DGGE investigations illustrating the detection of heteroplasmic and homoplasmic sequence variations of the mitochondrial cytochrome b gene. The arrow shows destabilizing sequence variations in a heteroplasmic state in the index patient (P5) who presented with dCMP (H: homoduplexes, h: heteroduplex) and homoplasmic patterns in the other patients with dCMP (P1 to P4 and P6 to 23).