Mitochondrial diseases are rare. An average doctor may see a few cases across an entire career, unless they specialise in rare or genetic conditions. Examples include:
- MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes)
- MERRF (myoclonic epilepsy with ragged-red fibers)
- LHON (Leber’s hereditary optic neuropathy)
Mitochondria
Mitochondria are organelles that live inside the cell cytoplasm. They are responsible for producing ATP for the cell.
The number of mitochondria in a cell varies depending on the function of that cell. Myocytes (muscle cells) have thousands of mitochondria, whereas adipocytes (fat cells) have few.
Mitochondria contain their own DNA, separate from the DNA in the cell nucleus. This DNA is arranged in a large circle, unlike the chromosomes found in the nucleus.
Mitochondrial Inheritance
At the time of conception, the sperm carrying the father’s genetic material enters the egg, and the DNA in the nuclei of both cells combines. The vast majority of the mitochondria in that first cell (called the zygote) come from the mother. All the mitochondria in the sperm are in the tail, which does not enter the egg. Therefore, the father almost never contributes any mitochondria to the zygote and, subsequently, the child. Therefore, mitochondrial DNA is primarily from the mother. This is called maternal inheritance.
Not all mitochondria within the mother’s cells will be affected by a specific disease gene. The proportion of affected mitochondria passed to the child will determine whether the individual is affected and the severity of the condition.
Last updated November 2025
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