̽��ֱ�� of Cambridge - genetic variant

‘Light skin’ gene mirrors socio-cultural boundaries in Indian population

fpjl2 — Wed, 13 Nov 2013 10:43:27 +0000

̽��ֱ��genetic mutation in SLC24A5 is known to be pivotal in the evolution of light skin, and is responsible for a significant part of the skin colour differences between Europeans and Africans.

Now, a new study has examined for the first time a large, uniform genetic sample collected directly in south India, and suggests that natural selection is not the sole factor in skin tone variation across the Indian sub-continent, and that cultural and linguistic traits still delineate this skin pigment genetic mutation.

̽��ֱ��results show that the gene is found with much higher frequency in Indo-European speaking groups that are more prevalent in the north-west of the country.

But the mutation is also high in populations groups known to have migrated north to south, such as the Saurashtrians, who - while native to Gujarat in north-west India - are now predominantly found in the Madurai district in its southernmost tip.

Researchers say that the study, published last week in the journal PLoS Genetics, shows that the genetic mutation in SLC24A5 has a common origin between Europeans and Indians.

But while the complete dominance of the gene in Europeans is likely to be solely down to natural selection, they say, the rich diversity of this genetic variant in India - high in some populations while non-existent in others, even neighbouring ones - has some correlation with factors of language, ancestral migration and distinct social practices such as limiting marriage partners to those with specific criteria.

̽��ֱ��researchers say the findings display an “intriguing interplay” between natural selection and the “unique history and structure” of populations inhabiting the Indian subcontinent.

“In India, this genetic variant doesn’t just follow a ‘classical’ theory of natural selection - that it’s lower in the south where darker skin protects against fiercer sunlight,” said study co-author Mircea Iliescu from Cambridge’s Biological Anthropology Division.

“ ̽��ֱ��distribution of the SLC24A5 genetic variant in India follows patterns very much influenced by population. Understanding the genetic architecture behind the remarkable skin colour variation found today in the populations of India has the potential to shed light on the wider mechanisms responsible for creating diversity throughout human evolution,” Iliescu said.

In the 1950s it was proposed that there was a massive wave of European migration into northern India a few thousand years ago, described as the ‘Aryan invasion’, which led to the collapse of the Harrapan Civilisation - a Bronze-Age Civilisation.

This theory, now considered widely discredited by many researchers due to the lack of archaeological evidence, is still a hugely debated issue in contemporary Indian politics - invoked by political parties in the southern states of India who claim that the southern populations, described by some as the ‘Dravidians’, are the truly indigenous people of India.

̽��ֱ��researchers say that, while speculative, they find it “hard to imagine” a large-scale population migration at a single point in history based on this study – since the presence of this genetic mutation is too widespread, with an average frequency of 53%, including the Austroasiatic language groups thought to have originated in southeast Asia.

They say the wide variation and complex pattern hints at the possibility of multiple “gene flows” into the sub-continent over a much longer period of time, some of which might be linked to the spread of agriculture; although the study does show higher frequencies of SLC24A5 in Indo-European speaking groups compared to so-called Dravidian populations.

̽��ֱ��researchers suggest that aspects of ‘social selection’, such as high levels of ‘endogamy’ - marriage within a particular group in accordance with custom - as a result of the caste system, has created a “mosaic pattern” for this skin pigmentation mutation across Indian populations.

“This study helps us to understand various other mechanisms that could have contributed or shaped the existing biological spectrum of human skin colour besides natural selection - driven by ultraviolet rays - and further understanding of this complex phenotypic trait,” said Chandana Basu Mallick, a co-author on the study from the ̽��ֱ�� of Tartu in Estonia.

“We are taking gradual steps towards understanding the evolutionary history of this adaptive trait, and the journey of our ancestors from fur to the diverse skin tones of the present day.”

“Our work addresses human diversity, diversity which should be celebrated,” added Iliescu. “It tries to explain the origins and history of this diversity - opening up a window into a different kind of history, not just a history of places and objects, but a living history which helps us to better understand ourselves.”

“Studies on Indian populations have been under-represented in the genomic era, and the understanding of Indian genetics is still at a very early stage. With this study, we hope we’ve brought valuable new understanding to the evolutionary genetics of Indian populations.”

Latest research shows that the presence of the genetic mutation for lighter skin - found in “almost 100%” of Europeans - broadly conforms to many cultural and linguistic differences, as well as ancestral, in the wider Indian population.

