Download What are genetic disorders?

What are genetic disorders?
Both environmental and genetic factors have roles in the development of any disease.
A genetic disorder is a disease caused by abnormalities in an individual’s genetic
material (genome). The four different types of genetic disorders are(1) single-gene,
(2) multifactorial, (3) chromosomal, and (4) mitochondrial.
(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. Genes code for
proteins, the molecules that carry out most of the work, perform most life functions,
and even make up the majority of cellular structures. 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, and hereditary hemochromatosis.
Single-gene disorders are inherited in recognizable patterns: autosomal dominant,
autosomal recessive, and X-linked. More information on the different modes of
inheritance is available from the following Web sites:
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Inheritance of Single Gene Defects - From the The Merck Manual of Diagnosis and
Therapy.
Inheritance Patterns of Monogenic Disorders - From the Genetic Interest Group in
the U.K.
Genetics - From the Medical Encyclopedia at MEDLINEplus.
(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. Its 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, arthritis, diabetes, cancer, and
obesity. 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.
Where can I learn more about different kinds of genetic disorders?
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Genetic Disorder Guide -- Find overviews of genetic disorders, Web portals and
directories, bibliographic databases, support groups, genetic health professionals,
genetic testing laboratories, and clinical trials information. This resource is part of
Gene Gateway, a Web-based guide to learning more about the genes, traits, and
disorders included on the Human Genome Landmarks poster. Order a print copy of
this poster or view it online.
National Organization for Rare Disorders -- NORD, a nonprofit organization, serves
as an international clearinghouse of information on over 5,000 rare disorders. Refer
to their Contact NORD page for telephone, TDD, and other contact information.
Genetic Alliance -- non-profit organization dedicated to helping individuals and
families who have genetic disorders. Tel: 202-966-5557, Fax: 202-966-8553,
[email protected]
Why do we have genes that cause genetic disorders?
Many genes are named for the disorders to which they have been linked. This can be
very confusing. For example, the gene associated with hereditary hemochromatosis is
called the “hemochromatosis gene.” This name implies that the gene exists for the
sole purpose of causing disease, which of course is not the case. The normal function
of a gene is to encode a protein, not cause illness. Disease occurs when genes are
unable to work properly. The hemochromatosis gene actually codes for a membrane
protein that works with other proteins to regulate iron absorption in cells. Like other
single-gene disorders, hemochromatosis occurs when a gene is mutated in a way that
prevents it from encoding a normal, functional protein product. See hereditary
hemochromatosis disorder and gene profiles for more information about this
condition.
Where can I learn more about genes associated with genetic disorders?
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Gene and Protein Database Guide -- A guide to resources for learning about genes
and the proteins they encode. Access gene databases, nucleotide and protein
sequence databases, sequence-similarity search tools, mutation resources, and
molecular structure databases. Find step-by-step instructions for using some of
these resources at the Bioinformatics Tools page.
NIH Genetic Disorders Topical Index -- List of resources by disorder.
NIH Office of Rare Diseases / Genetic and Rare Diseases Information Center -Information on genetic and rare diseases for patients, families, health care
professionals, and biomedical researchers.
Wikipedia Genetic Disorders and List of Genetic Disorders
New York Online Access to Health -- List of resources by disorder.
How does one interpret the diagnosis of a genetic disease? What does it
really mean for everyday life?
If you have been diagnosed with a genetic disease or have been recommended for
genetic testing, your doctor should refer you to a genetic counselor or medical
geneticist. With specialized backgrounds in medical genetics and counseling, genetic
counselors work with medical personnel (usually M.D. medical geneticists) to give
information, answer questions, and offer support to persons and families who have
genetic disorders, are undergoing gene testing, or may be at risk for inheriting genetic
disorders. They conduct one-on-one counseling in helping people understand the
disease, its implications for their lives and the lives of family members, and their
testing and treatment options. For more about what genetic counselors do, see the
Human Genome Project Genetic Counseling page or What is a Genetics
Consultation? provided by GeneTests.
National Resources for Locating Genetic Health Professionals By Area
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National Society of Genetic Counselors - Use ResourceLink.
American Board of Genetic Counseling - Search the Membership Directory, a
combined listing of members of the American Society of Human Genetics, Genetics
Society of America, American College of Medical Genetics, American Board of
Medical Genetics, and American Board of Genetic Counseling. For a list of all
members in a particular city or state, enter the location without entering any names.
Canadian Association of Genetic Counselors
Medical Geneticists are M.D.'s, Ph.D.'s, or M.D.-Ph.D.'s with specialized training in
the diagnosis of genetic disorders. To find a medical geneticist in your region,
contact the American College of Medical Genetics (ACMG) or search the
Membership Directory. For a list of all members in a particular city or state, enter
the location without entering any names.
Where can I learn more about genetic testing --availability,
implications, and background information?
