Genetic association of RIT2 rs12456492 polymorphism and Parkinson's disease susceptibility in Asian populations: a meta-analysis

Silencing Parkinson's risk allele Rit2 sex-specifically compromises motor function and dopamine neuron viability

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and arises from dopamine (DA) neuron death selectively in the substantia nigra pars compacta (SNc). Rit2 is a reported PD risk allele, and recent single cell transcriptomic studies identified a major RIT2 cluster in PD DA neurons, potentially linking Rit2 expression loss to a PD patient cohort. However, it is still unknown whether Rit2 loss itself impacts DA neuron function and/or viability. Here we report that conditional Rit2 silencing in mouse DA neurons drove motor dysfunction that occurred earlier in males than females and was rescued at early stages by either inhibiting the DA transporter (DAT) or with L-DOPA treatment. Motor dysfunction was accompanied by decreased DA release, striatal DA content, phenotypic DAergic markers, DA neurons, and DAergic terminals, with increased pSer129-alpha synuclein and pSer935-LRRK2 expression. These results provide clear evidence that Rit2 loss is causal for SNc cell death and motor dysfunction, and reveal key sex-specific differences in the response to Rit2 loss.

Genomic profile of Parkinson's disease in Asians

Parkinson's Disease (PD) has witnessed an alarming rise in prevalence, highlighting the suboptimal nature of early diagnostic and therapeutic strategies. To address this issue, genetic testing has emerged as a potential avenue. In this comprehensive review, we have meticulously summarized the variants associated with PD in Asian populations. Our review reveals that these variants exert their influence on diverse biological pathways, encompassing the autophagy-lysosome pathway, cholesterol metabolism, circadian rhythm regulation, immune system response, and synaptic function. Conventionally, PD has been linked to other diseases; however, our findings shed light on a shared genetic susceptibility among these conditions, implying an underlying pathophysiological mechanism that unifies them. Moreover, it is noteworthy that these PD-associated variants can significantly impact drug responses during therapeutic interventions. This review not only provides a consolidated overview of the genetic variants associated with PD in Asian populations but also contributes novel insights into the intricate relationships between PD and other diseases by elucidating shared genetic components. These findings underscore the importance of personalized approaches in diagnosing and treating PD based on individual genetic profiles to optimize patient outcomes.

Rit2 silencing in dopamine neurons drives a Parkinsonian phenotype

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and arises from dopamine (DA) neuron death selectively in the substantia nigra pars compacta (SNc). Rit2 is a reported PD risk allele, and recent single cell transcriptomic studies identified a major RIT2 cluster in PD DA neurons, potentially linking Rit2 expression loss to a PD patient cohort. However, it is still unknown whether Rit2 loss itself is causative for PD or PD-like symptoms. Here we report that conditional Rit2 silencing in mouse DA neurons drove motor dysfunction that occurred earlier in males than females and was rescued at early stages by either inhibiting the DA transporter (DAT) or with L-DOPA treatment. Motor dysfunction was accompanied by decreased DA release, striatal DA content, phenotypic DAergic markers, DA neurons, and DAergic terminals, with increased pSer129-alpha synuclein and pSer935-LRRK2 expression. These results provide the first evidence that Rit2 loss is causal for SNc cell death and a PD-like phenotype, and reveal key sex-specific differences in the response to Rit2 loss.

Association between RIT2 rs16976358 Polymorphism and Autism Spectrum Disorder in Asian Populations: A Meta-analysis

Background

Recent studies have shown that Ras-like without CAAX2 (RIT2) polymorphism is a susceptible factor for Parkinson's disease (PD) and autism spectrum disorder (ASD). SNP rs12456492 and rs16976358 show the emerging evidence of increased risk of PD and ASD, respectively. A meta-analysis examining the relationship between rs12456492 and PD was reported, but the association between rs16976358 and ASD has not been investigated.

