It occurs when the mitochondria do not work as well as they should due to another disease or condition.
Dysfunctional mitochondria fail to produce enough energy for cell function and can cause the body to have a “power shortage.” This shortage can affect organ function in any system of the body. As a result, mitochondrial disease takes many forms and is difficult to diagnose. Mutations in this mtDNA, mutations in nuclear DNA (DNA found in the nucleus of a cell) or a combination of both types of mutations can cause mitochondrial disease. Environmental toxins can also trigger Other causes of mitochondrial disease are mutations in genes of the nuclear DNA, whose gene products are imported into the mitochondria (mitochondrial proteins) as well as acquired mitochondrial conditions. Mitochondrial disorders may be caused by mutations, acquired or inherited, in mitochondrial DNA (mtDNA) or in nuclear genes that code for mitochondrial components. They may also be the result of acquired mitochondrial dysfunction due to adverse effects of drugs, infections, or other environmental causes (see MeSH). Mitochondrial diseases take on unique characteristics both because of the way the diseases are often inherited and because mitochondria are so critical to cell function. The subclass of these diseases that have neuromuscular disease symptoms are often called a mitochondrial myopathy. Mitochondrial disorders may be caused by mutations, acquired or inherited, in mitochondrial DNA (mtDNA) or in nuclear genes that code for mitochondrial components. They may also be the result of acquired mitochondrial dysfunction due to adverse effects of drugs, infections, or other environmental causes (see MeSH). Mitochondria are found in every cell of the human body except red blood cells, and convert the energy of food molecules into the ATP that powers most cell functions. Mitochondrial diseases are sometimes (about 15% of the time) caused by mutations in the mitochondrial DNA that affect mitochondrial function. Mitochondrial disorders may be caused by mutations, acquired or inherited, in mitochondrial DNA (mtDNA) or in nuclear genes that code for mitochondrial components. They may also be the result of acquired mitochondrial dysfunction due to adverse effects of drugs, infections, or other environmental causes (see MeSH). 1 Mitochondrial disease includes a group of neuromuscular diseases caused by damage to intracellular structures that produce energy, the mitochondria; disease symptoms usually involve muscle contractions that are weak or spontaneous. 2  There is no specific treatment for mitochondrial diseases (myopathies). *Mitochondiral myopathies facts medical author: Charles Patrick Davis, MD, PhD. 1  Mitochondrial disease includes a group of neuromuscular diseases caused by damage to intracellular structures that produce energy, the mitochondria; disease symptoms usually involve muscle contractions that are weak or spontaneous. Mitochondria are unique in that they have their own DNA called mtDNA. Mutations in this mtDNA, mutations in nuclear DNA (DNA found in the nucleus of a cell) or a combination of both types of mutations can cause mitochondrial disease. Environmental toxins can also trigger mitochondrial disease. Mitochondrial diseases result from failures of the mitochondria, specialized compartments present in every cell of the body except red blood cells. Mitochondria are responsible for creating more than 90% of the energy needed by the body to sustain life and support growth.  A: Mitochondria are tiny parts of almost every cell in your body. Mitochondria are like the power house of the cells. They turn sugar and oxygen into energy that the cells need to work. In mitochondrial diseases, the mitochondria cannot efficiently turn sugar and oxygen into energy, so the cells do not work correctly. Mitochondrial dysfunction occurs when the mitochondria do not work as well as they should due to another disease or condition. Many conditions can lead to secondary mitochondrial dysfunction including autism, Parkinson’s disease, Alzheimer’s disease, muscular dystrophy, Lou Gehrig’s disease, diabetes, and cancer. 
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what causes mitochondrial dysfunction