Genetic Disease (cont.)

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Chromosome abnormalities

Chromosomes, distinct structures made up of DNA and protein, are located in the nucleus of each cell. Because chromosomes are the carriers of the genetic material, abnormalities in chromosome number or structure can result in disease. Abnormalities in chromosomes typically occur due to a problem with cell division.

For example, Down syndrome or trisomy 21 is a common disorder that occurs when a person has three copies of chromosome 21. There are many other chromosome abnormalities including:

Diseases may also occur because of chromosomal translocation in which portions of two chromosomes are exchanged.

Mitochondrial inheritance

This type of genetic disorder is caused by mutations in the non-nuclear DNA of mitochondria. Mitochondria are small round or rod-like organelles that are involved in cellular respiration and found in the cytoplasm of plant and animal cells. Each mitochondrion may contain 5 to 10 circular pieces of DNA. Since egg cells, but not sperm cells, keep their mitochondria during fertilization, mitochondrial DNA is always inherited from the female parent.

Examples of mitochondrial disease include:

  • an eye disease called Leber's hereditary optic atrophy;
  • a type of epilepsy called MERRF which stands for myoclonic epilepsy with Ragged Red Fibers; and
  • a form of dementia called MELAS for mitochondrialencephalopathy, lactic acidosis and stroke-like episodes.
Medically Reviewed by a Doctor on 1/15/2014

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