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Last Updated: Tuesday, 27 June 2006, 08:01 GMT 09:01 UK
Can genes explain rising obesity?
By Emma Wilkinson

Fat man
Rising rates of obesity are also causing health problems in developing countries
Contrary to conventional wisdom, the obesity epidemic is not restricted to people in Western countries who eat bad diets and are not very active.

In developing countries, it is estimated that over 115 million people suffer from obesity-related problems.

Experts believe that in many of these people these problems are not due to lifestyle but a condition called metabolic syndrome.

Metabolic syndrome is characterised by increased abdominal fat, high blood pressure, high blood sugar, and high cholesterol.

There are many uncertainties about metabolic syndrome but one thing is certain - it cannot be explained entirely by genetics or lifestyle factors.

Humans are doing a fantastic job of mismatching themselves to their environment
Professor Mark Hanson

Instead Professor Mark Hanson, Director of Developmental Origins of Health and Disease Division and professor of cardiovascular science at the University of Southampton believes the answer lies in the study of epigenetics.

We inherit our genetic code from our parents. But this code needs to be interpreted so we also inherit the machinery for unlocking the code - known as epigenetic processes.

The epigenetic changes in the cell control what parts of our DNA are expressed and how - it is the method by which a liver cell or skin cell knows its specific function because of the genes that are switched on or off.

Researchers now believe that the environment can also prompt epigenetic changes which can affect future generations.

Professor Hanson argues that epigenetic programming in the womb is leading to the health problems associated with rapid industrialisation, especially in developing countries such as India and China.

During pregnancy

"The foetus gets a massive amount of information from its mother about the world it's going to live in once it's born.

"Her body composition, diet, lifestyle, all tell her baby about the world in which she lives which influences epigenetic processes in the offspring."

He explained that a child born in rural India would receive certain information from its mother in the womb about what kind of food there is in the outside world, how much there is to survive on and whether you sometimes have to go for long periods without any food.

The cells in the child's body would be prepared for this kind of lifestyle when the child was born.

INCREASING RATES OF DIABETES
Europe, USA, Australia and New Zealand 54%
India 151%
China 104%
Sub-saharan Africa 161%

But once an adult that child may move to the city, take an office job, be less active, and have ready access to larger quantities of food.

"Humans are doing a fantastic job of mismatching themselves to their environment."

"So you can set yourself up to be a hunter-gatherer but then you end up living in Manhatten where you can just ring for a pizza when you're hungry."

"There is evidence for effect being passed down to grandchildren and fathers and even grandfathers can determine risk," he added.

Current knowledge

So what do we know about epigenetics?

The term epigenetics was first coined in the 1940s to explain the interaction between genes and the environment.

But after the structure of DNA was discovered in the 1950s, research focused on genes as the blueprint of life.

It wasn't until the 1990's that epigenetic processes, biochemical and structural changes to DNA that controlled whether genes are 'on or off', were recognised as important in regulating how genes are expressed.

It explains why even identical twins have many differences by the time they are adults, because even though they have the same genes, changes in epigenetic controls over time in response to environmental factors, alter how those genes are expressed.

"I don't see how we draw the line between nature and nurture anymore - epigenetics is the link between the system." said Professor Hanson.

Dr Wolf Reik, at the Babraham Institute Laboratory of Developmental Genetics and Imprinting studies a process called epigenetic reprogramming - where the epigenetic code is reset, for example in embryos.

He explained it wasn't clear how many epigenetic traits were 'inheritable'.

"In general, there seems to be a system that wipes out things in the embryo but it's not clear how widespread that is.

He said that inheriting epigenetic traits made sense from an evolutionary point of view.

"There are conflicting processes, it could be of adaptive relevance and a good thing to protect the future but the jury is still out on that."

So if the 'epigenome' is responsible for a person's propensity to develop metabolic syndrome, can it be altered to give someone a better chance of fitting into their adult environment.

"Well it holds promise for diagnosis - it may help us pick out the individual at risk or maybe develop pharmaceuticals or even just counselling," said Professor Hanson

But Dr Reik added: "There are some factors that people are studying which can take methyl groups off histones and off DNA so that will be the key.

"But this will require a lot of work so this is not around the corner."






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