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Wednesday, April 18, 2012

Ötzi the Iceman Was Lactose Intolerant

Hey all of you out there reading this who are lactose intolerant. Whenever anyone makes fun of our shared condition remind them of one big thing: We're normal, they're mutants! [Cue scary music]

As I've written over and over again - here's a post from 2005 - most adult humans in the world are genetically unable to produce the enzyme named lactase, which digests the milk sugar lactose. For most of us, our parents were lactose intolerant and their parents were and theirs and so on all the way back to our earlier ancestors.

A couple of years later, big news hit the scientific community that shouldn't have been news at all: "Just 7000 years ago, Europeans were unable to digest milk, according to a new analysis of fossilised bone samples..." Most Europeans today are lactose tolerant - they produce lactase all their lives instead of stopping at some early age - because they are heirs to a long tradition of domesticating animals that produce milk. Milk is good for you - remember than every time someone claims that milk is poison - and people who could drink milk as adults had a small but significant advantage in living long enough to produce healthy babies. That allowed the mutation that kept the lactase going for life throughout European populations and their descendents, including many in the U.S. and Canada. Being able to use DNA to check on the actual genes of individual humans who lived thousands of years ago is a scientific marvel of the first order, but it has just confirmed what earlier scientists had been saying all along in this case.

And now similar DNA testing has been performed on the most famous neolithic European, to my knowledge the only one who has a name: Ötzi.

Ötzi the Iceman is a mummified body of a man who lived about 5300 years ago. Because he was buried in ice, he's much better perserved than almost anyone else from that era and scientists have jumped at the chance to examine every aspect of his being. He's known to have died at around the age of 46 from an arrow wound and had knee problems that may have made it harder for him to escape his enemy.

To get yet more tantalizing info, scientists have been working feverishly to decode his DNA to see what it tells them. And no surprise, no surprise, one of the obvious things that pops out is that he was lactose intolerant. As this story in the New York Times, Lactose Intolerant, Before Milk Was on Menu by Sindya N. Bhanoo reports:

[R]esearchers have sequenced the complete genome of the iceman, nicknamed Ötzi, and discovered even more intriguing details. They report in the journal Nature Communications that he had brown eyes and brown hair, was lactose intolerant and had Type O blood.

The lactose intolerance makes sense, said Albert Zink, an anthropologist at the European Academy of Research in Bolzano, Italy, who was one of the study’s authors.

"In early times, there was no need to digest milk as an adult because there were no domesticated animals," Dr. Zink said. "This genetic change took hundreds of years to occur."

The original study appeared in the journal Nature.
"New insights into the Tyrolean Iceman's origin and phenotype as inferred by whole-genome sequencing," by Andreas Keller et al., Nature Communications 3, Article number: 698, doi:10.1038/ncomms1701

The Tyrolean Iceman, a 5,300-year-old Copper age individual, was discovered in 1991 on the Tisenjoch Pass in the Italian part of the Ötztal Alps. Here we report the complete genome sequence of the Iceman and show 100% concordance between the previously reported mitochondrial genome sequence and the consensus sequence generated from our genomic data. We present indications for recent common ancestry between the Iceman and present-day inhabitants of the Tyrrhenian Sea, that the Iceman probably had brown eyes, belonged to blood group O and was lactose intolerant. His genetic predisposition shows an increased risk for coronary heart disease and may have contributed to the development of previously reported vascular calcifications. Sequences corresponding to ~60% of the genome of Borrelia burgdorferi are indicative of the earliest human case of infection with the pathogen for Lyme borreliosis.

Hmmm. I'm blood group O and I'm lactose intolerant. But I have blue eyes, the result of a different mutation. We're all mutants, just in different ways. And yes, I mean you too.

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