Methods

We searched literature from the databases PubMed, Embase, Google Scholar, ScienceDirect, EBSCOhost, OVID, Web of Science, and Wiley up to February 2021. Three studies including 1160 ASD cases and 1367 controls were eventually enrolled in the meta-analysis based on strict inclusion and exclusion criteria.

Results

All genetics models indicate a significant association between rs16976358 polymorphism and ASD susceptibility (C vs. T: p = 0.001; CC vs. TT: p = 0.001; CT vs. TT: p = 0.009; CC+CT vs. TT: p = 0.001; CC vs. CT+TT: p = 0.001; TT+CC vs. CT: p = 0.013). The results of sensitivity analysis and publication bias of Begg's and Egger's tests were stable in the models of allele (C vs. T), codominant (CC vs. TT), dominant (CC+CT vs. TT), and recessive (CC vs. CT+TT).

Conclusions

Our meta-analysis exhibits that the allele C, CC, and CT genotyping of rs16976358 suggest the risk for ASD, but additional studies using a large sample size and ethnically diverse populations need to be included in the future.

Dynamic control of the dopamine transporter in neurotransmission and homeostasis

The dopamine transporter (DAT) transports extracellular dopamine into the intracellular space contributing to the regulation of dopamine neurotransmission. A reduction of DAT density is implicated in Parkinson's disease (PD) by neuroimaging; dopamine turnover is dopamine turnover is elevated in early symptomatic PD and in presymptomatic individuals with monogenic mutations causal for parkinsonism. As an integral plasma membrane protein, DAT surface expression is dynamically regulated through endocytic trafficking, enabling flexible control of dopamine signaling in time and space, which in turn critically modulates movement, motivation and learning behavior. Yet the cellular machinery and functional implications of DAT trafficking remain enigmatic. In this review we summarize mechanisms governing DAT trafficking under normal physiological conditions and discuss how PD-linked mutations may disturb DAT homeostasis. We highlight the complexity of DAT trafficking and reveal DAT dysregulation as a common theme in genetic models of parkinsonism.

The association between the C-reactive protein gene +1444C/T polymorphism and Parkinson's disease susceptibility in a Chinese population

OBJECTIVE

C-reactive protein (CRP) is increased in Parkinson's disease (PD). The CRP +1444C/T (rs1130864) polymorphism is located in the 3' untranslated region (3'-UTR) and is associated with serum CRP concentrations. We explored the relationship between the CRP +1444C/T polymorphism and susceptibility to PD.

METHODS

A total of 1000 subjects from a Chinese population were recruited into this case-control study, including 500 PD patients and 500 healthy controls. The genotype of the CRP +1444C/T polymorphism was tested by Sanger sequencing, and the Hardy-Weinberg equilibrium (HWE) was assessed in the groups. The odds ratios and 95% confidence intervals were calculated to evaluate the strength of any correlations in allelic, dominant, recessive, and additive genetic models.

RESULTS

The genotypic distribution of the CRP +1444C/T polymorphism was consistent with HWE in controls, and markedly different with cases. The CRP +1444C/T polymorphism was associated with increased PD risk in allelic and dominant models in the overall and male population, but not the female subgroup.

CONCLUSION

The presence of a CRP +1444C/T polymorphism may be associated with an increased risk of PD in our Chinese population. Given the missing support for a role of this SNP in PD in the pre-existing GWAS, the SNP may not be genuinely associated with PD despite some positive candidate gene studies.

