Nuclear aggregates of NONO/SFPQ and A-to-I-edited RNA in Parkinson's disease and dementia with Lewy bodies.

Neurodegenerative diseases are commonly classified as proteinopathies that are defined by the aggregation of a specific protein. Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are classified as synucleinopathies since α-synuclein (α-syn)-containing inclusions histopathologically define these diseases. Unbiased biochemical analysis of PD and DLB patient material unexpectedly revealed novel pathological inclusions in the nucleus comprising adenosine-to-inosine (A-to-I)-edited mRNAs and NONO and SFPQ proteins. These inclusions showed no colocalization with Lewy bodies and accumulated at levels comparable to α-syn. NONO and SFPQ aggregates reduced the expression of the editing inhibitor ADAR3, increasing A-to-I editing mainly within human-specific, Alu-repeat regions of axon, synaptic, and mitochondrial transcripts. Inosine-containing transcripts aberrantly accumulated in the nucleus, bound tighter to recombinant purified SFPQ in vitro, and potentiated SFPQ aggregation in human dopamine neurons, resulting in a self-propagating pathological state. Our data offer new insight into the inclusion composition and pathophysiology of PD and DLB.

De novo FRMD5 Missense Variants in Patients with Childhood-Onset Ataxia, Prominent Nystagmus, and Seizures.

BACKGROUND: FRMD5 variants were recently identified in patients with developmental delay, ataxia, and eye movement abnormalities. OBJECTIVES: We describe 2 patients presenting with childhood-onset ataxia, nystagmus, and seizures carrying pathogenic de novo FRMD5 variants. Weighted gene co-expression network analysis (WGCNA) was performed to gain insights into the function of FRMD5 in the brain. METHODS: Trio-based whole-exome sequencing was performed in both patients, and CoExp web tool was used to conduct WGCNA. RESULTS: Both patients presented with developmental delay, childhood-onset ataxia, nystagmus, and seizures. Previously unreported findings were diffuse choreoathetosis and dystonia of the hands (patient 1) and areas of abnormal magnetic resonance imaging signal in the white matter (patient 2). WGCNA showed that FRMD5 belongs to gene networks involved in neurodevelopment and oligodendrocyte function. CONCLUSIONS: We expanded the phenotype of FRMD5-related disease and shed light on its role in brain function and development. We recommend including FRMD5 in the genetic workup of childhood-onset ataxia and nystagmus. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Alterations in Blood Methylome as Potential Epigenetic Biomarker in Sporadic Parkinson's Disease.

OBJECTIVE: To characterize DNA methylation (DNAm) differences between sporadic Parkinson's disease (PD) and healthy control (HC) individuals enrolled in the Parkinson's Progression Markers Initiative (PPMI). METHODS: Using whole blood, we characterized longitudinal differences in DNAm between sporadic PD patients (n = 196) and HCs (n = 86) enrolled in PPMI. RNA sequencing (RNAseq) was used to conduct gene expression analyses for genes mapped to differentially methylated cytosine-guanine sites (CpGs). RESULTS: At the time of patient enrollment, 5,178 CpGs were differentially methylated (2,683 hypermethylated and 2,495 hypomethylated) in PD compared to HC. Of these, 579 CpGs underwent significant methylation changes over 3 years. Several differentially methylated CpGs were found near the cytochrome P450 family 2 subfamily E member 1 (CYP2E1) gene. Additionally, multiple hypermethylated CpGs were associated with the N-myc downregulated gene family member 4 (NDRG4) gene. RNA-Seq analyses showed 75 differentially expressed genes in PD patients compared to controls. An integrative analysis of both differentially methylated sites and differentially expressed genes revealed 20 genes that exhibited hypomethylation concomitant with overexpression. Additionally, 1 gene, cathepsin H (CTSH), displayed hypermethylation that was associated with its decreased expression. INTERPRETATION: We provide initial evidence of alterations in DNAm in blood of PD patients that may serve as potential epigenetic biomarker of disease. To evaluate the significance of these changes throughout the progression of PD, additional profiling at longer intervals and during the prodromal stages of disease will be necessary. ANN NEUROL 2024;95:1162-1172.

NeuroBooster Array: A Genome-Wide Genotyping Platform to Study Neurological Disorders Across Diverse Populations.

