PLA2G6 variant in Parkinson's disease

PLA2G6 was reported recently as the causative gene for PARK14-linked autosomal recessive early-onset dystonia-parkinsonism. In a recent study in Singapore, heterozygous PLA2G6 p.P806R (c.2417C>G) mutation in exon 17 was reported to be a possible Parkinson's disease (PD)-related mutation. To determine the significance of the PLA2G6 mutation, we conducted an association study by performing direct sequencing of PLA2G6 exon 17 in 379 Japanese sporadic PD patients and 310 controls in the Japanese general population. In this group, we found 12 patients (12/379=3.16%) and 10 controls (10/310=3.23%) with a heterozygous p.P806R mutation (P=0.96, χ(2)=0.0019). Therefore, our large case-controlled study suggests that PLA2G6 p.P806R is not a disease-associated polymorphism in PD. Moreover, we performed direct sequencing of all exons and exon-intron boundaries of PLA2G6 in 116 Japanese patients with sporadic PD. Two single heterozygous variants (p.R301C or p.D331N) were found (both frequencies: 1/379 patients vs 0/310 controls) and the roles of their variants were unclear. Finally, combined with the previous report, our findings emphasize that PLA2G6 mutations are unlikely to be the major causes or risk factors of PD at least in Asian populations. However, further large studies in various populations are needed because patients with PLA2G6 mutations can show heterogeneous clinical features.     

Analysis of PLA2G6 gene mutation in sporadic early-onset parkinsonism patients from Chinese population

Recent studies have shown that PLA2G6 is a causative gene for PARK14-linked autosomal recessive early-onset complicated dystonia-parkinsonism, early-onset parkinsonism with frontotemporal dementia and autosomal recessive early-onset Parkinsonism without added complicated clinical features. In order to investigate the characteristics of PLA2G6 gene mutations in Chinese sporadic early-onset parkinsonism (EOP) patients, we performed polymerase chain reaction and DNA direct sequencing on a cohort of sporadic EOP patients from Chinese population. In this study, we found a novel heterozygous varient (p.G679V). Bioinformatics demonstrates that p.G679V exhibits highly conserved residues across species, which hints it might be a pathogenic mutation. Our result indicated that PLA2G6 mutations might not be a main cause of Chinese sporadic EOP.     

PARK2 gene mutations in early onset Parkinson's disease patients of South India

With the etiology being unclear till date, a combination of age, genetic and environmental factors are known to play a significant role in the pathogenesis of Parkinson's disease. Mutations in PARK2 gene have been implicated to cause autosomal recessive early onset PD. We analyzed the 12 coding exons of PARK2 gene in 16 early onset PD patients of South Indian ethnicity. PARK2 mutations were present in 68% of the early onset cases. We report the presence of four PARK2 sequence variants c.1239G>C, c.171+25T>C, c.202A>G, c.601G>A, and a novel insertion mutation, c.798_799insA in the exon 7 of PARK2 gene. These results suggest that mutations in PARK2 gene may be a common cause of PD among South Indian early onset patients.     

Quinone formation as dopaminergic neuron-specific oxidative stress in the pathogenesis of sporadic Parkinson's disease and neurotoxin-induced parkinsonism

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by dopaminergic neuron-specific degeneration in the substantia nigra. A number of gene mutations and deletions have been reported to play a role in the pathogenesis of familial PD. Moreover, a number of pathological and pharmacological studies on sporadic PD and dopaminergic neurotoxin-induced parkinsonism have hypothesized that mitochondrial dysfunction, inflammation, oxidative stress, and dysfunction of the ubiquitin-proteasome system all play important roles in the pathogenesis and progress of PD. However, these hypotheses do not yet fully explain the mechanisms of dopaminergic neuron-specific cell loss in PD. Recently, the neurotoxicity of dopamine quinone formation by auto-oxidation of dopamine has been shown to cause specific cell death of dopaminergic neurons in the pathogenesis of sporadic PD and dopaminergic neurotoxin-induced parkinsonism. Furthermore, this quinone formation is closely linked to other representative hypotheses in the pathogenesis of PD. In this article, we mainly review recent studies on the neurotoxicity of quinone formation as a dopaminergic neuron-specific oxidative stress and its role in the etiology of PD, in addition to several neuroprotective approaches against dopamine quinone-induced toxicity.     

