Genetic analysis of <Emphasis Type="Italic">heme oxygenase</Emphasis>-<Emphasis Type="Italic">1</Emphasis> (<Emphasis Type="Italic">HO-1</Emphasis>) in German Parkinson’s disease patients

Parkinson’s disease (PD) is characterized by the loss of dopaminergic neurons and the presence of intracytoplasmic inclusions (Lewy bodies). Iron, which is elevated in the substantia nigra (SN) of PD patients, seems to be of pivotal importance, because of its capacity to enhance the amplification of reactive-oxygen species. Therefore, it is tempting that the iron-releasing key enzyme in heme catabolism, heme oxygenase-1 (HO-1), may represent a candidate for a genetic susceptibility to PD. In the current study, we examined a (GT)n fragment length polymorphism in the promoter region, as well as three coding SNPs in the HO-1 gene in order to assess if certain genotypes are associated with PD. Furthermore, peripheral blood expression levels of HO-1 in PD patients and healthy probands were compared. However, our analyses did not reveal a significant association of these genetic markers in the HO-1 gene with an increased susceptibility to PD.     

Genetic association study between <Emphasis Type="Italic">RIT2</Emphasis> and Parkinson’s disease in a Han Chinese population

Recent several meta-analyses and certain case–control studies suggested that the Ras-like without CAAX 2 (RIT2) rs12456492 increased the risk of Parkinson’s disease (PD) in Asian and Caucasian populations. However, as so far, the association between RIT2 rs12456492 and PD is still controversial. We investigated genetic association of RIT2 rs12456492 with PD susceptibility in a Han Chinese population of 1747 ethnic Han Chinese subjects comprising 884 PD patients and 863 healthy controls. The minor allele frequency (MAF) of G at the RIT2 rs12456492 was not significantly different between the cases and the controls. Furthermore, no significant differences were observed in genotype distribution between PD patients and healthy controls for the RIT2 rs12456492, even after being stratified by age at onset and gender. In addition, we found that no significant differences were detected in the clinical manifestations for gender, age at onset, and onset symptoms between PD patients with AG + GG genotypes and those with AA genotypes. Our study from the mainland China demonstrates that RIT2 rs12456492 do not increase the risk of developing PD. Therefore, more replication studies in additional Chinese population and other cohorts are warranted to further clarify the role of RIT2 rs12456492 in PD susceptibility.     

The analysis of association between <Emphasis Type="Italic">SNCA</Emphasis>, <Emphasis Type="Italic">HUSEYO</Emphasis> and <Emphasis Type="Italic">CSMD1</Emphasis> gene variants and Parkinson’s disease in Iranian population

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disorder. Both genetic and environmental factors are involved in the etiology of the disease. Many studies have revealed the susceptibility genes and variations for PD which need further confirmation. Here we evaluated the association of variations in SNCA, HUSEYO and CSMD1 genes with PD. A case–control study was conducted with 489 PD patients and 489 healthy controls. DNA was extracted from peripheral blood of all subjects and rs356220 and rs11931074 in SNCA, rs2338971 in HUSEYO and rs12681349 in CSMD1 were genotyped using PCR–RFLP method. The genotypes and allele frequencies were significantly different between case and control groups for rs356220, rs11931074 and rs2338971 but not for rs12681349. We provided further evidence that rs356220 is associated with increased risk of PD supporting previous studies in Caucasian-based and Japanese populations. The association of rs11931074 with decreased risk of PD was also significant. This study revealed the first evidence of the association of rs2338971 with increased risk of PD in the Iranian population. Nevertheless, these findings need further validation via more replication studies.     

Genetic variability in <Emphasis Type="Italic">SNCA</Emphasis> and Parkinson’s disease

Over the last decades, increasing knowledge about the genetic architecture of Parkinson’s disease has provided novel insights into the pathogenesis of the disorder, generating hypotheses for further research. Characterizing the role of SNCA, encoding the α-synuclein protein, has been a particularly important aspect of this development. The identification of SNCA as the first gene implicated in monogenic parkinsonism led to the recognition of α-synuclein as a key protein in the pathogenesis and a major component of pathological hallmark lesions. An association between common variants in SNCA and risk of sporadic Parkinson’s disease has been established through numerous studies. We review our current understanding of SNCA variability contributing to Parkinson’s disease, highlighting the characterization of functionally relevant susceptibility alleles as a major future challenge. We argue that new strategies will be needed to pinpoint the variants that are ultimately responsible for the signals detected in association studies, where targeted resequencing may represent an attractive initial approach.     

