But while his choice has brought him financial and scientific rewards personally, it leaves others in Britain wondering: why do brain drains happen? How do we stop them? Do we need to stop them at all?
The answers to why Britain suffers brain drains in all sorts of fields of expertise, not only scientific, point up weaknesses that threaten the country's ability to compete in a global market where the smallest intellectual edge can make a huge difference to commercial competitiveness - and hence the health of a nation's citizens.
Five years ago, Professor Mullan was one of a six-strong team at St Mary's Hospital in London who found a genetic link to Alzheimer's disease, the degenerative brain disorder which affects 1 per cent of the population.
But within months, they had split up - the majority lured to the US by the promise of bigger research grants and better facilities. Today, those lures reeled in their catch, with new research published in the science journal Nature which suggests that highly reactive molecules (known as "free radicals") in the blood lead to the eventual nerve death found in Alzheimer's. And one of the key authors of that research was Professor Mullan.
"We were looking round after that first discovery for more resources to keep the research going," recalled Professor Mullan yesterday in his laboratory in the University of South Florida, where he has the chair in biological psychiatry. "We started looking around and it was the US that really looked promising. The British offers weren't tempting - not really. We might have achieved some expansion on our work, but it would have taken longer, and I'm not sure it would have happened."
Now he revels in the Florida climate and, more importantly, a scientific climate where companies and universities talk to each other, and are keen to do so. "I miss British culture," he says, with a mild sigh. "But in terms of research, I don't see any problems being here."
Worries about a scientific brain drain have plagued the science administration in the UK for years. But are they justified? The most recent study into the subject by the Royal Society, published 18 months ago, found that between 1975 and 1985, two-thirds of academics leaving Britain went to the US. But in 1994, the study found that exodus slowing down, with some expatriate British researchers returning home to provincial universities.
But according to John Mulvey, a retired physicist who is executive secretary of the pressure group Save British Science, "Very often the pure statistics tend to hide the real problem. It's not the absolute numbers of people going in either direction which really tells you about the level of any brain drain.
"If we lose people, what really hurts is the really small number who are leaders, and potential leaders, who depart and don't come back."
It is not only in science that the effects of the brain drain are felt. Professionals as diverse as auctioneers, GPs and art evaluaters have also been tempted abroad, or shifted there, in the face of what they see as indifference on the part of bureaucracy, bosses and the public to their work. Last year, Sir Peter Wakefield, former director of the National Art Collections Fund, said that he could see a permanent drift in the auctioneering of valuable works of art away from their traditional home in London. "There may be a few unsold paintings in New York, but, compared with London, it is enjoying a selling frenzy. It reflects the boom on Wall Street, as art follows wealth, and the gap between the two art centres is likely to keep widening over the next few years."
Another dealer commented, "Now Sotheby's is owned by Americans, Christie's will soon be taken over by Americans; soon the whole art world will be American."
Similarly, in 1994 British GPs were being offered substantial financial inducements - such as starting salaries of pounds 80,000 - to move to the US, where the promise of reforms to the US healthcare system (based, ironically, on the National Health Service) made their skills eminently saleable.
Archaeological evaluation also saw transatlantic poaching, with professors at British universities being offered substantial hikes in pay to move. As Mr Mulvey would point out, the people being enticed were not entire departments, but the leaders in their fields. He thinks, though, that that is still a crucial element which should be defended against loss.
"We want to retain high-quality scientists - the people who give science a good name and attract others into it. When you hear about British scientists discovering a gene, it's more inspiring than some anonymous event published in an international journal from US work. That doesn't fire the public imagination."
But there are other points to consider. "If we have to rely on public information, such as published work, then we are always going to be behind the game. What you want is to be in there, to have people closely associated with the research from both academia and industry so they can appreciate its importance. It's known as `tacit knowledge', and it's tremendously important. The frontiers of all sorts of science are advancing so rapidly that unless you are closely linked - by fax, e-mail or whatever - then you are going to miss out."
More important is the effect of such tacit knowledge on the eventual commercial exploitation of research work. One of the co-authors of the latest Nature paper on Alzheimer's works in the research laboratories of Nitromed, a pharmaceuticals company based in Cambridge, Massachusetts. Why does that matter? Because if the paper's findings do, as its authors hope, suggest a preventative treatment for Alzheimer's, then Nitromed will have a head start through its work; papers submitted to Nature are put through a painstaking checking process which can take months.
At the same time, American researchers always have a keen eye on the main chance - making themselves rich. If you invent and patent a groundbreaking discovery with wide-ranging applications, your financial future can be assured. If you can set up the company that exploits it, you too can be a millionaire.
In Britain, a number of biotechnology companies have been set up by this sort of co-operation. But to see real economic benefits in other walks of life from more commonplace scientific research, the university scientists have to find a receptive ear among existing companies in the high street, factories and office blocks.
But in Britain, commercial companies - apart from those in biotechnology, pharmaceuticals and chemistry - tend to be unwilling to talk to or co- operate with universities about the potential applications and needs for funding of promising research programmes.
"The story I keep hearing from colleagues at other universities is, `I showed another lot of Japanese visitors around the other day and they were all very interested, but I don't hear a thing from British companies'," says Mr Mulvey. A case of familiarity breeding contempt? Certainly the universities themselves are ready and willing to talk to companies. Their research funds have been cut drastically in the past decade, and the most recent Budget imposes a 50 per cent cut in real terms in the coming three years. "The universities' attitude has changed completely," says Mr Mulvey. "The scientists - and this includes the ones at the frontiers of science - are well aware of their role.
"But when they, or their colleagues, try to start up companies to exploit their research, venture capital companies in Britain won't back them. They end up having to go to the US for the money."Reuse content