COX5A and hyperinsulinemic hypoglycemia, familial, 4: In particular, a high rate of apoptosis was observed in skeletal muscle biopsies of single, large-scale mtDNA deletions and MELAS cases, where 34 000 fibres were analysed: apoptosis was observed only in ragged-red fibres, which were presenting with both mitochondrial proliferation and COX-deficiency [149].