<Emphasis Type="Italic">TOX3</Emphasis> Variants Are Involved in Restless Legs Syndrome and Parkinson’s Disease with Opposite Effects

Parkinson’s disease (PD) and restless legs syndrome (RLS) may be clinically and/or etiologically related, yet this association is under debate. Single-nucleotide polymorphisms (SNPs) in the TOX3 gene locus were implicated in both RLS and PD genome-wide association studies (GWASs), suggesting a potential pleiotropy. Two case-control cohorts including 644 PD patients, 457 RLS patients, and 945 controls were genotyped for one known RLS-related SNP (rs3104767) and one PD-related SNP (rs4784226) in the TOX3 locus. The associations between genotype and PD and RLS risk were tested using multivariate regression models. The allele frequencies of RLS-related SNP rs3104767 in RLS patients and controls were 0.35 and 0.43, respectively (OR 0.70, p?=?0.0007). Regression model suggested that this association is derived by homozygous carriage of rs3104767 (adjusted p?=?0.008). A nominal association was observed for homozygous carriers of the rs3104767 SNP in PD (OR 1.62, 95% CI 1.05–2.54, p?=?0.034), i.e., with an opposite direction of effect on RLS and PD, but this was not significant after Bonferroni correction. However, data from published GWASs of RLS and PD, and from the PDgene database, further supported these inverse associations. Our results confirm the association between the TOX3 SNP rs3104767 and RLS and suggest that TOX3 variants are involved in both RLS and PD, but with different or even opposite effects. Studies in larger populations of different ethnicities are required to further refine the TOX3 locus is involved in RLS and PD.     

Olfactory Dysfunction in Parkinson’s Disease Patients with the <Emphasis Type="Italic">LRRK2</Emphasis> G2385R Variant

Olfactory dysfunction has been reported in Parkinson’s disease (PD) patients carrying the LRRK2 G2019S variant in Caucasians but rarely in those with the LRRK2 G2385R variant. In this study, we performed genotyping for the LRRK2 G2385R variant in PD patients recruited from the Movement Disorder Clinic of Xuanwu Hospital in Beijing and in healthy controls randomly selected from the Beijing Longitudinal Study on Aging cohort. The “five-odor olfactory detection array”, an olfactory threshold test, was used to assess olfactory function. One hundred and eighty-six participants were enrolled, comprising 43 PD patients without (iPD) and 25 with (LRRK2-PD) the LRRK2 G2385R variant, and 118 healthy controls. Our results showed that the threshold of olfactory identification was significantly worse in PD patients than in controls, but not significantly different between the iPD and LRRK2-PD groups. These findings suggested that although olfactory function in LRRK2-PD patients is impaired, it is similar to that in iPD patients.     

Expression analysis of <Emphasis Type="Italic">GRIN2B</Emphasis>, <Emphasis Type="Italic">BDNF</Emphasis>, and <Emphasis Type="Italic">IL-1β</Emphasis> genes in the whole blood of epileptic patients

Epilepsy is a brain disorder with a global prevalence of 1%. It has been attributed to genetics and environmental factors. Despite efforts to identify the molecular pathology of epilepsy, the underlying mechanism is not understood yet. This study was carried out to compare GRIN2B, BDNF, and IL-1β gene expressions in 50 patients suffering from generalized epilepsy with tonic-colonic seizures and 50 age- and sex-matched healthy subjects using TaqMan Real-time PCR. Our results demonstrated significant upregulation of these genes in people with epilepsy compared with healthy subjects. We also found a positive correlation between GRIN2B and BDNF expression (r²=0.4619, p?<?0.0001), BDNF and IL-1β expression (r²?=?0.515, p?<?0.0001), and GRIN2B and IL-1β gene expressions (r²?=?0.666, p?<?0.0001) which implies the possibility to estimate the expression level of these genes by assessment of expression of one of them. Considering the results of the previous animal studies which showed upregulation of these genes in brain tissues of epileptic animals, the expression levels of GRIN2B, BDNF, and IL-1β in blood samples might be related to their expression in brain samples. Future studies are needed to assess the role of these genes in the pathogenesis of epilepsy and evaluate whether altered expression of these genes along with imaging methods can facilitate subtyping the epilepsy.     

