History is replete with examples of lethal medical interventions, such as inhaling mercury vapors to treat syphilis.1 While widely prescribed in the 1700s, this treatment fell out of vogue when scientists discovered that mercury causes heavy metal toxicity. In a study published in Forensic Science International: Genetics, a multidisciplinary research team used historical archives, genealogical tracing, and advanced genomic sequencing to identify a Swiss mummy who likely succumbed to mercury poisoning in the 1700s.2
“Why do we study mummies? We are interested in the past and what we can learn from it,” said Albert Zink, senior author of the study and director of the Institute for Mummy Studies at Eurac Research in Bolzano, Italy. This mummy’s identity was a mystery since her unearthing in 1975. In 2017, newly discovered archival records helped genealogists narrow down a candidate for the mummy’s identity, create a family tree, and identify three potential living descendants.2,3 Thus began the work of Zink’s team to confirm the mummy’s identity by comparing her DNA to that of her proposed living relatives.
In addition to being toxic, mercury also preserves mummies remarkably well. Frank Maixner, co-author and coordinator of the Institute for Mummy Studies at Eurac Research said that “mercury in higher concentrations inhibits post-mortem growth of microorganisms,” which may preserve tissue and DNA. Zink’s team isolated mitochondrial DNA (mtDNA)—the small circular chromosome in mitochondria that is inherited maternally—from the mummy’s tooth and from DNA samples provided by the proposed living relatives. They used DNA sequencing techniques to enrich for mtDNA, reconstruct the mitochondrial genomes, and screen for regions of shared mtDNA variability—which signal a pattern of inheritance—between the mummy and the potential descendants. Zink’s team found that the mummy and living individuals shared the same specific set of mtDNA variations, leading them to conclude that the mummy and living descendants were related.
Mark Thomas, an evolutionary geneticist at University College London, who was not involved in the study said, “the evidence from mtDNA seems to be strong,” and that future studies may benefit from additional statistical analysis. Thomas emphasized that aside from the historical, cultural, and personal importance of ancient DNA research, it creates opportunities to develop new scientific techniques, including statistical methodologies.
Why do we study mummies? We are interested in the past and what we can learn from it.
As for the mummy’s identity, Zink’s team validated the genealogists’ hypothesis: the mummy was Anna Catharina Bischoff, who lived from 1719 to 1787. Bischoff was a Basel resident and a pastor’s wife who devoted her life to supporting her community. She likely contracted syphilis while tending to patients, subsequently undergoing mercury inhalation treatment based on evidence of residual mercury in her mummified lung tissue. The mercury played a significant role in preserving her body, allowing Zink’s team to perform advanced ancient mtDNA sequencing techniques and validate the mummy’s identity across an uninterrupted maternal lineage of twenty-two generations. Christina Wurst, a PhD candidate at Eurac Research’s Institute for Mummy Studies and first author of the study, said, “The main point was that we were able to help give back an identity to this mummy based on the analysis of the mtDNA from still living, possible relatives. The study would not have been possible without the genealogy or the genetics.”
A surprising anecdotal discovery about Bischoff also emerged from the genealogical work related to this study. In 2018, evidence from historical records identified one of Bischoff’s descendants to be a well-known political figure—former British Prime Minister Boris Johnson. After learning about this finding, Johnson tweeted “Very excited to hear about my late great grand 'mummy' - a pioneer in sexual health care. Very proud.”4
- G. Tilles et al., “Le traitement de la syphilis par le mercure: une histoire thérapeutique exemplaire [The treatment of syphilis with mercury: an exemplary therapeutic history],” Hist Sci Med, 30(4):501-10, 1996.
- C. Wurst et al., “The Lady from Basel's Barfüsserkirche - Molecular confirmation of the mummy's identity through mitochondrial DNA of living relatives spanning 22 generations,” Forensic Sci Int Genet, 56:102604, 2022.
- G. Hotz et al., “Der rätselhafte Mumienfund aus der Barfüsserkirche in Basel. Ein aussergewöhnliches Beispiel interdisziplinärer Familienforschung,” Jahrbuch der Schweizerischen Gesellschaft für Familienforschung, 2018:1-30, 2018.
- B. Johnson, Twitter Post, Jan 25, 2018, 11:35 AM. https://twitter.com/borisjohnson/status/956566289044131840.