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

The Genetic Landscape of Sleep Disorders in Parkinson's Disease

Parknson's disease (PD) is the second most common neurodegenerative disease, affecting 1% of people aged over 60. PD is characterized by a wide range of motor symptoms, however the clinical spectrum of PD covers a wide range of non-motor symptoms, as well. Sleep disorders are among the most common non-motor symptoms of PD, can occur at any stage of the disease and significantly affect quality of life. These include rapid eye movement sleep behavior disorder (RBD), restless legs syndrome (RLS), excessive daytime sleepiness (EDS), insomnia, obstructive sleep apnea (OSA) and circadian rhythm disturbances. One of the main challenges in PD research is identifying individuals during the prodromal phase of the disease. Combining genetic and prodromal data may aid the early identification of individuals susceptible to PD. This review highlights current data regarding the genetic component of sleep disorders in PD patients, focusing on genes that have currently been associated with this PD co-morbidity.

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.

REM sleep behavior disorder and other sleep abnormalities in p. A53T SNCA mutation carriers

STUDY OBJECTIVES

Τo assess whether REM Sleep Behavior Disorder (RBD) and other sleep abnormalities occur in carriers of the p.A53T alpha-synuclein gene (SNCA) mutation, using both subjective and objective measures.

METHODS

We have assessed 15 p.A53T carriers (10 manifesting Parkinson's Disease [PD-A53T] and 5 asymptomatic carriers) with simultaneous Video-PSG (polysomnography) recording, the Epworth Sleepiness Scale (ESS) for daytime sleepiness, the Athens Insomnia Scale (AIS), the RBD Screening Questionnaire (RBDSQ) for clinical features of RBD, the Montreal Cognitive Assessment (MOCA) for cognition and the University of Pennsylvania Smell Identification Test (UPSIT) for olfaction.

RESULTS

In our cohort, 90% of PD carriers had at least one sleep disorder and 40% had two: 4 RBD, 1 Periodic Limb Movements (PLM), 1 RBD plus PLM, 2 RBD plus moderate Obstructive Sleep Apnea (OSA), and 1 moderate OSA plus Restless Leg Syndrome. No asymptomatic carrier manifested a confirmed sleep disorder. 6/7 PD carriers with RBD had abnormal olfactory testing and 4/7 MOCA below cut off. There was a correlation of both impaired olfaction and cognition with RBD.

CONCLUSIONS

RBD occurs in the majority of PD-A53T, in contrast to most other genetic forms of PD, in which RBD is uncommon. The paucity of a sleep disorder in the asymptomatic carriers suggests that such carriers have not yet reached the prodromal phase when such sleep disorders manifest. Hyposmia in almost all subjects with RBD and cognitive decline in most of them are indicative of the general pattern of disease progression, which however is not uniform.

Olfactory impairment as an early marker of Parkinson's disease in REM sleep behaviour disorder: a systematic review and meta-analysis

Olfactory impairment and rapid eye movement sleep behaviour disorder (RBD) are prodromal symptoms of Parkinson's disease (PD) that may be associated with each other. This review aims to investigate the significance of olfaction in the diagnosis and prognosis of patients with RBD and to assess moderating factors affecting olfactory performance. We searched articles on olfaction in RBD and PD in five electronic databases. We identified 32 studies for the systematic review and used 28 of those, including 2858 participants for meta-analysis. Results revealed significant deficits in odour identification (g=-1.80; 95% CI: -2.17 to -1.43), threshold (g=-1.29; 95% CI: -1.67 to -0.91), discrimination (g=-1.08; 95% CI: -1.28 to -0.87) and overall olfactory function (g=-1.64; 95% CI: -1.94 to -1.35) in patients with RBD. Except for the Unified Parkinson's Disease Rating Scale Part III scores, none of the known moderating variables (including age, sex, disease duration and years of education) accounted for the olfactory function heterogeneity in patients with RBD. We identified similar olfactory impairments in patients with RBD and patients with PD (either with or without underlying RBD). These findings suggest that olfactory impairment may be a sensitive and stable diagnostic biomarker of RBD and appears to be useful for identifying patients with idiopathic RBD at high risk for early conversion to PD.

Profiling Non-motor Symptoms in Monogenic Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease in the elder population, pathologically characterized by the progressive loss of dopaminergic neurons in the substantia nigra. While the precise mechanisms underlying the pathogenesis of PD remain unknown, various genetic factors have been proved to be associated with PD. To date, at least 23 loci and 19 disease-causing genes for PD have been identified. Although monogenic (often familial) cases account for less than 5% of all PD patients, exploring the phenotypes of monogenic PD can help us understand the disease pathogenesis and progression. Primary motor symptoms are important for PD diagnosis but only detectable at a relatively late stage. Despite typical motor symptoms, various non-motor symptoms (NMS) including sensory complaints, mental disorders, autonomic dysfunction, and sleep disturbances also have negative impacts on the quality of life in PD patients and pose major challenges for disease management. NMS is common in all stages of the PD course. NMS can occur long before the onset of PD motor symptoms or can present in the middle or late stage of the disease accompanied by motor symptoms. Therefore, the profiling and characterization of NMS in monogenic PD may help the diagnosis and differential diagnosis of PD, which thereby can execute early intervention to delay the disease progression. In this review, we summarize the characteristics, clinical phenotypes, especially the NMS of monogenic PD patients carrying mutations of SNCA, LRRK2, VPS35, Parkin, PINK1, DJ-1, and GBA. The clinical implications of this linkage between NMS and PD-related genes are also discussed.

