLA-C*04 (17%) which did not impact the risk of stroke (OR: 1.34, 95% CI: 0.67-2.65); however, HLA-C*06 (OR: 2.37, 95% CI: 1.01-5.54) increased the risk of stroke while HLA-C*07 protected from stroke (OR: 0.35, 95% CI: 0.13-0.93). None of the other HLA-C alleles were statistically significant (all CIs crossed OR of 1.00). The most frequent HLA-DRB1 allele was HLA-DRB1*16 (18%) which did not impact the risk of stroke (OR: 1.02, 95% CI:0.51-2.03) as were the other tested HLA-DRB1 alleles (all CIs crossed OR of 1.00).
Conclusions: HLA-C*06 is associated with an increased risk of stroke in patients with SCD while HLA-C*07 is protective from stroke in these patients. Early identification of high-risk patients would be beneficial for preventive intervention, such as chronic transfusion or bone marrow transplantation. The impact of these HLA alleles should be validated in other populations.

Disclosures
Al-Khabori: Shire (Takeda): Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; SOBI: Honoraria; Amgen: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Honoraria; NovoNardisk: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees.