Jewish Genetics: 75% of Jews Are Lactose Intolerant and 11 Other Facts

Almost half of Ashkenazim carry at least one of 38 genetic diseases, and our closest genetic relatives are Druze, Bedouin, Palestinians - and Italians.

Josie Glausiusz
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There's no such thing as a 'Jewish gene', but Jewish populations do share certain traits.
There's no such thing as a 'Jewish gene', but Jewish populations do share certain traits.Credit: Ayala Tal
Josie Glausiusz

Is there such a thing as a “Jewish gene”? No, there isn't. Jews and all other humans are 99.9 percent identical in their genetic make-up, and there is no gene known to exist in Jews that does not exist in other population groups.

Jewish communities around the word do share certain genetic traits with each other--some of which they also share with surrounding populations. These similarities have enabled scientists to trace the origins of Jewish communities around the world. Analysis of mutations that arose in specific communities – Ashkenazi, Sephardi and others – have aided our understanding of our ancestors' journeys, not to mention hereditary diseases. Here are 12 facts about Jewish genetics.

1. Two clusters: Jewish communities across the globe share a common "genetic thread", according to a 2010 study led by geneticist Harry Ostrer of Albert Einstein College of Medicine in New York. Genetic analysis of seven Jewish groups (Iranian, Iraqi, Syrian, Italian, Turkish, Greek and Ashkenazi) identified two distinct clusters that split about 2,500 years ago: European/Syrian Jews and Middle Eastern Iraqi and Iranian Jews.

Re-opening the Great Synagogue in Edirne, Turkey, March 26, 2015 - the first temple to open in Turkey in two generations. (Photo: Reuters)

2. Know thy neighbor: Ostrer's team also found strong genetic ties between each of the two groups and their non-Jewish neighbors: The closest genetic relatives of the Middle Eastern group are Druze, Bedouin and Palestinians, and for European Jews, it is Italians.

3. European ties: Two years later, the same team extended their study to include North African Jews. Their 2012 paper described two discrete genetic clusters: Djerban, Libyan, and Tunisian Jews, who are closely related to one another; and Algerian and Moroccan Jews, with distinct European ties—most likely stemming from the migration of tens of thousands of Sephardi Jews to the Mahgreb (Morocco, Algeria and Tunisia) following their expulsion from Spain in 1492.

4. Ethiopian Jews form their own distinct genetic cluster, most probably arising from Jewish founders who converted the local population.

Ethiopian Jews: Their own genetic cluster. (Photo: Daniel Bar-On)

5. Mother Europe? Curiously, a 2013 study of the maternal origins of Ashkenazi Jews suggests that their ancestors were prehistoric European women from the Northern Mediterranean—and not the Middle East or the Caucasus, as other research has posited. The study analyzed mitochondrial DNA (loops of genetic material passed down from mother to child in tiny organelles carried by their eggs).

Led by Martin B. Richards of the University of Leeds in the UK, the research suggests that 40 percent of the variation in Ashkenazi mitochondrial DNA can be traced to prehistoric Europe, indicating that the maternal ancestors of most modern Ashkenazi Jews converted to Judaism some 2,000 years ago.

6. Crusades and Black Death: The presence of distinct genetic mutations among different groups of Jews can also be traced to the history of our wanderings. Among Ashkenazim, it’s thought that rare mutations for certain genetic disorders may have arisen among a small founder population of Jews who migrated eastwards from Germany, France and England in the Middle Ages, following slaughter and expulsion that began with the Crusades in 1096. Together with the Black Death in 1347-8, this led to a severe reduction in these communities, from about 100,000 individuals in the 11th century to an estimated 10,000-20,000 Eastern European Jews in 1500.

Because these communities tended to marry among themselves, any mutations that may have arisen at random would have increased in prevalence among their numerous descendants.

Belvoir Fortress: The best-preserved Crusader remains in Israel. Photo: Emír Balduin Hallef Omar Ali al-Adid bin Abú Sharee al-Kerak, Wikimedia

7. Carrying mutations: Most mutations for "Jewish" genetic diseases are recessive, meaning that a child must inherit the mutation from both parents in order to show symptoms of the disease. Harboring one copy of the mutation means that the individual is a carrier of the disease.

According to the Jewish Genetic Disease Consortium, it is estimated that nearly one in two Ashkenazi Jews in the United States—the descendants of European Jews—is a carrier of at least one of 38 genetic diseases, including Tay-Sachs Disease, Gaucher Disease, and Bloom Syndrome. A separate panel of 16 genetic disorders, including Familial Mediterranean Fever and the blood disorder alpha-thalassemia, are found among Jews of Sephardi/Mizrahi origin.

8. Tay-Sachs, a memory? The JGDC recommends that all Jewish and Interfaith couples be screened for Jewish genetic diseases before conceiving a child. In Israel, a “national carrier screening program” was established in 2002. Under the program, genetic screening for Tay-Sachs is offered free of charge to Jews of Ashkenazi and North African descent, while free thalassemia carrier screening is offered to Druze and Arab populations and Jews originating in the Mediterranean, the Middle East and in the Central Asian countries of the former Soviet Union.

Thanks to prenatal diagnosis—and anonymous premarital testing among the Ultra-Orthodox communities—Tay-Sachs disease has virtually disappeared in Israel, while the prevalence of thalassemia has dropped dramatically.

9. The bottleneck: The extreme population shrinkage of Ashkenazi Jews in the Middle Ages, followed by dramatic expansion, created what is known as a “bottleneck effect.” Mutations that arose and spread among the resultant Ashkenazi population are thought to include genes that predispose to schizophrenia and bipolar disorder.

An illuminated Haggadah from the Middle Ages, specifically from 14th century Spain, Rylands Collection.

10. Cancer genes: Jews of Ashkenazi descent also have a higher prevalence of mutations that increase the risk of breast and ovarian cancer in women (which does not mean breast cancer is a "Jewish disease"). These genes, called BRCA1 and BRCA2, also increase a man’s risk of developing breast cancer and prostate cancer. Because of a 2013 U.S. Supreme Court ruling—which determined that naturally-occurring human genes cannot be patented—the $4000 price tag for testing for these two genes has dropped by about 75%.. The development may lead to greater availability of testing for carriers of these genes.

11. Priestly genes? About 50 percent of all Cohanim (the Jewish priestly class) harbor a distinct element on their Y-chromosome called the Cohen Modal Haplotype or CMH. Because this sex chromosome is passed down unchanged from father to son, geneticists have used this element to trace the patrilineal priestly dynasty to a common ancestral chromosome found 2,100–3,250 years ago, before the destruction of the First Temple. But it is not exclusive to Jews, either: CMH is also found among Bedouins, Yemenites, and Jordanians, lending support to “a Near Eastern origin of this lineage,” according to a 2009 report.

12. Salut! Some 20 percent of Jews carry a gene that protects against alcoholism, with the variant more common in Sephardim than in Ashkenazim. Notwithstanding our predilection for cheese-eating on Shavuot, we are also more prone to lactose intolerance: three-quarters of all Jews cannot digest this milk sugar, as compared to 90 percent of Asian-Americans. Ashkenazi Jews are also two-to-four times more likely to develop Crohn’s Disease, an inflammatory disorder of the digestive tract. And despite the persistent rumors, “there is currently no scientific evidence that Jewish achievement or intelligence has a genetic basis,” as geneticist Neil Risch of the University of California, San Francisco told Moment Magazine in 2012.

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