In India, this genetic variant doesn’t just follow a ‘classical’ theory of natural selection

Mircea Iliescu

Prasanth Chandran

“Where you are going is more important than how fast you are going”

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Finding the ‘genetic signposts’ of disease

ns480 — Sat, 01 Sep 2007 11:57:45 +0000

̽��ֱ��Wellcome Trust Case Control Consortium (WTCCC) brought together 50 research groups from dozens of institutions in the UK, including the Wellcome Trust Sanger Institute at Hinxton, Cambridge, and the ̽��ֱ�� of Cambridge. ̽��ֱ��success of the project depended both on capitalising on the knowledge built by the Human Genome Project and the HapMap Project, two consortia in which the Sanger Institute was a major partner, and also on the sheer size of the collaboration across the UK.

Dr Panos Deloukas, who led the team at the Sanger Institute, explains: ‘This was unprecedented in the UK. ̽��ֱ��sharing of samples and data on this scale has changed the ethos of the research community – through working with 50 laboratories across the country and conducting large-scale disease genetics at a level that has never been done before.’

̽��ֱ��collaborators contributed their large national collections of DNA samples collected from different patient groups – totalling an incredible 17,000 samples across the UK (2000 patients for each of the diseases studied plus 3000 healthy controls) – allowing over 10 billion pieces of genetic information to be analysed by genome scan using the Affymetrix GeneChip assay. Tiny genetic variations between individuals that predispose to type 1 and type 2 diabetes, Crohn’s disease, bipolar disorder, coronary heart disease, hypertension and rheumatoid arthritis were sought. By identifying these ‘genetic signposts’, scientists might understand which people are most at risk and why.

‘We have found 24 genomic regions with very strong evidence of harbouring variants that underlie six of the phenotypes we studied and we saw a spectrum of genetic architectures among these common diseases,’ explains Dr Deloukas. ‘Once we had these findings then the medical collaborators provided insight into the significance of the gene associations and tried to replicate them.’

Significant new breakthroughs have been made for Crohn’s disease and type 1 diabetes, and a link between the two diseases has been discovered. Dr Miles Parkes (Gastroenterology Unit, Addenbrooke’s Hospital, Cambridge) and Professor John Todd (Department of Medical Genetics, ̽��ֱ�� of Cambridge), both participants in the WTCCC, are now leading studies to follow up these findings. ‘It’s rewarding to see that the highly significant genetic associations are now being replicated in independent samples,’ says Dr Deloukas. ‘ ̽��ֱ��framework set up by the WTCCC clearly works.’

Dr Mark Walport, Director of the Wellcome Trust, views the WTCCC as a success: ‘It is an excellent illustration of the importance of knowing the human genome sequence and cataloguing its variations. Hopefully, with the insight gained into these diseases we will be able to make real progress in combating them.’

For more information on the Wellcome Trust Sanger Institute and the WTCCC (including a full list of participants), please go to www.sanger.ac.uk and www.wtccc.org.uk

One of the biggest projects ever undertaken to identify genetic variants that predispose some people to certain diseases was begun in 2005, thanks to £9 million funding from the Wellcome Trust. ̽��ֱ��ground-breaking results of this study were published in June this year.

It is an excellent illustration of the importance of knowing the human genome sequence and cataloguing its variations. Hopefully, with the insight gained into these diseases we will be able to make real progress in combating them.

Dr Mark Walport, Director of the Wellcome Trust

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̽��ֱ��Wellcome Trust

<div> <p> ̽��ֱ��Wellcome Trust is well known as the leading funder of biomedical research in the UK, spending many millions on major research projects that have tangible impacts on health and disease.</p> <p>This ethos is abundantly evident in the £9 million support given to the Wellcome Trust Case Control Consortium, a collaboration of leading human geneticists across the UK, to analyse thousands of DNA samples and identify genetic predispositions to common diseases. ̽��ֱ��Trust also embraces studies on how biomedical research affects people and society; the funding of a research project being undertaken in the ̽��ֱ�� of Cambridge’s Centre for Family Research is an example of this rounded view.</p> <p> ̽��ֱ��Wellcome Trust is the UK’s largest source of funds for biomedical research and the second largest medical research charity in the world. Spending around £500 million each year in the UK and internationally, the mission of the Trust is to support the brightest scientists with the best ideas, and to ‘respond flexibly to medical needs and scientific opportunities’. Through support of a broad portfolio of biomedical research from immunology and infectious diseases to physiological sciences, the Trust aims to make a difference by advancing understanding of the processes that underpin health and disease. And, as the leading funder of translation research in the UK, the Trust is also committed to translating research innovations into health benefits. Technology Transfer at the Trust can help bridge the gap between fundamental research and commercial application by funding research that is sometimes deemed ‘too early’ or ‘too high-risk’ to be pursued by the corporate healthcare or investment sectors.</p> <p>Perhaps less well known are the Trust’s funding streams across medical humanities and public engagement. Through these, the importance is recognised of engaging with society to foster an informed climate within which biomedical research can flourish. This understanding can inform many things, from the ethical conduct of research, to the development of public policy and regulatory environments, to the enlightened debate about biomedical science, its achievements, applications and implications.</p> </div>

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