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Jews and Increased Risk

Jewish Genetic Disorders
Jews and Increased Risk
Difficulties Identifying Jewish Patients
Genetic Screening Standards
Ashkenazi Jewish Genetic Disorders Testing Centers


"Jewish" Genetic Disorders
Regardless of ethnic or racial background, each of us has 5-50 potentially disease-causing genetic alterations, according to Francis S. Collins, MD, PhD of the Human Genome Research Institute. Small genetic differences exist between different ethnic groups. Certain ethnic groups have a higher risk for certain genetic conditions than the general population:

Northern European Caucasians: cystic fibrosis
African Americans: sickle cell disease
Mediterranean ancestry: Beta-thalassemia
Southeast Asian Ancestry: Alpha-thalassemia

The "Jewish" genetic disorders are a group of disorders that occur at a higher frequency among Jews than the general population, yet the disorders are not limited to the Jewish population. For example, Ashkenazi Jews are at increased risk for Tay-Sachs disease, but non-Jewish couples may still have children with Tay-Sachs. Most of the diseases that occur with increased frequency in the Ashkenazi Jewish population follow an autosomal recessive pattern of inheritance.

There is no "official" list of these conditions, however disorders known to occur at a higher incidence in an individual of Ashkenazi or Sephardic ancestry include Mendelian disorders, and diseases associate with predisposition genes.
To learn more about these disorders visit:
Ashkenazi disorders
Sephardic disorders

Major Jewish Communities
Ashkenazi Jewry
Ashkenazi Jews are a group of Jews whose ancestors lived in Central and Eastern Europe, e.g. Germany, Poland, Lithuania, and Russia. Persecution led to westward migration, including to America. Around 95% of Jews in North America are Ashkenazi.

Sephardic & Oriental Jewry
Distinct subgroups of Jews evolved in the Middle East, Mediterranean and Far East. For many purposes of identifying genetic disorders, Sephardic and Oriental Jews can be defined as any Jews who are not of Ashkenazi origin. However, this is a varied group with ancestors from Persia (Iran), Yemen, North Africa (e.g. Morocco, Tunisia), Spain, Italy, the Balkans, Iraq, India, etc. Additionally, there are some disorders that are unique to certain sub-populations in this group.

Jews and Increased Risk
Certain disorders are believed to have become more common among Jews, especially Ashkenazi Jews, because of at least two processes: the "founder effect" and "genetic drift."

Founder Effect and Genetic Drift
Founder Effect
Founder effect occurs when a small sub-group migrates from a larger original population. Isolation of the sub-group then results in a smaller pool of reproductive partners. Within this sub-group, is an individual or "founder" who carries a specific, disease-causing mutation. If the population remains "closed" and there is no gene admixture, a substantial number of individuals in future generations might be descended from this individual. Over generations this then would lead to an increased frequency of the mutation when compared with what would be seen within a larger, randomly mating population.

Ashkenazi Jews, like all Jewish populations, originated in the Middle East. For Ashkenazi Jews, the "founder effect" refers to the chance presence of gene mutations for certain disorders among the "founders" or ancestors who immigrated to Eastern Europe at the time of the Diaspora (70 A.D.). Prior to this time we presume that these disorders were no more common among Jews than among any other people.

Maintenance and promotion of the high frequency of particular genes through founder effect among Ashkenazi Jewish populations may have been due to endogamous customs, as well as social and physical isolation. The benefit, if any, of heterozygosity remains unclear. For example, a theory to explain the frequency of lysosomal storage disorders (e.g., Tay-Sachs, Gaucher disease, Mucolipidosis Type IV, Neimann-Pick disease) within the Ashkenazi population revolves around the idea of a heterozygote advantage, but evidence seems to suggest otherwise. In other ethnic groups, the hidden advantage of being a carrier for certain disorders is clear, as the sickle cell trait is for individuals of African descent in malarial areas.

Populations of Sephardic Jews, on the other hand, were probably influenced less by founder effect due to endogamy and more by heterozygote advantage than their Ashkenazi counterparts. This community tended to be less isolated. Examples of heterozygote advantage in this community include Beta-thalassemia and Glucose-6-phosphate dehydrogenase deficiency (G6PD), which provide a selective advantage in endemic areas such as Sub-Saharan Africa, Southern Asia, and the Middle East by possibly providing protection against malaria.

Genetic Drift
Genetic Drift is a random change in the allele frequency of a gene resulting from its transmission (by chance) at higher or lower frequency than predicted. This has greatest impact in small populations, and the strength of genetic drift increases as populations become smaller.

It may be that because Ashkenazi Jews tend to not marry outside of their faith and community, the relatively high frequency of these genes among Jews did not pass into other communities, nor were their effects diluted by the introduction of other genes from outside the Ashkenazi Jewish community. Therefore, genetic drift may have had a discernable impact upon the frequency of some disease gene alleles in the Ashkenazi Jewish population.

Difficulties Identifying Jewish Patients
Ashkenazi Jews and Sephardic Jews are at an increased risk for completely different disorders and both patients and physicians may be unaware of this fact. Because different Jewish groups are at risk for different disorders, identifying a patient’s religion may only be the first step to identifying their risk and determining what tests may be necessary. Jewish individuals and their physicians should be aware not only of their religion, but also of their ethnicity and ancestral countries of origin.

