The Role of VPS35 in the Pathobiology of Parkinson's Disease.

The vacuolar protein sorting 35 (VPS35) gene located on chromosome 16 has recently emerged as a cause of late-onset familial Parkinson's disease (PD) (PARK17). The gene encodes a 796-residue protein nearly ubiquitously expressed in human tissues. The protein localizes on endosomes where it assembles with other peripheral membrane proteins to form the retromer complex. How VPS35 mutations induce dopaminergic neuron degeneration in humans is still unclear. Because the retromer complex recycles the receptors that mediate the transport of hydrolase to lysosome, it has been suggested that VPS35 mutations lead to impaired lysosomal and autophagy function. Recent studies also demonstrated that VPS35 and the retromer complex influence mitochondrial homeostasis, suggesting that VPS35 mutations elicit mitochondrial dysfunction. More recent studies have identified a key role of VPS35 in neurotransmission, whilst others reported a functional interaction between VPS35 and other genes associated with familial PD, including α-SYNUCLEIN-PARKIN-LRRK2. Here, we review the biological role of VPS35 protein, the VPS35 mutations identified in human PD patients, and the potential molecular mechanism by which VPS35 mutations can induce progressive neurodegeneration in PD.

GBA-Related Parkinson's Disease: Dissection of Genotype-Phenotype Correlates in a Large Italian Cohort.

BACKGROUND: Variants in GBA are the most common genetic risk factor for Parkinson's disease (PD). The impact of different variants on the PD clinical spectrum is still unclear. OBJECTIVES: We determined the frequency of GBA-related PD in Italy and correlated GBA variants with motor and nonmotor features and their occurrence over time. METHODS: Sanger sequencing of the whole GBA gene was performed. Variants were classified as mild, severe, complex, and risk. ß-glucocerebrosidase activity was measured. The Kaplan-Meier method and Cox proportional hazard regression models were performed. RESULTS: Among 874 patients with PD, 36 variants were detected in 14.3%, including 20.4% early onset. Patients with GBA-PD had earlier and more frequent occurrence of several nonmotor symptoms. Patients with severe and complex GBA-PD had the highest burden of symptoms and a higher risk of hallucinations and cognitive impairment. Complex GBA-PD had the lowest ß-glucocerebrosidase activity. CONCLUSIONS: GBA-PD is highly prevalent in Italy. Different types of mutations underlie distinct phenotypic profiles. © 2020 International Parkinson and Movement Disorder Society.

Serum miR-30c-5p is a potential biomarker for multiple system atrophy.

Multiple system atrophy (MSA) is a neurodegenerative disease that belongs to the α synucleinopathies. Clinically, there is an overlap between MSA and Parkinson's disease (PD), especially at the early disease stage. However, these two pathologies differ in terms of disease progression. Currently, no biomarker exists to differentiate MSA from PD. MicroRNAs are non-coding RNAs implicated in gene expression regulation. MiRNAs modulate cellular activity and they control a range of physiological and pathological functions. miRNAs are found in biofluids, such as blood, serum, plasma, saliva, and cerebrospinal fluid. Many groups, including ours, found that circulating miRNAs are differently expressed in blood, plasma, serum and cerebrospinal fluid of PD and MSA patients. In the present study, our primary aim was to determine if serum mir-30-5p and mir-148b-5p can be used as biomarkers for early diagnosis of PD and/or MSA. Our secondary goal was to determine if serum levels of those miRNAs can be correlated with the patients' clinical profile. Using quantitative PCR (qPCR), we evaluated expression levels of miR-30c-5p and miR148b-5p in serum samples from PD (n = 56), MSA (n = 49), and healthy control (n = 50) subjects. We have found that miR-30c-5p is significantly upregulated in MSA if compared with PD and healthy control subjects. Moreover, serum miR-30c-5p levels correlate with disease duration in both MSA and PD. No significant difference was found in miR-148b-5p among MSA, PD and healthy control subjects. Our results suggest a possible role of serum miR-30-5p as a biomarker for diagnosis and progression of MSA.