α-Synuclein in Parkinson's Disease: Does a Prion-Like Mechanism of Propagation from Periphery to the Brain Play a Role?

Parkinson's disease (PD) is one of the most common neurodegenerative diseases, defined as motor and non-motor symptoms associated with the loss of dopaminergic neurons and a decreased release of dopamine (DA). Currently, PD patients are believed to have a neuropathological basis denoted by the presence of Lewy bodies (LBs) or Lewy neurites (LNs), which mostly comprise α-synuclein (α-syn) inclusions. Remarkably, there is a growing body of evidence indicating that the inclusions undergo template-directed aggregation and propagation via template-directed among the brain and peripheral organs, mainly in a prion-like manner. Interestingly, some studies reported that an integral loop was reminiscent of the mechanism of Parkinson's disease, denoting that α-syn as prionoid was transmitted from the periphery to the brain via specific pathways. Also the systematic life cycle of α-syn in the cellular level is illustrated. In this review, we critically assess landmark evidence in the field of Parkinson's disease with a focus on the genesis and prion-like propagation of the α-syn pathology. The anatomical and cell-to-cell evidences are discussed to depict the theory behind the propagation and transferred pathways. Furthermore, we highlight effective therapeutic perspectives and clinical trials targeting prion-like mechanisms. Major controversies surrounding this topic are also discussed.

Metformin as a Potential Neuroprotective Agent in Prodromal Parkinson's Disease-Viewpoint

To date, there are no clinically effective neuroprotective or disease-modifying treatments that can halt Parkinson's disease (PD) progression. The current clinical approach focuses on symptomatic management. This failure may relate to the complex neurobiology underpinning the development of PD and the absence of true translational animal models. In addition, clinical diagnosis of PD relies on presentation of motor symptoms which occur when the neuropathology is already established. These multiple factors could contribute to the unsuccessful development of neuroprotective treatments for PD. Prodromal symptoms develop years prior to formal diagnosis and may provide an excellent tool for early diagnosis and better trial design. Patients with idiopathic rapid eye movement behavior disorder (iRBD) have the highest risk of developing PD and could represent an excellent group to include in neuroprotective trials for PD. In addition, repurposing drugs with excellent safety profiles is an appealing strategy to accelerate drug discovery. The anti-diabetic drug metformin has been shown to target diverse cellular pathways implicated in PD progression. Multiple studies have, additionally, observed the benefits of metformin to counteract other age-related diseases. The purpose of this viewpoint is to discuss metformin's neuroprotective potential by outlining relevant mechanisms of action and the selection of iRBD patients for future clinical trials in PD.

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.

Variants in the SNCA Locus Are Associated With the Progression of Parkinson's Disease

Background: Genetic factors have a well-known influence on Parkinson's disease (PD) susceptibility; however, no previous studies have investigated the influence of SNCA mutations on the natural history of PD using a prospective follow-up study. The aim of this study was to assess the risk factors of variation of SNCA on the prognosis symptoms of PD patients.

Methods: Fifty PD patients were recruited with 38 v-PSG confirmed PD+RBD patients, and the median follow-up period was 30 months. All patients underwent a comprehensive clinical evaluation at baseline and follow-up, and six SNPs of SNCA (rs356165, rs3857053, rs1045722, rs894278, rs356186, and rs356219) were analyzed. Cox proportional hazards regression models and Kaplan–Meier plot analysis were used to assess the associations between the SNCA variation and the primary and secondary progression outcomes.

Results: Based on the clinical assessment, we found that hyposmia was substantially easier to aggravate. Regression analysis showed that patients with the T allele of rs1045722 and the G allele of rs356219 presented a 34 and 20% decreased risk of progression to the H-Y stage, respectively (p = 0.022; p = 0.005). While for rs894278, G allele patients showed a 47% decreased risk of olfactory dysfunction (p = 0.029). Further subgroup analysis showed that PD+RBD patients with rs356219/G exhibited a 30% and 20% decreased risk of progression on the H-Y stage and MoCA score (p = 0.038; p = 0.045).

Conclusions: Our results indicated that genetic variation in SNCA may contribute to variability natural progression of PD and could possibly be used as a prognostic marker.