A comparative study of Parkinson's disease and leucine-rich repeat kinase 2 p.G2019S parkinsonism

Parkinson disease is a progressive neurodegenerative disease for which leucine-rich repeat kinase 2 (LRRK2 carriers) p.G2019S confers substantial genotypic and population attributable risk. With informed consent, we have recruited clinical data from 778 patients from Tunisia (of which 266 have LRRK2 parkinsonism) and 580 unaffected subjects. Motor, autonomic, and cognitive assessments in idiopathic Parkinson disease and LRRK2 patients were compared with regression models. The age-associated cumulative incidence of LRRK2 parkinsonism was also estimated using case-control and family-based designs. LRRK2 parkinsonism patients had slightly less gastrointestinal dysfunction and rapid eye movement sleep disorder. Overall, disease penetrance in LRRK2 carriers was 80% by 70 years but women become affected a median 5 years younger than men. Idiopathic Parkinson disease patients with younger age at diagnosis have slower disease progression. However, age at diagnoses does not predict progression in LRRK2 parkinsonism. LRRK2 p.G2019S mutation is a useful aid to diagnosis and modifiers of disease in LRRK2 parkinsonism may aid in developing therapeutic targets.     

Analysis of LRRK 2 G 2019 S and I 2020 T mutations in Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 (LRRK 2), encoding dardarin protein, have been demonstrated to be linked to autosomal dominant Parkinson's disease (PD). In the present study the entire exon 41 of LRRK 2 gene was evaluated in a series of 174 PD patients recruited from Polish population, aged at the time of diagnosis 54.0+/-39.1 years, 21 of them had positive family history of PD with mean onset of the disease of 51.9+/-11.7 years as well as in 190 healthy controls aged 73.7+/-6.0 years. The mutations were evaluated by direct sequencing for mutations in exon 41 of LRRK 2 gene. In the studied patients no known mutations in exon 41 of LRRK 2 gene, including G 2019 S and I 2020 T were found, both in PD patients as well as in the controls. It can be concluded that the G 2019 S and I 2020 T mutations in exon 41 of LRRK 2 gene are rare causes of Parkinson disease in a Polish population.     

Onset and progression of disease in familial and sporadic Parkinson's disease

Lately different and rare genetic forms of Parkinson's disease (PD) have been described. Complete genomic screening has suggested that still undefined multiple genetic factors might underlie the development of PD. The course of PD patients with and without genetic background might be different. We compared the age at onset and progression of PD with (FH) and without (NFH) family history. Two hundred forty PD patients attending the outpatient Movement Disorders Clinic were evaluated. The age of onset (AO), the duration of disease until stage III of Hoehn and Yahr (YST3), until dementia (YDEM) and family history of PD were determined by interview, examination of medical files and of affected family members. Patients with young onset who reported another PD patient among their siblings were tested for parkin mutations. Statistical analysis used ANOVA, Fisher's Least Significant Difference, log-rank and Wilcoxon's tests for Kaplan-Meier survival curves taking stage III and dementia as end-points. Of the 240 patients (age 73.3 +/- 10.9 years), 29 (12%) had positive FH. Six of them carried parkin mutations. The AO was 33.5 +/- 8.1 (range 19-42) years for parkin carriers, 59.3 +/- 11.3 (range 34-76) for FH and 66.5 +/- 11.8 (27-91) years for NFH (P < 0.0001). The three groups were significantly different from each other (alpha = 0.05). Stage III and dementia were reached only in non-parkin patients. YST3 was 12.6 +/- 6.6 years for FH and 6.5 +/- 5.0 years for NFH (P < 0.0001). YDEM was 10.1 +/- 6.0 years for FH versus 4.7 +/- 4.5 years for NFH (P = 0.002). Kaplan-Meier survival analysis revealed faster motor (P = 0.0016) and mental decline (P = 0.02) in NFH versus FH. Our results showed that the AO of PD is younger in patients with FH. Motor and mental deterioration, however, showed a less steep course in familial PD patients.     

