The mitochondrion (mitochondria) is an organelle found in cells. Unlike other organelles, the mitochondrion has its own DNA, known as mitochondrial DNA (henceforth mtDNA), and divides and proliferates independently. Among many functions of mitochondria, the most prominent and well-elucidated function is ATP production, using nutrients gained from decomposed materials from food sources, like rice (carbohydrates and glucide), fish, and meat (protein and fat). ATP is an energy source that is important to maintain the activities of our body. Mitochondria produce an astounding portion, ~90% or more, of the energy used in our body.
Mitochondrial disease is caused by dysfunctional mitochondria, which have abnormal mtDNA or nuclear DNA. Cells with such mitochondria cannot gain sufficient energy and therefore deteriorate. Further worsening of mitochondrial function leads to cell death.
Organs that require a lot of energy suffer more serious damage, making the brain and muscles the most vulnerable (encephalomyopathy). Furthermore, mitochondrial diseases can cause problems in many organs, such as the eyes, ears, heart, liver, digestive tract, kidneys, endocrine system (thyroid gland and spleen), and blood. Thus, there are many types of mitochondrial diseases.