The Effects of SNCA rs894278 on Resting-State Brain Activity in Parkinson's Disease

The pathogenesis of Parkinson's disease (PD) is not well established. The rs894278 polymorphism of SNCA has been associated with PD. We performed this study to investigate the relationship between rs894278 and PD status on resting-state brain activity, by analyzing the amplitude of low-frequency fluctuation (ALFF). A total of 81 PD patients and 64 healthy controls were recruited. Disease severity and PD stage were evaluated in PD patients using the unified Parkinson's disease rating scale (UPDRS) and the Hoehn and Yahr (HY) scale, while the cognitive function of all participants was assessed using the mini-mental state examination (MMSE). All participants were genotyped for the rs894278 SNP and underwent a resting state functional magnetic resonance imaging scan. We found that the ALFF values of PD patients in the lingual gyrus and left caudate were lower than those of HCs; and the ALFF values for the right fusiform of participants with G allele were lower than those of participants without G allele. And we further revealed higher ALFF values in bilateral fusiform in rs894278-G carriers than in rs894278-G non-carriers in the PD group and lower ALFF values in bilateral fusiform in rs894278-G carriers than in rs894278-G non-carriers in the HC group. Our findings show that rs894278 and PD status interactively affect the brain activity of PD patients and HCs, and changes in the brain connectomes may play a key role in the pathogenesis of PD. Thus, our work sheds light on the mechanism underlying PD pathogenesis.

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.

Excessive Daytime Sleepiness and REM Sleep Behavior Disorders in Parkinson's Disease: A Narrative Review on Early Intervention With Implications to Neuroprotection

Sleep contributes to the consolidation of our memory and facilitates learning. Short term sleep deprivation temporarily reduces mnestic capacity, whereas long lasting sleep deprivation is associated with structural changes in the hippocampus and cortical areas. However, it is unknown whether early intervention and treatment of sleep disorders could have a neuroprotective effect. In neurodegenerative diseases sleep disorders can occur at preclinical stages and are frequently observed in patients with established Parkinson's disease (PD) and other α-synucleinopathies. REM sleep behavior disorder (RBD) is recognized as a hallmark for the development of α-synucleinopathies and may predict early cognitive decline, while excessive daytime sleepiness (EDS) is present in 12% of patients with PD before treatment initiation and increases continuously over time, causing substantial restrictions for the patients' social life. In more advanced disease, EDS is associated with dementia. Even though well recognized, limited attention has been given to genetics or the treatment of RBD and EDS in early PD. Systematic screening and early intervention can be expected to increase the patients' quality of life, but it remains unclear if this will also impact disease progression. Intervention studies in preclinical and early stages of α-synucleinopathies are needed to increase our understanding of the underlying pathomechanisms and may also provide important inroads to help clarify whether sleep disturbances are secondary to the neurodegenerative process or also contribute to disease exacerbation.

The Length of SNCA Rep1 Microsatellite May Influence Cognitive Evolution in Parkinson's Disease

Background

Alpha-synuclein is a constituent of Lewy bodies and mutations of its gene cause familial Parkinson's disease (PD). A previous study showed that a variant of the alpha-synuclein gene (SNCA), namely the 263 bp allele of Rep1 was associated with faster motor progression in PD. On the contrary, a recent report failed to detect a detrimental effect of Rep1 263 on both motor and cognitive outcomes in PD. Aim of this study was to evaluate the influence of the Rep1 variants on disease progression in PD patients.

Methods

We recruited and genotyped for SNCA Rep1 426 PD patients with age at onset ≥40 years and disease duration ≥4 years. We then analyzed frequency and time of occurrence of wearing-off, dyskinesia, freezing of gait, visual hallucinations, and dementia using a multivariate Cox's proportional hazards regression model.

Results

SNCA Rep1 263 carriers showed significantly increased risk of both dementia (HR = 3.03) and visual hallucinations (HR = 2.69) compared to 263 non-carriers. Risk of motor complications did not differ in the two groups.

Conclusion

SNCA Rep1 263 allele is associated with a worse cognitive outcome in PD.

Is Parkinson's Disease a Neurodevelopmental Disorder and Will Brain Organoids Help Us to Understand It?

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. The incidence of PD cases increases with age, accordingly classically PD is considered to be an age-associated neurodegenerative disease. In this review, the hypothesis that PD is actually a neurodevelopmental disorder that is compensated for a long time will be discussed. However, patients who suffer from PD typically do not show symptoms early in their lives. This implies that, if the hypothesis that PD has a significant neurodevelopmental component is correct, the developmental defects are compensated for a long time. Furthermore, these developmental defects might not causally lead to the disease but increase the susceptibility for disease onset after a "second hit." In this logic, deregulated developmental processes might represent the "first hit." Even a minor developmental defect could lead to a reduced compensatory capacity or reduced fault tolerance of the entire system. In such a case of an already imbalanced system one or more additional hits could perturb the entire system sufficiently to bring it out of balance and lead to the pathology and symptoms which we classify as PD. However, if the developmental hypothesis and the "multiple hit" hypothesis are correct, an early diagnosis of these developmental defects might allow the start of a therapy for at-risk individuals before disease pathology becomes severe and before symptoms occur. Modern stem cell technologies, including the generation of personalized brain organoids, might play an important role in these strategies.