Lack of evidence for association of UQCRC1 with Parkinson's disease in Europeans

Rare variant analysis of UQCRC1 in Chinese patients with early-onset Parkinson's disease

Mitochondrial ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) gene has been identified as a causative gene for autosomal dominant Parkinson's disease (PD), with the p.Y314S variant potentially associated with polyneuropathy in PD patients. The objectives of our study were to screen for UQCRC1 variants in Chinese patients with early-onset PD (EOPD) and explore the role of UQCRC1 in EOPD. We investigated the rare variants in 913 EOPD patients in our cohort using whole-exome sequencing, assessing their link to PD at both allele and gene levels. A total of 7 rare variants (minor allele frequency < 0.1%) of UQCRC1 were identified. However, no excessive burden of rare UQCRC1 variants was suggested in the EOPD patients. Further analysis with larger sample size and diverse regions is needed to determine the role of UQCRC1 in PD.

Genetic Movement Disorders Commonly Seen in Asians

The increasing availability of molecular genetic testing has changed the landscape of both genetic research and clinical practice. Not only is the pace of discovery of novel disease-causing genes accelerating but also the phenotypic spectra associated with previously known genes are expanding. These advancements lead to the awareness that some genetic movement disorders may cluster in certain ethnic populations and genetic pleiotropy may result in unique clinical presentations in specific ethnic groups. Thus, the characteristics, genetics and risk factors of movement disorders may differ between populations. Recognition of a particular clinical phenotype, combined with information about the ethnic origin of patients could lead to early and correct diagnosis and assist the development of future personalized medicine for patients with these disorders. Here, the Movement Disorders in Asia Task Force sought to review genetic movement disorders that are commonly seen in Asia, including Wilson's disease, spinocerebellar ataxias (SCA) types 12, 31, and 36, Gerstmann-Sträussler-Scheinker disease, PLA2G6-related parkinsonism, adult-onset neuronal intranuclear inclusion disease (NIID), and paroxysmal kinesigenic dyskinesia. We also review common disorders seen worldwide with specific mutations or presentations that occur frequently in Asians.

UQCRC1 variants in early-onset and familial Parkinson's disease in a Taiwanese cohort

Background

A recent Taiwanese study reported variants of the ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) gene linked to autosomal dominant parkinsonism with polyneuropathy. This study investigated the pathogenicity of UQCRC1 in a Taiwanese cohort of patients with Parkinson's disease (PD).

Method

This study involved 107 participants (98 with early-onset PD and nine with familial PD). All UQCRC1 coding exons and exon-intron boundaries were sequenced. The rarity and pathogenicity of the identified variants were analyzed. The carrier frequencies of our cohort and the Taiwan Biobank were compared through a Pearson's χ² or Fisher's exact test along with Bonferroni corrections.

Results

Three missense variants (c.643G > C, p.D215H; c.800C > G, p.P267R, and c.923A > G, p.N308S) and seven rare variants were identified. No significant differences in the missense-variant carrier frequency were noted between our cohort and individuals in the Taiwan Biobank. Furthermore, no significant associations were noted between the variants and the risk of PD.

Conclusions

Our study is not supporting a role of UQCRC1 variants in PD.

A genome on shaky ground: exploring the impact of mitochondrial DNA integrity on Parkinson's disease by highlighting the use of cybrid models

Mitochondria play important roles in the regulation of key cellular processes, including energy metabolism, oxidative stress response, and signaling towards cell death or survival, and are distinguished by carrying their own genome (mtDNA). Mitochondrial dysfunction has emerged as a prominent cellular mechanism involved in neurodegeneration, including Parkinson’s disease (PD), a neurodegenerative movement disorder, characterized by progressive loss of dopaminergic neurons and the occurrence of proteinaceous Lewy body inclusions. The contribution of mtDNA variants to PD pathogenesis has long been debated and is still not clearly answered. Cytoplasmic hybrid (cybrid) cell models provided evidence for a contribution of mtDNA variants to the PD phenotype. However, conclusive evidence of mtDNA mutations as genetic cause of PD is still lacking. Several models have shown a role of somatic, rather than inherited mtDNA variants in the impairment of mitochondrial function and neurodegeneration. Accordingly, several nuclear genes driving inherited forms of PD are linked to mtDNA quality control mechanisms, and idiopathic as well as familial PD tissues present increased mtDNA damage. In this review, we highlight the use of cybrids in this PD research field and summarize various aspects of how and to what extent mtDNA variants may contribute to the etiology of PD.

Monogenic Parkinson’s Disease: Genotype, Phenotype, Pathophysiology, and Genetic Testing

Parkinson’s disease may be caused by a single pathogenic variant (monogenic) in 5–10% of cases, but investigation of these disorders provides valuable pathophysiological insights. In this review, we discuss each genetic form with a focus on genotype, phenotype, pathophysiology, and the geographic and ethnic distribution. Well-established Parkinson’s disease genes include autosomal dominant forms (SNCA, LRRK2, and VPS35) and autosomal recessive forms (PRKN, PINK1 and DJ1). Furthermore, mutations in the GBA gene are a key risk factor for Parkinson’s disease, and there have been major developments for X-linked dystonia parkinsonism. Moreover, atypical or complex parkinsonism may be due to mutations in genes such as ATP13A2, DCTN1, DNAJC6, FBXO7, PLA2G6, and SYNJ1. Furthermore, numerous genes have recently been implicated in Parkinson’s disease, such as CHCHD2, LRP10, TMEM230, UQCRC1, and VPS13C. Additionally, we discuss the role of heterozygous mutations in autosomal recessive genes, the effect of having mutations in two Parkinson’s disease genes, the outcome of deep brain stimulation, and the role of genetic testing. We highlight that monogenic Parkinson’s disease is influenced by ethnicity and geographical differences, reinforcing the need for global efforts to pool large numbers of patients and identify novel candidate genes.