Where can information about genetic counseling be obtained?
The National Center for Education in Maternal and Child Health (NCEMCH) is a major link between sources of information, services and the professional in areas of maternal and child health, including medical genetics. It provides services including responding to requests for information, maintaining a resource center of educational materials, and publishing a variety of guides, directories, bibliographies and newsletters. It publishes A Guide to Selected National Genetic Voluntary Organizations. NCEMCH's address is 3520 Prospect St., N.W., Washington, D.C. 20057. The National Fragile X Foundation also exists with a network of over 50 resource centers throughout the United States and internationally. Its address is 1441 York St., Suite 215, Denver, Colo. 80206, and the telephone number is 1-800-688-8765.
References
Hagerman R.J. (1987). Current Problems in Pediatrics. 17:623-274. Hagerman, R.J. and McKenzie, P. (eds). (1992). The 1992 International Fragile X Conference Proceedings. Spectra Publishing, Dillon, CO.
Hagerman, R.J. and Silverman, AC (eds). (1991). Fragile X Syndrome: Diagnosis, Treatment and Research. Johns Hopkins University Press, Baltimore, MD.
Lachiewicz, A.M., Gullion, C.M., Spiridigliozzi, G.A. and Aylsworth, A.S. (1987). Declining IQs of young males with the fragile X syndrome. American Journal of Mental Retardation 92; (3): 272-278.
Lubs, H.A. (1969). A marker-X chromosome. American Journal of Human Genetics 21:231-278. Meryash, D.L. (1985). The fragile-X syndrome. In: Developmental Handicaps: Prevention and Treatment III. American Association of University Affiliated Programs (AAUAP), Silver Spring, MD. 63-81.
Sherman, S. (1991). Epidemiology. In Hagerman, R.J. and Silverman, AC (eds): Fragile X Syndrome: diagnosis, treatment and research. Johns Hopkins University Press, Baltimore, MD.
Sherman, S., et al. (1985). Further segregation analysis of the fragile X syndrome with special reference to transmitting males. Human Genetics 69:289-299.
Sutherland, G.R. (1979). Factors affecting expression in lymphocyte culture. American Journal of Medical Genetics; 31:125-13.
Turner, G., et al. (1986). Conference report: Second International Workshop on the fragile X and X-linked mental retardation. American Journal of Medical Genetics, 23:11-67.
Verkerk, AJMH, et al. (1991). Identification of a gene (FMR-1) containing a CGG repeat coincident with a breakpoint cluster region exhibiting length variation in fragile X syndrome. Cell; 65:905-914.
Warren, S.T. and Nelson, D.L. Molecular genetics of the fragile X syndrome. In Hagerman, R.J. and McKenzie, P. (eds). (1992). The 1992 International Fragile X Conference Proceedings. Spectra Publishing, Dillon, CO. pp 297-302.
Webb, T. (1986). Editorial comment. American Journal of Medical Genetics. 23:6-10.
Fragile X Syndrome - another view
Fragile X is an inherited condition known to cause intellectual difficulties, which range from mild learning disabilities to severe mental retardation and autism. One of the leading causes of mental retardation, fragile X syndrome affects approximately 1 in 1250 males and 1 in 2000 females. Delayed speech and language are common. Behavioral difficulties such as hyperactivity, a short attention span and poor eye contact also occur frequently. People with fragile X syndrome are generally healthy and live a normal life span. However, associated medical problems may include seizures, recurrent ear infections, and strabismus (a weak eye muscle).People with fragile X syndrome do not have an unusual appearance. Subtle facial features may be present, such as a long face, large ears and a prominent chin. These are often more obvious in adults than in children and in males than in females.Although there is no cure for fragile X syndrome, researchers are studying ways to improve available educational and medical intervention. When the diagnosis is made in a child or in an adult, educational and medical evaluations are recommended to assess a person's particular learning strengths and weaknesses, specific behavioral problems and individual medical needs.
How is Fragile X Syndrome Inherited?
Each cell in the human body has a set of small structures called chromosomes, which contain thousands of genes important in determining how people develop physically and mentally. Genes, in turn, are made of DNA. In May 1991 the gene causing fragile X syndrome was identified and was named FMR-1.One region of this gene varies in length from one person to another. This region, called the CGG repeat region, is quite short in most people and remains approximately the same length when passed from parent to child. Some people have a CGG repeat region which, is somewhat longer than usual. This intermediate length CGG repeat region is called a premutation. People with the premutation, also referred to as carriers, are intellectually normal and show no obvious signs of fragile X syndrome. However, the premutation may expand considerably when passed to a child from his or her mother. When this happens, it becomes a full mutation, which is the cause of developmental delay or mental retardation in fragile X syndrome. Almost all males with the full mutation and approximately half of the females with the full mutation are mentally retarded.Fragile X syndrome is more likely to affect males than females. This is because the FMR-1 gene is located on the X chromosome. Males have one X chromosome and one Y chromosome. Females have two X chromosomes. A father who is a carrier for fragile X syndrome will pass the fragile X premutation to each of his daughters but to none of his sons. For reasons not completely understood, a premutation passed to a daughter from her father does not expand to the size of a full mutation, and she shows no obvious symptoms or signs of the condition.
Children of women with either the premutation or the full mutation have a 50% chance of inheriting the expanded FMR-1 gene. The chance of mental impairment varies, but can occur in both boys and girls.
What Testing Can Be Done to Determine Whether a Person Has Fragile X Syndrome or Is a Carrier?
It is now recommended that direct DNA analysis be done for diagnosis of people with fragile X syndrome and for carrier testing of unaffected relatives. For this test, a small amount of blood is drawn. Direct DNA analysis measures the actual size of the FMR-1 gene to determine whether a person has no mutation, the premutation, or the full mutation.Who Should Be Considered for Fragile X Testing?
In general, specialists are now recommending that the following people be considered for fragile X testing:1. Any child or adult with mental retardation or developmental delay for which there is no known cause
2. Any individual diagnosed as autistic
3. Relatives of a person with unexplained mental retardation or developmental delay
4. Relatives of a person diagnosed with fragile X syndrome
5. Any individual who had fragile X testing prior to the availability of direct DNA analysis and whose results were questionable or inconclusive
If you are uncertain why the fragile X test is being recommended for you or a family member, you should ask your health care provider.Is Prenatal Testing for Fragile X Syndrome Available?
Fragile X syndrome can be diagnosed in an unbom baby during pregnancy. Prenatal fragile X testing is available to any person shown to have the premutation or full mutation.The preferred diagnostic technique is amniocentesis, which is usually done between 14 and 18 weeks of pregnancy. Amniocentesis is the withdrawal of a small amount of amniotic fluid (the water surrounding the developing fetus) from the uterus. The cells in the amniotic fluid sample are then tested by direct DNA analysis, the same test that is done on a blood sample. Couples considering prenatal diagnosis should talk to their health care provider or to a genetic counselor (preferably before becoming pregnant) to discuss the benefits and limitations of existing prenatal techniques.
How Can Genetic Counseling Help?
The information presented is intended as a guide for people considering fragile X testing. Your health care provider can help answer any further questions you may have about fragile X syndrome. Your health care provider may also want to refer you to a geneticist or genetic counselor for the following reasons:1. To review how fragile X is inherited
2. To help you understand why fragile X testing has been suggested for you or a family member
3. To explain your fragile X testing results
4. To explain which other family members may benefit from testing
5. To explain fragile X prenatal testing
6. To discuss your feelings or other concerns
7. To answer any other questions you may have
