SNCA Gene, but Not MAPT, Influences Onset Age of Parkinson's Disease in Chinese and Australians

MAPT allele and haplotype frequencies in Nigerian Africans: population distribution and association with Parkinson's disease risk and age at onset

BACKGROUND

The microtubule-associated protein tau ( MAPT ) gene is critical because of its putative role in the causal pathway of neurodegenerative diseases including Parkinson's disease (PD). However, there is a lack of clarity regarding the link between the main H1 haplotype and risk of PD. Inconsistencies in reported association may be driven by genetic variability in the populations studied to date. Data on MAPT haplotype frequencies in the general population and association studies exploring the role of MAPT haplotypes in conferring PD risk in black Africans are lacking.

OBJECTIVES

To determine the frequencies of MAPT haplotypes and explore the role of the H1 haplotype as a risk factor for PD risk and age at onset in Nigerian Africans.

METHODS

The haplotype and genotype frequencies of MAPT rs1052553 were analysed using PCR-based KASP™ in 907 individuals with PD and 1,022 age-matched neurologically normal controls from the Nigeria Parkinson's Disease Research (NPDR) network cohort. Clinical data related to PD included age at study, age at onset, and disease duration.

RESULTS

The frequency of the main MAPT H1 haplotype in this cohort was 98.7% in individuals with PD, and 99.1% in healthy controls (p=0.19). The H2 haplotype was present in 41/1929 (2.1%) of the cohort (PD - 1.3%; Controls - 0.9%; p=0.24). The most frequent MAPT genotype was H1H1 (PD - 97.5%, controls - 98.2%). The H1 haplotype was not associated with PD risk after accounting for gender and age at onset (Odds ratio for H1/H1 vs H1/H2 and H2/H2: 0.68 (95% CI:0.39-1.28); p=0.23).

CONCLUSIONS

Our findings support previous studies that report a low frequency of the MAPT H2 haplotype in black ancestry Africans, but document its occurrence in the Nigerian population (2.1%). In this cohort of black Africans with PD, the MAPT H1 haplotype was not associated with an increased risk or age at onset of PD.

Towards early detection of neurodegenerative diseases: A gut feeling

The gastrointestinal tract communicates with the nervous system through a bidirectional network of signaling pathways called the gut-brain axis, which consists of multiple connections, including the enteric nervous system, the vagus nerve, the immune system, endocrine signals, the microbiota, and its metabolites. Alteration of communications in the gut-brain axis is emerging as an overlooked cause of neuroinflammation. Neuroinflammation is a common feature of the pathogenic mechanisms involved in various neurodegenerative diseases (NDs) that are incurable and debilitating conditions resulting in progressive degeneration and death of neurons, such as in Alzheimer and Parkinson diseases. NDs are a leading cause of global death and disability, and the incidences are expected to increase in the following decades if prevention strategies and successful treatment remain elusive. To date, the etiology of NDs is unclear due to the complexity of the mechanisms of diseases involving genetic and environmental factors, including diet and microbiota. Emerging evidence suggests that changes in diet, alteration of the microbiota, and deregulation of metabolism in the intestinal epithelium influence the inflammatory status of the neurons linked to disease insurgence and progression. This review will describe the leading players of the so-called diet-microbiota-gut-brain (DMGB) axis in the context of NDs. We will report recent findings from studies in model organisms such as rodents and fruit flies that support the role of diets, commensals, and intestinal epithelial functions as an overlooked primary regulator of brain health. We will finish discussing the pivotal role of metabolisms of cellular organelles such as mitochondria and peroxisomes in maintaining the DMGB axis and how alteration of the latter can be used as early disease makers and novel therapeutic targets.

