Pediatric Mitochondrial diseases are a group of disorders relating to the mitochondria, the organelles that are the powerhouses of the eukaryotic cells that comprise higher-order life forms including humans. The mitochondria convert the energy of food molecules into the ATP that powers most cell functions.
Mitochondrial diseases comprise those disorders that in one way or another affect the function of the mitochondria and or are due to mitochondrial DNA. Mitochondrial diseases take on unique characteristics both because of the way the diseases are often inherited and because that mitochondria are so critical to cell function. The subclass of these diseases that have neuromuscular disease symptoms are often referred to as a mitochondrial myopathy.
Mitochondrial inheritance behaves differently from the sort of inheritance that we are most familiar with. Regular nuclear DNA has two copies per cell except for sperm and egg cells. One copy is inherited from the father and the other from the mother. Mitochondria, however, contain their own DNA, and contain typically from five to ten copies, all inherited from the mother (for more detailed inheritance patterns, see mitochondrial genetics). When mitochondria divide, the copies of DNA present are divided randomly between the two new mitochondria, and then those new mitochondria make more copies. As a result, if only a few of the DNA copies inherited from the mother are defective, mitochondrial division may cause most of the defective copies to end up in just one of the new mitochondria. Once more than half of the DNA copies are defective, mitochondrial disease begins to become apparent, this phenomenon is called “threshold expression” (1997, Chinnery).
It should be noted, however, that not all of the enzymes and other components necessary for proper mitochondrial function are encoded in the mitochondrial DNA. Most mitochondrial function is controlled by nuclear DNA instead.................
