Prevalent Genetic Diseases Among Ashkenazi Jews
A significant health characteristic of the Ashkenazi Jews population is the large number of genetic diseases that occur in them (see Purnell and Paulanka, 2003). These genetic disorders are the effects of genes that are normally not manifested because they are recessive, but if contributed by both parents, the gene can result in fatal disorders. Tay-Sachs disease is one of the most deadly genetic diseases prevalent in the Jewish American population, causing central nervous system degeneration and leading to a loss of motor control, impairment of vision and hearing, severe developmental delays, and generally death in early childhood. In addition to the widely recognized Tay-Sachs disease, a number of other deadly genetic diseases manifest in an abnormally high rate in Ashkenazi Jews (Purnell and Paulanka, 2003). Most of these are carried by several percentage of the Jewish population but as recessive genes and, therefore, do not affect individuals' health. It is estimated, however, that as many as 25 percent of the worldwide Ashkenazi Jews carry recessive genes for one or more of these disorders:
- Gaucher's disease, the most common of these prevalent genetic diseases, is a defect in enzyme metabolism that results in weakened bones, easy bruising and nosebleeds, and reduced growth
- Bloom's syndrome results in a relatively short stature, sensitivity to facial skin lesions, heightened susceptibility to respiratory tract and gastrointestinal tract illnesses, and leukemia
- Canavan's disease is a degenerative brain disease that causes developmental delays, loss of reflexes, and early death in childhood
- Familial dysautonomia, or Riley-Day syndrome, causes damage to the peripheral and autonomic nervous system, undermines development, and generally results in death by early adulthood
- Fanconi's anemia results in low blood cell counts and causes bone marrow failure
The prevalence of these genetic diseases among Ashkenazi Jews is thought to involve two genetic mechanisms referred to as the founder effect and genetic drift. The founder effect reflects an ancient trait that has increased in prevalence across time because of inbreeding patterns in a small population and the birth of many children from a founder with a genetic defect. Although such defects were likely recessive for the founder, they increased in relative frequency as descendants interbred. The principle of genetic drift notes that the in-group marriage patterns of the Ashkenazi Jews lead to a concentration of a range of recessive genetic diseases within descendants because the recessive genes were not diluted by different gene pools from outside their culture.
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