Background: Age at onset in Parkinson disease (PD) is a highly heritable quantitative trait for which a significant genetic influence is supported by multiple segregation analyses. Because genes associated with onset age may represent invaluable therapeutic targets to delay the disease, we sought to identify such genetic modifiers using a genomewide association study in familial PD. There have been previous genomewide association studies (GWAS) to identify genes influencing PD susceptibility, but this is the first to identify genes contributing to the variation in onset age. Methods: Initial analyses were performed using genotypes generated with the Illumina HumanCNV370Duo array in a sample of 857 unrelated, familial PD cases. Subsequently, a meta-analysis of imputed SNPs was performed combining the familial PD data with that from a previous GWAS of 440 idiopathic PD cases. The SNPs from the meta-analysis with the lowest p-values and consistency in the direction of effect for onset age were then genotyped in a replication sample of 747 idiopathic PD cases from the Parkinson Institute Biobank of Milan, Italy. Results: Meta-analysis across the three studies detected consistent association (p < 1 × 10-5) with five SNPs, none of which reached genomewide significance. On chromosome 11, the SNP with the lowest p-value (rs10767971; p = 5.4 × 10-7) lies between the genes QSER1 and PRRG4. Near the PARK3 linkage region on chromosome 2p13, association was observed with a SNP (rs7577851; p = 8.7 × 10-6) which lies in an intron of the AAK1 gene. This gene is closely related to GAK, identified as a possible PD susceptibility gene in the GWAS of the familial PD cases. Conclusion: Taken together, these results suggest an influence of genes involved in endocytosis and lysosomal sorting in PD pathogenesis.
Bibliographical noteFunding Information:
This project was supported by R01 NS37167, R01 NS036711, the Robert P. & Judith N. Goldberg Foundation, the Bumpus Foundation and the Harvard NeuroDiscovery Center. This study used samples from the NINDS Human Genetics Resource Center DNA and Cell Line Repository http:// ccr.coriell.org/ninds, as well as clinical data.
Funding support for the Mayo-Perlegen LEAPS (Linked Efforts to Accelerate Parkinson's Solutions) Collaboration Study was provided by the Michael J. Fox Foundation. Additional support was provided by the NIH grants ES10751 and NS33978. The datasets used for the analyses described in this manuscript were obtained from dbGaP found at http:// www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/
Genotyping services were provided by the Center for Inherited Disease Research (CIDR). CIDR is fully funded through a federal contract from the National Institutes of Health to The Johns Hopkins University, contract number HHSN268200782096C. We particularly thank Drs. Kimberly Doheny and Elizabeth Pugh from CIDR and Mr. Justin Paschall from NCBI for their assistance.
DNA samples contributed by the Parkinson Institute - Istituti Clinici di Per-fezionamento, Milan, Italy were from the "Human genetic bank of patients affected by PD and parkinsonisms", supported by Italian Telethon grant n. GTB07001 and by the "Fondazione Grigioni per il Morbo di Parkinson".
A portion of this research was conducted using the Linux Cluster for Genetic Analysis (LinGA-II) funded by the Robert Dawson Evans Endowment of the Department of Medicine at Boston University School of Medicine and Boston Medical Center.