There are five enzyme-protein complexes in the respiratory chain. The majority are encoded by nuclear DNA and transported across the mitochondrial membrane. Mitochondrial DNA encodes the rest. Since mitochondria and their DNA are maternally-transmitted, these defects are passed down from a mother to her children. There appears to be preferential involvement of myocytes and neurons, cells known for their terminal differentiation.
Mitochondrial function declines with age.
It generally occurs sporadically in the population since large deletions are not viable and are not transmitted. This may give ragged red fibers . Type 1 fibers usually store lipids in small amounts. Mitochondrial oxidative metabolism requires transport of fatty acids into the mitochondrial matrix. Carrier deficiency limits transport and impairs respiration.