Genetic Disorders
Genetic DisordersIntroduction
Genetic Disorders are medical conditions that are caused by an error in a
person's genes. Some of them appear as a birth defect, while others do not
become distinct until later in life. Genetic disorders can range from those that
cause death to those that produce only mild problems, such as color blindness
or an extra pinky. Scientists have distinguished more than 9,000 genetic
disorders. Some are exceptionally rare while others are quite common.
Types of Genetic Disorders
There are three types of genetic disorders. The first one is categorized as
single-gene disorders. A second category of genetic diseases is chromosomal
disorders which involves abnormalities of chromosomes in which too much or
too little chromosome material is present. The third category would be the
multifactorial disorders.
Single-gene disorders result from errors within an individual gene. An
example of one would be Huntington�s disease. This condition affects 1 in
10,000 and usually doesn�t affect the person until they are 30 or 40 years old. A person with this disease develops uncontrolled movements and may have
problems with coordination, thinking, and judgment. A weakening of the
nerve cells in the brain causes these symptoms and later results in death.
Another single-gene disorder is the Tay Sachs Disease. People who
inherit the faulty Tay Sachs gene lack a crucial enzyme that is needed to break
down fatty substances in brain and nerve cells. As a result, these substances
build up in such large quantities that the central nervous system
gradually stops functioning and the person dies. Symptoms usually become
evident within the first six months of life, and most children die before reaching the age of four. 1 in 3,600 people of eastern European Jewish ancestry carry it.
A category of single-gene disorders known as X-linked disorders involves
genes located on the X chromosome, one of the two sex chromosomes. An
example of an X-linked disorder is hemophilia. People with hemophilia usually
lack 1 of the 14 or more proteins called clotting factors that repair a cut or torn blood vessel. Therefore, when they have an injury their bodies are unable to stop bleeding. About 1 in 10,000 men have hemophilia A.
Chromosomal disorders are caused by the presence of an extra or missing
whole or partial chromosome. Down syndrome is the most common, affecting
about 1 in 800 newborns. People with Down syndrome have three copies of
the autosomal chromosome known as number 21 instead of the normal pair of...
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