The Landscape of Monogenic Parkinson's Disease in Populations of Non-European Ancestry: A Narrative Review

Genetic variants associated with idiopathic Parkinson's disease in Latin America: A systematic review

Idiopathic Parkinson's disease (PD) constitutes a complex trait influenced by genetic, environmental, and lifestyle factors, with an estimated heritability of nearly 30%. However, a large proportion of the heritable variation linked to PD remains uncertain, partly due to ancestral bias. Expanding research into Hispanic populations can contribute to address this gap. To review the evidence of genetic variants associated with idiopathic PD in Latin America. A PRISMA-compliant systematic review was conducted in MEDLINE, EMBASE and LILACS, compiling studies published up to February 7, 2025. Nineteen case-control studies were included. Two hypothesis-free studies identified rs525496 near H2BW1 as a protective factor and rs356182 in SNCA as a risk factor through XWAS and GWAS, respectively. Seventeen hypothesis-driven studies examined over three hundred variants, identifying nineteen genetic markers; risk factors included one INDEL in NR4A2, CNV burdens in PRKN, SNCA, and PLA2G6, along with fourteen variants in six loci including GBA, APOEε4, MTHFR, LRRK2, and SNCA. Three SNPs in the PICALM, ALDH1A1, and APOE-ε3 loci were identified as protective factors. Additionally, six SNCA variant haplotypes appear to increase PD risk, while two NR4A2 INDELs haplotypes showed mixed effects. This review summarized genetic loci associated with idiopathic PD in Latin American populations evidencing an overlap with European findings as well as novel loci, although awaiting replication and validation. These observations contribute to the understanding of genetic configuration of the disease and highlight the need for further genomic research in underrepresented groups that include local ancestry analysis within admixed cohorts to guide development of personalized treatments and population-specific interventions.

A Global Perspective of GBA1-Related Parkinson's Disease: A Narrative Review

Parkinson's disease (PD) is considered to be the second most prominent neurodegenerative disease and has a global prevalence. Glucocerebrosidase (GBA1) gene mutations represent a significant hereditary risk factor for the development of PD and have a profound impact on the motor and cognitive progression of the disease. The aim of this review is to summarize the literature data on the prevalence, type, and peculiarities of GBA1 mutations in populations of different ethnic backgrounds. We reviewed articles spanning the 2000-2024 period. GBA1-related PD has a worldwide distribution. It has long been recognized that pathogenic GBA1 mutations are particularly common in certain ethnic populations, including PD patients of Ashkenazi Jewish ancestry. Moreover, a considerable number of studies focused on European ancestry patients from Europe and North America have revealed a high proportion (up to 15%) of carriers among the PD population. GBA1 mutations also appear to play an important role in patient groups with an East Asian background, although the frequency of specific variants may differ as compared to those of European ancestry. Notably, the assessment of underrepresented populations in other parts of Asia (including India) and Latin America is in the spotlight of current research, while a variant with a newly described pathogenic mechanism has been reported in Sub-Saharan Africans. Given the importance of GBA1 mutations for PD genetics and clinical phenotype, a focused assessment of the prevalence and type of GBA1 variants in distinct ethnic populations will possibly inform ongoing PD-related clinical studies and facilitate upcoming therapeutic trials.

Genetic heterogeneity of early onset Parkinson disease: The dilemma of clinico-genetic correlation

With advances in genetic testing increasing proportion of early onset Parkinson disease (EOPD) are being identified to have an underlying genetic aetiology. This is can be in the form of either highly penetrant genes associated with phenotypes with monogenic or mendelian inheritance patterns or those genes known as risk factor genes which confer an increased risk of PD in an individual. Both of them can modify the phenotypic manifestation in a patient with PD. This improved knowledge has helped in deciphering the intricate role of various cellular pathways in the pathophysiology of PD including both early and late and even sporadic PD. However, the phenotypic and genotypic heterogeneity is a major challenge. Different deleterious alterations in a same gene can result in a spectrum of presentation spanning from juvenile to late onset and typical to atypical parkinsonism manifestation. Similarly, a single phenotype can occur due to abnormality in two or more different genes. This conundrum poses a dilemma in the clinical approach and in understanding the clinico-genetic correlation. Understanding the clinico-genetic correlation carries even more importance especially when genetic testing is either not accessible or affordable or in many regions both. In this narrative review, we aim to discuss briefly the approach to various PARK gene related EOPD and describe in detail the clinico-genetic correlation of individual type of PARK gene related genetic EOPD with respect to their classical clinical presentation, pathophysiology, investigation findings and treatment response to medication and surgery.

Ancestry-specific gene expression in peripheral monocytes mediates risk of neurodegenerative disease

It is hypothesised that peripheral immune states responding to regional environmental triggers contribute to central neurodegeneration. Region-specific genetic selection pressures require this hypothesis to be assessed in an ancestry specific manner. Here we utilise genome-wide association studies and expression quantitative trait loci from African, East Asian and European ancestries to show that genes causing neurodegeneration are preferentially expressed in innate rather than adaptive immune cells, and that expression of these genes mediates the risk of neurodegenerative disease in monocytes in an ancestry-specific manner.

Towards a Global View of Parkinson's Disease Genetics

Parkinson's disease (PD) is a global health challenge, yet historically studies of PD have taken place predominantly in European populations. Recent genetics research conducted in non-European populations has revealed novel population-specific genetic loci linked to PD risk, highlighting the importance of studying PD globally. These insights have broadened our understanding of PD etiology, which is crucial for developing disease-modifying interventions. This review comprehensively explores the global genetic landscape of PD, emphasizing the scientific rationale for studying underrepresented populations. It underscores challenges, such as genotype-phenotype heterogeneity and inclusion difficulties for non-European participants, emphasizing the ongoing need for diverse and inclusive research in PD. ANN NEUROL 2024;95:831-842.