Ashkenazi Jewish Carrier Testing

The term Ashkenazi refers to individuals descended from the medieval Jewish communities of the Rhineland in the west of Germany. Many Ashkenazi Jews (AJ) migrated to other parts of Europe, with the majority migrating eastward.

The conditions for which carrier screening is offered are more common in individuals of Ashkenazi Jewish descent than other ethnic groups because of specific mutations that occurred in "founders" of the population. Because Jewish individuals historically married within their own ethnic group, these mutations increased in frequency over generations.

• What are the Ashkenazi Jewish genetic disorders?
• Who should consider carrier screening?
• When should testing be done?
• What will the results tell me?
• How do I arrange screening?

What are the Ashkenazi Jewish genetic disorders?

Screening is available for eleven genetic disorders. Carrier frequency is different for each condition — the overall chance of being a carrier for at least one of these diseases is 1 in 4 to 1 in 5 for someone of AJ descent.

Of these conditions, Canavan disease and Tay-Sachs disease are among the most common and severe. Both are progressive conditions with no effective treatment options at this time. Canavan disease and Tay Sachs disease are usually fatal in childhood.

Cystic fibrosis (CF) is also common in individuals of Caucasian ancestry. All of these disorders are also found in non-Jewish individuals, but with lower incidence (with the exception of CF).

Clinically Available Screening for Individuals of Ashkenazi Jewish Descent*

Condition	Disease Incidence	Carrier Frequency	Carrier Detection Rate
Tay Sachs disease	1/3,000	1/30	98%
Canavan disease	1/6,400	1/40	98%
Cystic Fibrosis	1/3,000	1/29	97%
Familial Dysautonomia	1/3,600	1/32	99%
Bloom syndrome	1/40,000	1/100	97%
Fanconi Anemia group C	1/32,000	1/89	99%
Gaucher disease	1/900	1/15	95%
Mucolipidosis type IV	1/62,500	1/127	95%
Niemann-Pick disease type A	1/32,000	1/90	95%
Glycogen Storage 1a	1/20,000	1/71	99%
Maple syrup urine disease	1/26,000	1/81	99%

* Disease incidence, carrier frequency and detection rates among individuals who are not of Ashkenazi Jewish descent are available by contacting a genetic counselor at the UCSF Prenatal Diagnostic Center.

Who should consider carrier screening?

Based on recommendations from the American College of Medical Genetics, the American College of Obstetrics and Gynecology, and other groups, you should consider carrier screening if you, your partner, or both are of AJ descent.

Carrier screening is typically performed stepwise by screening the individual with AJ ancestry. It is recommended to start with testing of the Ashkenazi Jewish partner and to test the non-Jewish member of the couple only if the Jewish partner is a carrier of any of the diseases. Carrier screening is less sensitive and less informative in non-Jewish individuals.

When both partners are AJ, carrier screening can be done on either partner. Carrier screening can be done simultaneously for both parents, if time is a constraint.

When should testing be done?

The ideal time to undergo carrier screening is before pregnancy, but carrier screening can be done during pregnancy. If you are already pregnant, we recommend having carrier screening as early in the pregnancy as possible so the results are available to you for further decision making.

What will the results tell me?

All of these conditions are inherited in an autosomal recessive manner. Your test could reveal several different results:

• If both parents are carriers for the same genetic disease, then there is a 1 in 4, or 25 percent chance of the condition in each of their pregnancies. Therefore, there is a 3 in 4, or 75 percent chance that each pregnancy would be unaffected.
  Prenatal diagnosis by chorionic villus sampling (CVS) at 10 to 13 weeks, or by amniocentesis at 15 to 20 weeks can diagnose these disorders. Techniques for diagnosing the disease might also be available prior to pregnancy using in vitro fertilization (IVF) and preimplantation genetic diagnosis.
• When one parent is a carrier of a particular disease and the other parent is not a carrier, the couple is not at increased risk to have a child with that disease. Instead, there is a 1 in 2, or 50 percent chance of having a child who is an unaffected carrier like the one parent. Prenatal diagnosis is not recommended.
• If one parent undergoes screening initially and all the testing is negative, then no further screening or testing is recommended.

How do I arrange screening?

If you are interested in pursuing carrier screening for some or all of these conditions, please contact the Prenatal Diagnostic Center for an appointment.

Please note that medical insurance plans vary widely. Plans may cover the cost of screening at different rates. Our office can help you determine your plan's coverage and facilitate an insurance authorization if required.