Medical genetics of Jews – Wikipedia, the free encyclopedia

The medical genetics of Jews is the study, screening, and treatment of genetic disorders more common in particular Jewish populations than in the population as a whole.[1] The genetics of Ashkenazi Jews have been particularly well-studied, resulting in the discovery of many genetic disorders associated with this ethnic group. In contrast, the medical genetics of Sephardic Jews and Mizrahi Jews are more complicated, since they are more genetically diverse and consequently no genetic disorders are more common in these groups as a whole; instead, they tend to have the genetic diseases common in their various countries of origin.[1][2] Several organizations, such as Dor Yeshorim,[3] offer screening for Ashkenazi genetic diseases, and these screening programs have had a significant impact, in particular by reducing the number of cases of TaySachs disease.[4]

Different ethnic groups tend to suffer from different rates of hereditary diseases, with some being more common, and some less common. Hereditary diseases, particularly hemophilia, were recognized early in Jewish history, even being described in the Talmud.[5] However, the scientific study of hereditary disease in Jewish populations was initially hindered by scientific racism, which believed in racial supremacism.[6][7]

However, modern studies on the genetics of particular ethnic groups have the tightly defined purpose of avoiding the birth of children with genetic diseases, or identifying people at particular risk of developing a disease in the future.[6] Consequently, the Jewish community has been very supportive of modern genetic testing programs, although this unusually high degree of cooperation has raised concerns that it might lead to the false perception that Jews are more susceptible to genetic diseases than other groups of people.[5]

However, most populations contain hundreds of alleles that could potentially cause disease and most people are heterozygotes for one or two recessive alleles that would be lethal in a homozygote.[8] Although the overall frequency of disease-causing alleles does not vary much between populations, the practice of consanguineous marriage (marriage between second cousins or closer relatives) is common in some Jewish communities, which produces a small increase in the number of children with congenital defects.[9]

According to Daphna Birenbaum Carmeli at the University of Haifa, Jewish populations have been studied more thoroughly than most other human populations because:[10]

The result is a form of ascertainment bias. This has sometimes created an impression that Jews are more susceptible to genetic disease than other populations. Carmeli writes, "Jews are over-represented in human genetic literature, particularly in mutation-related contexts."[10] Another factor that may aid genetic research in this community is that Jewish culture results in excellent medical care, which is coupled to a strong interest in the community's history and demography.[11]

This set of advantages have led to Ashkenazi Jews in particular being used in many genetic studies, not just in the study of genetic diseases. For example, a series of publications on Ashkenazi centenarians established their longevity was strongly inherited and associated with lower rates of age-related diseases.[12] This "healthy aging" phenotype may be due to higher levels of telomerase in these individuals.[13]

The most detailed genetic analysis study of Ashkenazi was published in September 2014 by Shai Carmon and his team at Columbia University. The results of the detailed study show that today's 10 million Ashkenai Jews descend from a population only 350 individuals who lived about 600-800 years ago. That population derived from both Europe and the Middle East. [14]There is evidence that the population bottleneck may have allowed deleterious alleles to become more prevalent in the population due to genetic drift.[15] As a result, this group has been particularly intensively studied, so many mutations have been identified as common in Ashkenazis.[16] Of these diseases, many also occur in other Jewish groups and in non-Jewish populations, although the specific mutation which causes the disease may vary between populations. For example, two different mutations in the glucocerebrosidase gene causes Gaucher's disease in Ashkenazis, which is their most common genetic disease, but only one of these mutations is found in non-Jewish groups.[4] A few diseases are unique to this group; for example, familial dysautonomia is almost unknown in other populations.[4]

TaySachs disease, a fatal illness of children that causes mental deterioration prior to death, was historically more prevalent among Ashkenazi Jews,[18] although high levels of the disease are also found in some Pennsylvania Dutch, southern Louisiana Cajun, and eastern Quebec French Canadian populations.[19] Since the 1970s, however, proactive genetic testing has been quite effective in eliminating TaySachs from the Ashkenazi Jewish population.[20]

Gaucher's disease, in which lipids accumulate in inappropriate locations, occurs most frequently among Ashkenazi Jews;[21] the mutation is carried by roughly one in every 15 Ashkenazi Jews, compared to one in 100 of the general American population.[22] Gaucher's disease can cause brain damage and seizures, but these effects are not usually present in the form manifested among Ashkenazi Jews; while sufferers still bruise easily, and it can still potentially rupture the spleen, it generally has only a minor impact on life expectancy.