MITOCHONDRIAl diseases are a group of disorders caused by pathologic dysfunction of the MITOCHONDRIAl respiratory chain. They present with a wide range of clinical expression. Although neurologic impairment is a common manifestation but they can affect other systems, either exclusively or in combination. MITOCHONDRIA are intracellular organelles found in almost all human cells. They are responsible for aerobic metabolism through oxidative phosphorylation, which leads to energy production in the form of adenosine triphosphate (ATP). Each human cell contains on average hundreds to thousands of MITOCHONDRIA. The exception is mature red blood cells, which rely exclusively on anaerobic metabolism and contain no MITOCHONDRIA.