Background Results of various studies highlighted the role of altered mitochondrial DNA (mtDNA) levels in Huntington’s disease (HD) and other poly-Q disorders, but with contradictory conclusions depending on the cell type.

Aims The aim of this work was to find correlation between mtDNA level determined in two tissue samples of HD patients (blood and fibroblasts) and various parameters of HD severity and haplogroups. Another aim of this study was to find the reason of discrepancies between previously published studies concerning levels of mtDNA in cells of HD patients.

Methods Samples of blood and fibroblasts from 84 HD patients, and 79 controls were analysed for mtDNA levels. The relative mtDNA copy number in leukocytes and fibroblast cultures were determined using real-time quantitative PCR. Haplogroup were determined using a combination of Sanger sequencing and PCR-RFLP. Statistical analysis was performed to searching for correlation between all obtained results.

Results Although the type of haplogroup had no influence on the mtDNA level, and there was no correlation between mtDNA level in leukocytes in HD patients and various parameters of HD severity, some considerable differences between HD patients and controls were found. The average mtDNA/nDNA relative copy number was significantly higher in leukocytes, but lower in fibroblasts, of symptomatic HD patients relative to the control group. Moreover, HD women displayed higher mtDNA levels in leukocytes than HD men.

Conclusions Because of the largest population analysed to date, these results might contribute to explanation of discrepancies between previously published studies. We suggest that a size of the investigated population, kind of cells from which DNA is isolated, and also specific treatments of patients could significantly affect results of mtDNA copy number estimation in HD.

This project is funded by National Research Centre, Poland, No UMO-2011/03/B/NZ2/01422.