Who should consider genetic testing?

Inherited diseases such as cystic fibrosis often occur in families with no known risk of them. Gene mutations can pass silently for generations until two carriers mate; then children have a one-in-four chance of getting the disease.

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Some insurers cover genetic testing to see if parents carry a gene, and prenatal testing to see if a baby has a disease or a condition like Down syndrome. The risk of certain genes varies by racial and ethnic groups.

The American College of Medical Genetics says that women who are pregnant or considering pregnancy should be offered testing for cystic fibrosis, a lung disease, and spinal muscular atrophy, a relatively common and devastating neurological disorder.

If you're an Ashkenazi, or Eastern European Jew, testing for nine diseases is recommended, including the neurological disorders Tay-Sachs, familial dysautonomia and Gaucher disease.

Blacks should consider testing for sickle cell disease. Blacks, Hispanics, Asians and Mediterranean people are more likely than other groups to carry genes that cause thalassemia, a serious blood disorder.

All pregnant women should be offered testing for Down syndrome, which is caused by an extra chromosome, not hereditary genes.