The contribution of Parkin,PINK1 and DJ‐1 genes to selective neuronal degeneration in Parkinson's disease

Parkinson's disease (PD) is characterised by selective and severe degeneration of the substantia nigra pars compacta and the locus coeruleus (LC), which underlies the most prominent symptoms. Although α‐synuclein accumulation has long been established to play a causal role in the disease, it alone cannot explain the selective degenerative pattern. Recent evidence shows that the selective vulnerability could arise due to the large presence of cytosolic catecholamines and Ca²⁺ ions in the substantia nigra pars compacta and LC specifically that can be aberrantly affected by α‐synuclein accumulation. Moreover, each has its own toxic potential, and disturbance of one can exacerbate the toxic effects of the others. This presents a mechanism unique to these areas that can lead to a vicious degenerative cycle. Interestingly, in familial variants of PD, the exact same brain areas are affected, implying the underlying process is likely the same. However, the exact disease mechanisms of many of these genetic variants remain unclear. Here, we review the effects of the PD‐related genes Parkin, PINK1 and DJ‐1. We establish that these mutant varieties can set in motion the same degenerative process involving α‐synuclein, cytosolic catecholamines and Ca²⁺. Additionally, we show indications that model organisms might not accurately represent all components of this central mechanism, explaining why Parkin, PINK1 and DJ‐1 model organisms often lack a convincing PD‐like phenotype.     

Systematic Review and UK‐Based Study of PARK2 (parkin), PINK1, PARK7 (DJ‐1) and LRRK2 in early‐onset Parkinson's disease

Approximately 3.6% of patients with Parkinson's disease develop symptoms before age 45. Early‐onset Parkinson's disease (EOPD) patients have a higher familial recurrence risk than late‐onset patients, and 3 main recessive EOPD genes have been described. We aimed to establish the prevalence of mutations in these genes in a UK cohort and in previous studies. We screened 136 EOPD probands from a high‐ascertainment regional and community‐based prevalence study for pathogenic mutations in PARK2 (parkin), PINK1, PARK7 (DJ‐1), and exon 41 of LRRK2. We also carried out a systematic review, calculating the proportion of cases with pathogenic mutations in previously reported studies. We identified 5 patients with pathogenic PARK2, 1 patient with PINK1, and 1 with LRRK2 mutations. The rate of mutations overall was 5.1%. Mutations were more common in patients with age at onset (AAO) < 40 (9.5%), an affected first‐degree relative (6.9%), an affected sibling (28.6%), or parental consanguinity (50%). In our study EOPD mutation carriers were more likely to present with rigidity and dystonia, and 6 of 7 mutation carriers had lower limb symptoms at onset. Our systematic review included information from >5800 unique cases. Overall, the weighted mean proportion of cases with PARK2 (parkin), PINK1, and PARK7 (DJ‐1) mutations was 8.6%, 3.7%, and 0.4%, respectively. PINK1 mutations were more common in Asian subjects. The overall frequency of mutations in known EOPD genes was lower than previously estimated. Our study shows an increased likelihood of mutations in patients with lower AAO, family history, or parental consanguinity. © 2012 Movement Disorder Society.     

Animal models of Parkinson's disease: Similarities and differences between the disease and models

Parkinson's disease (PD) is a progressive movement disorder characterized by resting tremor, rigidity, akinesia, and postural instability. In addition, PD is characterized by the appearance of Lewy bodies in the remaining neurons. The exact etiology for this disease is still unknown. However, genetic–environmental interaction could contribute to the pathomechanisms of PD. Indeed, seven causative genes responsible for familial PD have been identified. Since discovery of familial PD (FPD), genetic PD models have been developed. Moreover, new PD models using neurotoxins have been reported. In this review, the similarities between human PD and PD models such as genetic mice and Drosophila models are reviewed.     

The emerging role of Rab GTPases in the pathogenesis of Parkinson's disease

The identification of pathogenic mutations in Ras analog in brain 39B (RAB39B) and Ras analog in brain 32 (RAB32) that cause Parkinson's disease (PD) has highlighted the emerging role of protein trafficking in disease pathogenesis. Ras analog in brain (Rab) Guanosine triphosphatase (GTPase) function as master regulators of membrane trafficking, including vesicle formation, movement along cytoskeletal networks, and membrane fusion. Recent studies have linked Rab GTPases with α‐synuclein, Leucine‐rich repeat kinase 2, and Vacuolar protein sorting 35, 3 key proteins in PD pathogenesis. In this review, we discuss the various RAB GTPases associated with PD, current progress in the research, and potential future directions. Investigations into the function of RAB GTPases will likely provide significant insight into the etiology of PD and identify novel therapeutic targets for a currently incurable disease. © 2018 International Parkinson and Movement Disorder Society     

PINK1 mutations in a Brazilian cohort of early‐onset Parkinson's disease patients