A systematic review of associations between common SNCA variants and clinical heterogeneity in Parkinson's disease

There is great heterogeneity in both the clinical presentation and rate of disease progression among patients with Parkinson’s disease (PD). This can pose prognostic difficulties in a clinical setting, and a greater understanding of the risk factors that contribute to modify disease course is of clear importance for optimizing patient care and clinical trial design. Genetic variants in SNCA are an established risk factor for PD and are candidates to modify disease presentation and progression. This systematic review aimed to summarize all available primary research reporting the association of SNCA polymorphisms with features of PD. We systematically searched PubMed and Web of Science, from inception to 1 June 2020, for studies evaluating the association of common SNCA variants with age at onset (AAO) or any clinical feature attributed to PD in patients with idiopathic PD. Fifty-eight studies were included in the review that investigated the association between SNCA polymorphisms and a broad range of outcomes, including motor and cognitive impairment, sleep disorders, mental health, hyposmia, or AAO. The most reproducible findings were with the REP1 polymorphism or rs356219 and an earlier AAO, but no clear associations were identified with an SNCA polymorphism and any individual clinical outcome. The results of this comprehensive summary suggest that, while there is evidence that genetic variance in the SNCA region may have a small impact on clinical outcomes in PD, the mechanisms underlying the association of SNCA polymorphisms with PD risk may not be a major factor driving clinical heterogeneity in PD.

Genetics of synucleins in neurodegenerative diseases

The SNCA locus currently has an indisputable role in Parkinson's disease and other synucleinopathies. The role of genetic variability in the other members of the synuclein family (SNCB and SNCG) in disease is far less clear. In this review, we critically assess the pathogenicity, main characteristics, and roles of genetic variants in these genes reported to be causative of synucleinopathies. We also summarize the different association signals identified in the SNCA locus that have been associated with risk for disease. We take a bird's eye view of the variability currently reported in the general population for the three genes and use these data to infer on the potential relationship between each of the genes and human disease.

Association of MAPT subhaplotypes with clinical and demographic features in Parkinson's disease

Objective

To determine whether distinct microtubule‐associated protein tau MAPT H1 subhaplotypes are associated with clinical and demographic features in Parkinson’s disease.

Methods

A retrospective cohort study included 855 unrelated Caucasian patients with Parkinson’s disease who were seen by Movement Disorder specialists at the Mayo Clinic Florida between 1998 and 2016. The primary outcome measures were specific demographic and clinical features of Parkinson’s disease, including age at onset, disease progression, survival, motor signs, dementia, dystonia, dyskinesia, autonomic dysfunction, impulse control disorder, psychiatric features, REM sleep behavior disorder, restless legs syndrome, and Parkinson’s disease subtype. Specific clinical features were measured at the initial visit and most recent visit. These outcomes were assessed for association with MAPT H1 subhaplotypes, which were defined by six haplotype tagging variants.

Results

Median onset age was 64 years (range: 22‐94 years); 548 (64%) of patients were male. Significant associations (P < 0.0029) were observed between MAPT H1b and orthostatic hypotension (OR = 1.72, P = 0.001); between H1j and rest tremor (OR = 0.15; P < 0.001) as well as REM sleep behavior disorder (OR = 3.87, P < 0.001); between H1r and bradykinesia (OR = 0.11; P < 0.001); and between H1v and restless legs syndrome (OR = 4.02, P = 0.002).

Interpretation

Four MAPT H1 subhaplotypes, but not the H2 haplotype, were significantly associated with specific clinical features in Parkinson’s disease. MAPT haplotypic structure may explain some of the phenotypic variability in disease. Replication of our findings will be critical to fully resolve the Parkinson’s disease risk association signal at Chr17q21.

Subtyping of Parkinson's Disease - Where Are We Up To?

Heterogenous clinical presentations of Parkinson's disease have aroused several attempts in its subtyping for the purpose of strategic implementation of treatment in order to maximise therapeutic effects. Apart from a priori classifications based purely on motor features, cluster analysis studies have achieved little success in receiving widespread adoption. A priori classifications demonstrate that their chosen factors, whether it be age or certain motor symptoms, do have an influence on subtypes. However, the cluster analysis approach is able to integrate these factors and other clinical features to produce subtypes. Differences in inclusion criteria from datasets, in variable selection and in methodology between cluster analysis studies have made it difficult to compare the subtypes. This has impeded such subtypes from clinical applications. This review analysed existing subtypes of Parkinson's disease, and suggested that future research should aim to discover subtypes that are robustly replicable across multiple datasets rather than focussing on one dataset at a time. Hopefully, through clinical applicable subtyping of Parkinson's disease would lead to translation of these subtypes into research and clinical use.

