Mitochondrial diseases are the result of mutations in DNA that alter the function of proteins or RNA that usually reside in mitochondria. Since mitochondria are responsible for producing energy in cells that are needed for the body, mitochondrial diseases involve cell injury and cell death. 

Mitochondrial diseases are often inherited. Symptoms include poor growth, loss of muscle coordination, weakness, visual and auditory issues, learning disabilities, heart, liver, and kidney disease, and neurological issues.

Since the effects can be so varied, mitochondrial disease is seen as a spectrum.