[Analysis of the relationship between mitochondrial DNA deletion and clinical complexity of mitochondrial disease]

To analyze the relationship between proportion of mitochondrial DNA 4 977 bp deletion (ΔmtDNA(4977)) or copy number in blood and the clinical complexity to find the pathogenesis of mitochondrial disease.

A total of 160 patients with mitochondrial disease and 101 healthy controls of Peking University First Hospital from December 2003 to December 2013 were collected in this study. Their peripheral blood showed no hot-point mutation which detected by polymerase chain reaction-restriction fragment length polymorphism. All the patients were divided into younger group (age<10y) and elder group (10y≤age<20y). The incidence of ΔmtDNA(4977) was detected by real-time quantitative PCR. Internal gene was used to calculate the number of mitochondrial DNA in each cell. Statistical analysis were carried out by the independent t-test, one-way ANOVA and Spearman's bivariate correlation analysis.

ΔmtDNA (4977) proportion in the younger group was (2.66 ± 0.63)% and in the elder group was (3.09 ± 0.74)%, both of them were higher than that of healthy control group with the same age (the younger group: t=8.57, P<0.01; the elder group: t=4.38, P<0.01); ΔmtDNA(4977) copy number per cell in the younger group was (2.79 ± 0.50) copy and in the elder group was (2.97 ± 0.48) copy, both of them were higher than that of healthy control group with the same age (the younger group: t=4.50, P<0.01; the elder group: t=-3.67, P<0.01). The ΔmtDNA (4977) proportion was positively correlated with the complexity of the mitochondrial disease(the younger group: r=0.519, P<0.01; the elder group: r=0.772, P<0.01). The ΔmtDNA (4977) copy number per cell was positively correlated with the complexity of the mitochondrial disease(the younger group: r=0.389, P<0.01; the elder group: r=0.607, P<0.05). However, the total mtDNA copy number per cell was negatively correlated with the complexity of the mitochondrial disease (the younger group: r=-0.260, P<0.01; the elder group: r=-0.430, P<0.05).

The proportion or copy number of ΔmtDNA (4977) or total mtDNA copy number in blood are correlated with the complexity of mitochondrial diseases, especially the proportion of ΔmtDNA (4977).