SNCA rs11931074 polymorphism correlates with spontaneous brain activity and motor symptoms in Chinese patients with Parkinson's disease

The α-synuclein (SNCA) gene is thought to be involved in levels of α-synuclein and influence the susceptibility for the development of Parkinson's disease (PD). The aim of the present study is to explore the association among SNCA rs1193074 polymorphism, spontaneous brain activity and clinical symptoms in PD patients. 62 PD patients and 47 healthy controls (HC) were recruited and underwent resting-state functional magnetic resonance imaging (rs-fMRI) scans. Also blood sample of each participant was genotyped for rs11931074 polymorphism (PD: TT = 19, GT = 32, GG = 11; HC: TT = 10, GT = 25, GG = 12) and then examined to ascertain the influence of different genotypes on regional brain activity with amplitude low-frequency fluctuation analysis (ALFF). Furthermore, we evaluated the relationship among genotypes, interactive brain region and clinical symptoms in PD. Compared with HC subjects, PD patients showed decreased ALFF values in right lingual gyrus and increased ALFF values in right cerebellum posterior lobe. Significant interaction of ''groups × genotypes'' was found in the right angular gyrus, where there were higher ALFF values in TT genotype than in GT or GG genotype in the PD group and there was a contrary trend in the HC group. And further Spearman's correlative analyses revealed that ALFF values in right angular gyrus were negatively associated with unified Parkinson's disease rating scale (UPDRS) III score in PD-TT genotype. Our study shows for the first time that SNCA rs11931074 polymorphism might modulate brain functional alterations and correlate with motor symptoms in Chinese PD patients.

Genetic Impact on Clinical Features in Parkinson's Disease: A Study on SNCA-rs11931074

SNCA-rs11931074 had been demonstrated to be strongly correlated with PD risk. However, there was lack of comprehensive analysis of SNCA-rs11931074-related clinical features which may help explain clinical heterogeneity of PD. In our study, we performed association analyses on the relationship between SNCA-rs11931074 and motor symptoms, nonmotor symptoms, and comorbidities in PD. 611 rs11931074 carriers and 113 rs11931074 noncarriers were enrolled. In the clinical phenotype analyses, the Unified Parkinson's Disease Rating Scale part II (UPDRS II) and part III (UPDRS III) scores of rs11931074 carriers were lower than those of noncarriers (SC: −0.083, p=0.035; SC: −0.140, p ≤ 0.001). The Charlson Comorbidity Index (CCI) score of carriers was lower than that of noncarriers (SC: −0.097, p=0.009). No significant statistical differences were found between the variant and other clinical features such as motor complications and nonmotor symptoms. The SNCA-rs11931074 carriers may present with more benign clinical profiles than noncarriers with less severe motor symptoms and comorbidity burden.

Identification of genetic risk factors in the Chinese population implicates a role of immune system in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a leading cause of mortality among the elderly. We performed a whole-genome sequencing study of AD in the Chinese population. In addition to the variants identified in or around the APOE locus (sentinel variant rs73052335, P = 1.44 × 10^-14), two common variants, GCH1 (rs72713460, P = 4.36 × 10^-5) and KCNJ15 (rs928771, P = 3.60 × 10^-6), were identified and further verified for their possible risk effects for AD in three small non-Asian AD cohorts. Genotype-phenotype analysis showed that KCNJ15 variant rs928771 affects the onset age of AD, with earlier disease onset in minor allele carriers. In addition, altered expression level of the KCNJ15 transcript can be observed in the blood of AD subjects. Moreover, the risk variants of GCH1 and KCNJ15 are associated with changes in their transcript levels in specific tissues, as well as changes of plasma biomarkers levels in AD subjects. Importantly, network analysis of hippocampus and blood transcriptome datasets suggests that the risk variants in the APOE, GCH1, and KCNJ15 loci might exert their functions through their regulatory effects on immune-related pathways. Taking these data together, we identified common variants of GCH1 and KCNJ15 in the Chinese population that contribute to AD risk. These variants may exert their functional effects through the immune system.

