Has decoding the genome lived up to hype?

When scientists first decoded the human genome there was much excitement.

But in this week's Scrubbing Up, scientist Dr Caroline Wright says that progress has not been as significant as might have been hoped a decade ago.

Genome sequencing. Pic:Carol and Mike Werner, Visuals unlimited/SPL What future hopes do genetics hold?

In 2000, an international press briefing with Bill Clinton and Tony Blair announced the completion of the first draft sequence of the human genome. It promised to revolutionise medicine, offering new genetic tests and better treatments.

Now, 10 years on, it's time to take stock of where we are at and perhaps admit that progress has not been as rapid as we may have wished for.

Scientists have made enormous advances in understanding genetic variation and its role in disease. They have identified hundreds of genetic variants linked to common diseases.

But this research has served to highlight how complex the human genome actually is.

Taking time

Like all things in medicine, it takes time for something discovered in a lab to then be used in clinical practice. Currently the benefits to patients from studies of the genetic basis of common diseases are very limited.

Start Quote

We are unlikely to be able to predict the likelihood of developing disease in individual patients”

End Quote Dr Caroline Wright

But by comparing differences found - and in particular, differences between large groups of people with a particular disease and groups of healthy individuals - scientists are now able to investigate the genetic basis of common diseases.

They have been able to uncover a treasure trove of hitherto unknown links between specific genetic variants and diseases such as cancer, diabetes and cardiovascular disease.

Does this mean that we will soon see genetic tests that tell us whether we will get type 2 diabetes or whether we face heart problems later in life?

Probably not. But that doesn't mean these genetic studies won't eventually help improve our health and reduce disease.

For some inherited disorders such as Huntington's disease and cystic fibrosis, where a change in just a single gene causes a potentially devastating condition, highly predictive genetic tests already available.

But scientists are now finding that most common diseases are far more complex.

Exceptions

Most diseases are not caused by one gene alone - there is no 'obesity gene' or 'heart disease gene' - but by the interaction of lots of genetic and environmental factors.

By analysing which genetic variants an individual possesses and combining their expected effects it is possible to calculate if a person is more or less likely to get a particular disease than the rest of the population.

This could allow us to divide the general population into risk categories, in order to better target monitoring and preventative strategies, such as screening for breast and bowel cancer, to those at greatest risk.

Unfortunately, because the individual risks associated are generally very small, and the genetic variations are very common, for most diseases this means we are unlikely to be able to predict the likelihood of developing disease in individual patients.

However, there are a few noteworthy exceptions - for example, age-related macular degeneration - where the genetic risks explain a substantial proportion of the disease and which , when combined with other non-genetic factors, might be able to accurately identify individuals who will develop the disease in future.

Start Quote

By improving our understanding of genes and how they cause disease, these studies open the way to better treatments by identifying a plethora of new drug targets”

End Quote Dr Caroline Wright

Although specialised genetics services already exist throughout the NHS for managing inherited diseases, in the not-so-distant future we may all be able to get our full genomes sequenced, as costs continue to plummet.

This offers potentially even greater benefits to human health, such as identifying rare genetic changes that cause inherited disease and personalising cancer treatments.

However, it also poses difficult ethical questions and will have a major impact on the NHS in terms of the way clinical services are developed, organised and delivered.

So what will this cost the NHS? Integrating new technologies into clinical practice inevitably costs money but this may be offset by efficiency savings and more effective, personalised therapies. However, these changes are still some way off, and predicting their economic impact is difficult until we know what benefits they offer patients.

Perhaps the most important contribution of genetics for most people still lies in the future. By improving our understanding of genes and how they cause disease, these studies open the way to better treatments by identifying a plethora of new drug targets.

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