Causes and Symptoms (Magill’s Medical Guide, Sixth Edition)
Congenital disorders can be the result of genetic factors, environmental exposure, infection during pregnancy, or a deficiency or lack of a substance required for proper fetal development.
Genetic defects include defective genes, extra chromosomal material, and missing chromosomal material. Examples of defects from a single gene include Huntington’s disease, cystic fibrosis, and Tay-Sachs disease. Huntington’s disease is caused by an autosomal dominant gene (inheritance of the disease from one parent will produce the disease). Cystic fibrosis and Tay-Sachs disease are autosomal recessives (inheritance of the gene from both parents is necessary for expression of the disease). Huntington’s disease is a progressive and fatal deterioration of the central nervous system with an onset in middle age. Patients with cystic fibrosis produce excessive mucus in their lungs, pancreas, and other secretory organs. The secretions in the lungs clog respiratory passages, causing pulmonary damage, and subject the patient to life-threatening infection. Secretions in the pancreas prevent the flow of enzymes into the intestines and damage the pancreatic islet cells, resulting in diabetes. Tay-Sachs disease is a fatal disorder in which a fatty substance known as ganglioside GM2 builds up in tissues and nerve cells in the brain. Even with meticulous medical care, death usually occurs by age four.
In some types of defects due to...
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Treatment and Therapy (Magill’s Medical Guide, Sixth Edition)
As is the case with all disorders, prevention is preferable to treatment. Avoidance of harmful substances during pregnancy (mind-altering drugs, alcohol, and tobacco) is essential; adequate nutrition, including vitamin supplements, is extremely important. Exposure to infectious agents (rubella, HIV, syphilis) should be avoided. Certain medications can increase the risk of birth defects, such as isotretinoin (Accutane) and etretinate (Tegison) for the treatment of acne and phenytoin (Dilantin) and carbamezapine (Tegretol) for the treatment of epilepsy. Any woman who is pregnant or contemplating pregnancy should consult a health care professional in regard to any medication, prescription or nonprescription.
Screening tests such as the triple test are blood tests that can screen for genetic abnormalities. Chorionic villus sampling (CVS) and amniocentesis can definitively diagnose genetic abnormalities. These tests can diagnose disorders such as Down syndrome and trisomy 18. Single-gene defects can also be diagnosed with CVS or amniocentesis, particularly in cases where a family history of the defect is present. Prenatal diagnosis allows the parents the ability to choose whether to continue with the pregnancy. If they opt to continue with the pregnancy, it gives them time to seek counseling and join support groups to help them cope with caring for a child with a genetic abnormality.
Treatment for congenital disorders...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Genetic disorders have been recognized for centuries; however, the genetic basis was not understood until the latter half of the twentieth century. Down syndrome and cystic fibrosis are two typical examples. English physician John Down noted that Down syndrome was a specific type of mental disability with distinct physical features. For centuries, the foreheads of children with cystic fibrosis were licked; if a salty taste was noted, the child was deemed to be bewitched and expected to die soon. It was not until the 1990’s that the mutated gene that caused the disease was identified.
In addition to Down syndrome and cystic fibrosis, rapid progress has been made in the past two decades in regard to genetic abnormalities. The locations of defective genes have been mapped, and alleles (different forms of a gene) have been identified. Research is ongoing for the treatment of genetic abnormalities. Currently, treatment is mainly limited to surgical correction of defects (correction of a cardiac abnormality in a child with Down syndrome), medical therapy (enzyme therapy for a child with cystic fibrosis), and supportive care (pulmonary therapy to loosen secretions in a child with cystic fibrosis). The most promising treatment for specific gene defects rests in the field of stem cell research. Single-gene defects may be curable via gene therapy in the near future. To date, most of the studies have been animal or in vitro...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
American Pregnancy Association. http://www.american pregnancy.org.
Amniocentesis Report. http://www.amniocentesis.org.
Cummings, Michael. Human Heredity: Principles and Issues. 8th ed. Belmont, Calif.: Brooks/Cole, 2008. A comprehensive yet accessible introduction to all aspects of human genetics.
Cystic Fibrosis Foundation. http://www.cff.org.
Lewis, Ricki. Human Genetics. 8th ed. New York: McGraw-Hill, 2007. A basic human genetics reference text written by a practicing genetics counselor.
March of Dimes. http://www.marchofdimes.com.
Rapp, Rayna. Testing Women, Testing the Fetus: The Social Impact of Amniocentesis in America. New York: Routledge, 2000. Examines the social impact and cultural meaning of currently available prenatal tests.
Scriver, Charles. The Metabolic and Molecular Bases of Inherited Disease. 8th ed. 4 vols. New York: McGraw-Hill, 2007. A comprehensive reference indispensable to those in the field, as well as a much broader audience.
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