Hyposmia Is Associated with RBD for PD Patients with Variants of SNCA

Objective: Hyposmia may occur simultaneously with REM sleep behavior disorder (RBD) as a specific phenotype in Parkinson's Diseases (PD), of which the disease progression is fast. In the study, we tried to identify whether the genotypic characteristics could participate in the co-occurrence of hyposmia and RBD in PD patients.

Methods: 152 PD patients were recruited from the Department of Neurology, Ruijin Hospital affiliated to Shanghai JiaoTong University School of Medicine from 2011 to 2016, with comprehensive clinical assessment performing. Two SNPs of SNCA (rs11931074 and rs894278) in 105 patients were also analyzed.

Results: Overall, 84 of 152 PD patients (55.3%) were diagnosed with RBD after PSG evaluation. After regression analysis, higher levels of three parts of UPDRS and SCOPA-AUT scores were all associated with increased risk of RBD in PD patients, respectively. While for olfactory function, we didn't find significant correlation between hyposmia and RBD in PD patients. However, we found that in the group of minor G allele of rs894278, patients with lower score of SS-16 had a 4.76-fold risk of suffering from RBD in patients (95% CI: 1.39–16.67; p = 0.013). Furthermore, we analyzed SNP associated gene expression by eQTL analysis in Genevar database and found that GG genotype of rs894278 was associated with higher levels of α-synuclein in Nerve tissue (p = 1.5E-8) while TT genotype of rs11931074 was associated with higher levels of α-synuclein in Brain (p = 0.0082), which suggesting a potential functional relevance with different symptoms of PD.

Conclusions: Hyposmia was associated with RBD in PD patients with the minor G allele of rs894278, which represent one specific subtype of PD. This study could provide more detail information about PD subtype of RBD with hyposmia in the future.

Genetic Variants in SNCA and the Risk of Sporadic Parkinson's Disease and Clinical Outcomes: A Review

There is increasing evidence of the contribution of genetic susceptibility to the etiology of Parkinson's disease (PD). Genetic variations in the SNCA gene are well established by linkage and genome-wide association studies. Positive associations of single nucleotide polymorphisms (SNPs) in SNCA and increased risk for PD were found. However, the role of SNCA variants in individual traits or phenotypes of PD is unknown. Here, we reviewed the current literature and identified 57 studies, performed in fourteen different countries, that investigated SNCA variants and susceptibility to PD. We discussed the findings based on environmental factors, history of PD, clinical outcomes, and ethnicity. In conclusion, SNPs within the SNCA gene can modify the susceptibility to PD, leading to increased or decreased risk. The risk associations of some SNPs varied among samples. Of notice, no studies in South American or African populations were found. There is little information about the effects of these variants on particular clinical aspects of PD, such as motor and nonmotor symptoms. Similarly, evidence of possible interactions between SNCA SNPs and environmental factors or disease progression is scarce. There is a need to expand the clinical applicability of these data as well as to investigate the role of SNCA SNPs in populations with different ethnic backgrounds.

Variants in SNCA Gene Are Associated with Parkinson's Disease Risk and Cognitive Symptoms in a Brazilian Sample

