Genetic and Clinical Determinants of Stroke in Sickle Cell Patients: Insights from a Nigerian Cohort
Authors: Olaosebikan Rasaq , Crowgey Erin L. , Abdullahi Shehu Umar , Wudil Binta Jibir , Gambo Safiya , Ramakrishnaiah Raghu H , Bello Muhammad , Gezawa Abubakar Shehu , Ebruke Bernard , Franke Karl R , Obaro Stephen , Kolb Anders , Kraft Walter , Miller Robin E 
Published: December 2024

Introduction: Sickle cell disease (SCD) is prevalent in sub-Saharan Africa. Phenotypic diversity in patients with similar SCD genotypes may result from genetic and environmental factors. Nigeria has the highest SCD prevalence, with homozygous SCD (HbSS) being the most severe form. Stroke affects about 11% of children under 20 years with SCD (Ohene-Frempong, Weiner, et al. 1998), primarily ischemic, involving medium to large intracranial arteries. Specific single nucleotide polymorphisms have been linked to ischemic stroke risk in some populations. (Earley, Kelly et al. 2023). This study aimed to identify genetic factors associated with early-age large-vessel stroke in SCD using whole-exome sequencing (WES) in a Nigerian cohort.

Methods: The protocol was approved by the IRBs of TJU, Nemours, and 3 Nigerian sites. Subjects with SCD who experienced large vessel stroke early in life (16 years or less) were enrolled, along with controls (SCD patients without stroke). Subjects were recruited from 3SCD clinics in Kano Metropolis, Nigeria. Inclusion criteria were confirmed SCD diagnosis (SS and Sβ0 thalassemia genotypes), abnormal transcranial doppler (TCD) measurements, and clinical evidence of stroke confirmed by MRI by age 16. Controls included SCD patients (SS and Sβ0) aged 16-26 years without clinical stroke and at least one normal TCD. All cases underwent Magnetic Resonance Angiography (MRA) to establish arteriopathy. Immediate family members of subjects &gt;16 years (siblings and parents) were used per best practice trio analysis to annotate variants with appropriate Mendelian inheritance patterns. WES was performed using SureSelect XT HS (Agilent) and Human All Exon V7 Rev B capture probes for library preparation on all samples. Libraries were sequenced on a NextSeq 550 to 50M paired-end 150bp reads. Variants were called using the GATK suite of algorithms following best practice guidelines and annotated using the VarSeq algorithm, including AlphaMissense annotations.

Results: The control group had a median age of 21 years, and the stroke group had a median age of 9 years. The stroke group had a higher proportion of males (60%) compared to controls (30%) (p &lt; 0.05). Fifty percent of the stroke group and 73% of the controls had a history of acute chest syndrome. History of avascular necrosis (7.5%), heart disease (2.5%), and splenic sequestration (1.3%) were present only in controls. Malaria (1.3%), sepsis (2.5%), and hand-foot syndrome (59%) affected the stroke group. History of priapism (6.3%) and leg ulcers (10%) had similar rates in both groups. Using AlphaMissense annotations, nine genes were identified to have more damaging mutations in the stroke cohort compared to the control cohort (odds ratio &gt; 1 and p &lt; 0.05). Pathway enrichment analysis utilizing genes prioritized with an odds ratio &gt; 1 identified cadherin signaling, cellular junction/adhesion, and WNT signaling as significant (p &lt; 0.05). The role of cellular adhesion has been previously described in SCD stroke subjects (Oni, Brito et al. 2024). The genes that we found that showed significance in our analysis include ADAMTSL2, ADCY9, OR3A1, OR3A2, XRRA1, ABTB2, CLDN18, CPNE7, EIF3A, SLC7A6, UBA7, PDE6A, GLOD5, and PCDHA1.

Conclusion: Genes in the ADCY9 and ADAMSL2 families have been reported in previous studies to be associated with ischemic stroke. Though the small sample size limits this study, it offers preliminary insights into the genetic and clinical determinants of stroke in SCD patients in Northern Nigeria. The identified candidate genes potentially hold biological significance for the stroke phenotype; however, additional research with a larger sample size is required to validate these associations. These findings underscore the need for further whole-exome sequencing studies in Nigerian patients with the stroke/arteriopathy phenotype, which may augment our understanding of this severe complication. An in-depth examination of the genetic modifiers associated with stroke in SCD could lead to enhanced predictive models and targeted preventive interventions, reducing the burden of stroke in affected individuals. Our team has identified additional datasets in the United States to help validate molecular signatures of interest, inspiring us to continue our work in this important field.