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What are genetic disorders

Page history last edited by Mark Temple 13 years, 2 months ago

A genetic disorder is a disease caused by abnormalities in an individual’s genome.

The four different types of genetic disorders are:


(1) Single-gene (also called Mendelian or monogenic)

This type is caused by changes or mutations that occur in the DNA sequence of one gene. When a gene is mutated so that its protein product can no longer carry out its normal function, a disorder can result. There are more than 6,000 known single-gene disorders, which occur in about 1 out of every 200 births.

Some examples are:

      cystic fibrosis

     sickle cell anemia

     Marfan syndrome

     Huntington’s disease

     hereditary hemochromatosis.


Single-gene disorders are inherited in recognizable patterns:

     autosomal dominant

     autosomal recessive



(2) Multifactorial (also called complex or polygenic)

This type is caused by a combination of environmental factors and mutations in multiple genes. For example, different genes that influence breast cancer susceptibility have been found on chromosomes 6, 11, 13, 14, 15, 17, and 22.

It's more complicated nature makes it much more difficult to analyze than single-gene or chromosomal disorders. Some of the most common chronic disorders are multifactorial.

Examples include:

     heart disease

     high blood pressure

     Alzheimer’s disease





Multifactorial inheritance also is associated with heritable traits such as fingerprint patterns, height, eye color, and skin color.


(3) Chromosomal

Chromosomes, distinct structures made up of DNA and protein, are located in the nucleus of each cell. Because chromosomes are carriers of genetic material, such abnormalities in chromosome structure as missing or extra copies or gross breaks and rejoinings (translocations) can result in disease. Some types of major chromosomal abnormalities can be detected by microscopic examination. Down syndrome or trisomy 21 is a common disorder that occurs when a person has three copies of chromosome 21.


(4) Mitochondrial

This relatively rare type of genetic disorder is caused by mutations in the nonchromosomal DNA of mitochondria. Mitochondria are small round or rod-like organelles 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.


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