Large-scale pathway specific polygenic risk and transcriptomic community network analysis identifies novel functional pathways in Parkinson disease.

Polygenic inheritance plays a central role in Parkinson disease (PD). A priority in elucidating PD etiology lies in defining the biological basis of genetic risk. Unraveling how risk leads to disruption will yield disease-modifying therapeutic targets that may be effective. Here, we utilized a high-throughput and hypothesis-free approach to determine biological processes underlying PD using the largest currently available cohorts of genetic and gene expression data from International Parkinson's Disease Genetics Consortium (IPDGC) and the Accelerating Medicines Partnership-Parkinson's disease initiative (AMP-PD), among other sources. We applied large-scale gene-set specific polygenic risk score (PRS) analyses to assess the role of common variation on PD risk focusing on publicly annotated gene sets representative of curated pathways. We nominated specific molecular sub-processes underlying protein misfolding and aggregation, post-translational protein modification, immune response, membrane and intracellular trafficking, lipid and vitamin metabolism, synaptic transmission, endosomal-lysosomal dysfunction, chromatin remodeling and apoptosis mediated by caspases among the main contributors to PD etiology. We assessed the impact of rare variation on PD risk in an independent cohort of whole-genome sequencing data and found evidence for a burden of rare damaging alleles in a range of processes, including neuronal transmission-related pathways and immune response. We explored enrichment linked to expression cell specificity patterns using single-cell gene expression data and demonstrated a significant risk pattern for dopaminergic neurons, serotonergic neurons, hypothalamic GABAergic neurons, and neural progenitors. Subsequently, we created a novel way of building de novo pathways by constructing a network expression community map using transcriptomic data derived from the blood of PD patients, which revealed functional enrichment in inflammatory signaling pathways, cell death machinery related processes, and dysregulation of mitochondrial homeostasis. Our analyses highlight several specific promising pathways and genes for functional prioritization and provide a cellular context in which such work should be done.

Parkinson's disease polygenic risk score is not associated with impulse control disorders: A longitudinal study.

OBJECTIVE: To examine the relationship between a Parkinson's disease (PD) polygenic risk score (PRS) and impulse control disorders (ICDs) in PD. BACKGROUND: Genome wide association studies (GWAS) have brought forth a PRS associated with increased risk of PD and younger disease onset. ICDs are frequent adverse effects of dopaminergic drugs and are also more frequent in patients with younger disease onset. It is unknown whether ICDs and PD share genetic susceptibility. METHODS: We used data from a multicenter longitudinal cohort of PD patients with annual visits up to 6 years (DIG-PD). At each visit ICDs, defined as compulsive gambling, buying, eating, or sexual behavior were evaluated by movement disorders specialists. We genotyped DNAs using the Megachip assay (Illumina) and calculated a weighted PRS based on 90 SNPs associated with PD. We estimated the association between PRS and prevalence of ICDs at each visit using Poisson generalized estimating equations, adjusted for dopaminergic treatment and other known risk factors for ICDs. RESULTS: Of 403 patients, 185 developed ICDs. Patients with younger age at onset had a higher prevalence of ICDs (p < 0.001) as well as higher PRS values (p = 0.06). At baseline, there was no association between the PRS and ICDs (overall, p = 0.84). The prevalence of ICDs increased over time similarly across the quartiles of the PRS (overall, p = 0.88; DA users, p = 0.99). CONCLUSION: Despite younger disease onset being associated with both higher PRS and ICD prevalence, our findings are not in favor of common susceptibility genes for PD and ICDs.

Paraneoplastic optic neuropathy and cerebellar ataxia with small cell carcinoma of the lung.

Bilateral optic neuropathy and subacute cerebellar ataxia were manifestations of a paraneoplastic neurologic disorder in a woman found to have small cell carcinoma of the lung. Serologic tests revealed a neuronal autoantibody specific for CRMP-5, a 62-kd member of the collapsin response-mediating protein family. Unexplained optic neuropathy in the setting of subacute cerebellar ataxia should cause suspicion of a paraneoplastic disorder and prompt testing for this autoantibody, especially in patients at risk for lung carcinoma.

Expression of N-methyl-D-aspartate receptor subunit mRNAs in the human brain: striatum and globus pallidus.

N-methyl-D-aspartate receptors (NRs) play an important role in basal ganglia function. By using in situ hybridization with ribonucleotide probes, we investigated the regional and cellular distribution of NR subunit mRNA expression in the human basal ganglia: caudate nucleus, putamen, lateral globus pallidus (LGP), and medial globus pallidus (MGP). Analysis of both film autoradiograms and emulsion-dipped slides revealed distinct distribution patterns for each subunit. On film autoradiograms, the signal for NR1, NR2B, and NR2C in the striatum (STR) was higher than in globus pallidus (GP). The NR2D probe gave a stronger signal in GP than in STR. For NR2A we found a signal in all regions. Analysis of emulsion-dipped sections demonstrated that in striatal neurons, the NR2B signal was higher than in GP neurons. In GP neurons, NR2D was more abundant than in striatal neurons. Despite the relatively low signal on film for NR2C in GP, we found a slightly higher signal in GP per neuron than in STR since in the pallidal areas neurons were sparse but intensely labeled. NR1 and NR2A were more evenly distributed over neurons of STR and GP Between the different parts of STR and GP, we observed only minor differences in the expression of NRs. In MGP a subpopulation of neurons exhibiting low NR2D signals could be separated from the majority of neurons showing an intense NR2D signal. Since the physiological properties of NRs are dependent on subunit composition, these data suggest a high degree of regional specialization of NR properties in the human basal ganglia.