Genome-wide genotyping platforms have the capacity to capture genetic variation across different populations, but there have been disparities in the representation of population-dependent genetic diversity. The motivation for pursuing this endeavor was to create a comprehensive genome-wide array capable of encompassing a wide range of neuro-specific content for the Global Parkinson's Genetics Program (GP2) and the Center for Alzheimer's and Related Dementias (CARD). CARD aims to increase diversity in genetic studies, using this array as a tool to foster inclusivity. GP2 is the first supported resource project of the Aligning Science Across Parkinson's (ASAP) initiative that aims to support a collaborative global effort aimed at significantly accelerating the discovery of genetic factors contributing to Parkinson's disease and atypical parkinsonism by generating genome-wide data for over 200,000 individuals in a multi-ancestry context. Here, we present the Illumina NeuroBooster array (NBA), a novel, high-throughput and cost-effective custom-designed content platform to screen for genetic variation in neurological disorders across diverse populations. The NBA contains a backbone of 1,914,934 variants (Infinium Global Diversity Array) complemented with custom content of 95,273 variants implicated in over 70 neurological conditions or traits with potential neurological complications. Furthermore, the platform includes over 10,000 tagging variants to facilitate imputation and analyses of neurodegenerative disease-related GWAS loci across diverse populations. The NBA can identify low frequency variants and accurately impute over 15 million common variants from the latest release of the TOPMed Imputation Server as of August 2023 (reference of over 300 million variants and 90,000 participants). We envisage this valuable tool will standardize genetic studies in neurological disorders across different ancestral groups, allowing researchers to perform genetic research inclusively and at a global scale.

Genome-wide association study stratified by MAPT haplotypes identifies potential novel loci in Parkinson's disease.

Objective: To identify genetic factors that may modify the effects of the MAPT locus in Parkinson's disease (PD). Methods: We used data from the International Parkinson's Disease Genomics Consortium (IPDGC) and the UK biobank (UKBB). We stratified the IPDGC cohort for carriers of the H1/H1 genotype (PD patients n=8,492 and controls n=6,765) and carriers of the H2 haplotype (with either H1/H2 or H2/H2 genotypes, patients n=4,779 and controls n=4,849) to perform genome-wide association studies (GWASs). Then, we performed replication analyses in the UKBB data. To study the association of rare variants in the new nominated genes, we performed burden analyses in two cohorts (Accelerating Medicines Partnership - Parkinson Disease and UKBB) with a total sample size PD patients n=2,943 and controls n=18,486. Results: We identified a novel locus associated with PD among MAPT H1/H1 carriers near EMP1 (rs56312722, OR=0.88, 95%CI= 0.84-0.92, p= 1.80E-08), and a novel locus associated with PD among MAPT H2 carriers near VANGL1 (rs11590278, OR=1.69 95%CI=1.40-2.03, p=2.72E-08). Similar analysis of the UKBB data did not replicate these results and rs11590278 near VANGL1 did have similar effect size and direction in carriers of H2 haplotype, albeit not statistically significant (OR= 1.32, 95%CI= 0.94-1.86, p=0.17). Rare EMP1 variants with high CADD scores were associated with PD in the MAPT H2 stratified analysis (p=9.46E-05), mainly driven by the p.V11G variant. Interpretation: We identified several loci potentially associated with PD stratified by MAPT haplotype and larger replication studies are required to confirm these associations.

Variants in ATP5F1B are associated with dominantly inherited dystonia.

ATP5F1B is a subunit of the mitochondrial ATP synthase or complex V of the mitochondrial respiratory chain. Pathogenic variants in nuclear genes encoding assembly factors or structural subunits are associated with complex V deficiency, typically characterized by autosomal recessive inheritance and multisystem phenotypes. Movement disorders have been described in a subset of cases carrying autosomal dominant variants in structural subunits genes ATP5F1A and ATP5MC3. Here, we report the identification of two different ATP5F1B missense variants (c.1000A>C; p.Thr334Pro and c.1445T>C; p.Val482Ala) segregating with early-onset isolated dystonia in two families, both with autosomal dominant mode of inheritance and incomplete penetrance. Functional studies in mutant fibroblasts revealed no decrease of ATP5F1B protein amount but severe reduction of complex V activity and impaired mitochondrial membrane potential, suggesting a dominant-negative effect. In conclusion, our study describes a new candidate gene associated with isolated dystonia and confirms that heterozygous variants in genes encoding subunits of the mitochondrial ATP synthase may cause autosomal dominant isolated dystonia with incomplete penetrance, likely through a dominant-negative mechanism.

Melanin and Neuromelanin: Linking Skin Pigmentation and Parkinson's Disease.