Lower functional connectivity of default mode network in cognitively normal young adults with mutation of <Emphasis Type="Italic">APP</Emphasis>, <Emphasis Type="Italic">presenilins</Emphasis> and <Emphasis Type="Italic">APOE ε4</Emphasis>

In this study, we used resting-state functional magnetic resonance imaging to explore the genetic effects of amyloid precursor protein (APP) or presenilins mutation and apolipoprotein E (APOE) ε4 on the default-mode network (DMN) in cognitively intact young adults (24.1 ± 2.5 years). Both the APP or presenilin-1/2 group and the APOE ε4 group had significantly lower DMN functional connectivity (FC) in the some brain regions like precuneus/middle cingulate cortices (PCu/MCC) than controls (AlphaSim corrected, P < 0.05). Only a lower FC tendency was demonstrated (control < APOE ε4 < APP or presenilin-1/2 group). Moreover, lower FC in PCu/MCC is correlated with some neuropsychological assessments such as similarity test in APOE ε4 group. These findings indicate that DMN FC alteration in APP or presenilin-1/2 or APOE ε4 subjects is prior to the occurrence of neurological alterations and clinical symptoms, and DMN FC might be a valuable biomarker to detect genetic risk in the preclinical stage.     

<Emphasis Type="Italic">hVMAT2</Emphasis>: A Target of Individualized Medication for Parkinson’s Disease

Vesicular monoamine transporter 2 (VMAT2) is responsible for sequestering cytosolically toxic dopamine into intracellular secretory vesicles. Animal genetic studies have suggested that reduced VMAT2 activity contributes to the genetic etiology of Parkinson’s disease (PD), but this role has not been established in humans. Based on human genetic association and meta-analysis, we first confirm the human VMAT2 (hVMAT2 or SLC18A2) promoter as a risk factor for PD in both family and unrelated US white people: marker rs363324 at –11.5 kb in the hVMAT2 promoter is reproducibly associated with PD in a cohort of nuclear families (p = 0.04506 in early-onset PD) and 3 unrelated US white people (meta-analysis p = 0.01879). In SH-SY5Y cells, low activity-associated hVMAT2 promoter confers high methylpiperidinopyrazole iodide cytotoxicity, which is likely attributed to functional polymorphisms bound by nuclear proteins. Interestingly, treatments with the dopamine neuron-protecting agent puerarin upregulates the promoter activity in a haplotype- and cell line-dependent manner. These pharmacogenetic findings suggest that hVMAT2 could be a risk factor and imply it as a target of genetic medications for PD.     

No Association of <Emphasis Type="Italic">LOXL1</Emphasis> Gene Polymorphisms with Alzheimer’s Disease

Aggregation of amyloid-beta is one of the major characteristics in brains of patients with Alzheimer’s disease (AD). Although several mechanisms behind the formation of such aggregates have been suggested the regulatory factors are still unknown. The present study aimed at investigating the association of lysyl oxidase-like 1 (LOXL1) polymorphisms with AD diagnosis and cerebrospinal fluid biomarkers (CSF) for the disease. Proteins of the lysyl oxidase (LOX) family are involved in cross-linking extracellular matrix proteins to insoluble fibers and have been associated with neurodegenerative diseases including AD. Genetic polymorphisms in LOXL1 (rs1048661, rs3825942, and rs2165241) have been linked to exfoliation syndrome and exfoliation glaucoma, conditions that have shown association with AD. The polymorphisms were genotyped by Taqman allelic discrimination in a study sample including AD patients (n = 318) and controls (n = 575). In a subgroup of the population, the polymorphisms were analyzed in relation to APOE ε4 genotype and to CSF (T-tau, P-tau, and Aβ_1–42). No evidence for associations of these polymorphisms with risk for AD or any of the studied CSF biomarkers measured was found. These results do not support LOXL1 as being a major risk gene for AD.     

