Expression profiling of substantia nigra in Parkinson disease, progressive supranuclear palsy, and frontotemporal dementia with parkinsonism.

BACKGROUND: Parkinson disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra. Genes contributing to rare mendelian forms of PD have been identified, but the genes involved in the more common idiopathic PD are not well understood. OBJECTIVES: To identify genes important to PD pathogenesis using microarrays and to investigate their potential to aid in diagnosing parkinsonism. DESIGN: Microarray expression analysis of postmortem substantia nigra tissue. PATIENTS: Substantia nigra samples from 14 unrelated individuals were analyzed, including 6 with PD, 2 with progressive supranuclear palsy, 1 with frontotemporal dementia with parkinsonism, and 5 control subjects. MAIN OUTCOME MEASURES: Identification of genes significantly differentially expressed (P<.05) using Affymetrix U133A microarrays. RESULTS: There were 142 genes that were significantly differentially expressed between PD cases and controls and 96 genes that were significantly differentially expressed between the combined progressive supranuclear palsy and frontotemporal dementia with parkinsonism cases and controls. The 12 genes common to all 3 disorders may be related to secondary effects. Hierarchical cluster analysis after exclusion of these 12 genes differentiated 4 of the 6 PD cases from progressive supranuclear palsy and frontotemporal dementia with parkinsonism. CONCLUSIONS: Four main molecular pathways are altered in PD substantia nigra: chaperones, ubiquitination, vesicle trafficking, and nuclear-encoded mitochondrial genes. These results correlate well with expression analyses performed in several PD animal models. Expression analyses have promising potential to aid in postmortem diagnostic evaluation of parkinsonism.

Genomic convergence to identify candidate genes for Parkinson disease: SAGE analysis of the substantia nigra.

Genomic convergence is a multistep approach that combines gene expression with genomic linkage to identify and prioritize susceptibility genes for complex disease. As a first step, we previously performed linkage analysis on 174 multiplex Parkinson's disease (PD) families, identifying five peaks for PD risk and two for genes affecting age at onset (AAO) in PD [Hauser et al., Hum Mol Genet 2003;12:671-677]. We report here the next step: serial analysis of gene expression [SAGE; Scott et al., JAMA 2001;286:2239-2242] to analyze substantia nigra tissue from three PD patients and two age-matched controls. We find 933 differentially expressed genes (P<0.05) between PD and controls, but of these, only 50 genes represented by unique SAGE tags map within our previously described PD linkage regions. Furthermore, genes encoded by mitochondrial DNA are expressed 1.5-fold higher in PD patients versus controls, without an increase in the corresponding nuclear-encoded mitochondrial components, suggesting an increase in mtDNA genomes in PD or a disjunction with nuclear expression. The next step in the genomic convergence process will be to screen these 50 high-quality candidate genes for association with PD risk susceptibility and genetic effects on AAO.