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PCR analysis of platelet mtDNA: lack of specific changes in Parkinson's disease
M S Sandy1, J W Langston, M T Smith
1California Parkinson's Foundation, San Jose 95128.
Abstract:
An alteration within the mitochondrial DNA (mtDNA) has been hypothesized to underlie the deficiencies in mitochondrial complex I activity observed in the platelets, striatal muscle, and brain tissue of individuals with Parkinson's disease. Here we utilized the polymerase chain reaction (PCR) to analyze mtDNA obtained from the platelets of nonmedicated patients with early Parkinson's disease (n = 8) and aged-matched controls (n = 6) for the presence of deletion(s) or addition(s) equal to or greater than 50-100 base pairs. Initial attention was focused upon detecting a 4.977 kb deletion previously found in the brains of parkinsonian patients and some aged controls. Indeed, a large deletion of approximately 5.0 kb was observed in the platelet mtDNA from all parkinsonian individuals. However, this defect was also found in all age-matched controls as well as in a group of young healthy subjects (n = 5). In addition, we searched for the presence of smaller changes in platelet mtDNA from parkinsonian patients by PCR analysis of four mtDNA segments that code for seven of the complex I polypeptides. No large deletions or additions were detected within these four regions of mtDNA in any of the disease or age-matched control samples. We conclude that (a) a 4.977 kb deletion is apparently present in a subpopulation of platelet mtDNA from all individuals, and (b) no macrosequence alteration in mtDNA is likely to underlie the deficiency in complex I activity reported in platelet mitochondria from parkinsonian patients.
Insights
Mitochondrial DNA (mtDNA) large deletions are common in Parkinson's disease patients and controls, suggesting they do not cause complex I deficiency. Further analysis found no significant mtDNA alterations in Parkinson's patients.
Area of Science:
- Neuroscience
- Genetics
- Biochemistry
Background:
- Mitochondrial dysfunction, specifically complex I deficiency, is implicated in Parkinson's disease (PD).
- Alterations in mitochondrial DNA (mtDNA) have been hypothesized as a cause for this deficiency in PD patients.
- Previous studies noted a specific large deletion in brain mtDNA of PD patients.
Purpose of the Study:
- To investigate the presence of large deletions or additions in platelet mtDNA of early-stage Parkinson's disease patients.
- To determine if a previously identified 4.977 kb deletion in brain mtDNA is also present in platelet mtDNA and if it correlates with PD.
- To analyze for smaller mtDNA alterations in platelet complex I genes in PD patients.
Main Methods:
- Polymerase chain reaction (PCR) was used to analyze platelet mtDNA from nonmedicated PD patients and age-matched controls.
- Specific primers were used to detect a 4.977 kb deletion and to amplify four mtDNA segments encoding complex I polypeptides.
- Analysis focused on deletions or additions greater than or equal to 50-100 base pairs.
Main Results:
- A large deletion of approximately 5.0 kb was detected in platelet mtDNA of all PD individuals, but also in all age-matched controls and young healthy subjects.
- No large deletions or additions were found in the analyzed mtDNA segments of complex I genes in any PD or control samples.
- The 4.977 kb deletion appears to be a common finding in platelet mtDNA across all studied groups.
Conclusions:
- The 4.977 kb deletion is present in a subpopulation of platelet mtDNA in all individuals, regardless of Parkinson's disease status.
- Large sequence alterations in mtDNA are unlikely to be the primary cause of the complex I activity deficiency observed in platelet mitochondria of Parkinson's disease patients.