Data on the frequency of PINK1 mutations in Brazilian patients with early‐onset Parkinson's disease (EOPD) are lacking. The aim of this report was to investigate mutations of the PINK1 gene in a cohort of Brazilian patients with EOPD. Sixty consecutive familial or sporadic EOPD patients were included. All eight PINK1 exons and exon‐intron boundaries were analyzed. We did not find any pathogenic mutation of PINK1 in our cohort. Single Nucleotide Polymorphisms (SNP) were identified in 46.7% of the patients and in 45.9% of controls (P = 0.9). The SNPs identified in our patients had already been described in previous reports. The results of our study support the hypothesis that mutations in PINK1 may not be a relevant cause of EOPD. In Brazil, if we consider only EOPD patients, it seems that parkin and LRRK2 mutations are more common. © 2009 Movement Disorder Society     

Analysis of 14 LRRK2 mutations in Parkinson's plus syndromes and late-onset Parkinson's disease.

The pleomorphic pathology of postmortem LRRK2-positive patients and the frequent association with late-onset Parkinson's disease (LOPD) symptoms suggest that LRRK2 mutations may play a role in Parkinson's Plus disorders and LOPD. Published studies primarily focus on the common G2019S mutation. Analysis of a spectrum of LRRK2 mutations in Parkinson's Plus disorders has yet to be reported. We investigated 14 leucine-rich repeat kinase 2 (LRRK2) mutations in a cohort of Parkinson's Plus disorders and LOPD. A total of 458 patients with progressive supranuclear palsy (PSP), multiple system atrophy (MSA), corticobasal ganglionic degeneration (CBGD), atypical Parkinsonism (AP), and LOPD were screened for 14 mutations that span exons 19 to 41 of the LRRK2 gene. Among the LOPD cases, 1 patient was found to harbor the R1441C mutation. He presented with typical features of PD at age of 58 years old and responded well to levodopa. We did not detect any of the 14 mutations in PSP, MSA, CBGD, and AP patients. We highlight the first case of LRRK2 R1441C mutation in late onset sporadic PD of non-European ancestry. Furthermore, extensive mutational screen found LRRK2 mutations to be rare among patients who presented with PSP, MSA, CBGD, and AP.     

Pathogenicity of LRRK2 P755L variant in Parkinson's disease

A heterozygous 2264C→T variant (P755L) in LRRK2 gene has been reported to be a likely pathogenic variant among ethnic Chinese patients with Parkinson's disease (PD). In a case control study, we performed genetic analysis of the P755L variant in an independent cohort of Chinese patients with PD and controls. The P755L variant was present in 4/204 (2.0%) of PD compared with 6/235 (2.6%) of controls (odds ratio = 0.76, 95% CI 0.23, 2.6, P = 0.76). All subjects carried the heterozygous genotype. Subset analysis in the group ≥65 years of age revealed a prevalence of 2.8% in PD compared with 3.1% in controls (odds ratio = 0.92, 95% CI 022, 3.7, P = 0.9), and in the group <65 years of age showed a 0% in PD versus 2.1% in controls (P = 0.2). The phenotype of patients with PD with the P755L variant was generally similar to other patients with PD and none of the carriers reported a positive family history. The lack of functional data, absence of segregation of the variant with disease, and the presence of the variant in apparently healthy individuals suggest that P755L is possibly a rare polymorphism in the Chinese population. Further validation of our findings in other populations would be important. © 2008 Movement Disorder Society     

Recessive Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disease caused by loss of dopaminergic neurons in the substantia nigra pars compacta. Although the etiology of PD remains unclear, it is now clear that genetic factors contribute to the pathogenesis of the disease. Recently, several causative genes have been identified in monogenic forms of PD. Accumulating evidence indicates that their gene products play important roles in mitochondrial function, oxidative stress response, and the ubiquitin-proteasome system, which are also implicated in sporadic PD, suggesting that these gene products share a common pathway to nigral degeneration in both familial and sporadic PD. Here, we review recent advances in knowledge about genes associated with recessive PD, including parkin, PINK1, and DJ-1.     

A novel LRRK2 mutation in an Austrian cohort of patients with Parkinson's disease.

To investigate the frequency of mutations in the Leucine-Rich Repeat Kinase 2 gene (LRRK2) in a sample of Austrian Parkinson's disease (PD) patients, we sequenced the complete coding region in 16 patients with autosomal dominant PD. Furthermore, we sequenced exons 31, 35, and 41 additionally in 146 patients with idiopathic PD and 30 patients with dementia with Lewy bodies. Furthermore, all 192 patients were screened for 21 putative LRRK2 mutations. While the most common mutation G2019S and the risk variant G2385R were not found in our samples, we detected a novel missense mutation (S973N) in a patient with familial, late-onset and dopa-responsive PD.