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• What are genetic disorders?
• Where can I learn more about different kinds of genetic disorders?
• Why do we have genes that cause genetic disorders?
• Where can I learn more about genes associated with genetic disorders?
• How does one interpret the diagnosis of a genetic disease? What does it really mean for everyday life?
• Where can I learn more about genetic testing - availability, implications, and background information?
• What are some of the ethical, legal, and social implications of being susceptible to or diagnosed with a genetic disease?
• More Information

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:

• 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?

• 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. View poster 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, info@geneticalliance.org

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?

• 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

• 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.

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:

• 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.
• 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.

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.

• 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.

Genetics Sites

• 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 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 Web-based educational module that covers basic concepts of inheritance through up-to-the-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

• 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).