Association of RIT2 and RAB7L1 with Parkinson's disease: a case-control study in a Taiwanese cohort and a meta-analysis in Asian populations

Several genome-wide association studies and meta-analyses on Parkinson's disease (PD)-related genes have identified several risk foci in Ras-related genes, particularly among Caucasian individuals. However, the corresponding results have been controversial among Asian individuals. We investigated whether 2 single-nucleotide polymorphisms of Ras-related genes, RIT2 (rs12456492) and RAB7L1 (rs823118), are associated with PD risk in Taiwanese individuals. In addition, we conducted a meta-analysis of all studies related to rs12456492 in Asian populations to resolve inconsistency in this locus. In total, 1103 Taiwanese individuals (588 patients with PD and 515 controls) and 1111 Taiwanese individuals (594 patients with PD and 517 controls) were genotyped for rs12456492 and rs823118. However, we could not confirm the association of rs12456492 and rs823118 with PD. Our current meta-analysis involving the rs12456492(A/G) variant demonstrated that the GG + GA genotypes, GG genotypes, and G allele may be risk factors for PD. RIT2 may increase PD risk in Asian individuals. The discrepancies between Caucasian and Asian populations may be due to differences in geographic region-specific genetic backgrounds and gene-environmental interactions.

Candidate biomarkers for Parkinson's disease

Parkinson's disease (PD) is one of the most common diseases associated with neurodegenerative disorders. It affects 3% to 4% of the population over the age of 65 years. The neuropathological dominant symptoms of PD include the destruction of neurons in the substantia nigra, thus causing striatal dopamine deficiency and the presence of intracellular inclusions that contain aggregates of α‑synuclein. The premature form of PD is familial and is known as early onset PD (EOPD). It involves a small portion of patients with PD, displaying symptoms before the age of 60 years. Although individuals who are suffering from the EOPD may have genetic changes, the molecular mechanisms that differentiate between EOPD and late onset PD (LOPD) remain unclear. Owing to the complexity of discriminating between the different forms, treatment, and management of PD, the identification of biomarkers for early diagnosis seems necessary. For this purpose, many studies have been undertaken for the introduction of several biological molecules through various techniques as potential biomarkers. The main focus of these studies was on α-synuclein. However, there are other molecules that are potential biomarkers, such as microRNAs and peptoids. In this article, we tried to review some of these studies.

Associations of TAP1 genetic polymorphisms with atopic diseases: asthma, rhinitis and dermatitis

Controversial findings have been reported regarding to the effect of the transporter associated with antigen processing 1 (TAP1) polymorphisms exerted on the atopic diseases susceptibility. To gain a better understanding of the effects of TAP1 polymorphisms on the risk of atopic diseases, a retrospective study was carried out to evaluate the association of the most common TAP1 polymorphisms, rs1057141 and rs1135216, with the risk of atopic diseases. From studies published in PubMed, Embase, and Web of Science up to July 2017, ten eligible studies were selected for meta-analysis. The pooled results from rs1135216 polymorphism showed increased risk of atopic diseases in homozygote and recessive comparison. From the subgroup analysis by ethnicity, it was found that rs1135216 polymorphism contributed to atopic diseases susceptibility among Africans in all the five genetic models. Subgroup analysis by atopic types indicated significant association of TAP1 polymorphism rs1135216 with asthma in the allele, dominant and recessive models and with allergic rhinitis in the recessive model. As to rs1057141, increased risk of atopic disease in the allelic, dominant and heterozygous model was found in African population. Overall, this meta-analysis study demonstrated that rs1135216 polymorphism may contribute to atopic diseases susceptibility in Asians and Africans as assessed in this study. However, well designed large-scale case-control studies are needed to confirm such preliminary findings.

MicroRNAs and Target Genes As Biomarkers for the Diagnosis of Early Onset of Parkinson Disease

