Assessment of the mitochondrial network morphology. (A) Representative micrographs of cells with different mitochondrial network morphology. The different categories are indicated. Arrow heads accentuate tubular structures in the mitochondrial network classified as "intermediate". Scale bar, 20 μm. (B) Cells have been classified by two independent qualified persons in a blinded experiment with a third person taking the micrographs (n > 100 for each group). The number of cells that exhibit tubular mitochondrial network morphology is reduced in patients' fibroblasts compared to a control. (C) Amplification of a 12.5 kb mtDNA fragment did not reveal any specific mtDNA deletions for patients or controls. Ntc - non template control.