Alzheimer’s Disease Risk Variant rs2373115 Regulates <Emphasis Type="Italic">GAB2</Emphasis> and <Emphasis Type="Italic">NARS2</Emphasis> Expression in Human Brain Tissues

Genetic association studies have identified significant association between the GAB2 rs2373115 variant and Alzheimer’s disease (AD). However, it is unknown whether rs2373115 affects the regulation of nearby genes. Here, we evaluate the potential effect of rs2373115 on gene expression using multiple eQTL (expression quantitative trait loci) datasets from human brain tissues from the Mayo Clinic brain expression genome-wide association study (eGWAS), the UK Brain Expression Consortium (UKBEC), the Genotype-Tissue Expression (GTEx) project, and the Brain xQTL Serve. Our findings indicate that the rs2373115 C allele is associated with increased NARS2 expression, and both reduced and increased GAB2 expression in human tissues. Using a large-scale AD case-control expression dataset, we found increased GAB2 expression and reduced NARS2 expression in AD cases compared with controls. We believe that our findings provide important information regarding the rs2373115 variant and expression of nearby genes with respect to AD risk.     

A Novel <Emphasis Type="Italic">SYNJ1</Emphasis> Mutation in a Tunisian Family with Juvenile Parkinson’s Disease Associated with Epilepsy

We investigated the effect of a set of SNPs within 5 genes identified by GWASs as possible risk genes for schizophrenia (SCZ) in two independent samples, comprising 176 SCZ patients and 326 controls of Korean origin and 83 SCZ patients and 194 controls of Italian origin. The PANSS was used to assess psychopathology severity and antipsychotic response (AR). Several clinical features were assessed at recruitment. In the Korean sample, the SP4 gene haplotype rs2282888-rs2237304-rs10272006-rs12673091 (p?=?0.02) was associated with SCZ. In the Italian sample, PPP3CC rs11780915 (genotypic: p?=?0.006; allelic: p?=?0.001) and rs2249098 (genotypic: p?=?0.0004; allelic: p?=?0.00006) were associated with SCZ, as well as the PPP3CC rs11780915-rs10108011-rs2249098 and the ZNF804A rs7603001-rs1344706 haplotypes (p?=?0.03 and p?=?0.02). Several RORA variants were associated with AR in both the samples, although only the haplotype rs1020729-rs1871858 in the Korean sample survived to the statistical correction (p?=?0.01). Exploratory analyses suggested that: (1) PPP3CC, ST8SIA2, and SP4 genes may modulate psychotic symptoms, and (2) RORA and ZNF804A genes may influence AR. Our results partially support a role for these genes in SCZ and AR. Analyses in well phenotyped samples may help to refine the role of the genes identified by GWASs.     

Oxidative Stress and <Emphasis Type="Italic">β</Emphasis>-Amyloid Protein in Alzheimer’s Disease

Oxidative stress has been proposed to be an important factor in the pathogenesis of Alzheimer’s disease (AD) and contributed to β-amyloid (Aβ) generation. Interaction between oxidative stress and neuro-inflammation leads to Aβ generation. AD is associated with an increase in blood–brain barrier (BBB) permeability due to tight junction involvement. Oxidative stress decreases the expression of low-density lipoprotein receptor-related protein 1 and up-regulates receptor for advanced glycation end products in BBB and increases the BBB permeability, which could potentially lead to increased deposition of Aβ within AD brain. Apoptosis takes place in the pathogenesis of AD, and oxidative stress contributes to apoptosis through both extrinsic pathway and intrinsic pathway. Oxidative stress-induced apoptosis may be a potential factor to Aβ generation. Aβ generation requires two sequential cleavages of APP, with the two proteolytic enzymes: β-secretase and γ-secretase. Oxidative damage up-regulates Aβ via inducing activity of β- and γ-secretases. In this review, we will focus on the mechanism and pathway that oxidative stress contributes to Aβ generation.     

Variable <Emphasis Type="Italic">PARK2</Emphasis> Mutations Cause Early-Onset Parkinson’s Disease in a Small Restricted Population

Early-onset Parkinson’s disease (EOPD) is less common than the typical adult-onset PD and may be associated with a genetic etiology. Mutations in several genes are known to cause autosomal recessive (AR) PD. This study aimed to detect the etiology of EOPD in consanguineous families or families living in a specific small geographic region in Israel. Six families with EOPD affecting more than a single individual were recruited. Homozygous mapping analysis using a single-nucleotide polymorphism-based array was performed in all families, followed by Sanger sequencing of related genes based on the mapping results. In addition, all families underwent PARK2 sequencing and testing for large deletions and duplications in PD-associated genes. Different truncating mutations were detected in the PARK2 gene among affected individuals of three families: c.996C>A (p.Cys332X) and c.101delA in either homozygous or compound heterozygous fashion. Exon 4 deletion was detected in a heterozygous manner in a late-onset PD and in homozygous state in early-onset disease in the same family. No disease-causing mutations were detected in any other tested genes. In total, mutations in the PARK2 gene were detected in four of the six tested families with a history of EOPD. These results further demonstrate the role of PARK2 in AR PD. We recommend genetic analysis for the PARK2 gene when AR PD is suspected.     