Among the neurodegenerative disorders, Parkinson's disease (PD) ranks as the second most common disorder with a higher prevalence in individuals aged over 60 years old. Younger individuals may also be affected with PD which is known as early onset PD (EOPD). Despite similarities between the characteristics of EOPD and late onset PD (LODP), EOPD patients experience much longer disease manifestations and poorer quality of life. Although some individuals are more prone to have EOPD due to certain genetic alterations, the molecular mechanisms that differentiate between EOPD and LOPD remains unclear. Recent findings in PD patients revealed that there were differences in the genetic profiles of PD patients compared to healthy controls, as well as between EOPD and LOPD patients. There were variants identified that correlated with the decline of cognitive and motor symptoms as well as non-motor symptoms in PD. There were also specific microRNAs that correlated with PD progression, and since microRNAs have been shown to be involved in the maintenance of neuronal development, mitochondrial dysfunction and oxidative stress, there is a strong possibility that these microRNAs can be potentially used to differentiate between subsets of PD patients. PD is mainly diagnosed at the late stage, when almost majority of the dopaminergic neurons are lost. Therefore, identification of molecular biomarkers for early detection of PD is important. Given that miRNAs are crucial in controlling the gene expression, these regulatory microRNAs and their target genes could be used as biomarkers for early diagnosis of PD. In this article, we discussed the genes involved and their regulatory miRNAs, regarding their roles in PD progression, based on the findings of significantly altered microRNAs in EOPD studies. We also discussed the potential of these miRNAs as molecular biomarkers for early diagnosis.

Ras-like without CAAX 2 (RIT2): a susceptibility gene for autism spectrum disorder

Ras-like without CAAX2 (RIT2) which encodes a GTP-binding protein has recently been reported as a new susceptibility gene for Autism Spectrum Disorders (ASD) in a genome-wide association study. Since the gene is suggested to be involved in the pathogenesis of different neurological diseases, we investigated the association of two single nucleotide polymorphisms (SNP) rs16976358 and rs4130047 of this gene with ASD in Iranian patients. A total of 1004 individuals, comprising 532 ASD cases and 472 healthy subjects participated in this study. Allele frequency analyses showed significant over-presentation of rs16976358-C allele in cases versus controls (P < 0.0001). In addition, rs16976358 CC genotype (OR (95% CI) =3.57(1.72-7.69) and P < 0.0001) and rs4130047 CC genotype (OR (95% CI) =0.64(0.43-0.97) and P = 0.035) were associated with ASD in recessive inheritance model. Besides, haplotype analysis demonstrated an association between the C/T haplotype block (rs16976358/rs4130047) and ASD (OR (95%CI) = 0.44 (0.31-0.62), P < 0.0001). Altogether, our findings provided additional confirmation for the RIT2 gene participation in ASD risk and suggested the rs16976358 variant as a possible genetic risk factor for this disorder.

Polymorphism in MIR4697 but not VPS13C, GCH1, or SIPA1L2 is associated with risk of Parkinson's disease in a Han Chinese population

A large meta-analysis recently identified six new loci associated with risk of PD, but subsequent studies have given discrepant results. Here we conducted a case-control study in a Han Chinese population in an attempt to clarify risk associations in Chinese. Among the four single-nucleotide polymorphisms (SNPs) that we examined - VPS13C-rs2414739, MIR4697-rs329648, GCH1-rs11158026, and SIPA1L2- rs10797576 we detected a significant association between rs329648 and risk of developing PD in a recessive model. This association remained significant after adjusting for gender and age (OR 1.87, 95%CI 1.295-2.694, p=8.21×10^-4) or Bonferroni correction. The T allele of rs329648 occurred significantly more frequently among patients with PD than among healthy controls (OR 1.22, 95%CI 1.033-1.443, p=0.02), while there was no statistic significant after Bonferroni correction. Subgroup analysis showed a significant association specifically among males in a recessive model (OR 1.943, 95%CI 1.200-3.147, p=0.007). In contrast, genotye and allele frequencies at rs329648 did not differ significantly between female patients with PD and healthy female controls, or between patients with early-onset or late-onset PD. Our results suggest that rs329648 is associated with risk of developing PD in the Han Chinese population. Our findings should be verified in further studies, and they highlight the need for functional studies of MIR4697.

Genetic Determinants of Parkinson's Disease: Can They Help to Stratify the Patients Based on the Underlying Molecular Defect?

