Genome-Wide Polygenic Score Predicts Large Number of High Risk Individuals in Monogenic Undiagnosed Young Onset Parkinson's Disease Patients from India

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.

Clinico-Genetic Profiles of Seven Patients With PINK1-Related Parkinson's Disease: A Case Series From a Tertiary Care Centre in India and a Review of the Literature

OBJECTIVE

Recessive variants in the PINK1 gene are known causes of early-onset Parkinson's disease (EOPD). To describe the clinical features and genetic profiles of patients with PINK1-related Parkinson's disease (PARK-PINK1) mutations.

METHODS

We conducted a retrospective chart review of the demographic, clinical and genetic details of patients from our database carrying biallelic PINK1 variants.

RESULTS

A total of 7 patients whose median age at onset was 33 years (range: 20-49) were recruited. All had asymmetrical onset, tremors were present in 4 patients, abnormal posturing was present in 2 patients, and slowness was present in 1 patient. The parkinsonism phenotype was noted in 6 patients (with dystonia in four) and isolated dystonia in one. Among the 6 patients with parkinsonism, five had rest tremors, all had good levodopa responses, and four had motor fluctuations with choreiform dyskinesia. Exome sequencing revealed biallelic pathogenic/likely pathogenic variants, five of which were novel.

CONCLUSION

PARK-PINK1 presents as an EOPD with tremor-predominant phenotype, good levodopa-responsiveness, early motor fluctuation and dyskinesia. We describe five novel variants in PINK1 gene.

Genetic architecture of a single cohort of 230 Indian Parkinson's Disease patients

INTRODUCTION

Indian Parkinson's Disease (PD) patients are severely underrepresented in terms of genetic studies and little is known about the frequency of variants and their impact on motor and nonmotor symptoms (NMS).

METHODS

This retrospective cross-sectional study was conducted in PD patients undergoing treatment at a tertiary care hospital from India. Patients were advised genetic testing if they had (i) age at onset (AAO) of motor symptoms at or before 50 years (EOPD), (ii) positive family history of PD, parkinsonism or dystonia. All patients underwent whole exome sequencing and potentially pathogenic variants were identified.

RESULTS

Clinical and genetic data were available for 230 (163 males, 70.4 %) patients. Thirty-five pathogenic and likely pathogenic variants in various PD genes were identified in 47 patients resulting in a yield of 20.4 %. In the remaining, 82 patients had either variants of uncertain significance or had variants in genes not associated with parkinsonism and 101 patients did not have any non-benign variants. Patients with genetically mediated PD had a lower AAO and statistically greater frequency of dystonia (36.2 %), postural instability (29.8 %) and mood disorder (29.8 %) and a higher Hoehn and Yahr score (2.9). Among the 47 patients, 11 patients had PARK-PRKN, six patients had PARK-PLA2G6, and 22 patients had PARK-GBA1.

CONCLUSION

Around one-fifth of early-onset PD can have an underlying monogenetic cause. PARK-GBA1, PARK-PRKN and PARK-PLA2G6 are the commoner causes of genetically mediated PD in India. Patients with genetic cause had an earlier age at onset, and more frequent dystonia, postural instability and dyskinesia.

The Genetic Drivers of Juvenile, Young, and Early-Onset Parkinson's Disease in India

BACKGROUND

Recent studies have advanced our understanding of the genetic drivers of Parkinson's disease (PD). Rare variants in more than 20 genes are considered causal for PD, and the latest PD genome-wide association study (GWAS) identified 90 independent risk loci. However, there remains a gap in our understanding of PD genetics outside of the European populations in which the vast majority of these studies were focused.

OBJECTIVE

The aim was to identify genetic risk factors for PD in a South Asian population.

METHODS

A total of 674 PD subjects predominantly with age of onset (AoO) ≤50 years (encompassing juvenile, young, or early-onset PD) were recruited from 10 specialty movement disorder centers across India over a 2-year period; 1376 control subjects were selected from the reference population GenomeAsia, Phase 2. We performed various case-only and case-control genetic analyses for PD diagnosis and AoO.

RESULTS

A genome-wide significant signal for PD diagnosis was identified in the SNCA region, strongly colocalizing with SNCA region signal from European PD GWAS. PD cases with pathogenic mutations in PD genes exhibited, on average, lower PD polygenic risk scores than PD cases lacking any PD gene mutations. Gene burden studies of rare, predicted deleterious variants identified BSN, encoding the presynaptic protein Bassoon that has been previously associated with neurodegenerative disease.

CONCLUSIONS

This study constitutes the largest genetic investigation of PD in a South Asian population to date. Future work should seek to expand sample numbers in this population to enable improved statistical power to detect PD genes in this understudied group. © 2023 Denali Therapeutics and The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

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

INTRODUCTION

There has been a bias in the existing literature on Parkinson's disease (PD) genetics as most studies involved patients of European ancestry, mostly in Europe and North America. Our target was to review published research data on the genetic profile of PD patients of non-European or mixed ancestry.

METHODS

We reviewed articles published during the 2000-2023 period, focusing on the genetic status of PD patients of non-European origin (Indian, East and Central Asian, Latin American, sub-Saharan African and Pacific islands).

RESULTS

There were substantial differences regarding monogenic PD forms between patients of European and non-European ancestry. The G2019S Leucine Rich Repeat Kinase 2 (LRRK2) mutation was rather scarce in non-European populations. In contrast, East Asian patients carried different mutations like p.I2020T, which is common in Japan. Parkin (PRKN) variants had a global distribution, being common in early-onset PD in Indians, in East Asians, and in early-onset Mexicans. Furthermore, they were occasionally present in Black African PD patients. PTEN-induced kinase 1 (PINK1) and PD protein 7 (DJ-1) variants were described in Indian, East Asian and Pacific Islands populations. Glucocerebrosidase gene variants (GBA1), which represent an important predisposing factor for PD, were found in East and Southeast Asian and Indian populations. Different GBA1 variants have been reported in Black African populations and Latin Americans.

CONCLUSIONS

Existing data reveal a pronounced heterogeneity in the genetic background of PD. A number of common variants in populations of European ancestry appeared to be absent or scarce in patients of diverse ethnic backgrounds. Large-scale studies that include genetic screening in African, Asian or Latin American populations are underway. The outcomes of such efforts will facilitate further clinical studies and will possibly contribute to the identification of either new pathogenic mutations in already described genes or novel PD-related genes.

South Asian medical cohorts reveal strong founder effects and high rates of homozygosity

The benefits of large-scale genetic studies for healthcare of the populations studied are well documented, but these genetic studies have traditionally ignored people from some parts of the world, such as South Asia. Here we describe whole genome sequence (WGS) data from 4806 individuals recruited from the healthcare delivery systems of Pakistan, India and Bangladesh, combined with WGS from 927 individuals from isolated South Asian populations. We characterize population structure in South Asia and describe a genotyping array (SARGAM) and imputation reference panel that are optimized for South Asian genomes. We find evidence for high rates of reproductive isolation, endogamy and consanguinity that vary across the subcontinent and that lead to levels of rare homozygotes that reach 100 times that seen in outbred populations. Founder effects increase the power to associate functional variants with disease processes and make South Asia a uniquely powerful place for population-scale genetic studies.