Neuromelanin-containing dopaminergic neurons in the substantia nigra pars compacta (SNpc) are the most vulnerable neurons in Parkinson's disease (PD). Recent work suggests that the accumulation of oxidized dopamine and neuromelanin mediate the convergence of mitochondrial and lysosomal dysfunction in patient-derived neurons. In addition, the expression of human tyrosinase in mouse SNpc led to the formation of neuromelanin resulting in the degeneration of nigral dopaminergic neurons, further highlighting the importance of neuromelanin in PD. The potential role of neuromelanin in PD pathogenesis has been supported by epidemiological observations, whereby individuals with lighter pigmentation or cutaneous malignant melanoma exhibit higher incidence of PD. Because neuromelanin and melanin share many functional characteristics and overlapping biosynthetic pathways, it has been postulated that genes involved in skin pigmentation and melanin formation may play a role in the susceptibility of vulnerable midbrain dopaminergic neurons to neurodegeneration. Here, we highlight potential mechanisms that may explain the link between skin pigmentation and PD, focusing on the role of skin pigmentation genes in the pathogenesis of PD. We also discuss the importance of genetic ancestry in assessing the contribution of pigmentation-related genes to risk of PD. © 2022 International Parkinson and Movement Disorder Society.

Genome-wide contribution of common short-tandem repeats to Parkinson's disease genetic risk.

Parkinson's disease is a complex neurodegenerative disorder with a strong genetic component, for which most known disease-associated variants are single nucleotide polymorphisms (SNPs) and small insertions and deletions (indels). DNA repetitive elements account for >50% of the human genome; however, little is known of their contribution to Parkinson's disease aetiology. While select short tandem repeats (STRs) within candidate genes have been studied in Parkinson's disease, their genome-wide contribution remains unknown. Here we present the first genome-wide association study of STRs in Parkinson's disease. Through a meta-analysis of 16 imputed genome-wide association study cohorts from the International Parkinson's Disease Genomic Consortium (IPDGC), totalling 39 087 individuals (16 642 cases and 22 445 controls of European ancestry), we identified 34 genome-wide significant STR loci (P < 5.34 × 10-6), with the strongest signal located in KANSL1 [chr17:44 205 351:[T]11, P = 3 × 10-39, odds ratio = 1.31 (95% confidence interval = 1.26-1.36)]. Conditional-joint analyses suggested that four significant STRs mapping nearby NDUFAF2, TRIML2, MIRNA-129-1 and NCOR1 were independent from known risk SNPs. Including STRs in heritability estimates increased the variance explained by SNPs alone. Gene expression analysis of STRs (eSTRs) in RNA sequencing data from 13 brain regions identified significant associations of STRs influencing the expression of multiple genes, including known Parkinson's disease genes. Further functional annotation of candidate STRs revealed that significant eSTRs within NUDFAF2 and ZSWIM7 overlap with regulatory features and are associated with change in the expression levels of nearby genes. Here, we show that STRs at known and novel candidate loci contribute to Parkinson's disease risk and have functional effects in disease-relevant tissues and pathways, supporting previously reported disease-associated genes and giving further evidence for their functional prioritization. These data represent a valuable resource for researchers currently dissecting Parkinson's disease risk loci.

Novel THAP1 missense variant with incomplete penetrance in a case of generalized young onset dystonia showing good response to deep brain stimulation.

We describe a case of young onset generalized dystonia, harboring a previously unreported likely pathogenic THAP1 missense variant (c.109 G > A; p.Glu37Lys) that was inherited from her unaffected father. Moreover, we report a positive effect of deep brain stimulation, particularly on the cervical component of dystonia.

Novel bi-allelic FBXO7 variants in a family with early-onset typical Parkinson's disease.

Bi-allelic mutations in FBXO7 are classically associated with a complex phenotype, known as parkinsonian-pyramidal syndrome. We describe two brothers affected by typical early onset Parkinson's disease (EOPD), who carry novel compound heterozygous variants in FBXO7. Our report highlights that typical EOPD can be part of an expanding FBXO7-related phenotype.

Gene-based burden analysis of damaging private variants in PRKN, PARK7 and PINK1 in Parkinson's disease cohorts of European descent.

