Genome Paints a Better Portrait of the Iceman: DNA Reveals Otzi Had Lyme Disease, Lactose Intolerance
Saey, Tina Hesman, Science News
By peering deeply into the DNA of the mummy known as Otzi, geneticists have expanded the profile of the 5,300-year-old Iceman: He had brown eyes, brown hair and blood type O, was lactose intolerant and his modern-day relatives live on Corsica and Sardinia.
These vital statistics come from an analysis of the Tyrolean man's complete genetic blueprint, reported online February 28 in Nature Communications. The DNA analysis also reveals that the Iceman, found frozen and well-preserved in the Italian Alps in 1991, carried genetic risk factors for heart disease. And he was infected with the bacterium that causes Lyme disease, making him the oldest known case of the disorder.
For the new study, researchers led by Albert Zink, an anthropologist at the European Academy of Bolzano in Italy, removed a bit of Otzi's hip bone and extracted DNA from the sample. The mummy's fresh-frozen state helped preserve his DNA, making deciphering a complete genetic blueprint easier than for most ancient samples, says Niels Lynnerup, a forensic anthropologist at the University of Copenhagen. "It is much better DNA than you can get from one dry old bone," he says.
Otzi's brown eyes and lactose intolerance are evidence that scientists are right about the pace of evolution of some human traits, says John Hawks, an anthropologist at the University of Wisconsin-Madison. Mutations that gave rise to genes for blue eyes and the ability to digest dairy products into adulthood arose sometime within the last 10,000 years but took many, many generations to spread throughout Europe. (Most evidence suggests the lactose tolerance gene was widespread in Europeans by the Middle Ages.)
People living in Otzi's time "had the dairy animals, but what they didn't have was enough generations for the gene to become common," Hawks says. The finding that the Iceman was lactose intolerant supports that picture. "We were right about this gene. It is new."
Previous studies of Otzi's genetic past examined DNA only from cells' energy-making factories, called mitochondria. People inherit mitochondria from their mothers, and mitochondrial DNA can be used to trace a person's maternallineage. Otzi's mitochondria carry some genetic variants not seen in modern Europeans, leading scientists to think that his maternal line has died out.
In the new study, researchers examined all of the Iceman's DNA, including his Y chromosome. Since Y chromosomes are passed from father to son, certain molecular signatures there can help identify relatives from the father's side of the family. Otzi's Y chromosome contains genetic variants that are rare in Europe today, and found mainly in people who live on the islands of Corsica and Sardinia.
A decade ago scientists might have concluded that this shared DNA meant that Otzi's people migrated from the Alps and settled on the Mediterranean islands, Hawks says. But now most think that Corsicans and Sardinians probably aren't direct descendants of the Iceman's people, but simply bear genetic signatures common throughout Europe in Otzi's day.
The Iceman may well be related to present-day people from the southern Alps where he lived and died, Zink says. Scientists don't have DNA samples from many people in the Tyrolean Alps with which to compare Otzi's DNA, leaving open the possibility that researchers may yet discover other modern-day relatives. …