Jewish Genetic Diseases
As researchers decode DNA, new findings and procedures bring hope to sufferers.
“The high‑frequency genetic disorders specific to Ashkenazim are different from those of the surrounding populations [Poles, Germans],” Dr. Bach explains. “Sephardim, however, tend to share hereditary diseases with their host population. This is believed to result not from intermarriage, but from natural selection. Kurds and Kurdish Jews, for example, have a genetic predisposition toward thalassemia, an inherited blood disorder. Crippling though thalassemia can be, it protects healthy carriers against a severe form of malaria, and may thus have been genetically selected.”
All these diseases are autosomal recessive disorders, which means that for a child to inherit any one of them, parents must each carry a copy of the affected gene—though they are not themselves affected—and they must pass that gene on. When both parents are carriers, there is one in four chance they will have an affected child and a 50‑percent chance their child will be a carrier.
Until recently, the best help doctors could give was to identify carriers as the appropriate blood tests were developed and test the unborn babies [fetuses] of couples at risk. With termination of affected pregnancies problematic for many couples, an Orthodox nonprofit group was established in 1983 in New York to test Jewish teenagers for the most common recessive Ashkenazic diseases, and help avoid marriages between matched carriers. Known as Dor Yeshorim, with Hadassah as its Israel testing center, the group’s strategy, it claims, has eliminated Tay-Sachs by 90 percent.
“We test well over 10,000 people a year,” asserts Dr. Bach. “Despite that, hundreds of families with affected members, usually children, attend our clinic.”
There is growing hope for families the screening failed to protect. With massive impetus from the international Human Genome Project and new technologies, researchers are finally moving to track down the culprit genes.
“The search area is unimaginably vast,” Dr. Bach explains. “Each of our 100,000 genes comprises four chemical sub‑units or nucleic acids, with each of these combined in an almost limitless variety of sequences.”
There are an estimated three billion of these chemical sequences in the human genome. It is from among them that Dr. Bach and his team identified the genetic misprint that triggers mucolipidosis IV (ML4). The disorder, which impairs crawling, walking, talking and learning basic skills, was first described by Hadassah physicians 26 years ago. Discovery of the mutant gene will lead the way, he believes, to treatment, either as protein replacement or gene therapy.
“The more we know about a disorder, the closer we come to treating it successfully,” he says. “We know, for example, that Tay‑Sachs, Canavanas, Niemann‑Pick type A and Thatcher result from missing enzymes and the fatal accumulation of substances they’re designed to break down.”
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