Tracking disease and human migration through genetics

By Grant Jacobs 16/02/2010

A recent article on the internet and several research papers are reminder of the power of modern genetic and bioinformatic analysis to reveal insights to the history of human disease and human migrations.

(Source: wikipedia)
(Source: wikipedia)

Ian York, who writes Mystery Rays From Outer Space, has recently posted a very interesting article Leprosy and the Silk Road. His article pulls together the results of three new reports, in Science, Nature and Nature Genetics. (You’ll need to be a subscriber to access the full articles.)

Please read Ian’s article for the full details: I’m only going to talk about one aspect here, and briefly at that. The genome of microbe that causes leprosy, Mycobacterium leprae, this microbe has been sequenced and compared with isolates of this disease-causing ’bug’ taken from different parts of the world revealing the path the leprosy has taken across the planet over thousands of years. Ian’s article has the details, but in broad terms leprosy originated in East Africa and spread east via the Silk Road, independently west into Europe and later to the Americas via European migration.

What intrigues me is how this and many other studies are pulling together the story of human migrations and how we lived in exquisite detail.

Some information relates to disease, such as the work Ian reports, showing the emergence and spread of disease along with migration or colonisation.

(Source: wikipedia, data originally from mitomap)
(Source: wikipedia, data originally from mitomap; numbers are thousands of years before present time. High-resolution version available at wikipedia.)

There are studies comparing languages to track the migration of people, including one from a New Zealand research group examining migration across the Pacific.

Other studies link specific traits with parts of the world or agricultural practices. People who are tolerant of lactose as adults (e.g. able to drink milk as adults) have particular genetic ’markers’ associated with that trait. However, the genetic markers are different in different places. For example, it has been shown, that lactose tolerance in North Africa is associated with a different genetic change than is seen in lactose tolerant people in Europe, suggesting that lactose tolerance in adults arose independently in North Africa to Europe, possibly as a result of use of camel milk as opposed to cow milk and a lack of mixing between European and North African people.

What strikes me is how all these many different studies–I’ve only given a tiny sample here–are converging to create a very detailed picture of our past. What group of people went where. What kind of food were they eating. What diseases did they take with them. (Similar studies can reveal the ’movements’ of crop plants or animals, too.)

Genetics, accompanied by bioinformatics (used to analyse the genetic data), is adding a lot of new elements to this ever more intricate picture.

Besides the more formal studies, there are also ’genetic genealogy’ services, such as those offered by Genetic Genealogy or Roots For Real, who offer to take a DNA sample (usually a cheek swab), screen your DNA for a ’markers’ that which, when compared with those collected elsewhere in the world, can be indicative–in broad terms–of the ancestral groups you came from.

These articles also appeal as I’ve travelled a little myself, including portions of the Silk Road, visiting Bukhara, Khiva and so on. It puts another layer on my travels. I can image not just the people migrating but also the microbial ’baggage’ they took with them.

Footnote (added 17-Feb-2010):

Those interested in more information about leprosy today may wish to check out the website of LEPRA an UK-based organisation devoted to assisting leprosy sufferers. They have an on-line copy of their magazine. (Click on the magazine to see it in full-screen mode. There are PDF copies available to download.)

Other posts that might interest you in Code for Life:

Map shows New Zealand with lowest death rate on earth in 1856, over 11 in 1000 dying

Rubella, not a benign disease if experienced during early pregnancy

Deleting a gene can turn an ovary into a testis in adult mammals

Developing bioinformatics methods: by who and how

Explore ancient science books on-line

Monday potpourri: maps, malaria in the USA, cholera in Dunedin and vaccines

Genetic tests and personalised medicine

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