NEW YORK – An ancient DNA analysis by investigators in the US, Israel, Germany, and elsewhere suggests Ashkenazi Jewish populations can be traced back to a pronounced founder event that took place prior to the 14th century. Further, while medieval Ashkenazi Jewish individuals appeared to have genetic heterogeneity, that diversity has decreased in present-day populations.
"Our ancient DNA data allowed us to identify patterns in the history of [Ashkenazi Jewish individuals] that would not have been detectable from modern genetic variation," co-senior and co-corresponding authors David Reich, at Harvard and the Broad Institute, and Shai Carmi, with the Hebrew University of Jerusalem, and their colleagues wrote in Cell on Wednesday, noting that the population "was more structured during the Middle Ages than it is today."
For their analysis, the researchers focused on samples from a medieval Jewish cemetery in the German town of Erfurt in the state of Thuringia, where a Jewish population was present prior to a 1349 pogrom that wiped out or banished Erfurt's Jewish individuals. A second Jewish group came back to Erfurt around five years later, they added, ultimately leading to one of the largest Jewish populations in the country.
"As part of this study, we engaged with rabbinical authorities who reviewed our proposed research plan and approved the project under the conditions that only detached teeth are used, and that the analysis is performed only on already excavated individuals," the authors explained, noting that that study was subsequently approved by Thuringia's Jewish community.
After attempting to extract and sequence DNA from tooth samples for 38 ancient individuals, the team was left with enriched and non-enriched sequence libraries for 33 Ashkenazi Jewish individuals between the ages of roughly 5 and 60 years old. Based on radiocarbon data from a subset of the samples, the investigators placed the samples as being from between the late 1200s and the year 1400, with archaeological clues hinting that the cemetery site may have belonged to the region's second Jewish community.
With genetic data spanning 1.24 million SNPs found genome-wide in ancient samples from 19 female and 14 male representatives, the researchers found members of two nuclear families, including a mother with two children and a father-daughter pair, along with more distantly related individuals.
Together with available genetic data from the Human Origins dataset for almost 1,000 Jewish and non-Jewish individuals from present-day European populations and other modern-day data, the ancient samples pointed to shared ancestry between ancient and present-day Ashkenazi Jewish populations.
"Today, if you compare Ashkenazi Jews from the United States and Israel, they're very similar genetically, almost like the same population regardless of where they live," Carmi said in a statement.
The team's results, though, suggested that the medieval population was far more genetically diverse than Ashkenazi Jewish individuals today. In particular, the ancient Erfurt individuals showed genetic ties to modern-day Ashkenazi Jewish individuals and to populations in the European Mediterranean, with genetic variation that fell along a relatively broad spectrum between Southern European, Middle Eastern, and Central/Eastern European populations.
From their findings, the researchers suggested that the Erfurt region was home to an Ashkenazi Jewish group with Sephardic Jewish-like ancestry that resembles Ashkenazi Jewish groups in Western Europe today, while a second Erfurt Ashkenazi Jewish group with more pronounced European ancestry that seems to have subsequently admixed with individuals with Eastern European-related ancestry.
With the help of additional genome sequence data for hundreds of modern Ashkenazi Jewish individuals — along with identity-by-descent haplotype, mitochondrial DNA, and pathogenic variant profiling — the researchers flagged a pre-14th century founder event that formed the ancient Ashkenazi Jewish population, which appeared to be followed by a significant population bottleneck.
These and other data also offered an opportunity to profile potentially pathogenic variants shared by medieval Erfurt and present-day Ashkenazi Jewish individuals, ranging from breast and ovarian cancer-related BRCA1 variants to gene variants linked to Gaucher disease, Parkinson's disease, retinitis pigmentosa, or other conditions.
"Overall," the authors reported, "our results suggest that the [Ashkenazi Jewish] founder event and the acquisition of the main sources of ancestry pre-dated the 14th century and highlight late medieval genetic heterogeneity no longer present in modern [Ashkenazi Jewish populations]."