What the genome can do for you

Gene genie: Novel treatments may spring from new data

All the rows, all the ethical problems and all the money spent in pursuing the human code for life will have been well worth it if it fulfils even some of its medical promise.

The potential prizes certainly glitter. In the far future, it may be possible to prevent genetic diseases from being inherited by cutting them out of the gene pool once and for all, so-called germline engineering.

At the nearer end of the time scale, genetic tests are allowing people to choose suitable therapies and lifestyles to beat disease.

And in between, lie further tantalising prospects:

• thousands of new drugs for previously untreatable diseases,
• drugs tailored to individuals, so with far fewer side effects,
• the ability to replace faulty genes, short-circuiting diseases at source.

But the work of turning the base pair data into the gold of new treatments has already begun, according to Dr Francis Collins, head of the US National Human Genome Research Institute.

"I keep a tally of the genes that are responsible for human diseases that are identified over the course of a year. In a good year, in times gone by, there might have been two or three. Last year, there have been 29 discovered."

Private companies have also combed the data to find genes that play roles in diabetes, asthma, psoriasis and migraines.

Genetic screening

The first use many new gene discoveries are put to is creating diagnostic tests. Over four million genetic tests are now conducted every year in US alone.

For example, haemochromatosis is one of the most common inherited diseases and leads to high levels of iron in the blood. This can lead to organ failure and death by the age of 50.

Previously, diagnosis was only possible by taking a tissue sample from the liver - a painful and risky procedure. Now, however, a drop of blood is enough for a genetic test and regular blood lettings and a careful diet can allow sufferers to live normally.

Many cancers and heart disease are almost certainly influenced by genetic factors, so forewarning patients of their susceptibilities would allow them to make informed lifestyle choices and help prevent future illness.

One key area of flagging up gene defects is the study of single nucleotide polymorphisms (SNPs). These are mutations affecting just one single base pair in a person's DNA.

They may not cause a disease but may be a very effective signpost for a particular problem, which is why a consortium of major drug companies is spending £28m on tracking down hundreds of thousands of SNPs.

Tailor-made drugs

It is estimated that adverse reactions to prescribed medicines result in two million people in the US being hospitalised each year - 100,000 of these die.

The difficulty is that every human being is unique. And so, while a particular medicine may be effective for some people, it could be seriously damaging to others.

The new data about the human genome will begin to make identifying these groups possible. This would obviously save suffering but even if the drug is simply ineffective for a genetic group, considerable cost savings are possible.

This approach is already in use, for example in the treatment of leukaemia, but it will only become of widespread benefit when testing is possible in a doctor's surgery.

Brand new drugs

Targets are what drug companies call the parts of biological molecules they attack with drugs to fight disease, and the human genome information looks like providing more targets than any shooting gallery.

Currently, the knowledge of human molecular biology is such that the targets are counted in hundreds but the genome promises thousands.

This approach, disabling harmful molecules, matches most closely the current research practices of the large pharmaceutical companies, and so this is the area which most excites them.

"The greatest impact, most quickly, of the human genome data is the ability to identify new targets upon which drugs can act," says Dr Ian Purvis, UK associate director of molecular genetics at GlaxoWellcome.

Gene therapy

Gene therapy, using the genes themselves as medicines, is in many ways the most obvious application of the human genome data. But it is also the most controversial, with a number of deaths linked to experimental treatments.

Single gene disorders

Over 4,000 illnesses are caused by faults in single genes:

Cystic fibrosis

Huntington's chorea

Sickle cell anaemia

Muscular dystrophy

The ideal focus for gene therapy is on single gene disorders, such as cystic fibrosis. Here one abnormal gene can be cut out and replaced by a healthy version, delivered by a tamed virus.

But although over one million people in Britain suffer from inherited illnesses, individually the disorders are rather rare. This means the potential market for a company is small.

At best, this would mean the treatment was expensive. At worst, it could mean the treatment was not developed at all.

More common diseases, such as cancers, diabetes and schizophrenia, involve complex interactions between faults in several genes and so are not so amenable to gene therapy.

Furthermore, knocking out a faulty gene is not without risk - for example, the gene for sickle cell anaemia also gives some resistance to malaria.

Nonetheless, recent successes for gene therapy in treating haemophilia and "bubble" children with Severe Combined Immunodeficiency means gene therapy research will continue.

Germline engineering

The most extreme suggested use for the human genome data is editing the DNA inheritance bequeathed from one generation to the next.

Such a scenario involves identifying an abnormal gene and then correcting it in the cells which are used to pass genetic information to offspring - eggs and sperm.

No subsequent generation would then be afflicted by their ancestors' gene defect.

However, such irreversible tampering with the code for life will only be allowed after major ethical reservations and safety concerns over possible unexpected results of the changes, are addressed.

Hope or hype

There is little doubt that the revelation of the human genome will benefit healthcare in the short and long term.

But many of the treatments will be expensive and will do nothing to avoid the damage caused by viral and bacterial diseases.

It has been suggested that a brave new world awaits us in which all ailments can be monitored from a daily mouth swab inserted into a DNA reader in our bathroom cabinets.

But Dr Ian Purvis says: "It could be that like, a long time in the future, but that is based on the rather arrogant view humanity has that it will understand everything we find - and we never have in the past."

By BBC News Online's Dr Damian Carrington