Abstract
Multiple system atrophy (MSA) and Parkinson’s disease (PD) are progressive neurodegenerative disorders with overlapping clinical, biochemical and genetic features. To test the hypothesis that the Parkinson’s disease genes parkin and PINK1 also play a role in the pathogenesis of MSA, we performed a mutational screening study involving 87 pathology-proven MSA cases. In parkin we identified eight sequence variants and four heterozygous deletions, and in PINK1 we identified nine variants of which two silent mutations have not been previously reported (p.Gly189Gly and p.Arg337Arg). The frequencies of the observed variants were not significantly different from previously published control data and none of the possibly pathogenic variants were found in a homozygous state. Our results indicate that genetic variants at the parkin and PINK1 loci do not play a critical role in the pathogenesis of MSA.
Keywords: multiple system atrophy, Parkinson’s disease, PINK1, parkin
1. Introduction
Multiple system atrophy (MSA) and Parkinson’s disease (PD) are progressive neurodegenerative disorders with largely unknown molecular pathogeneses. Similarities at the biochemical, clinical and genetic levels between both neurodegenerative diseases are increasingly appreciated. In both disorders deposition of abnormally phosphorylated, fibrillar α-synuclein can be found, - in PD typically in the form of neuronal aggregates called Lewy bodies and in MSA predominantly in the form of glial cytoplasmic inclusions (Spillantini, et al., 1998). MSA and PD present with similar clinical features that are often indistinguishable in early disease stages. Recently, we demonstrated that genetic risk variants at the SNCA locus, coding for α-synuclein, increase risk for both PD and MSA (Scholz, et al., 2008,Scholz, et al., 2009). Taken together, these observations indicate that other genes implicated in the pathogenesis of PD should also be considered as candidates risk genes for MSA.
Homozygous mutations in parkin and PTEN-induced putative kinase 1 (PINK1) are common causes for early-onset PD, and recent evidence suggests that heterozygous mutations may also be relevant in the pathogenesis of late-onset PD (Klein, et al., 2007). To test whether mutations in parkin and PINK1 are involved in the pathogenesis of MSA, we performed mutational screening of parkin and PINK1 in 87 autopsy-proven MSA samples.
2. Methods
We studied 87 Caucasian MSA cases from the Queen Square Brain Bank for Neurological Disorders, London, UK. Control subjects consisted of 276 neurologically normal Caucasian controls in which we have previously screened both parkin and PINK1 (Brooks, et al., 2009). In this control cohort, we observed 15 sequence variants, two heterozygous deletions and one heterozygous duplication in parkin and seven sequence variants in PINK1. None of the control subjects carried a copy number variant in PINK1. In all 87 MSA cases we sequenced the entire coding sequence and the flanking exon-intron boundaries of parkin (NM_004562.1) and PINK1 (NM_0032409.2) using standard methods described elsewhere (Brooks, et al., 2009). Gene dosage for parkin exons 1–12 was determined using 5’-FAM fluorescently labeled probes (Applied Biosystems, CA, USA) on an ABI Prism 7900 Sequence Detection System (Applied Biosystems). The dosage of each parkin exon relative to β-globin and normalized to the control DNA was determined using the 2−ΔΔCt method (Livak and Schmittgen, 2001). We did not screen PINK1 for copy number mutations. Fisher’s exact tests on allelic association of parkin and PINK1 variants between cases and controls were calculated using PLINK software (version 1.04) (Purcell, et al., 2007). A p value of <0.0029 was considered statistically significant (two-sided α of 0.05 divided by 17 tests). The number of copy number changes in MSA cases and in controls was compared using a chi-squared test. The study was approved by the appropriate institutional review boards and written informed consent was obtained for each patient.
3. Results
In this study, we screened parkin and PINK1 in 87 neuropathologically confirmed MSA patients (the results are summarized in the Table and a schematic illustration is shown in Supplementary Fig. 1). No clearly pathogenic homozygous mutations, homozygous copy number changes or compound heterozygous mutations were found in the cases. In parkin we identified eight sequence variants and four heterozygous deletions, and in PINK1 we identified nine sequence variants of which two silent mutations have not been previously reported (c.661C>A = p.Gly189Gly and c.1105C>T = p.Arg337Arg; chromatograms are shown in Supplementary Fig. 2). None of the identified variants were associated with disease after Bonferroni correction for multiple testing. Copy number changes in parkin were not significantly overrepresented in cases versus controls (p value = 0.08).
Table.
