Genetic Analysis of Patients With Sickle Cell Anemia and Stroke Before 4 Years of Age Suggest an Important Role for Apoliprotein E.

Abstract

Ischemic stroke is a devastating complication affecting children with sickle cell anemia. Genetic factors are likely to be important in determining the risk of stroke but are poorly defined. We have studied a cohort of 19 children who had an overt ischemic stroke before 4 years of age. We predicted genetic determinants of stroke would be more prominent in this group. We performed whole exome sequencing on this cohort and applied 2 hypotheses to our variant filtering. First, we looked for strong, potentially mono- or oligogenic variants for ischemic stroke, and second, we considered that more common polygenic variants will be enriched in our cohort. Candidate variants emerging from both strategies were validated in a cohort of 283 patients with sickle cell anemia and known pediatric cerebrovascular outcomes. We used principal component analysis in this cohort to control for relatedness and population substructure. Our primary finding was that the Apoliprotein E genotypes ε2/ε4 and ε4/ ε4, defined by the interplay of rs7412 and rs429358, were associated with increased stroke risk, with an odds ratio of 4.35 ([95% CI, 1.85-10.0] P=0.0011) for ischemic stroke in the validation cohort. We also found that rs2297518 in NOS (NO synthase) 2 (odds ratio, 2.25 [95% CI, 1.21-4.19]; P=0.014) and rs2230123 in signal transducer and activator of transcription (odds ratio, 2.60 [95% CI, 1.30-5.20]; P=0.009) both had increased odds ratios for ischemic stroke, although these two variants were below the threshold for statistical significance after correction for multiple testing. These data identify new loci for future functional investigations into cerebrovascular disease in sickle cell anemia. Based on African population reference allele frequencies, the Apoliprotein E genotypes would be present in about 10% of children with sickle cell anemia and represent a genetic risk factor that is potentially modifiable by both dietary and pharmaceutical manipulation of its dyslipidemic effects.