Technology brings new life to the study of diseases in old bones
(23 October 2012)
New technology that can analyse diseases in ancient skeletons has yielded fascinating results in a study led by Durham University.
Professor Charlotte Roberts of Durham’s Department of Archaeology, working in partnership with Professor Terry Brown from the University of Manchester, used a new system that can scrutinise millions of gene sequences within seconds. They used the method to identify tuberculosis (TB) genes in a female skeleton from the 19th Century found in a Leeds crypt.
Their study is part of wider research into the identification of strains of TB in skeletons spanning nearly two thousands years, from 100 AD to the late 19th century. It is hoped that understanding how the disease has evolved over time will help improve treatments and vaccines. TB rates have been increasing around the world since the early 1990s and it is estimated that one third of the world’s population has latent TB. After HIV, it kills more people than any other infectious disease.
Certain strains of TB affect the sufferer's bones, especially in the spine. The marks made by the disease remain evident long after the person's death. This helped Professor Roberts find suitable skeletons to screen for TB genes.
She sourced 500 skeletons from across Europe that showed evidence of TB, dating from the Roman period to the 19th century. Bone samples from these skeletons were screened for TB DNA, and 100 of these were chosen for this study.
Professor Roberts said: "So many skeletons were needed as it's very hard to tell if any DNA will have survived in the bones. You don't really know if there will be any present until you start screening and previously, that has been a lengthy process."
Terry Brown then took forward the search for TB DNA in the skeletons. Each small section of bone was ground up and placed in a solution. This was then put in a special machine which captured every gene sequence in the DNA. Millions of sequences were then processed by computer. Professor Brown and his team then searched these sequences for TB. Because it is a bacterial disease, the bacteria's DNA can remain in the bones after death.
Professor Brown said: "Previously we could only scan the bone sample for specific genes. We wouldn’t see everything that was there which meant we could easily miss other genetic information that could be relevant. Using this hybridization screening meant we could search for different strains of TB, not just one."
About 280 sequences in the Leeds skeleton were found to match known TB genes. The data identified the strain of TB as one that is uncommon today, but was known to have been present in North America in the 19th century. Indeed, it was found to be very similar to a strain recorded in a TB patient in New York in 1905.
Professor Brown added: “The fact that this particular strain of TB was found in both North America and in the skeleton from 19th century Yorkshire is not necessarily unusual; there were many migrants from Britain to America during the 19th century so it makes sense that TB strains were spread.”
Because the method means it is possible for TB DNA that isn’t from the bone but from surrounding soil in the sample to be detected, the results were crosschecked using the more conventional method of DNA identification known as polymerase chain reaction and found to be accurate. Their findings have now being published in the journal The Proceedings of the National Academy of Sciences.
Professor Roberts said: “We’re really pleased with the results of this study and to establish that the technology works. It will save a lot of time in the future. We now hope to publish more of the huge amounts of data we have acquired from the sequencing”
The scientists hope to compare their results with similar studies being done in America to assess what TB strains have also been identified there. They are interested in studying which strains were brought to the country by migrants and what impact those had on the native strains of the disease.