Recessive mutations in PRKN, PARK7, and PINK1 are established causes of early-onset Parkinson's disease (EOPD). Previous studies have interrogated the role of heterozygous variants in these genes but mainly focused on rare (minor allele frequency [MAF] <1%) damaging variants or established mutations. Here, we assessed heterozygous private PRKN, PARK7 and PINK1 variants in PD risk in four large-scale PD case-control datasets by performing gene-wise burden analyses using sequencing data totaling 5,829 PD cases and 7,221 controls, and summary allele counts from 9,501 PD cases and 48,207 controls. Results showed no significant burden in all three genes after meta-analyses. Burden in EOPD (age at onset <50 years) and late-onset PD (≥50 years) remained nonsignificant. In summary, we found no evidence to support the association of the excess burden of heterozygous private variants in PRKN, PARK7, and PINK1 with PD risk in the European population. Larger, more diverse cohorts are needed to accurately determine their role in PD.

Mid51/Fis1 mitochondrial oligomerization complex drives lysosomal untethering and network dynamics.

Lysosomes are highly dynamic organelles implicated in multiple diseases. Using live super-resolution microscopy, we found that lysosomal tethering events rarely undergo lysosomal fusion, but rather untether over time to reorganize the lysosomal network. Inter-lysosomal untethering events are driven by a mitochondrial Mid51/Fis1 complex that undergoes coupled oligomerization on the outer mitochondrial membrane. Importantly, Fis1 oligomerization mediates TBC1D15 (Rab7-GAP) mitochondrial recruitment to drive inter-lysosomal untethering via Rab7 GTP hydrolysis. Moreover, inhibiting Fis1 oligomerization by either mutant Fis1 or a Mid51 oligomerization mutant potentially associated with Parkinson's disease prevents lysosomal untethering events, resulting in misregulated lysosomal network dynamics. In contrast, dominant optic atrophy-linked mutant Mid51, which does not inhibit Mid51/Fis1 coupled oligomerization, does not disrupt downstream lysosomal dynamics. As Fis1 conversely also regulates Mid51 oligomerization, our work further highlights an oligomeric Mid51/Fis1 mitochondrial complex that mechanistically couples together both Drp1 and Rab7 GTP hydrolysis machinery at mitochondria-lysosome contact sites. These findings have significant implications for organelle networks in cellular homeostasis and human disease.

Homozygous might be hemizygous: CRISPR/Cas9 editing in iPSCs results in detrimental on-target defects that escape standard quality controls.

The ability to precisely edit the genome of human induced pluripotent stem cell (iPSC) lines using CRISPR/Cas9 has enabled the development of cellular models that can address genotype to phenotype relationships. While genome editing is becoming an essential tool in iPSC-based disease modeling studies, there is no established quality control workflow for edited cells. Moreover, large on-target deletions and insertions that occur through DNA repair mechanisms have recently been uncovered in CRISPR/Cas9-edited loci. Yet the frequency of these events in human iPSCs remains unclear, as they can be difficult to detect. We examined 27 iPSC clones generated after targeting 9 loci and found that 33% had acquired large, on-target genomic defects, including insertions and loss of heterozygosity. Critically, all defects had escaped standard PCR and Sanger sequencing analysis. We describe a cost-efficient quality control strategy that successfully identified all edited clones with detrimental on-target events and could facilitate the integrity of iPSC-based studies.

Biallelic AOPEP Loss-of-Function Variants Cause Progressive Dystonia with Prominent Limb Involvement.

BACKGROUND: Monogenic causes of isolated dystonia are heterogeneous. Assembling cohorts of affected individuals sufficiently large to establish new gene-disease relationships can be challenging. OBJECTIVE: We sought to expand the catalogue of monogenic etiologies for isolated dystonia. METHODS: After the discovery of a candidate variant in a multicenter exome-sequenced cohort of affected individuals with dystonia, we queried online platforms and genomic data repositories worldwide to identify subjects with matching genotypic profiles. RESULTS: Seven different biallelic loss-of-function variants in AOPEP were detected in five probands from four unrelated families with strongly overlapping phenotypes. In one proband, we observed a homozygous nonsense variant (c.1477C>T [p.Arg493*]). A second proband harbored compound heterozygous nonsense variants (c.763C>T [p.Arg255*]; c.777G>A [p.Trp259*]), whereas a third proband possessed a frameshift variant (c.696_697delAG [p.Ala234Serfs*5]) in trans with a splice-disrupting alteration (c.2041-1G>A). Two probands (siblings) from a fourth family shared compound heterozygous frameshift alleles (c.1215delT [p.Val406Cysfs*14]; c.1744delA [p.Met582Cysfs*6]). All variants were rare and expected to result in truncated proteins devoid of functionally important amino acid sequence. AOPEP, widely expressed in developing and adult human brain, encodes a zinc-dependent aminopeptidase, a member of a class of proteolytic enzymes implicated in synaptogenesis and neural maintenance. The probands presented with disabling progressive dystonia predominantly affecting upper and lower extremities, with variable involvement of craniocervical muscles. Dystonia was unaccompanied by any additional symptoms in three families, whereas the fourth family presented co-occurring late-onset parkinsonism. CONCLUSIONS: Our findings suggest a likely causative role of predicted inactivating biallelic AOPEP variants in cases of autosomal recessive dystonia. Additional studies are warranted to understand the pathophysiology associated with loss-of-function variation in AOPEP. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Dyshomeostatic modulation of Ca2+-activated K+ channels in a human neuronal model of KCNQ2 encephalopathy.

