Page last updated at 10:10 GMT, Tuesday, 9 December 2008

Worldwide search for asthma clue

By Rebecca Harrison
BBC Horizon

Tristan da Cunha
Tristan da Cunha offers a great chance for scientific study

In the middle of the South Atlantic, 1,500 miles from any other land mass lies the most remote inhabited island in the world, Tristan da Cunha.

This in itself is quite extraordinary, but the island is also unique for an entirely different reason - half of its 261 residents suffer from asthma.

Dr Noe Zamel, of the University of Toronto, first recognised this phenomenon when he met the islanders after they were evacuated to Britain in 1961, when the island's volcano erupted.

Studying for his PhD at the time, Dr Zamel was part of the team of scientists assembled to learn everything they could about this unique population.

"I was in charge of doing the pulmonary function tests and I was amazed that every second Tristanian that I tested had evidence of airway obstruction caused by asthma" said Dr Zamel.

After the volcano calmed, the islanders returned home, followed eventually in 1993 by Dr Zamel. His quest was to discover what was behind the asthma pandemic.

No air pollution

Dr Zamel knew the island was pristine.

"From the air pollution point of view, Tristan da Cunha is the safest place in the planet. There is basically no industry and the winds are so strong that the air here is as pure as it can be."

So the answer, Dr Zamel deduced, must lie in their genes.

With only seven surnames amongst the entire island, the population has a very homogenous gene pool.

Tristan da Cunha inhabitants Lillie Swain, Theresa Green and Doreen Swain
Rates of asthma are very high on Tristan da Cunha

"So with the smaller sample size we could achieve what would be required with thousands and thousands of other populations," he said.

By analysing the islanders' genes Dr Zamel achieved what would have been impossible with any other population - the isolation of one particular gene - known as ESE3.

This gene is involved with the deposition of collagen in the airways. If the gene is faulty then the airway walls are thickened and constricted, making it more difficult to breathe.

Barbados clue

However, Dr Zamel's discovery in Tristan da Cunha is exceptional, and it does not explain the allergy explosion in the rest of the world.

Professor Gideon Lack, the Head of Paediatric Allergy at Guys and St Thomas' , explains the extent of the problem.

Dr Noe Zamel
Dr Zamel is carrying out research on Tristan da Cunha

"Twenty percent of schoolchildren carry an asthma inhaler. That's one in five children," he said.

"Similar numbers of young children, 20%, suffer symptoms of eczema. About thirty to forty percent of patients suffer hay fever."

At least part of the answer behind the allergy explosion in the rest of the world may lie on the sundrenched shores of Barbados.

Barbados has so many people suffering from asthma that part of the A&E ward in the Queen Elizabeth Hospital in Bridgetown is dedicated entirely for patients coming in with asthma attacks.

Dr Harold Watson who runs this asthma bay explains the degree of the problem.

"In a typical busy day we can see 30 asthma patients per eight hour shift passing through."

Modern home

Associate Professor Kathleen Barnes, of Johns Hopkins University, has been investigating why the island has become so allergic in recent years.

"Barbados really is a microcosm of what's happening globally, it's gone through a very rapid period of change over a very short period of time," she said.

Allergies are the price we pay for our modernization over time
Professor Kathleen Barnes
Johns Hopkins University

Over the past 20 years, Professor Barnes and her team have analysed the homes on the island in minute detail, collecting dust samples, and monitoring allergen levels.

Professor Barnes' results are enlightening. "We believe that in the modern home there are a variety of factors that contribute to this exposure.

"Indoor carpeting, better upholstered furniture and so on. All of these things combined contributed to these higher levels of allergen."

Studies such as this are illustrating that the modern home that many of us desire is greatly increasing our exposure to allergens, the substances that induce allergies such as dust mites.

The people of Tristan da Cunha are only part of the jigsaw that is the global allergy explosion.

It is hoped that with the discovery of the gene that contributes to asthma, medications will be developed to target the disease worldwide.

With Dr Zamel's latest visit to the island, accompanied by the Horizon team, he collected more DNA samples to further his studies.

However, it is clear that the answer does not only lie in our genetics.

'Price we pay'

Like the people of Barbados, we are changing our environment so rapidly that our bodies simply can not keep pace.

Dr Barnes goes on to explain: "Allergies are the price we pay for our modernization over time.

"This convergence if you will of various environmental factors, rapid changes in the domestic environment, changes in lifestyle due to rapid modernisation - all of the cars on the streets and the pollution that comes from these cars.

"It's sort of this perfect storm if you will."

Many of us are living the dream, the Western lifestyle. However, with more than 300 million asthmatics worldwide, and a third of all adults in the UK affected by allergy, perhaps this dream is at the cost of our own health.

Horizon: Allergy Planet is on BBC Two, on 9 December at 2100GMT.

The Story of Asthma Island is on BBC Four, on 9 December 2200GMT.

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