It’s now possible to access genetic testing from your living room or office, without the need to visit a health professional. There are many reasons why you might like to get 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.
Now another option might be available - 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. That means it would be as affordable as your average computer.
Direct-to-consumer genetic tests have received much attention in recent years, with companies such as 23andMe and Navigenics offering online genetic tests for anyone with a few hundred dollars to spare. Sending off a DNA sample to one of these companies will get you a detailed report about your personal risk of developing more than 200 conditions including breast cancer, lupus, diabetes, alcohol dependence, obesity, schizophrenia, Alzheimer’s disease and traits, such as earwax type.
These targeted genetic tests are different from whole genome sequencing and there’s a big difference between the two types of analyses.
The complexity of the human genome
To understand the difference between targeted genetic tests and whole genome sequencing, imagine your whole genome is a telephone book with about three billion individual letters. Targeted genetic testing involves turning to specific pages within the telephone book and examining only those bits. Whole genome sequencing, on the other hand, is like printing out the entire telephone book.
If you’re contemplating paying for a whole genome sequence, there are some important facts worth noting.
Unless your whole genome sequence is accompanied by a detailed report interpreting what it contains (and possibly an experienced geneticist to answer your questions), it will be like opening up a telephone book written in a foreign language.
Even with a full report interpreting your genome sequence, current knowledge extends only to a tiny part of the human genome. So even with an accompanying report to interpret your genome, the vast majority of it will remain meaningless and be of no use to you or your doctor.
Unpacking the results
Only about 3,500 of the 23,000 genes in the genome have been connected to a particular disease or diseases anyway. And the genetic basis for common illnesses such as cancer, heart disease and diabetes remain largely unknown.
Our knowledge of genetics is evolving so rapidly that the meaning of the report you receive will change over time as new information becomes available. In fact, the report you receive now will be very different from the one you would receive if you waited five years. Not only would there be more information in the future, there could be new ways to understand what we already know.
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, there are preventative and treatment options available. But, for other conditions, such as Huntington’s disease, little can be done to prevent onset.
Handling the information
Research shows individuals react in different ways to genetic test results. For some, having information about their genetic risk is comforting, relieving uncertainty and allowing them to make reproductive decisions with increased knowledge. For others, the information can be distressing and emotionally challenging.
Most research, including the studies mentioned above, has measured the impact of genetic knowledge in people who have received results in a supportive environment with professional counselling. But we know little about the implications of receiving information about multiple genetic conditions at once, with minimal support, advice or counselling.
Finally, most genetic diseases and conditions being researched are influenced by multiple genetic and environmental factors. This means that a range of known and unknown genes contribute to their onset, in addition to a range of lifestyle factors. The information given to individuals is likely to be nothing more than a range of probabilities.
You might find out that you have a 20% higher chance of heart attack than the general population. What would 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, analyse and compare whole genomes in such a quick 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.
But if you’re not a biomedical researcher or a clinician wanting to prescribe the most effective drugs possible, whole genome sequencing may well be of limited value to you… for now.