Genetic Diseases: How informed are you?

By Subha Dhanaraj

Individuals of Ashkenazi Jewish descent and those with Jewish ancestry from Eastern Europe are more likely to be carriers of certain recessive genetic diseases than other populations of people. These devastating, and often deadly, diseases include Tay-Sachs, Canavan, Gaucher, and Niemann-Pick. Fortunately, genetic testing and counseling can help you understand and identify your risk factors.

A carrier is an individual within a given population who possesses the genetic mutation responsible for causing the associated disease. However, a carrier will not actually have the disease. He or she is simply at risk for having offspring with the disease if he or she has children with another carrier. In other words, for a child to have Tay-Sachs, Canavan, Gaucher, etc., the child must have received one gene from each parent with the genetic mutation causing the disease in question. Such inheritance is called "autosomal recessive inheritance." If both parents are carriers, a child will have a one in four chance of having the associated disease, and a one in two chance of being a carrier for the disease.

The most common autosomal recessive genetic diseases among individuals of Ashkenazi Jewish descent are:

Tay-Sachs Disease: Beginning in the fetus early in pregnancy, Tay-Sachs disease causes the eventual destruction of the central nervous system. The presence of Tay-Sachs becomes evident in a child with the disease when he or she is a few months old. The central nervous system gradually fails and a child with Tay-Sachs usually dies by the age of five. According to a study in the Journal of Medical Genetics, if you are of Ashkenazi Jewish descent, you are ten times more likely to carry the gene causing Tay-Sachs than if you were a member of another population.
Gaucher Disease: Approximately one in ten in Jews of Eastern European descent carry the genetic mutation for this disease. Gaucher disease, although not usually deadly, involves metabolic errors. Children with this condition will have spleens that enlarge to the point where surgery is usually necessary and a thinning of their bones that will cause debilitating joint problems during the course of their lives.
Canavan Disease: When a child is born with Canavan disease, he or she will have an enzyme deficiency that will result in the deterioration of his or her central nervous system. Most children with Canavan do not reach the age of five, although some do live into young adulthood. One in forty Ashkenazi Jews have the genetic mutation for Canavan.
Niemann-Pick Disease: Although Niemann-Pick disease is found in several forms, Types A and B Niemann-Pick seem more prevalent among the Ashkenazi Jewish population than in other ethnic groups. Approximately one in a thousand Jews of Ashkenazi descent carry the genetic mutation responsible for Niemann-Pick. Children with the Type A form of this neurological disease no not reach the age of three. Those with the Type B form may survive into young adulthood.

Luckily, testing is available for these diseases. Individuals who may carry a gene for one of these recessive genetic diseases, as well as several others, can partake in a simple blood test that will identify what, if any, genetic mutations may be present in his or her DNA. Such DNA testing can identify about 98% of the individuals carrying the genetic mutations that code for these diseases. In addition to this carrier testing, expecting couples have several alternatives to determine if any of these diseases are present in their fetus. Traditional amniocentesis, which is usually formed at sixteen weeks into the pregnancy, can be used to detect the presence of the stated genetic diseases and many others. A newer technique, chronic villus sampling (CVS), involves the examination of placental tissue at the tenth week of pregnancy to identify genetic abnormalities.

As with many other diseases and medical conditions, prevention is the best cure. Although medical science is rapidly improving medical treatments for the aforementioned conditions, there are no cures for these deadly diseases. Please undergo carrier testing if you and your partner are thinking of conceiving. And, if you are already pregnant, amniocentesis or CVS will allow you to make informed decisions. You can find a listing of carrier testing facilities located throughout the United States at www.ntsad.org/ntsad/labsus.htm. A listing of certified laboratories in other countries can be found at www.ntsad.org/ntsad/labworld.htm.

Subha Dhanaraj is a freelance writer.