Expression of N-methyl-D-aspartate receptor subunit mRNAs in the human brain: hippocampus and cortex.

N-methyl-D-aspartate receptor (NR) activation in the hippocampus and neocortex plays a central role in memory and cognitive function. We analyzed the cellular expression of the five NR subunit (NR1 and NR2A-D) mRNAs in these regions with in situ hybridization and human ribonucleotide probes. Film autoradiograms demonstrated a distinct pattern of hybridization signal in the hippocampal complex and the neocortex with probes for NR1, NR2A, and NR2B mRNA. NR2C and NR2D probes yielded scattered signals without a distinct organization. At the emulsion level, the NR1 probe produced high-density hybridization signals across the hippocampal complex. NR2A mRNA was higher in dentate granule cells and pyramidal cells in CA1 and subiculum compared to hilus neurons. NR2B mRNA expression was moderate throughout, with higher expression in dentate granule cells, CA1 and CA3 pyramidal cells than in hilus neurons. In the hippocampal complex, the NR2C probe signal was not different from background in any region, whereas the NR2D probe signal resulted in low to moderate grain densities. We analyzed NR subunit mRNA expression in the prefrontal, parietal, primary visual, and motor cortices. All areas displayed strong NR1 hybridization signals. NR2A and NR2B mRNAs were expressed in cortical areas and layers. NR2C mRNA was expressed at low levels in distinct layers that differed by region and the NR2D signal was equally moderate throughout all regions. Pyramidal cells in both hippocampus and neocortex express NR1, NR2A, NR2B, and, to a lesser extent, NR2D mRNA. Interneurons or granular layer neurons and some glial cells express NR2C mRNA.

Expression of N-methyl-D-aspartate receptor subunit mRNA in the human brain: mesencephalic dopaminergic neurons.

Evidence is accumulating that glutamate-mediated excitotoxicity plays an important role in neuronal degeneration in Parkinson's disease (PD). In addition, alterations in excitatory amino acid neurotransmission in the basal ganglia contribute to the clinical manifestations of motor dysfunction. However, detailed knowledge of the anatomical distribution and subtype specificity of glutamate receptors in the dopamine neurons of human substantia nigra (SN) has been lacking. In order to test the hypothesis that selective expression of particular N-methyl-D-aspartate receptor (NR) subunit mRNA contributes to the differential vulnerability of specific neuronal populations to excitotoxic injury in PD, we have used a quantitative dual label, in situ hybridization technique with ribonucleotide probes to examine the cellular distribution of NR subunit mRNA in postmortem human mesencephalic dopaminergic neurons from subjects with no known neurological disorder. Analysis of both film autoradiograms and emulsion-dipped sections demonstrated significant labeling of nigral neurons for each NR subunit. Neuronal labeling was most intense for the NR1 and NR2D subunits, with low level labeling for the remaining subunits. In addition, we examined four subregions of the ventral mesencephalon for differential expression of NR subunit mRNA. For all NR subunits, the pars lateralis (PL) exhibited the most intense signal, while neurons of the ventral tier substantia nigra pars compacta (SNpc) failed to demonstrate a preponderance of a particular subunit. These results demonstrate that NRs are expressed to a significant degree in dopaminergic neurons of the SN and that their distribution does not correlate with the characteristic pattern of neuronal degeneration in PD.

Frataxin gene of Friedreich's ataxia is targeted to mitochondria.

Friedreich's ataxia is caused by a triplet repeat expansion in intron 1, a noncoding region of the frataxin gene (X25). We have generated a chimeric gene composed of the frataxin gene fused with the green fluorescent protein (GFP) gene as a reporter. Transfection of the fusion construct into living COS cells revealed that the frataxin-GFP construct localizes to organelles that double-label with 8-(4'-chloromethyl) phenyl-2,3,5,6,11,12,14,15-octahydro-1H,4H,10H-13H-diquinolizin o-8H-xanthylium chloride (CMXRos), a novel mitochondrial dye. Thus, frataxin appears to be a nuclear-encoded mitochondrial protein.

Cellular distribution of NMDA glutamate receptor subunit mRNAs in the human cerebellum.

We have used a quantitative in situ hybridization method with human ribonucleotide probes to examine the regional and cellular distribution of N-methyl-D-aspartate receptor (NMDAR) subunit mRNAs in the human cerebellum. Purkinje cells showed very dense labeling for NMDAR1 mRNA, dense labeling for NMDAR2A mRNA, and moderate labeling for NMDAR2D mRNA, whereas labeling for NMDAR2C mRNA was low. Granule cells showed high hybridization signals for the NMDAR1 and NMDAR2C mRNAs and moderate signals for the NMDAR2A and NMDAR2D mRNAs. In addition intense labeling with the NMDAR2B probe was observed in medium-sized neurons with chromophilic cell bodies in the upper part of the granule cell layer, most likely representing Golgi cells. Neurons in the molecular layer, i.e., basket cells and stellate cells, showed moderate hybridization signals for NMDAR1 and NMDAR2D and low signal for NMDAR2C. Each type of cerebellar neuron analyzed displayed a distinct NMDAR2 subunit profile, suggesting that they are likely to have NMDA receptors with distinct properties.