Broadening the phenotype of <Emphasis Type="Italic">TARDBP</Emphasis> mutations: the <Emphasis Type="Italic">TARDBP</Emphasis> Ala382Thr mutation and Parkinson’s disease in Sardinia

Mutations in the TARDBP gene are a cause of autosomal dominant amyotrophic lateral sclerosis (ALS) and of frontotemporal lobar degeneration (FTLD), but they have not been found so far in patients with Parkinson’s disease (PD). A founder TARDBP mutation (p.Ala382Thr) was recently identified as the cause of ~30% of ALS cases in Sardinia, a Mediterranean genetic isolate. We studied 327 consecutive Sardinian patients with clinically diagnosed PD (88 familial, 239 sporadic) and 578 Sardinian controls. One family with FTLD and parkinsonism was also included. The p.Ala382Thr heterozygous mutation was detected in eight unrelated PD patients (2.5%). The three patients from the FTLD/parkinsonism family also carried this mutation. Within the control group, there were three heterozygous mutation carriers. During follow-up, one of these individuals developed motoneuron disease and another, a rapidly progressive dementia; the third remains healthy at the age of 79 but two close relatives developed motoneuron disease and dementia. The eight PD patients carrying the p.Ala382Thr mutation had all sporadic disease presentation. Their average onset age was 70.0 years (SD 9.4, range 51–79), which is later but not significantly different from that of the patients who did not carry this mutation. In conclusion, we expand the clinical spectrum associated with TARDBP mutations to FTLD with parkinsonism without motoneuron disease and to clinically definite PD. The TDP-43 protein might be directly involved in a broader neurodegenerative spectrum, including not only motoneuron disease and FTLD but also PD.     

Attenuation of β-Amyloid Toxicity <Emphasis Type="Italic">In Vitro</Emphasis> and <Emphasis Type="Italic">In Vivo</Emphasis> by Accelerated Aggregation

Accumulation and aggregation of β-amyloid (Aβ) peptides result in neuronal death, leading to cognitive dysfunction in Alzheimer’s disease. The self-assembled Aβ molecules form various intermediate aggregates including oligomers that are more toxic to neurons than the mature aggregates, including fibrils. Thus, one strategy to alleviate Aβ toxicity is to facilitate the conversion of Aβ intermediates to larger aggregates such as fibrils. In this study, we designed a peptide named A3 that significantly enhanced the formation of amorphous aggregates of Aβ by accelerating the aggregation kinetics. Thioflavin T fluorescence experiments revealed an accelerated aggregation of Aβ monomers, accompanying reduced Aβ cytotoxicity. Transgenic Caenorhabditis elegans over-expressing amyloid precursor protein exhibited paralysis due to the accumulation of Aβ oligomers, and this phenotype was attenuated by feeding the animals with A3 peptide. These findings suggest that the Aβ aggregation-promotion effect can potentially be useful for developing strategies to reduce Aβ toxicity.     

Phenotype analysis in patients with early onset Parkinson’s disease with and without <Emphasis Type="Italic">parkin</Emphasis> mutations

The data regarding whether parkin genotype attributes phenotypic variation are conflicting. Since the incidence of parkin mutations is very low in patients with an age at onset (AAO) of >40 years, previous studies have unfairly compared phenotypes of two early onset Parkinson’s disease (EOPD) groups with different AAOs. Thus, we compared the clinical features between patients with and without parkin mutations in EOPD with an AAO of ≤40 years. Of the 124 patients with EOPD with an AAO of ≤40 years who were recruited and screened for parkin mutations, 84 completed assessments for comparison of the phenotype according to parkin genotype. Fourteen of the 84 subjects carried two parkin mutations; 6, a single mutation; and 64, no mutations. Patients with two mutations had significantly younger AAOs, longer duration of PD, and more common family history than patients without parkin mutations. Otherwise, motor and nonmotor symptoms did not differ between them. Subgroup analysis of EOPD with an AAO of ≤35 years revealed similar results. Phenotype of EOPD may depend on early AAOs rather than presence of parkin mutations.