Mutations in KCNQ2, which encodes a pore-forming K+ channel subunit responsible for neuronal M-current, cause neonatal epileptic encephalopathy, a complex disorder presenting with severe early-onset seizures and impaired neurodevelopment. The condition is exceptionally difficult to treat, partially because the effects of KCNQ2 mutations on the development and function of human neurons are unknown. Here, we used induced pluripotent stem cells (iPSCs) and gene editing to establish a disease model and measured the functional properties of differentiated excitatory neurons. We find that patient iPSC-derived neurons exhibit faster action potential repolarization, larger post-burst afterhyperpolarization and a functional enhancement of Ca2+-activated K+ channels. These properties, which can be recapitulated by chronic inhibition of M-current in control neurons, facilitate a burst-suppression firing pattern that is reminiscent of the interictal electroencephalography pattern in patients. Our findings suggest that dyshomeostatic mechanisms compound KCNQ2 loss-of-function leading to alterations in the neurodevelopmental trajectory of patient iPSC-derived neurons.

MED27 Variants Cause Developmental Delay, Dystonia, and Cerebellar Hypoplasia.

The Mediator multiprotein complex functions as a regulator of RNA polymerase II-catalyzed gene transcription. In this study, exome sequencing detected biallelic putative disease-causing variants in MED27, encoding Mediator complex subunit 27, in 16 patients from 11 families with a novel neurodevelopmental syndrome. Patient phenotypes are highly homogeneous, including global developmental delay, intellectual disability, axial hypotonia with distal spasticity, dystonic movements, and cerebellar hypoplasia. Seizures and cataracts were noted in severely affected individuals. Identification of multiple patients with biallelic MED27 variants supports the critical role of MED27 in normal human neural development, particularly for the cerebellum. ANN NEUROL 2021;89:828-833.

Assessing the relationship between monoallelic PRKN mutations and Parkinson's risk.

Biallelic Parkin (PRKN) mutations cause autosomal recessive Parkinson's disease (PD); however, the role of monoallelic PRKN mutations as a risk factor for PD remains unclear. We investigated the role of single heterozygous PRKN mutations in three large independent case-control cohorts totalling 10 858 PD cases and 8328 controls. Overall, after exclusion of biallelic carriers, single PRKN mutations were more common in PD than controls conferring a >1.5-fold increase in the risk of PD [P-value (P) = 0.035], with meta-analysis (19 574 PD cases and 468 488 controls) confirming increased risk [Odds ratio (OR) = 1.65, P = 3.69E-07]. Carriers were shown to have significantly younger ages at the onset compared with non-carriers (NeuroX: 56.4 vs. 61.4 years; exome: 38.5 vs. 43.1 years). Stratifying by mutation type, we provide preliminary evidence for a more pathogenic risk profile for single PRKN copy number variant (CNV) carriers compared with single nucleotide variant carriers. Studies that did not assess biallelic PRKN mutations or consist of predominantly early-onset cases may be biasing these estimates, and removal of these resulted in a loss of association (OR = 1.23, P = 0.614; n = 4). Importantly, when we looked for additional CNVs in 30% of PD cases with apparent monoallellic PRKN mutations, we found that 44% had biallelic mutations, suggesting that previous estimates may be influenced by cryptic biallelic mutation status. While this study supports the association of single PRKN mutations with PD, it highlights confounding effects; therefore, caution is needed when interpreting current risk estimates. Together, we demonstrate that comprehensive assessment of biallelic mutation status is essential when elucidating PD risk associated with monoallelic PRKN mutations.