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Researchers Report Findings from Ancient 'Iceman' Genome

NEW YORK (GenomeWeb News) – Researchers have sequenced the genome of a mummified, 5,300-year-old Tyrolean Iceman known as Ötzi, using information in his genome to look more closely at his ancestry and to determine some of his physical features and disease predispositions.

Findings from Ötzi's genome, reported online yesterday in Nature Communications by a German and Italian-led team, indicate that he most probably had brown eyes and trouble digesting milk, for example. From other SNPs present in his genome, investigators suspect that Ötzi was at elevated cardiovascular disease risk — consistent with vascular features previously found in his mummified remains.

Meanwhile, metagenomic analyses uncovered DNA sequences representing some 60 percent of the genome of a Lyme-disease causing bacterial species called Borrelia burgdorferi, hinting that Ötzi was the earliest known sufferer of the bacterial affliction, senior author Albert Zink, head of the European Academy of Bozen/Bolzano's Institute for Mummies and the Iceman, and colleagues explained.

Ötzi's mummified remains were discovered in the Italian Alps in 1991. Since then, he has been the subject of extensive study, Zink and his co-authors noted. "Speculation on his origin, his life habits, and the circumstances surrounding his demise initiated a variety of morphological, biochemical, and molecular analyses."

Results of the Tyrolean Iceman mitochondrial genome sequencing effort, reported by another team in Current Biology in 2008, indicated that the man belonged to a previously unknown branch of a mitochondrial haplogroup that's still relatively common in Europe.

With the availability of his complete genome — sequenced to an average coverage of 7.6 times coverage using Life Technologies' SOLiD 4 instrument — researchers are now able to glean new details about Ötzi's relationship to existing European populations.

From Y chromosome data, the team determined that Ötzi belonged to a G2a4-L91 sub-group of the Y chromosome haplogroup G that is found most frequently in present-day populations in northern Sardinia and southern Corsica.

His autosomal genotype patterns also clustered most closely with those found in southern and southwestern Europe.

Among the 2.2 million SNPs identified in the genome, including 1.7 million that are already housed in dbSNP, the team also found several variants that offer information about Ötzi's traits and disease propensities.

For example, the researchers did not find a variant in the MCM6 gene that has been tied to the ability to digest lactase as an adult, suggesting Ötzi was lactose intolerant. Other patterns in the genome indicate that the man probably had brown eyes and type O blood.

He also carried several SNPs that have been linked to coronary heart disease and/or ischemic stroke risk, along with at least one variant that has been associated with atherosclerosis in men.

Although they are not able to confirm all of their genetic predictions, Ötzi's relatively well-preserved remains had at least some features that seem to jive with information gleaned from the genome — most notably, calcifications in some of his arteries that appear to be consistent with coronary artery disease.

That finding, in particular, has grabbed researchers' attention, since the ancient man did not seem to have some of the most common risk factors associated with heart disease today, such as a sedentary lifestyle or excess weight.

"The evidence that such a genetic predisposition already existed in Ötzi's lifetime is of huge interest to us," senior author Zink said in a statement. "It indicates that cardiovascular disease is by no means an illness chiefly associated with modern lifestyles."

A genome browser intended to provide access to and analysis of Ötzi's genome sequence by other members of the research community is available online.

"This browser contains all the aligned sequencing reads to the Human Genome Reference 19, provides a basic level of annotation including individual [SNPs], insertions and deletions, and gene identification," the study's authors explained. "We have also incorporated a query engine for more complicated analysis routines, such as the comparison of the Iceman's genome to other contemporary genomes."