Mitochondria are known as the powerhouse of the cell, this is because they convert the energy from food into a form (Adenosine triphosphate – ATP) that cells can use. Although most of the DNA is present in the chromosomes encased within the nucleus, mitochondria also have some amount of their DNA in them, known as mitochondrial DNA. In some cells, inherited variants in mitochondrial DNA can lead to problems with growth, development and function of the body’s system. The effects of this condition are seen in organs or tissues that require a lot of energy, such as the heart, brain and muscles.