Contents
Introduction
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 Huntingtons disease. This condition affects 1 in
10,000 and usually doesnt 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
number 21 chromosomes. They usually have mild to severe learning disabilities. They also have physical traits that include a small skull, an extra fold of skin at the inner corner of each eye, a flattened bridge of the nose, and a large, protruding tongue.
A person with Klinefelter syndrome, which affects about 1 in 500 males,
has two X chromosomes and one Y chromosome. Males with Klinefelter
syndrome are typically tall, and they may have some feminine characteristics.
They also may have minor problems with learning and are usually infertile.
Another chromosomal disorder is Turner syndrome. It affects 1 in 2,500
to 5,000 females. In this disorder, a female has one functioning X chromosome
instead of two. Characteristics of females with this condition are typically
short, with a thick, webbed neck. They may have mild problems with learning,
and they usually are infertile because they lack normal ovaries.
Genetic Screening
There are many different types of genetic screening. Clinical geneticists
can use several screening tests to determine whether a person has a genetic
disorder or is at risk of having a child with a genetic disorder. Some are
routine when a baby is born. Among adults they are completely voluntarily.
Treatments for Genetic Disorders
There are no permanent cures for genetic disorders but there are treatments that are available. Most genetic disorders are treated using more than one type of treatment, because of their complex and varied symptoms. For example, children with cystic fibrosis usually take pancreatic enzymes that help digest food and inhale medicines. These are formulated to break up mucus in air passages. Parents of these children regularly pat their chest and back to loosen mucus in the lungs. In some instances, surgeons may perform a lung transplantation to save a patient’s life.
Gene therapy will eventually cure some diseases in the future. Gene therapy alters the genetic makeup of certain cells and it was first used in 1990 to treat children with an ADA deficiency. Children with this deficiency cannot develop normally due to a poor immune system. They lack the immunity to fight off infections and typically die within the first years of life. In experiments
using gene therapy, a modified virus was used to carry a normal ADA gene to the patient’s immune cells. It led to normal immune function in those cells. Gene therapy has also produced promising results in treating a rare
immunologic disorder called chronic granulomatous disease, and there is hope
in the treatment of cystic fibrosis and hemophilia for the future.
