Carrier Testing for Jewish Genetic Disorders: Some straightforward answers to common questions

Jewish individuals whose ancestors were from Germany, Russia, the Ukraine, Poland, and Hungary are probably Ashkenazi.  The majority of Jewish families who migrated to the United States after the early 1800's are Ashkenazi.  Sephardic Jews are those whose ancestors were Spanish or Portuguese prior to the Inquisition.  Most Sephardic Jewish families in the United States either emigrated from Israel, Latin America, or the Middle East relatively recently or emigrated from Holland or Spain by the mid 1700's.

Tay-Sachs disease, Canavan disease, familial dysautonomia, Niemann-Pick (type A) disease, Fanconi anemia (group C), Bloom syndrome, Gaucher disease (the non-neuronopathic type), mucolipidosis type IV, and glycogen storage disease type 1.  These are all uncommon conditions that are predominantly found in persons of Ashkenazi ancestry.  [Tay-Sachs disease is also found in persons of French-Canadian (Acadian) ancestry and, rarely, in mixed Jewish/non Jewish couples.]  Although not strictly a disorder of European Jews, cystic fibrosis is often included in an Ashkenazi heritage screening panel, since it occurs with the same frequency in European Jews as in members of the non-Jewish Caucasian population (approximately 1/3,000).  Except for Tay-Sachs disease and cystic fibrosis, these disorders are uncommon in Sephardic Jews.  All except cystic fibrosis are extremely rare in persons who do not have Ashkenazi ancestors.

All are autosomal recessive, which means both members of a couple must be carriers in order to have an affected child, in which case the risk of an affected child is 25% for each pregnancy.  In the United States, carriers of Tay-Sachs disease, Canavan disease, familial dysautonomia, and Bloom syndrome are predominantly of European-Jewish ancestry.  Carrier frequencies in Ashkenazi Jews range from 1/30 (for Tay-Sachs disease) to 1/100 (for Bloom syndrome).  The carrier frequency for non Jews is probably 10 fold lower for all of the conditions other than cystic fibrosis.  There are no outward physical manifestations in persons who are carriers for any of these disorders.

Tay-Sachs, Canavan, and Niemann-Pick diseases are neurodegenerative disorders.  That is, at a certain point, usually in infancy or childhood, there is progressive deterioration in the nervous system.  Growth and development are typically normal until neurologic problems develop.  The signs of familial dysautonomia, a disorder that can be quite difficult for physicians to diagnose, include abnormal regulation of body temperature, feeding problems, abnormal sweating, and insensitivity to pain.  Individuals with Bloom syndrome and Fanconi anemia have slow growth and often die at a young age from cancer.  Fanconi anemia, unlike Bloom syndrome, also involves learning problems and/or mental retardation, and Bloom syndrome patients have immune deficiency.  The "Jewish" type of Gaucher disease often results in anemia, enlarged spleen, and bone cysts in adults.  However, no neurologic problems or cognitive impairment is present.  Many adults with Gaucher disease have minimal or no symptoms, and carrier screening for Gaucher disease has identified affected individuals who do not have any apparent manifestations of the disease.  Cystic fibrosis is a condition that results in chronic lung disease (see Cystic Fibrosis: information for patients ).  Of all these conditions, only Gaucher disease is treatable.

While rare, except for the "Jewish" form of Gaucher disease, each of these serious medical conditions is untreatable or only partially treatable.

Recently developed DNA based (molecular) techniques permit highly sensitive carrier screening for these disorders on a small blood sample.  If either member of an Ashkenazi couple screens negative for these conditions, it is highly unlikely that a child will be affected.  This is comforting to many couples.  If both members of a couple are carriers, prenatal diagnosis is possible, so that couple would not have to continue a pregnancy in which the baby has any of these conditions.

Many Jewish couples have been offered, and have had, carrier testing for Tay-Sachs disease.  If this is the case, it may still be wise to have testing for the other conditions.  It is up to the individual to decide.

Ideally, screening results (which typically take 1-3 weeks to complete) would be available prior to, or early in pregnancy.  This allows for early planning if either or both members of a couple are discovered to be carriers.  Screening one member of a couple and then the other (if the carrier testing is positive) is one alternative.  The other is to screen both members of a couple simultaneously.  You doctor can advise you which is preferable in your situation.

No!  It is entirely your choice.  Geneticists, physicians, and rabbis have been recommending Tay-Sachs carrier testing for decades.  Canavan disease carrier testing is also recommended for Jewish couples.  Many obstetricians feel that testing for some or all of these other conditions is also important.  In any case, the decision should be made by the individual(s) after being given all of the relevant information.

Except for cystic fibrosis, which is equally frequent in Jews and Gentiles, and Tay-Sachs disease, which occasionally (1/30,000) occurs in mixed couples, carrier testing is only recommended when both prospective parents are Jewish.

Your obstetrician should have written information on Ashkenazi heritage carrier testing.  If desired, your obstetrician can make a referral to a geneticist.  The geneticist, after obtaining a complete family history and reviewing relevant medical information, will be able to discuss the issue in more detail, arrange the actual carrier testing, interpret the results of testing, and make recommendations for further testing and/or prenatal diagnosis.

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