13 July 2015

We will tell you for the genes :)

12 facts about Jewish genetics

Translated by Ganna Rudenko, Jewishnews 

Is there a "Jewish gene"? No. Jews and all other people are 99.9% the same, and science does not know a single characteristic gene that would be only in Jews and would not manifest itself in other ethnic groups. But representatives of Jewish communities around the world do have similar features, although some of them are inherent in neighboring nationalities. This similarity helped scientists trace the origins of the Jewish ethnic group. The analysis of mutations that occurred in some Jewish communities – Ashkenazim, Sephardim and others – helped us to understand not only how our ancestors migrated, but also what hereditary diseases they acquired. Here are 12 discoveries that we have made as a result of our "genetic research".

1. Two clusters

Jewish communities around the world have a common "genetic thread" – these are the conclusions of a scientific paper published in 2010 by geneticist Harry Ostrer from the Albert Einstein College of Medicine in New York. Genetic analysis of seven Jewish groups (Iranian, Iraqi, Syrian, Italian, Turkish, Greek Jews and Ashkenazim) revealed the existence of two clusters into which a single nation was divided about 2500 years ago: the Jews of Europe, Syria and Middle Eastern Iraqi and Iranian Jews.

2. Know your neighbor

A group of researchers led by Ostrer also established the presence of genetic links between the two aforementioned groups and their non-Jewish neighbors. The closest genetic relatives of Jews in the Middle East are Druze, Bedouins and Palestinians, and for European Jews – Italians.

3. European connections

Two years ago, the same group of scientists included North African regions in the geography of their research. Their 2012 paper states that the Jews of this region can be divided into two genetic groups. These are Djerbian, Libyan and Tunisian Jews, who are very closely related to each other (the first group), as well as Algerian and Moroccan (the second group), who have a clear connection with European Jews – most likely due to the migration of Sephardim to the Maghreb states (Morocco, Algeria and Tunisia) after their expulsion from Spain in 1492.

4. Ethiopian Jews form their own special genetic cluster

It seems to date back to the Jewish missionaries who brought the religion of the Jews to these parts. 

5. Mom-Europe?

Surprisingly, studies published in 2013 showed that the ancestors of Jews along the Ashkenazi line were prehistoric women who lived on the territory of modern Europe – on the northern coast of the Mediterranean Sea, and not in the Middle East and the Caucasus mountains, as other scientists noted. As part of this study, the genes that are in the mitochondrial DNA transmitted through the maternal line in tiny egg organoids were analyzed.

A study conducted by Martin B. Richards of the University of Leeds in the UK suggests that 40% of Ashkenazi mitochondrial DNA variations "lead" to the population of prehistoric Europe. This allows us to conclude that the ancestors of most modern Ashkenazim converted to Judaism about 2000 years ago.

6. The Crusades and the Black Death

Certain genetic mutations among different groups of Jews also appeared during the migration. In the case of the Ashkenazim, it is believed that rare genetic anomalies leading to a number of diseases first arose in a small group of Jews of this branch, who went east from Germany, France and England in the Middle Ages, fleeing from the massacre and persecution during the First Crusade in 1096. The plague epidemic in Europe in 1347-8 also led to a large-scale reduction of the Jewish community. If in the 11th century about 100 thousand Jews lived in Eastern Europe, then in 1500 there were only 10-20 thousand of them left.

Because of this, there were many related marriages in these communities, and any possible random mutations that would have been less common in a large community in these circumstances spread and were passed on to numerous descendants.

7. Transmissible mutations

Most mutations of "Jewish" genetic diseases are recessive. This means that the child shows symptoms of the disease only if both parents are carriers of this gene. If a person has only one copy of the mutated gene, he becomes a carrier of this disease. According to the Consortium of Genetic Diseases of Jews (KGZE), approximately one in two Ashkenazim in the United States – i.e. descendants of European Jews – is a carrier of one of 38 genetic diseases, including Tay-Sachs disease, Gaucher disease and Bloom syndrome. In turn, Sephardim and Mizrahim have a set of 16 genetic diseases, including Mediterranean family fever and alpha-thalassemia.

8. Erasing genetic memory

Before conceiving a child, the KGZE recommends that all Jewish couples, as well as couples in which only one of the spouses belongs to the Jewish people, undergo an examination that will help to find out whether they are carriers of genetic diseases. In 2002, Israel even introduced a special genetic screening program, in which Ashkenazi and North African Jews can do a free test to identify mutated genes responsible for Tay–Sachs disease. Druze and representatives of Arab nationality, as well as Jews whose ancestors lived on the Mediterranean coast, the Middle East and Central Asian countries that were part of the USSR, can undergo a free genetic test in order to find out if they are carriers of the gene responsible for the development of thalassemia.

Thanks to prenatal screenings and anonymous premarital tests for representatives of ultra-Orthodox communities, today Tay-Sachs disease is practically not found in Israel, and the number of cases of inheritance of thalassemia has significantly decreased.

9. Bottleneck

In the Middle Ages, there was a sharp reduction in the number of Ashkenazim, followed by a sharp growth of this community, which led to the "bottleneck" effect. It is believed that the mutations that appeared and spread among Ashkenazim affected the genes that are responsible for the possibility of developing schizophrenia and bipolar disorder.

10. Cancer genes

Among Ashkenazim, gene mutations are also common, which increase the risk of developing breast and ovarian cancer (but this does not mean that breast cancer is a Jewish disease). Abnormalities of the BRCA1 and BRCA2 genes also increase the risk of developing breast and prostate cancer in men. In 2013, the US Supreme Court ordered clinics to reduce the cost of screening the population for these mutations by 75% – from $4,000 to $249. Thanks to this, more people will now be able to be tested and find out whether they are carriers of healthy or mutated BRCA1 and BRCA2 genes.

11. Priests by blood?

Almost 50% of Cohens (people from the clergy class in Judaism) revealed the Cohen model of the haploid genotype transmitted with the Y chromosome (CMH – Cohen Modal Haplotype). This chromosome is passed down the male line, from father to son, and in 2009, researchers were able to trace through it a branch of the male dynasty of priests going back to ancient times. It was found that a common chromosome (i.e. a common ancestor) appeared 2100-3250 years ago, even before the destruction of the First Temple. But CMH is not unique to Jews – this model of the haploid genotype is also found in Bedouins, Yemenis and Jordanians, which indicates the Middle Eastern origin of this branch.

12. So let's drink to it!

About 20% of Jews are carriers of a gene that prevents the development of alcoholism – most of these "persistent" among Sephardim and Ashkenazim. Despite the tradition of eating dairy dishes on Shavuot, many adult Jews suffer from lactose intolerance – three quarters of all Jews are unable to digest this milk sugar (for comparison, 90% of Asian Americans suffer from it). Ashkenazim are also prone to the development of Crohn's disease, chronic inflammation of the gastrointestinal tract. And despite endless talk about the unique Jewish way of thinking, geneticist Neil Risch from the University of California claims that "there is no scientific evidence for a genetic explanation of Jewish success or special intellectual abilities of Jews yet."

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