Expanding the Spectrum of GBA1-Associated Neurodegenerative Diseases in an Italian Family.

BACKGROUND: Heterozygous mutations in GBA1 gene are known as most common genetic risk factor for Parkinson's disease (PD). However, role of GBA1 mutations in non-α-synuclein disorders is unclear. CASES: Case index, 76 year-old woman referred to our movement disorders outpatient clinic for 2-year history of gait impairment, falls and motor slowness, with partial response to levodopa. Clinical and instrumental examinations were consistent with Progressive Supranuclear Palsy-Corticobasal Syndrome (PSP-CBS). Case 2 is older sister reporting depressive symptoms; however, she had dementia (MMSE 18/30), gait apraxia and vertical supranuclear gaze palsy (VSNGP). Case 3 is her deceased older sister who had been diagnosed with Corticobasal Syndrome (CBS). Case 4, older brother had been diagnosed with Parkinson's disease-dementia (PDD) with good response to levodopa. Two affected living siblings harboring same genetic variant. CONCLUSIONS: To our knowledge, this is the first family showing such intrafamilial variability ranging from CBS to PDD to dementia.

Genetic characterization of a cohort with familial parkinsonism and cognitive-behavioral syndrome: A Next Generation Sequencing study.

OBJECTIVE: To perform the genetic characterization of a cohort with familial parkinsonism and cognitive-behavioral syndrome. METHODS: A Next Generation Sequencing - based targeted sequencing of 32 genes associated to various neurodegenerative phenotypes, plus a screening for SNCA Copy Number Variations and C9orf72 repeat expansion, was applied in a cohort of 85 Italian patients presenting with parkinsonism and cognitive and/or behavioral syndrome and a positive familial history for any neurodegenerative disorder (i.e., dementia, movement disorders, amyotrophic lateral sclerosis). RESULTS: Through this combined genetic approach, we detected potentially relevant genetic variants in 25.8% of patients with familial parkinsonism and cognitive and/or behavioral syndrome. Peculiar phenotypes are described (Cortico-basal syndrome with APP, Posterior Cortical Atrophy with GBA, Progressive Supranuclear Palsy-like with GRN, Multiple System Atrophy with TARDBP). The majority of patients presented a rigid-bradykinetic parkinsonian syndrome, while rest tremor was less common. Myoclonic jerks, pyramidal signs, dystonic postures and vertical gaze disturbances were more frequently associated with the presence of a pathogenic variant in one of the tested genes. CONCLUSIONS: Given the syndromic approach adopted in our study, we were able to provide a detailed clinical description of patients beyond the boundaries of specific clinical diagnoses and describe peculiar phenotypes. This observation further supports the knowledge that genetic disorders present phenotypic overlaps across different neurodegenerative syndromes, highlighting the limitations of current clinical diagnostic criteria defining sharp boundaries between distinct conditions.

Clinical and Molecular Characterization of a Novel Progranulin Deletion Associated with Different Phenotypes.

BACKGROUND: Mutations in the GRN gene are causative for an autosomal dominant form of frontotemporal dementia. OBJECTIVE/METHODS: The objective of the present study is to describe clinical and molecular features of three siblings harboring the GRN deletion NM_002087.3:c.295_308delTGCCCACGGGGCTT, p.(Cys99Profs*15) identified with next generation sequencing. RESULTS: Our patients demonstrated heterogeneous clinical phenotypes, such as progressive supranuclear palsy-like in the proband and the behavioral variant of frontotemporal dementia in the two affected siblings. Progranulin haploinsufficiency was revealed by both gene expression and protein analyses. CONCLUSION: The pathogenicity of the novel GRN deletion c.295_308del TGCCCACGGGGCTT is confirmed by both functional analysis and segregation in three affected siblings.