Parkinson's disease (PD) is a sporadic progressive neurodegenerative brain disorder with a relatively strong genetic background. We have reviewed the current literature about the genetic factors that could be indicative of pathophysiological pathways of PD and their applications in everyday clinical practice. Information on novel risk genes is coming from several genome-wide association studies (GWASs) and their meta-analyses. GWASs that have been performed so far enabled the identification of 24 loci as PD risk factors. These loci take part in numerous cellular processes that may contribute to PD pathology: protein aggregation, protein, and membrane trafficking, lysosomal autophagy, immune response, synaptic function, endocytosis, inflammation, and metabolic pathways are among the most important ones. The identified single nucleotide polymorphisms are usually located in the non-coding regions and their functionality remains to be determined, although they presumably influence gene expression. It is important to be aware of a very low contribution of a single genetic risk factor to PD development; therefore, novel prognostic indices need to account for the cumulative nature of genetic risk factors. A better understanding of PD pathophysiology and its genetic background will help to elucidate the underlying pathological processes. Such knowledge may help physicians to recognize subjects with the highest risk for the development of PD, and provide an opportunity for the identification of novel potential targets for neuroprotective treatment. Moreover, it may enable stratification of the PD patients according to their genetic fingerprint to properly personalize their treatment as well as supportive measures.

Genetic associations of the thyroid stimulating hormone receptor gene with Graves diseases and Graves ophthalmopathy: A meta-analysis

Graves' disease (GD) is a common thyroid disease, and Graves ophthalmopathy(GO) is the most common extra-thyroidal manifestation of GD. Genetic associations of the thyroid stimulating hormone receptor (TSHR) gene with GD and GO have been studied in different population groups for a long time. We aimed to obtain a more precise estimation of the effects of TSHR single nucleotide polymorphisms (SNPs) on GD/GO using a meta-analysis. Publications were searched on Pub Med and EMBASE up to December 30, 2015. Eight studies involving three SNPs (rs179247, rs12101255, and rs2268458), which included 4790 cases and 5350 controls, met the selection criteria. The pooled odds ratios (OR) and the 95% confidence intervals (CI) were estimated. SNPs rs179247 (dominant model [GG + GA vs. AA]: OR = 0.66, 95%CI: 0.61-0.73, P = 0.000, I(2) = 0%) and rs12101255 (dominant model [TT + TC vs. CC]: OR = 1.67, 95%CI: 1.53-1.83, P = 0.000, I(2) = 0%) were significantly associated with GD in all of the genetic models. TSHR rs12101255 and rs2268458 polymorphisms had no association between GO and GD (GD without GO). The results indicate that rs179247 and rs12101255 are likely to be genetic biomarkers for GD. Further studies with different population groups and larger sample sizes are needed to confirm the genetic associations of the TSHR gene with GD/GO.

Possible association of CCDC62 rs12817488 polymorphism and Parkinson's disease risk in Chinese population: a meta-analysis

Conflicting results identifying the association between coiled-coil domain containing 62 (CCDC62) polymorphism, rs12817488, and Parkinson’s disease (PD) have been reported. To clarify whether rs12817488 is related to PD risk in Chinese population, we carried out this meta-analysis by searching literature from PubMed and Embase database regarding this polymorphism. Three eligible studies involving 1616 cases and 1649 controls were included in this meta-analysis. Our results showed statistically significant association between rs12817488 and PD risk in all four genetic models. Stratification by gender revealed similar results in both subgroup in these genetic models except for recessive model, in which rs12817488 was not significantly associated with PD in male subgroup. Unstable result was found in recessive model via sensitivity analysis, and publication bias was observed in recessive model as well, indicating that the pooled result from recessive model should be cautiously treated. Our meta-analysis implicates a possible relationship between rs12817488 and PD risk in Chinese population. Further validation of this association in large sample size study with different gender is warranted.