Box plots showing the relative difference in distribution of mtDNA copy number per cell between patients with ESRD and healthy control subjects frequency matched for age. Box plots showing the relative difference in distribution of mtDNA copy number per cell between patients with ESRD and healthy control subjects frequency matched for age. (Top) No significant difference (age <50 yr) between the two groups but in older individuals (age ≥50 yr) (bottom), healthy control subjects showed a higher mtDNA copy number than did patients with ESRD (P = 0.001) Madhumathi Rao et al. JASN 2009;20:189-196 ©2009 by American Society of Nephrology