For over 4000 years, certain human abnormalities have been noted to run in families, but the "WHY" of the observations did not become apparent until the advent of modern genetics and the recognition of how genetic information is transmitted. Before then one only heard the admonition, "it's in the blood" (thought to refer more to bloodline rather than some abnormal element in the blood).

Present day medicine has recognized how genetic diseases are inherited based on an understanding of the nature of DNA, genes, and chromosomes. Scientists are presently trying to "map" the chromosomes, to determine the location and function of all of the thousands of genes in each chromosome. This will ultimately help in diagnosing and treating genetic disorders.

However, until science has the ability to treat some of the more disastrous (and ultimately fatal) genetic disorders, the best remaining recourse is prevention. Prevention of genetically transmitted diseases can consist of major choices: abstinence from pregnancy, egg or sperm donation, preimplantation/prenatal diagnosis and termination or early treatment of affected pregnancies.

Prenatal diagnosis involves testing fetal cells, amniotic fluid, or amniotic membranes to detect fetal abnormalities. Preimplantation diagnosis is a new technique only available in specialized centers. It involves in vitro fertilization and genetic testing of the resulting embryos prior to implanting only those embryos found not to have the abnormal gene(s).

Genetic counseling (and prenatal diagnosis) provides parents with the knowledge to make intelligent, informed decisions regarding possible pregnancy and its outcome. Based on genetic counseling, some parents (in the face of possibly lethal genetic disease) have forgone pregnancy and adopted children while others have opted for egg or sperm donation from an anonymous donor who is not likely to be a carrier of the specific disease.

Many diseases transmitted as a single gene defect can now be diagnosed very early in pregnancy. Because of this some parents have elected to become pregnant and then, early in the pregnancy, had the disease status of the fetus determined. The pregnancy is continued if the fetus is disease-free. Parents who decide to continue the pregnancy with a defective fetus may be able to better prepare to care for the infant by being informed about the disease in advance. For example, genetic diseases where a component of the diet is not tolerated can lead to specialized diets for the mother and newborn baby.

RELATED TOPICS:
Autosomal dominant
Autosomal recessive
Sex-linked dominant
Sex-linked recessive

For detailed information, see heredity and disease (genetics).