AT first sight it seemed an open and shut case. The patient standing before genetics expert Professor John Burt seemed to have all the trademark characteristics of Huntington's disease, a much-feared inherited brain disorder.

Like all Huntington's cases the patient suffered bouts of uncontrollable jerky movements, caused by loss of nerve cells. But Prof Burt, professor of clinical genetics at Newcastle University, became suspicious as he took the patient's history.

If this was truly Huntington's disease - named after an American doctor who lived between 1850 and 1916 - why was the patient's intellectual ability unaffected?

One of the traits of Huntington's is alternating excitement and depression following be dementia. But this patient was intellectually unimpaired. Could this be a wholly separate genetic disease, unknown to the world?

Since experts began keeping a record of genetic diseases in the 1960s the number of separate conditions identified by scientists has steadily climbed from around 1,000 to more than 10,000.

Prof Burt, who believes that the final total of genetic diseases could eventually reach 15,000, suspected he could be on the trail of a previously undiscovered disease.

Looking back he recalls: "I wasn't convinced by the clinical features. The symptoms did not ring true."

His suspicions led to a series of tests on members of the same family and tantalising evidence that he had indeed stumbled on a new genetic disease.

"I announced in 1990 that we had found a new disease, but we couldn't prove it until more modern techniques came along. The Genome project gave us the tools so that a couple of scientists can do in a few months, what would have taken an army of people just a few years ago," he explains. More than a decade after that first encounter, Prof Burt and his team at the Institute of Human Genetics in Newcastle are close to tracking down the gene responsible for causing the, as yet unnamed, condition.

The team announced at the recent American Society of Human Genetics conference in Philadelphia that they had localised the defective gene to chromosome 19, one of 46 chromosomes within every cell of every human being.

"We have shown that the gene has been running in a large extended family in Cumbria since 1800 and perhaps earlier. We are now working flat out to identify which gene on chromosome 19 contains the 'spelling mistake' that caused this terrible disease," says Prof Burt, speaking from his office in the Centre For Life complex.

"We are confident, thanks to the tools given to us by the Human Genome Project, that we will identify that gene within a matter of weeks."

While the disease began in Cumbria, when the genetic make-up of a single individual man or woman spontaneously mutated, it may now have spread far and wide.

"It will be largely confined to the North-West corner of England but there is no doubt that it will extend to families in the North-East," he says.

Because it can be traced back to a time when migration across the world was the norm for many people fleeing poverty, it could now have taken root in America and Australia and other former outposts of Empire.

Prof Burt is in touch with genetic scientists in other parts of the world who are trying to track the disease overseas.

While there is great intellectual curiosity about the new disease, there is also an over-riding need to identify and offer counselling to anyone who may be affected and - most importantly - to come up with a way of treating the disease.

"If your parents had this new disease you have a 50/50 chance of inheriting either the working copy or the faulty copy of the gene. Since it does not come on until your 40s, or sometimes later, most people will have had their kids by then," says Prof Burt.

Until very recently, it has not been possible to identify who carries the gene. For Prof Burt and his team the challenge now is to develop a way of treating the condition, or even better, stopping it happening before it starts.

One of the most promising potential treatments for the new disease - and for many other genetically transmitted conditions - would be to give carriers of the faulty gene a stem cell implant.

At the moment the only source of such cells are embyronic cells. Every day large numbers are made as a by-product of test tube baby treatment (in vitro fertilisation) and eventually discarded.

The stem cells, extracted from embryos under 14 days old, possess the ability to develop into any kind of tissue in the body depending on what chemical cues they are given.

Grown in the laboratory, they could be used to make replacement tissue for treating a range of diseases. Last month Canadian researchers created new heart muscle in rats using stem cells extracted from the animal's own bone marrow. Of 22 rats with damaged hearts treated, 20 grew new heart muscle.

Scientists also believe they could be used to treat damaged genes. Stem cells from some future cell bank could replace the cells that have been genetically damaged.

Another way might be to use the techniques developed by the team who successfully cloned Dolly the sheep. This involves taking the nucleus from an adult patient's cell and inserting it into a human egg, whose own nucleus has been removed.

The egg would then subdivide and grow into an embryo. While still at the size of a pinhead, containing about 100 cells, the embyro would be cannibalised to extract the stem cells.

"It is called therapeutic cloning. The cells grown in this way are geneticaly identical to the patient," say Prof Burn.

Despite the exciting prospects opening up for doctors and their patients there is a cloud looming on the horizon. At the moment genetic scientists all over Britain have had to put work on using stem cells on hold because the issue is to be debated by MPs next month. MPs and peers are to be given a free vote on whether the law should be relaxed to permit therapeutic cloning.

Prof Burn says: "There is resistance to the technology on the grounds that somehow it will be a slippery slope to cloning people, which is understandable, but wrong. That is against the law. But the danger is that if they vote against it then we will not be able to develop these new treatments, which are enormously promising for many chronic diseases."