Hi, this is Tom, and in this episode I'm going to be going through

mitochondrial inheritance. And you can find notes at zero to finals.com slash mitochondrial inheritance

and in the zero to finals pediatrics book. And you can find flashcards and questions at

members.0.0 to finals.com. So let's jump straight in. Mitochondrial diseases are rare. An average

doctor may see a few cases across an entire career unless they specialize in rare or genetic

conditions.

Examples include M-E-L-A-S, which stands for mitochondrial, encephalomyopathy, lactic acidosis, and stroke-like episodes, M-E-R-R-F, which stands for myoclonic epilepsy with ragged red fibers, and L-H-O-N, which stands for

Labor's Hereditary Optic Neuropathy. Let's talk about mitochondria. Mitochondria are organelles that live inside the cell

cytoplasm. They're responsible for producing ATP for the cell. ATP is what the cell uses for

energy. The number of mitochondria in a cell varies depending on the function of that cell.

Myocytes or muscle cells, which are very active, have thousands of mitochondria, whereas adipocytes or

fat cells, have very few. Mitochondria contain their own DNA, which is separate and different from the DNA that's found

in the cell nucleus. The mitochondrial DNA is arranged in a large circle, unlike the chromosomes

that are found in the nucleus. Let's talk about 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 of these cells combines. The vast majority of the mitochondria in that first cell, which is called

the zygote, comes from the mother. All the father's mitochondria, which are in the sperm,

are located in the tail of the sperm, which does not enter the egg. Therefore, the father almost never contributes any mitochondria to the zygote and subsequently to the child.

Therefore, mitochondrial DNA is primarily inherited from the mother, and 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 by the mitochondrial disorder and the severity of the condition.

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