Alpha-2 macroglobulin I1000 V polymorphism in Chinese sporadic Alzheimer's disease and Parkinson's disease

Several lines of evidence have revealed some overlapping pathologies in Alzheimer's disease (AD) and Parkinson's disease (PD). Although the alpha-2 macroglobulin gene (A2M) might be a risk factor of these two neurodegenerative diseases, conclusions from different studies have remained conflicting. Here we studied the role of A2M I1000 V polymorphism in both AD and PD in a Chinese Han population. We found that the A2M I/V genotype is associated with both AD (odds ratio (OR)=2.55, 95% confidential interval (95% CI): 1.20-5.43, attributable fraction (AF)=13.65%) and PD (OR=3.03, 95% CI: 1.30-7.02, AF=16.51%). After classifying according to the age of onset, this association is only detected in early-onset AD patients (OR=3.96, 95% CI: 1.28-12.26) and late-onset PD patients (OR=2.61, 95% CI: 0.97-7.09). Therefore, we conclude that in our samples, the A2M I/V genotype might be a susceptibility variant, even with minor effect, for both sporadic AD and PD.     

PLA2G6 mutations associated with a continuous clinical spectrum from neuroaxonal dystrophy to hereditary spastic paraplegia

PLA2G6‐associated neurodegeneration (PLAN) and hereditary spastic paraplegia (HSP) are 2 groups of heterogeneous neurodegenerative diseases. In this study, we report PLA2G6 gene mutations in 3 families from Turkey, Morocco, and Romania. Two affected Turkish siblings presenting HSP adds the disease to PLAN phenotypes. They were homozygous for the PLA2G6 missense c.2239C>T, p.Arg747Trp variant and the ages of onset were 9 and 21. Parkinsonism, dystonia or cognitive decline were not the clinical elements in these patients contrary to the cases that has been previously reported with the same variant, however, iron accumulation was evident in their cranial magnetic resonance imaging. The Moroccan patient was homozygous for a novel missense c.1786C>T, p.Leu596Phe variant and the Romanian patient had 2 novel mutations; c.1898C>T, p.Ala633Val and c.1765_1768del, p.Ser589ThrfsTer76. Both of these patients conformed better to childhood onset PLAN with the age of onset at 4 and 7 years, respectively. Interestingly, all identified mutations were affecting the highly conserved patatin‐like phospholipase domain of the PLA2G6 protein.     

A study of LRRK2 mutations and Parkinson's disease in Brazil

Mutations in the Leucine-rich repeat kinase 2 (LRRK2) gene are known as a common cause of Parkinson's disease (PD) among patients from different geographic origins. In this study, we evaluated the prevalence of LRRK2 mutations in exons 31 and 41 in a cohort of 154 consecutive, unrelated Brazilian patients with familial or sporadic PD, including early and late onset patients. The LRRK2 p.G2019S mutation was present in heterozygous state in three index cases (approximately 2%), and in three additional relatives. No carriers of this mutation were found among 250 control chromosomes. Clinically, all mutation-positive patients presented a typical PD phenotype and a good response to levodopa. Mutation segregation analysis in a large sibling showed incomplete penetrance of the p.G2019S. Our findings suggest that the LRRK2 p.G2019S mutation has a substantial contribution to PD susceptibility among Brazilian population and add new clues to current research of this disease.     

The sepiapterin reductase gene region reveals association in the PARK3 locus: analysis of familial and sporadic Parkinson's disease in European populations

Background

Parkinson''s disease is a genetically complex disease with mixed mode of inheritance. Recently, a haplotype across the sepiapterin reductase (SPR) gene, which is located in the PARK3 linkage region, was shown to modulate age of onset of Parkinson''s disease in sibships from North America.

Objective

To make a thorough assessment of the SPR gene region in sporadic Parkinson''s disease.

