At one point in the 1970s, genetic counselors adopted a radical stance on the issue of intermarriage: They routinely advised Jews who carried the genetic mutation that leads to a rare neurological genetic disease found in the Ashkenazic population to marry non-Jews. Their logic was that if a carrier bore offspring with a non-Jew, the likelihood of the child inheriting the genetic mutation would be greatly reduced.
But, as it turned out, the science was flawed. The disease, torsion dystonia, which causes voluntary muscles to spasm and can leave its sufferers wheelchair-bound, was believed to be carried by a recessive gene, thereby requiring two carriers to pass on the mutation. But it was later discovered that the disease is carried by a dominant gene. In practical terms, this meant the child would inherit the mutation regardless of whom the mutation carrier chose as a mate.
Despite the revelation of faulty science a decade later, the advice doled out by a cadre of genetic counselors — specialists who instruct prospective parents on how to avoid passing on genetic diseases — goes a long way toward illuminating the intersection of science and the so-called “intermarriage debate.” That debate has raged with extra intensity since 1990, when a national Jewish-population survey found that 52% of American Jews were marrying outside the faith. In response to what was perceived as a crisis of assimilation, some advocated for greater outreach to the intermarried, while others used the study to affirm their staunch opposition to the increasingly common practice. But are there genetic benefits to intermarriage?
According to Harry Ostrer , director of the human genetics program at the New York University School of Medicine, there has been a noticeable decrease in the number of Jews carrying the mutations for Jewish genetic diseases, in part due to intermarriage. “For people who come who report Jewish ancestry, we’re seeing that the frequency of specific mutations appears to be dropping over time, because people have mixed ancestry,” said Ostrer. “They’re three-quarters Jewish,” he added, “not fully.”
While this may be the case, having children with a non-Jew is not a surefire way to avoid passing on a carrier gene, experts say. Most agree that the likelihood is significantly reduced when one parent is of a different ethnic origin, but some say that having a gentile parent can give a false sense of security when it comes to assessing the risk of passing on Jewish genetic diseases.
“Genetic disease can happen in any population, and it’s not just because of your ethnic background,” said Vivian Weinblatt, a genetic counselor and past president of the National Society of Genetic Counselors. “So if you were to say, ‘Well, I just won’t marry a Jewish person,’ you’re fooling yourself.”
Weinblatt, who has spent the past 19 years counseling prospective parents, said that while Jews are at greater risk for the classic set of about 12 Jewish genetic diseases — including Tay-Sachs, Canavan disease and Gaucher disease — non-Jews can also be carriers of genetic mutations. Often, said Weinblatt, the Jewish parent will be screened for the genetic mutations that commonly cause the disorders, but the non-Jewish parent won’t undergo testing. Alternatively, if the non-Jewish parent does get screened, his or her carrier gene may go undetected simply because it is a different mutation.
In the case of Canavan, routine screening will reveal whether the prospective Jewish parent is a carrier 99% of the time, said Weinblatt. But in non-Jews, the defect won’t show up in a full half of those tested because they may not carry the specifically Jewish mutation; instead, they could carry a gene mutation unique to their ethnic group. French Canadians, for example, are carriers of a different Tay-Sachs mutation than Ashkenazic Jews. “So you could be reassured that great, my non-Jewish husband isn’t a carrier, but he still could be,” said Weinblatt.
In the Ultra-Orthodox Jewish community, where Jews only marry other Jews, routine testing for genetic diseases has drastically reduced their prevalence. Dor Yeshorim, the Committee for the Prevention of Jewish Genetic Diseases, based in Williamsburg, Brooklyn, provides testing worldwide for Orthodox Jews. If two prospective mates are found to carry the same genetic mutation, they are advised not to marry.
But in the broader Jewish community, where Jews frequently marry gentiles, the opposite experiment is inadvertently under way. Still, some experts contend that there is little value in marrying outside the faith, if it’s being done in the name of the health of prospective children. “There’s no real advantage to marrying non-Jews at this point” if the intent is to spare children Jewish genetic diseases, said Dr. Neil Risch, director of the Institute for Human Genetics at the University of California, San Francisco. “There’s no unintended benefit when it comes to the genetics,” he said, adding that both parental and prenatal testing are effective means of detecting potential disease.
In the case of Tay-Sachs disease, which affects the central nervous system, the majority of cases are now found in non-Jews, Risch said. And that, he said, “didn’t happen because Jews were marrying non-Jews, it happened because of the education.”