Rizig, Mie and Bandres-Ciga, Sara and Mohamed, Wael Mohamed Yousef
(2023)
Identification of genetic risk loci and causal insights associated with Parkinson’s disease in African and African admixed populations: a genome-wide association study.
The Lancet Neurology, 22 (11).
pp. 1015-1025.
ISSN 1474-4422
E-ISSN 1474-4465
Abstract
Background An understanding of the genetic mechanisms underlying diseases in ancestrally diverse populations is
an important step towards development of targeted treatments. Research in African and African admixed populations
can enable mapping of complex traits, because of their genetic diversity, extensive population substructure, and
distinct linkage disequilibrium patterns. We aimed to do a comprehensive genome-wide assessment in African and
African admixed individuals to better understand the genetic architecture of Parkinson’s disease in these underserved
populations.
Methods We performed a genome-wide association study (GWAS) in people of African and African admixed ancestry
with and without Parkinson’s disease. Individuals were included from several cohorts that were available as a part of the
Global Parkinson’s Genetics Program, the International Parkinson’s Disease Genomics Consortium Africa, and 23andMe.
A diagnosis of Parkinson’s disease was confirmed clinically by a movement disorder specialist for every individual in each
cohort, except for 23andMe, in which it was self-reported based on clinical diagnosis. We characterised ancestry-specific
risk, differential haplotype structure and admixture, coding and structural genetic variation, and enzymatic activity.
Findings We included 197918 individuals (1488 cases and 196430 controls) in our genome-wide analysis. We identified
a novel common risk factor for Parkinson’s disease (overall meta-analysis odds ratio for risk of Parkinson’s disease
1·58 [95% CI 1·37–1·80], p=2·397×10–
¹⁴) and age at onset at the GBA1 locus, rs3115534-G (age at onset β=–2·00
[SE=0·57], p=0·0005, for African ancestry; and β=–4·15 [0·58], p=0·015, for African admixed ancestry), which was rare
in non-African or non-African admixed populations. Downstream short-read and long-read whole-genome sequencing
analyses did not reveal any coding or structural variant underlying the GWAS signal. The identified signal seems to be
associated with decreased glucocerebrosidase activity.
Interpretation Our study identified a novel genetic risk factor in GBA1 in people of African ancestry, which has not
been seen in European populations, and it could be a major mechanistic basis of Parkinson’s disease in African
populations. This population-specific variant exerts substantial risk on Parkinson’s disease as compared with common
variation identified through GWAS and it was found to be present in 39% of the cases assessed in this study. This
finding highlights the importance of understanding ancestry-specific genetic risk in complex diseases, a particularly
crucial point as the Parkinson’s disease field moves towards targeted treatments in clinical trials. The distinctive
genetics of African populations highlights the need for equitable inclusion of ancestrally diverse groups in future
trials, which will be a valuable step towards gaining insights into novel genetic determinants underlying the causes of
Parkinson’s disease. This finding opens new avenues towards RNA-based and other therapeutic strategies aimed at
reducing lifetime risk of Parkinson’s disease.
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