02 February 2015
Professor of human genetics and embryology at the Institute for Women’s Health at University College LondonAppeared in BioNews 788
23andMe offer direct-to-consumer DNA analysis. Customers order a collection kit over the internet - essentially a tube you spit into and return to the company. About six weeks later the results arrive by email. At no point is there any involvement from a physician or genetic counsellor to explain what is being tested for or the consequences of the results.
23andMe use a single nucleotide polymorphism (SNP) array that tests for markers in five different categories: genes leading to inherited conditions, genetic risks, traits, genes affecting drug response and ancestry. The service costs £125 per person. I think most people taking this test are going to assume that nothing will show up - as I did.
Genetic conditions are very complex, even when there's just one faulty gene involved. For example, over 1,000 different mutations can give rise to cystic fibrosis. 23andMe only tests for one or a few mutations in each gene, so using this test does not mean that you are not at risk of the disease they are testing for.
Many genetic diseases are multifactorial; they can be affected by both genes and environment, and some disorders show varying penetrance, so carrying the faulty gene does not necessarily mean you will get the disorder. As you can see, it's complicated.
All of the 43 inherited conditions in this test are recessive, so to have the disorder you would need to inherit two faulty genes; one each from your mother and father. The majority of the disorders they test for are early onset, so any adult taking the test should already know that they have the condition. Included in the 43 genes are a large number of very rare inherited conditions for someone with a European ancestry, such as Gaucher disease and maple syrup urine disease, both of which are common in those of Ashkenazi Jewish ancestry.
Eleven genetic risk genes are tested by 23andMe, including Alzheimer's, Parkinson's, and the breast and ovarian cancer risk genes BRCA1 and 2.
In my view, 23andMe should not include these three disorders on their genetic testing panel. Due to the potentially life-altering nature of the test results, 23andMe have 'locked' these results, but unfortunately this only means that you need to do two extra clicks to gain access. Once you know your genetic status for these disorders, the information cannot be taken back.
The 23andMe test for the BRCA1 and 2 genes are unlikely to be positive for someone of European decent as they only test for the three common mutations affecting Ashkenazi Jews. Also, the majority of breast cancer is not genetically inherited and so even if someone is free of BRCA1 and 2 mutations, it does not mean you will not get breast or ovarian cancer.
Parkinson's is a serious disorder of the brain's motor centre and current treatment is effective in few people but only ever serves to slow the disorder, not cure it. A friend recently diagnosed with Parkinson's told me that he is glad he did not know they were at risk before their diagnosis.
And then Alzheimer's has no treatment or cure. I would have preferred to have opted out of receiving this information but this was not possible.
The other genes assessed in the genetic risk section are not as controversial and include hypertrophic cardiomyopathy and inherited thrombophilia (factor V Leiden), which increases the risk of deep vein thrombosis. I discovered that I was at five times the risk of getting deep vein thrombosis, but I could not find anywhere what the base value was. I have already been emailed by a company selling compression stockings!
23andMe look at 40 genetic traits which cover a range of random, mainly useless information, including breast morphology, how many teeth at age 12, birth weight, bitter taste perception, eye colour, earwax type, age of first period, red hair and pain sensitivity - you get the idea. I found out I was lactose intolerant and had increased pain sensitivity, the significance of which is debatable.
The test also analyses 12 genetic variations related to how people respond to drugs. These may indicate differences in sensitivity or in the likelihood or severity of side effects. This is quite complex information, which would need to be decoded by a physician and is only relevant if you were having a particular drug treatment.
For ancestry, 23andMe determines what percentage of your DNA comes from 31 populations worldwide. I found that I was 68 percent European and 28 percent South Asian. This information can be shared with others on the 23andMe database, anonymously or named, and some people have found close relatives. I only had third to sixth cousins in the database.
For me, having my DNA analysed by 23andMe was an interesting experience but it took me several days to go through the overwhelming amount of genetic information I was supplied with (and I know something about genetics!)
I found the web site difficult to navigate and the information of varying quality. I cannot imagine what a person who knows little about genetics would gain from this information – confusion, stress, anxiety? Some of the information is benign, but some is sensitive and cannot be taken lightly.
Direct-to-consumer genetic analysis is on the rise and people should be given the opportunity to 'personalise' their results so that any unwanted information on genetic disorders or risk is not divulged.
The Holy Grail will be next-generation sequencing which can read the full sequence of your genetic code and this is already offered over the internet. Sequencing is also performed for non-invasive prenatal testing at around ten weeks of pregnancy (this has not yet been fully rolled out across the NHS), but currently only looks at a few chromosomes of the fetus. In the future it should be possible to test the full genome during pregnancy so every child will be born knowing their genetic code. It is essential that the role of the genetic counsellor be embraced so that the full potential of this information is understood.