Three main reasons can make it difficult to identify patients of Jewish origin:

  1. Self-identity of patients
  2. Lack of awareness of ethnic distinctions by physicians
  3. Lack of awareness of ethnic distinctions by patients.

However, when trying to determine the ethnic or religious identity of patients, historical sensitivities must be taken into account. This is especially important in regard to the self-identity of patients. Jews have always been sensitive to issues of race and religion, particularly since World War II and that sensitivity reflects the way Jews identify themselves today. Especially in the United States, the Jewish community is not at all homogenous in beliefs and attitudes, and varies as well with respect to both ancestral origin and birthplace of individuals. This can be reflected in the ways Jews identify themselves. For example, children of holocaust survivors may not have been raised Jewish or identify themselves as being a part of the Jewish faith, yet they may be aware of having Jewish ancestry.

Maintaining a balance between the patient’s own self-identity and their possible overall lack of knowledge should be attempted by physicians during consultations. Determining whether a patient is merely Jewish or not may not be sufficient in making correct diagnoses. Knowing a patient’s ancestry can allow for easier diagnosis and insure that correct testing is performed.

Questions to consider asking prior to carrier testing:
Are you Jewish?
Are both of your parents Jewish?
What is your ethnicity?
What countries do your ancestors come from?
Are you Ashkenazi or Sephardic?

After the Roman dispersion of the Jews in 70 A.D., which resulted in the Diaspora, Jews migrated to Eastern and Southern Europe and other locations in the Middle East and North Africa. Later, during the early parts of the 20th century, Jews fleeing Europe because of war and persecution immigrated to a number of other countries, including locations in South America and the Caribbean, South Africa, Australia, the Middle East, the United States and Canada, and Asia. Today, Jewish populations are still in flux. Recently, changing economic and political climates in Europe and South America have caused many Jews to emigrate to the United States. For example, the end of communism in Russia and the economic plunge in Argentina have caused new waves of Ashkenazi Jewish migration to the United States and Israel.

Genetic Screening Standards

After years of petitioning by physicians and parent groups, the American College of Obstetrics and Gynecology (ACOG) is now recommending that individuals of Ashkenazi Jewish background be offered carrier screening for familial dysautonomia (FD). ACOG already recommends that individuals of Ashkenazi Jewish ancestry be offered carrier screening for Tay-Sachs disease, Canavan disease, and cystic fibrosis as part of routine obstetrical care. Based on the criteria used to justify offering carrier screening for these disorders, the ACOG Committee on Genetics now recommends that carrier screening for FD be offered as well. The familial dysautonomia gene (IKBKAP), located on chromosome 9, was discovered in 2001. Carrier testing for FD detects ~99% of carriers in the Ashkenazi Jewish population.

ACOG recommends this screening be offered prior to conception or in early pregnancy in order to afford the couple optimal time to consider reproductive and testing options. If only one member of the couple is Ashkenazi Jewish, it is recommended that that member be tested first and if found to be a carrier, testing can proceed with the non-Ashkenazi Jewish member. The ethnicity of the non-Ashkenazi Jewish member will determine the carrier frequency and detection rate, which may impact the ability to accurately predict the couple’s chance to have a child with the disorder.

For individuals who are only partly Ashkenazi Jewish, it is important to offer carrier screening as well. They, of course, have a reduced risk to be a carrier for one of these disorders but it has been recommended that carrier screening for Tay-Sachs disease, Canavan disease, cystic cibrosis, and familial dysautonomia still be offered if the individual is of Ashkenazi Jewish ancestry. Please note that their residual risk after testing would also be different than that of an individual who has 100% Ashkenazi Jewish ancestry.

The health care provider should also make available information regarding carrier screening for other disorders found to be more common in the Ashkenazi Jewish population. ACOG indicates that genetic counseling may play a role in these discussions.

Members may access the entire position statement from the ACOG Committee on Genetics in the August 2004 issue of the journal, Obstetrics and Gynecology. Non-members may write (no calls, please) to ACOG and request that a copy of the Committee Opinion #298 be mailed to them. It cannot be faxed or emailed but will be mailed first-class. Either email your request to ACOG at resources@acog.org or write to ACOG Resource Center, PO Box 96920, Washington, DC 20090-6920.

Ashkenazi Jewish Genetic Disorders Testing Centers

The table below provides an overview of labs that perform testing for Jewish genetic disorders. This table is provided to assist health professionals in finding testing locations, but is not a complete list and is subject to change. The Chicago Center for Jewish Genetic Disorders does not endorse any specific testing company. This information was obtained from geneclinics.org in January 2003. There are other companies performing testing that are not listed in this table.
Click here to open table

A more in depth discussion on screening and testing, as well as on lab locations, can be found at Gene Clinics.
Gene Tests/Gene Clinics
http://www.genetests.org/

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the Michael Reese Health Trust

© 2003 Chicago Center for Jewish Genetic Disorders

Jewish Federation of Metropolitan ChicagoChildren's Memorial Hospital


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