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Should you have your whole genome sequenced?

Research News
Friday, April 20, 2012 - 10:54am

Have you ever contemplated having a genetic test? Maybe someone in your family has a genetic condition and you've been curious about whether you too might develop it in the future. Or maybe you've had the opportunity to be part of a research project that involves genetic testing, offered through your workplace, school or university.

It seems that yet another option might soon be available to you; whole genome sequencing. The race to develop fast and affordable methods for sequencing an entire genome has been on for some time now, and the $1000 genome sequence might soon be within reach for all of us, meaning it would be as affordable as your average computer.

The question is; would you want to have your whole genome sequenced?

Direct-to-consumer genetic tests have received much attention over recent years, with companies such as 23andMe and Navigenics offering online genetic tests for anyone who has a few hundred dollars to spare. Sending off a DNA sample to one of these companies will provide you with a detailed report about your personal risk of developing more than 200 conditions and traits, including breast cancer, lupus, diabetes, alcohol dependence, obesity, schizophrenia, Alzheimer disease and even earwax type.

Companies offering online direct-to-consumer genetic tests currently use targeted genetic testing to provide information about genetic risk, instead of whole genome sequencing. There's a big difference between these two types of analysis, and it helps to understand the difference by imagining your whole genome is a telephone book with about 3 billion individual letters. Targeted genetic testing involves turning to specific pages within the telephone book and examining those bits only. Whole genome sequencing, on the other hand, is akin to printing out the entire telephone book.

If you're contemplating paying for a whole genome sequence, there are some important facts worth noting.

First, unless your whole genome sequence is accompanied by a detailed report interpreting what it contains (and possibly an experienced geneticist to answer your resulting questions) it will be much like opening up a telephone book in a foreign language.

Second, even with a full report interpreting your genome sequence, current knowledge extends only to a tiny part of the human genome and so, even with an accompanying report to interpret your genome, the vast majority of your genome sequence will remain meaningless and thus be of no use to you, or your doctor. For example only about 3,500 of the 23,000 genes in the genome have been connected to a particular disease or diseases. The genetic basis for common diseases such as cancer, heart disease and diabetes remains largely unknown.

Third, our knowledge of genetics is evolving so rapidly that the report you receive about your full genome will alter over time as new information becomes known. The report you receive now will be very different from the report you would receive if you waited five years, as much more will be known then, both altering and adding to the information you would receive now.

Fourth, and perhaps most significantly, for a small proportion of people, serious genetic mutations will be found. For some genetic conditions, such as the risk of breast and ovarian cancer due to mutations in the BRCA1 or BRCA2 genes, preventative and treatment options are available to decrease the risk of developing the condition later in life. However, for other conditions, such as Huntington disease, there is little that can be done to prevent them. Such testing can also identify that a person's parents were closely related, including that the person was the result of incest.

Research indicates that individuals experience a variety of reactions following receipt of a genetic test result. For some people, having information about their future level of genetic risk is comforting, relieving a sense of uncertainty and allowing them to plan for their future and make reproductive decisions with increased knowledge. For others, the information can be distressing and highly challenging. Most research that has measured the impact of genetic knowledge has studied people who received results in a supportive environment with associated genetic counselling. We therefore know little about the implications of receiving information about multiple genetic conditions at once, with minimal support, advice or counselling.

Finally, most of the genetic diseases and conditions being researched currently occur due to a combination of multiple genetic and environmental influences, meaning that a range of known and unknown genes contribute to their onset, in addition to a range of known and unknown lifestyle factors. This means that the information provided to individuals is likely to be nothing more than a range of probabilities. For example, you might find out that you have a 20% higher chance of heart attack than the general population. But what will you do with this information? Exercise more? Eat less saturated fat? Stop smoking? Do you really need your whole genome sequenced in order to follow this widely recommended advice?

Of course, faster and cheaper whole genome sequencing has some exciting repercussions as well. The implications for biomedical research are considerable, and are likely to greatly expand our understanding of the genetic basis of common diseases. Being able to sequence and then analyse and compare whole genomes in such a fast and inexpensive way is also likely to bring about important advances in our study of pharmacogenomics, where drugs are prescribed specifically to best match an individual's genome, in order to obtain the highest possible benefit.

However, if you are not a biomedical researcher and you are not a clinician wanting to prescribe the most effective drugs possible, whole genome sequencing may well be of limited value ... for now.

*This opinion piece was written by Dr Rony Duncan and Professor Martin Delatycki from the Institute for The Conversation*