Jews of Eastern European origin are struck hardest by Tay-Sachs disease, which causes death by the age of 4 or 5 years. At birth, the afflicted children appear normal, but development slows by the age of 6 months, and mental and motor deterioration begin. Approximately 1 in every 25 to 30 Jews of Eastern European origin carries the defective gene, which is recessive—increasing the likelihood of passing on the disorder. Tay-Sachs disease occurs when a gene fails to produce an enzyme that breaks down fatty materials in the brain and nervous system. As a result, fat accumulates and destroys nerve cells, causing loss of coordination, blindness, and finally death.

Sickle-cell anemia mainly affects people of African descent. It appeared thousands of years ago in equatorial Africa, and increased resistance to malaria among carriers of the defective gene. Estimates are that 10% of the African American population in the United States carry the sickle-cell trait. In patients with sickle-cell anemia, the red blood cells are distorted and angular, not round. Because of the cells’ shape, they encounter difficulty in passing through the blood vessels.
The cells tend to pile up and clump, producing oxygen starvation accompanied by considerable pain. The body then acts to eliminate these cells, and anemia results.