Novel functional insights into ischemic stroke biology provided by the first genome-wide association study of stroke in indigenous Africans

BACKGROUND

African ancestry populations have the highest burden of stroke worldwide, yet the genetic basis of stroke in these populations is obscure. The Stroke Investigative Research and Educational Network (SIREN) is a multicenter study involving 16 sites in West Africa. We conducted the first-ever genome-wide association study (GWAS) of stroke in indigenous Africans.

METHODS

Cases were consecutively recruited consenting adults (aged > 18 years) with neuroimaging-confirmed ischemic stroke. Stroke-free controls were ascertained using a locally validated Questionnaire for Verifying Stroke-Free Status. DNA genotyping with the H3Africa array was performed, and following initial quality control, GWAS datasets were imputed into the NIH Trans-Omics for Precision Medicine (TOPMed) release2 from BioData Catalyst. Furthermore, we performed fine-mapping, trans-ethnic meta-analysis, and in silico functional characterization to identify likely causal variants with a functional interpretation.

RESULTS

We observed genome-wide significant (P-value < 5.0E-8) SNPs associations near AADACL2 and miRNA (MIR5186) genes in chromosome 3 after adjusting for hypertension, diabetes, dyslipidemia, and cardiac status in the base model as covariates. SNPs near the miRNA (MIR4458) gene in chromosome 5 were also associated with stroke (P-value < 1.0E-6). The putative genes near AADACL2, MIR5186, and MIR4458 genes were protective and novel. SNPs associations with stroke in chromosome 2 were more than 77 kb from the closest gene LINC01854 and SNPs in chromosome 7 were more than 116 kb to the closest gene LINC01446 (P-value < 1.0E-6). In addition, we observed SNPs in genes STXBP5-AS1 (chromosome 6), GALTN9 (chromosome 12), FANCA (chromosome 16), and DLGAP1 (chromosome 18) (P-value < 1.0E-6). Both genomic regions near genes AADACL2 and MIR4458 remained significant following fine mapping.

CONCLUSIONS

Our findings identify potential roles of regulatory miRNA, intergenic non-coding DNA, and intronic non-coding RNA in the biology of ischemic stroke. These findings reveal new molecular targets that promise to help close the current gaps in accurate African ancestry-based genetic stroke's risk prediction and development of new targeted interventions to prevent or treat stroke.

Genetic Epidemiology and Associated Diseases of APOL1: A Narrative Review

BACKGROUND

The Apolipoprotein 1 (APOL1) protein is a product of the human APOL1 gene located on chromosome 22q13.1 and performs functions including lipid transport and metabolism, programmed cell death, autophagy and innate immunity against intracellular pathogens. It is unique among its gene family in its possession of a signal peptide that confers on it the ability for export out of the cell and into the blood stream. The aim of this review is to explore the genetic epidemiology and biology of the APOL1 gene, describe its association with different renal and extra-renal disorders and highlight the timelines of the discoveries of the various associations.

METHODS

A literature search was carried out using combination of terms including "apolipoproteins", "apolipoprotein L", "APOL1", "genetics of APOL1", "Chronic Kidney Disease (CKD) and APOL1"," APOL1 and associated diseases" covering the period January 1990 to April 2020.

RESULTS

High frequency of the APOL1 gene arose as a result of natural selection in East and West Africa, regions endemic for Trypanosoma brucei infection. High frequencies are also reported among individuals of African ancestry in North America. APOL1 G1 and G2 variants protect against Trypanosoma brucei rhodesiense having overcome their virulence through the serum trypanolytic factor. Although protective against infection from trypanosomes, these alleles have also been shown to increase the risk of several disorders including various forms of chronic kidney diseases, schizophrenia, stroke, cancer, and pre - eclampsia.

CONCLUSION

The elucidation of the APOL1 gene has deepened understanding of racial disparities in health and disease. Growing understanding of the genetics and functions of APOL1 has potential to enhance translational benefits for development of new biomarkers, preventive and therapeutic interventions in the context of precision medicine.