Sequence variants at the parkin and PINK1 loci in 87 MSA cases
| Nucleotide Change |
Amino Acid Change |
Location | Mutation Type |
Alleles in Cases |
Alleles in Controls† |
p value |
|---|---|---|---|---|---|---|
| parkin | ||||||
| c.258C>T | p.Arg42Cys | exon 2 | missense | 1 / 175 | 0 / 552 | 0.242 |
| c.272+25C | - | intron 2 | intronic | 34 / 142 | 115 / 437 | 0.747 |
| c.514-20T | - | intron 3 | intronic | 13 / 163 | 44 / 508 | 0.873 |
| c.601G>A | p.Ser167Asn | exon 4 | missense | 2 / 174 | 9 / 543 | 1 |
| c.835G>A | p.Arg234Gln | exon 6 | missense | 1 / 175 | 0 / 552 | 0.242 |
| c.1239G>C | p.Val380Leu | exon 10 | missense | 33 / 143 | 99 / 453 | 0.823 |
| c.1281G>A | p.Asp394Asn | exon 11 | missense | 12 / 162 | 14 / 538 | 0.016 |
| c.1444C>T | p.Pro437Leu | exon 12 | missense | 1 / 175 | 0 /552 | 0.242 |
| PINK1 | ||||||
| c.283C>T | p.Leu63Leu | exon 1 | silent | 36 / 130 | 88 / 464 | 0.101 |
| c.438A>T | p.Gln115Leu | exon 1 | missense | 12 / 154 | 32 / 520 | 0.467 |
| c.482-7A | - | intron 1 | intronic | 21 / 147 | 69 / 483 | 1 |
| c.661C>A | p.Gly189Gly | exon 2 | silent | 1 / 167 | 0 / 552 | 0.233 |
| c. 1054-5G | - | intron 4 | intronic | 20 / 156 | 67 / 485 | 0.894 |
| c.1105C>T | p.Arg337Arg | exon 5 | silent | 1 / 175 | 0 / 552 | 0.242 |
| c.1112G>A | p.Ala340Thr | exon 5 | missense | 9 / 167 | 18 / 534 | 0.257 |
| c.1189C>T | p.Ser365Ser | exon 5 | silent | 1 / 175 | 0 / 552 | 0.242 |
| c.1656A>C | p.Asn521Thr | exon 8 | missense | 53 / 121 | 152 / 400 | 0.499 |
mutational screening results of normal controls have been published elsewhere (see Brooks et al., 2009).
4. Discussion
We report the first comprehensive mutation screening investigating the role of genetic variants in parkin and PINK1 in pathology-proven MSA cases. Clearly pathogenic homozygous mutations were not identified. Although heterozygous variants were relatively common, these alleles/copy number variants were not statistically significantly associated with disease, and their pathogenicity is unproven (Table). We conclude that genetic variants in parkin and PINK1 are not commonly associated with MSA.
Supplementary Material
Acknowledgements
We thank the patients and their families for supporting our research. DNA panels from the NINDS Human Genetics Resource Center DNA and Cell Line Repository (http://ccr.coriell.org/ninds) were used in this study, as well as clinical data. We would like to thank the following submitters that contributed samples to these DNA panels: Drs. Russell Buono, Petra Kaufman, Eric Sorenson, Catherine Lomen-Hoerth, David Simon, John Hardy, Robert Brown, Okun Mandel, Micheline Gravel, Peter Bosch, Paul Gordon, Dennis Dickson, Zbigniew Wszolek, Matthew Farrer, Daniel Newman, Laura Sams, Angela Gresham, Edward Kasarskis, Kapil Sethi, Frederick Wooten, Anthony Crawley, Nickolas Maragakis, Robert Miller, Robert Hamill, Jayaraman Rao, Burton Scott, Ray Watts, and Kevin Boylan. This research was funded in part by the Intramural Research Program of the National Institute on Aging and the National Institute on Neurological Disorders and Stroke, Department of Health and Human Services; project numbers Z01-AG000957-06 (J.A.B, A.J.I., J.D., S.W.S., A.B.S.). We gratefully acknowledge support by the Medical Research Council (MRC) (H.H. G108/638 Clinician Scientist Fellowship; N.W., J.A.H.), the Michael J. Fox Foundation (H.H., J.A.H.), the Reta Lila Weston Institute for Neurological Studies (J.A.H., T.R., A.L., J.H.), the Sarah Matheson Trust for Multiple System Atrophy (H.H., T.R., J.H.), the Alzheimer Research Trust (J.A.H.), the National Organization for Rare Disorders (NORD) (H.H.), Ataxia UK (H.H.) and the Progressive Supranuclear Palsy (Europe) Association (J.A.H., T.R., J.H., A.L.).
Footnotes
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Disclosure statement
All authors have reviewed the contents of the manuscript being submitted, approve of its contents and validate the accuracy of the data. None of the authors has conflicts of interest including any financial, personal or other relationships with other people or organizations within three years of beginning the work submitted that could inappropriately influence (bias) their work. This research has not been previously published, has not been submitted elsewhere and will not be submitted elsewhere while under consideration at Neurobiology of Aging.
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