A pathway-based analysis provides additional support for an immune-related genetic susceptibility to Parkinson's disease.
Peter Holmans, Valentina Moskvina, Lesley Jones, Manu Sharma, International Parkinson's Disease Genomics Consortium, Alexey Vedernikov, Finja Buchel, Mohamad Saad, Mohamad Sadd, Jose M Bras, Francesco Bettella, Nayia Nicolaou, Javier Simón-Sánchez, Florian Mittag, J Raphael Gibbs, Claudia Schulte, Alexandra Durr, Rita Guerreiro, Dena Hernandez, Alexis Brice, Hreinn Stefánsson, Kari Majamaa, Thomas Gasser, Peter Heutink, Nicholas W Wood, Maria Martinez, Andrew B Singleton, Michael A Nalls, John Hardy, Huw R Morris, Nigel M Williams
Author Information
Peter Holmans: Department of Psychological Medicine and Neurology, Institute of Psychological Medicine and Clinical Neurosciences, MRC Centre in Neuropsychiatric Genetics and Genomics, Cardiff University School of Medicine, Cardiff CF14 4XN, UK.
Parkinson's disease (PD) is the second most common neurodegenerative disease affecting 1-2% in people >60 and 3-4% in people >80. Genome-wide association (GWA) studies have now implicated significant evidence for association in at least 18 genomic regions. We have studied a large PD-meta analysis and identified a significant excess of SNPs (P < 1 × 10(-16)) that are associated with PD but fall short of the genome-wide significance threshold. This result was independent of variants at the 18 previously implicated regions and implies the presence of additional polygenic risk alleles. To understand how these loci increase risk of PD, we applied a pathway-based analysis, testing for biological functions that were significantly enriched for genes containing variants associated with PD. Analysing two independent GWA studies, we identified that both had a significant excess in the number of functional categories enriched for PD-associated genes (minimum P = 0.014 and P = 0.006, respectively). Moreover, 58 categories were significantly enriched for associated genes in both GWA studies (P < 0.001), implicating genes involved in the 'regulation of leucocyte/lymphocyte activity' and also 'cytokine-mediated signalling' as conferring an increased susceptibility to PD. These results were unaltered by the exclusion of all 178 genes that were present at the 18 genomic regions previously reported to be strongly associated with PD (including the HLA locus). Our findings, therefore, provide independent support to the strong association signal at the HLA locus and imply that the immune-related genetic susceptibility to PD is likely to be more widespread in the genome than previously appreciated.
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