Mitochondrial diseases result from failures of the mitochondria, specialized compartments present in every cell in the body except red blood cells. Mitochondria are responsible for creating 90% of the energy needed by the body to sustain life and support growth. When they fail, less and less energy is generated in the cell. Cell injury and even death follow. If this process is repeated throughout the body, whole systems begin to fail, and the life of the person in whom this is happening is severely compromised. The disease primarily affects children, but adult onset is becoming more and more common.
Diseases of the mitochondria appear to cause the most damage to cells of the brain, heart, liver, skeletal muscles, kidney and the endocrine and respiratory systems.
Source: United Mitochondrial Disease Foundation