Methods

A linkage study in 122 European sibship families with five microsatellite and 17 single nucleotide polymorphism (SNP) markers in and around the SPR gene region, and an association analysis in 340 sporadic cases of Parkinson''s disease and 680 control subjects from Germany with 40 SNPs. Linkage was evaluated by non‐parametric linkage scores and genotypic or haplotype association was tested by regression analysis, assuming different risk effect models.

Results

Significant LOD scores between 2 and 3 were obtained at the two SPR‐flanking markers D2S2110 and D2S1394 and seven SNP markers around the SPR gene. We found the previously reported promoter SNP rs1876487 also significantly associated with age of onset in our sib pair families (p‐value 0.02). One strong linkage disequilibrium (LD) block of 45 kb including the entire SPR gene was observed. Within this LD block all 14 inter‐correlated SNPs were significantly associated with Parkinson''s disease affection status (p‐value 0.004).

Conclusions

DNA polymorphisms in a highly intercorrelated LD block, which includes the SPR gene, appear to be associated with both sporadic and familial Parkinson''s disease. This confirms a previous study showing that SPR potentially modulates the onset of or risk for Parkinson''s disease.     

Infantile onset progressive cerebellar atrophy and anterior horn cell Degeneration-A novel phenotype associated with mutations in the PLA2G6 gene

Pontocerebellar hypoplasia (PCH) encompasses a group of neurodegenerative disorders. There are ten known subtypes with common characteristics of pontine and cerebellar hypoplasia or atrophy, neocortical atrophy, and microcephaly. PCH is associated with anterior horn cell degeneration in PCH1a and PCH1b due to mutations in the VRK1 and EXOSC3 genes. Late onset PCH1 has been described in single case reports. The molecular etiology remains mostly unknown. We describe two siblings from a consanguineous Moslem Arabic family with a unique combination of progressive cerebellar atrophy and a SMA-like anterior horn cell degeneration due to a homozygous mutation in the PLA2G6 gene (NM_003560.2). The PLA2G6 gene encodes phospholipase A2 beta, which is involved in the remodeling of membrane phospholipids, signal transduction and calcium signaling, cell proliferation and apoptosis. Mutations in PLA2G6 are known to cause Neurodegeneration with brain iron accumulation 2 (NBIA2): Our patients have some similarities with NBIA2; both are characterized by rapidly progressive psychomotor regression and cerebellar atrophy. However, NBIA2 is not known to exhibit anterior horn cell degeneration.Our patients' phenotype is more consistent with late onset PCH1; thus, indicating that the spectrum of clinical and radiological presentations of PLA2G6 mutations should be extended and that this gene should be included in the molecular evaluation of patients with late onset PCH1.     

CARD15 variants in patients with sporadic Parkinson's disease

Recent reports have proven the importance of genetic factors and inflammation in the pathogenesis of sporadic Parkinson's disease (PD). In the current study, the frequency of CARD15/NOD2 gene variants (R702W, G908R, L1007fs), previously associated with Crohn's disease--a common inflammatory bowel disease, have been examined in a group of 308 sporadic PD patients and 220 healthy controls. Significantly higher frequency of total CARD15 variant alleles in PD patients (13.0%) compared to the controls (8.0%, p<0.02) was observed. 24.0% of PD patients carried at least one CARD15 variant allele compared to 15.5% of healthy controls (p<0.02, OR=1.73). The results of the study suggest, that the polymorphism in CARD15/NOD2 gene may be a risk factor for sporadic PD development, and support the concept of inflammatory pathogenesis of PD.     

PARK11 is not linked with Parkinson's disease in European families

Parkinson's disease (PD) is a genetically heterogeneous disease. Recently, significant linkage has been reported to a 39.5 cM region on the long arm of chromosome 2 (2q36-37; PARK11) in North American Parkinson families under an autosomal dominant model of inheritance. We have performed a replication study to confirm linkage to this region in a European population. Linkage analysis in 153 individuals from 45 European families with a strong family history of PD did not show any significant LOD score in this region. Therefore, PARK11 does not seem to play a major role for familial PD in the European population.