Technion researchers: Israeli Druse provide a unique 'genetic snapshot'

Study shows the Druse harbor a remarkable diversity of mitochondrial DNA types.

druse feature88 (photo credit: )
druse feature88
(photo credit: )
The Druse community in Israel provides a "genetic snapshot" of the Middle East in antiquity and represents the descendants of the diverse lineages of people living in the region over tens of thousands of years," according to a study led by Prof. Karl Skorecki of the Technion-Israel Institute of Technology and Rambam Medical Center. The research team, which has just published its findings in the on-line journal Public Library of Science, notes that they are consistent with Druse oral tradition that the adherents of the religion came from diverse ancestral lineages. Skorecki, who several years ago aroused international interest by proving that he and other members of the Jewish priestly tribe (kohanim) share a common set of genetic markers, headed an international team that included Drs. Doron Behar and Liran Shlush of the Technion, Druse co-authors Fuad Basis of Rambam and former Technion student Yarin Hadid, scientists at the Weizmann Institute of Science in Rehovot and US researchers. After taking genetic samples from 311 Druse households in 20 villages, they quickly discovered an unusually high frequency of a mitochondrial DNA haplogroup - a distinct collection of genetic markers called haplogroup X. Mitochondrial DNA is passed down from every mother to her children. These markers are found at low frequencies throughout the world and are not confined to a specific geographical region, unlike most mitochondrial DNA haplogroups. "The Druse harbor a remarkable diversity of mitochondrial DNA types or lineages that appear to have separated from each other many thousands of years ago," according to the researchers. But instead of dispersing throughout the world after their separation - just like adult children moving away from their parents - the full range of lineages can still be found within the small, tightly-knit Druse population, said Skorecki, who is director of nephrology and molecular medicine at the Technion. Thus, he said, the Druse represent a well-preserved "genetic sanctuary, or living relic" that provides a glimpse of the genetic diversity of the region in ancient times. He explained that the religious minority - who number about one million in the mountainous parts of Israel, Lebanon, Syria and Jordan - have lived for centuries in remote, mountainous regions. Marriage outside the group is discouraged, first cousins often marry and it's impossible to convert to the religion, an offshoot of Islam. Unlike other monotheistic religions, the Druse have not looked for converts since shortly after the "Dawa" (revelation) of the religion in 1017. This, along with other cultural and political practices, may have kept the Druse a people apart for at least a thousand years, according to the researchers. The genetic discovery could also be a boon to medical understanding, as the diversity of mitochondrial DNA types within the Druse offers a unique opportunity for researchers to study whether people in different mitochondrial DNA lineages are predisposed to different kinds of diseases. Skorecki offers metabolic syndrome - the combination of insulin resistance, high cholesterol and abdominal obesity that can lead to type 2 diabetes - as an example. Mitochondria are the energy factories within every cell, so one could expect that differences in mitochondrial DNA are linked to different predispositions to energy-related diseases such as metabolic syndrome, he explained. But untangling the connections between mitochondrial DNA lineages and a disease like metabolic syndrome has proven elusive, since it would potentially involve gathering data on many thousands of people spread throughout the world who live in different environments that have their own significant effects on disease. With the Druse, "you can look at 150 kinds of mitochondrial DNA within one group with a similar environment and be able to see the specific contribution of these variations" to disease, Skorecki said. The findings also guide the approach to screen for genetic disease among the Druse. Instead of scanning for disease-linked genes associated with an entire population - as is the case with Ashkenazi Jews - it may make sense to screen within smaller groups. "Since they are comprised of so many distinct lineages, genetic disease may vary from clan to clan and village to village," Skorecki explained.