Jewish American Heritage Month

Posted By richards on October 3, 2015

Ashkenazi Jews, that is, those Jews of Eastern European origin, constitute more than 80 percent of all world Jewry. The early founders of the Ashkenazi community made their way to Europe during Roman rule, but the majority of the founders of the population came more recently from the region of present day Israel, moved to Spain, France, and Italy, and then in the 10th century into the Rhineland valley in Germany. It is estimated that prior to 1096, the first Crusade, the entire Jewish population of Germany comprised 20,000 people.

The consequence of the unique demographic history of the Ashkenazi Jews is that they have a more homogeneous genetic background compared to the general population.

There are several rare genetic diseases, which occur with a particularly high incidence among Ashkenazi Jews, including Tay-Sachs, Gaucher disease, Bloom syndrome, Idiopathic torsion dystonia, Familial dysautonomia, Factor XI deficiency, and more. For many of these disorders in which a causative gene has been identified, a specific mutation was found to be the cause of most cases of the disease in Ashkenazi Jews.

The frequencies of the common mutations of most of these diseases are between 1/16 and 1/110 among Ashkenazi Jews. Each of these mutations is found mainly in the context of a single haplotype, a finding consistent with a single founder of each mutation. For example, the gene causing Familial dysautonomia (FD) was mapped to a segment of chromosome 9 using Ashkenazi families. The candidate region was confirmed by haplotype analysis; haplotype sharing among 435 out of 441 FD chromosomes revealed a strong founder effect.

Age estimations were calculated by a genetic clock for most of the high frequency diseases listed above. The origin of the investigated mutations can be all dated to between the 9th and 14th centuries and is consistent with the early migration of Jews to Europe and the founding of the Jewish community in Eastern Europe. The high frequency of some genetic disorders among the Ashkenazi Jews (less than 1/100) indicates that the founder chromosome carrying the disease allele was introduced into a very small population, probably in the order of about 100 unrelated individuals. The demographic expansion that followed the early migration maintained the high frequency of these alleles and was probably also affected by genetic drift.

Goodman, R.M. (1979). Genetic diseases among Ashkenazi Jews. New York: Raven Press. pp. xiii, 440.

Motulsky, A.G. (1995). Jewish diseases and origins. Natural Genetics 9:99-101.

Zlotogora, J. (1994). High frequencies of human genetic diseases: founder effect with genetic drift or selection? American Journal of Medical Genetics 49:10-3.

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Category: Ashkenazi
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