Dysregulation of the causative genes for hereditary parkinsonism in the midbrain in Parkinson's disease.

BACKGROUND AND OBJECTIVES: Many hereditary movement disorders with complex phenotypes without a locus symbol prefix for familial PD present as parkinsonism; however, the dysregulation of genes associated with these phenotypes in the SNpc of PD patients has not been systematically studied.

METHODS: Gene set enrichment analyses were performed using 10 previously published genome-wide expression datasets obtained by laser-captured microdissection of pigmented neurons in the SNpc. A custom-curated gene set for hereditary parkinsonism consisting of causative genes (n = 78) related to disorders with a parkinsonism phenotype, but not necessarily idiopathic or monogenic PD, was constructed from the Online Mendelian Inheritance in Man database.

RESULTS: In 9 of the 10 gene expression data sets, gene set enrichment analysis showed that the disease-causing genes for hereditary parkinsonism were downregulated in the SNpc in PD patients compared to controls (nominal P values <0.05 in five studies). Among the 63 leading edge subset genes representing downregulated genes in PD, 79.4% were genes without a locus symbol prefix for familial PD. A meta-gene set enrichment analysis performed with a random-effect model showed an association between the gene set for hereditary parkinsonism and PD with a negative normalized enrichment score value (-1.40; 95% CI: -1.52∼-1.28; P < 6.2E-05).

CONCLUSION: Disease-causing genes with a parkinsonism phenotype are downregulated in the SNpc in PD. Our study highlights the importance of genes associated with hereditary movement disorders with parkinsonism in understanding the pathogenesis of PD. © 2017 International Parkinson and Movement Disorder Society.