An increasing number of gene tests are becoming available commercially, although
the scientific community continues to debate the best way to deliver them to the
public and to medical communities that are often unaware of their scientific and social
implications. While some of these tests have greatly improved and even saved lives,
scientists remain unsure of how to interpret many of the test results. Also, patients
taking the tests may face significant risks, including jeopardizing their employment or
insurance status. And because genetic information is shared, these risks can extend to
family members as well. To learn more about gene testing, see the following
resources:
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Fact Sheet on Gene Testing from the Human Genome Project Information Web site.
Gene Tests and Testing Laboratories - Access genetic testing resources that provide
listings of laboratories and available tests. Part of the Genetic Disorder Guide at
Gene Gateway.
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What Can the New Gene Tests Tell Us? - Article from the Judges' Journal of the
American Bar Association (1997).
Understanding Gene Testing - Booklet from the National Institutes of Health.
Human Gene Testing - An in-depth look at gene testing from the National Academy
of Sciences Beyond Discovery: The Path from Research to Human Benefit project.
Evaluating Gene Testing - A brief guide from the Human Genome Project
Information Web site.
Clairvoyance and Caution - A chapter written by Nancy Wexler about the the issues
associated with undergoing a predictive test when no prevention or cure exists.
From the book The Code of Codes edited by Daniel Kevles and Leroy Hood. Harvard
University Press, 1992.
Wikipedia: Genetic Testing.
What are some of the ethical, legal, and social implications of being
diagnosed with a genetic disease?
Are patients being properly informed about the risks and limitations of genetic
technology? How does personal genetic information affect an individual and society's
perceptions of that individual? Who owns and controls genetic information? If you are
tested for or diagnosed with a genetic disorder and this information becomes a part of
your medical record, insurance companies, employers, and other agencies mat be able
to access this information. Without adequate legal measures to protect individuals
from misuse of their medical information, individuals diagnosed with certain genetic
conditions potentially could be denied insurance coverage, employment, or other
benefits.
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Ethical, Legal, and Social Issues of the HGP
Your Genes, Your Choices (1997) - An online booklet about the ethical, legal, and
social implications of genome research.
More Information
Genetics Sites
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Genomics and Its Impact on Science and Society: The Human Genome Project and
Beyond (2003) - This primer covers basic science, the Human Genome Project, what
we know so far, ELSI, medicine, benefits, future scientific challenges, and more.
Medicine and the New Genetics - From the Human Genome Project Information
Web site. Includes information about new pharmaceuticals and therapies resulting
from genomic research. The site is designed to help physicians, nurses, genetic
counselors, and other medical personnel keep abreast of genomic medicine.
The Science Behind the Human Genome Project - Basic genetics, genome draft
sequence, and post genome science.
Genome Glossary - A glossary of genetic terms from the U.S. Department of Energy
Human Genome Program.
Genetic Science Learning Center - An excellent source for online multimedia tutorials
and activities covering such topics as basic genetics, chromosomes, genetic
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disorders, cloning, stem cells, and genetic testing. Browser requirements: Internet
Explorer 6, Netscape Navigator 6.x, or Mozilla 1.x.
Dolan DNA Learning Center (DNALC) - This Web site from Cold Spring Harbor
Laboratory has numerous educational tools. DNA Interactive is a multimedia site
dedicated to the discovery of the complementary pairing of DNA bases and the
scientists who contributed to this discovery. Your Genes, Your Health is an online
multimedia encyclopedia of genetic disorders. DNA From the Beginning is a Webbased educational module that covers basic concepts of inheritance through up-tothe-minute methods of DNA analysis. Other resources at this site include an Image
Archive on the American Eugenics Movement; BioServers (bioinformatics tools for
students and teachers); Biology Animation Library; and Restriction Maps and
Nucleotide Sequences of pAMP, pKAN & pBLU Plasmids.
Blazing a Genetic Trail - An introduction to research on mutant genes and hereditary
diseases. Published in 1991 from the Howard Hughes Medical Institute.
To Know Ourselves - An overview of the Human Genome Project published in 1996.
From the U.S. Department of Energy.
Professional Genetics Societies
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The American Society of Human Genetics is the primary professional organization of
human geneticists in North America. Current membership includes medical doctors,
research scientists, and genetic counselors. The society publishes The American
Journal of Human Genetics. Address: 9650 Rockville Pike; Bethesda, MD 20814-3998
(301/571-1825).
The Genetics Society of America publishes the scientific journal Genetics, sponsors
several national meetings each year, and cooperates in organizing an international
congress every 5 years under the auspices of the International Genetic Federation.
Address: 9650 Rockville Pike; Bethesda, MD 20814-3998 (301/571-1825).
The National Society of Genetic Counselors publishes the Journal of Genetic
Counseling and a quarterly newsletter, Perspectives in Genetic Counseling. The
society also sponsors education conferences and offers members a job connection
service. Address: 233 Canterbury Drive; Wallingford, PA 19086 (215/872-7608, Fax: 1192).
This Web site is being continuously updated, and HGMIS appreciates your input.
Please send updates, questions, or comments to [email protected].