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The following glossary includes some of the words you may encounter related to Fragile X Syndrome. We suggest that you review other sources that may be available in order to further your understanding of Fragile X Syndrome.
5 to 40 copies
40 to 54 copies
55 to 200 copies
Although these ranges are most frequently seen, it is possible to receive a result that does not correlate with this chart.
Each species has a specific number of chromosomes; humans have 23 pairs of chromosomes. During fertilization the sperm and egg unite making pairs of chromosomes in the new organism, half the number coming from each parent. Although the basic genetic components of heredity are passed equally, they combine themselves in an almost infinite number of ways. When unexpected changes occur in gene combinations, they are called mutations. These mutations can cause physical malformation due to the absence of a substance the body needs for proper functioning.
The genetic material is deoxyribonucleic acid, or DNA. The DNA in each chromosome is a single, long, thin, continuous molecule and genes are parts of that molecule. DNA is a chain of minute subunits known as nucleotide bases, so each gene includes many bases. Four different kinds of bases exist in the chain, adenine(A), guanine(G), cytosine(C) and thymine(T), and their sequence in a gene determines its properties.
Genes exert their effects through the molecules they produce, known as proteins. Proteins are chains of amino acids and the sequence of bases in the DNA determines the sequence of amino acids in the protein by means of the genetic code. The sequence of amino acids in a protein dictates whether it will become part of the structure of the organism or an enzyme for promoting a particular chemical reaction. Thus, changes in the DNA can produce changes that affect the structure or the chemistry of an organism.
Experiments with recombinant DNA are closely regulated and those involving infectious agents are permitted only under the strictest conditions of containment. In the United States, experimental protocols for the use of somatic cell gene therapy are reviewed by the National Institute of Health (NIH) and the Food and Drug Administration (FDA). The FDA has already approved human drugs and vaccines, diagnostic devices, and food processing enzymes produced through recombinant DNA technology.
Genetic engineering involves the manipulation of deoxyribonucleic acid, or DNA. Important tools in this process are restriction enzymes, which are produced by various species of bacteria. Restriction enzymes can recognize a particular sequence of the chain of chemical units, called nucleotide bases that make up the DNA molecule and cut the DNA at that location. Fragments of DNA generated in this way can be joined using other enzymes called ligases. Restriction enzymes and ligases therefore allow the specific cutting and reassembling of portions of DNA. Also important in the manipulation of DNA are vectors, which are pieces of DNA that can self-replicate (produce copies of themselves) independent of the DNA in the host cell in which they are grown. Examples of vectors include plasmids, viruses, and yeast. These vectors permit the generation of multiple copies of a particular piece of DNA, making this a useful method for generating sufficient quantities of material with which to work. The process of engineering a DNA fragment into a vector is called “cloning,” because multiple copies of an identical molecule are produced.
A mutation can lead to a change in an organism resulting from a chemical change in the structure of the gene. Change will first be reflected in the RNA copy, then in the enzyme or other protein that the RNA supervises, and finally in the appearance of new traits in the living organism. The mutation occurs because of the alteration in one or more base pairs of the DNA molecule, garbling the existing genetic code. In the long DNA strand, it takes only a single different pair of bases to produce a different organism. As with other genes, mutations may be either dominant or recessive. Mutations may result in no change in the organism or produce minimal to drastic alterations.
Genetic tests can identify mutations within genes, and therefore offer accurate diagnosis of patients with single gene disorders. These tests can also identify unaffected carriers of genetic disease or even unaffected individuals before onset of their symptoms.
Children's Hospital's main campus is located in the Lawrenceville neighborhood. Our main hospital address is:
Children’s Hospital of Pittsburgh of UPMC
One Children’s Hospital Way
4401 Penn Ave.
Pittsburgh, PA 15224
In addition to the main hospital, Children's has many convenient locations in other neighborhoods throughout the greater Pittsburgh region.
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