Genetic susceptibility contributes to the etiology of sporadic Parkinson's Disease (PD) and worldwide studies have found positive associations of polymorphisms in the alpha-synuclein gene (SNCA) with the risk for PD. However, little is known about the influence of variants of SNCA in individual traits or phenotypical aspects of PD. Further, there is a lack of studies with Latin-American samples. We evaluated the association between SNCA single nucleotide polymorphisms (single nucleotide polymorphisms, SNPs - rs2583988, rs356219, rs2736990, and rs11931074) and PD risk in a Brazilians sample. In addition, we investigated their potential interactions with environmental factors and specific clinical outcomes (motor and cognitive impairments, depression, and anxiety). A total of 105 PD patients and 101 controls participated in the study. Single locus analysis showed that the risk allele of all SNPs were more frequent in PD patients (p < 0.05), and the associations of SNPs rs2583988, rs356219, and rs2736990 with increased PD risk were confirmed. Further, the G-rs356219 and C-rs2736990 alleles were associated with early onset PD. T-rs2583988, G-rs356219 and C-2736990 alleles were significantly more frequent in PD patients with cognitive impairments than controls in this condition. In addition, in a logistic regression model, we found an association of cognitive impairment with PD, and the practice of cognitive activity and smoking habits had a protective effect. This study shows for the first time an association of SNCA polymorphism and PD in a South-American sample. In addition, we found an interaction between SNP rs356219 and a specific clinical outcome, i.e., the increased risk for cognitive impairment in PD patients.

Genetic Architecture of MAPT Gene Region in Parkinson Disease Subtypes

The microtubule-associated protein tau (MAPT) region has been conceptualized as a model of the interaction between genetics and functional disease outcomes in neurodegenerative disorders, such as Parkinson disease (PD). Indeed, haplotype-specific differences in expression and alternative splicing of MAPT transcripts affect cellular functions at different levels, increasing susceptibility to a range of neurodegenerative processes. In order to evaluate a possible link between MAPT variants, PD risk and PD motor phenotype, we analyzed the genetic architecture of MAPT in a cohort of PD patients. We observed a statistically significant association between the H1 haplotype and PD risk (79.5 vs 69.5%; χ² = 9.9; OR, 1.7; 95% CI, 1.2–2.4; p = 0.002). The effect was more evident in non tremor dominant (TD) PD subjects (NTD-PD) (82 vs 69.5%; χ² = 13.6; OR, 2.03; 95% CI, 1.4–3; p = 0.0003), while no difference emerged between PD subgroup of tremor dominant patients (TD-PD) and control subjects. Examination of specific intra-H1 variations showed that the H1h subhaplotype was overrepresented in NTD-PD patients compared with controls (p = 0.007; OR, 2.9; 95% CI, 1.3–6.3). Although we cannot exclude that MAPT variation may be associated with ethnicity, our results may support the hypothesis that MAPT H1 clade and a specific H1 subhaplotype influence the risk of PD and modulate the clinical expression of the disease, including motor phenotype.

Variants in the SNCA gene associate with motor progression while variants in the MAPT gene associate with the severity of Parkinson's disease

INTRODUCTION

It is well known that α-synuclein (SNCA) and microtubule associated protein (MAPT) genes predispose individuals to develop Parkinson's disease (PD). However, whether these genes contribute to differences in the variable progression observed in PD is obscure. This study aims to evaluate the association of common variants in SNCA (rs11931074, rs894278) and MAPT (rs242557_H1c haplotype, rs3744456) genes with the severity and duration of motor and cognitive performance.

METHODS

296 Chinese patients with PD were recruited from Shanghai Ruijin Hospital. Motor performance was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS-III) and Hoehn &Yahar (H&Y) stages and cognitive performance using the Mini-Mental Status Examination (MMSE). Genetic associations were analysed using general linear modelling for severity and Cox regression analysis for duration to motor (UPDRS-III≥36 or H&Y ≥ 3, average duration 13 years) and cognitive (MMSE<27, average duration 8 years) cutoffs, covarying for age and gender.

RESULTS

The severity of motor function associated with synergic interaction of SNCA (rs11931074) and MAPT (rs3744456) (p ≤ 0.05) while longer survival to the motor cutoff associated with SNCA (rs11931074/T, HR = 0.4, p = 0.03). Increased severity of cognitive function associated with MAPT (H1c haplotype, p = 0.05) with none of the risk alleles chosen associated with survival to the cognitive cutoff (p > 0.05).

CONCLUSION

Our findings add further data showing that common variants in SNCA and MAPT genes contribute to variability in progression of PD, with SNCA variants associating with motor progression while MAPT variants associated with clinical severity.