Have you been tempted to avail yourself of the services of a mail order DNA testing company? Or perhaps an ‘alternative’ health practitioner has urged you to get a genetic test done in order to identify your risk of various diseases, and to select the correct diet, supplement and exercise regime for your unique DNA profile.
Well, according to the largest meta-analysis ever published on the relationships between common gene mutations and a slew of diseases and conditions that afflict humans, if the reason for peeking into your genetic code is to find out what health problems you’re at risk of, you’re probably wasting your hard-earned money.
The article, Assessing the performance of genome-wide association studies for predicting disease risk, was published by a research team led by David Wishart, professor in the University of Alberta’s Department of Biological Sciences and the Department of Computing Science. (In the era of big data, biologists also need to know a thing or two about computers.)
Wishart’s team developed a software package called Gwas WIZard (whimsically abbreviated to G-WIZ) to analyse over twenty years’ worth of data from genome-wide association studies (GWAS) for 219 diseases and conditions.
GWAS are comprehensive genetic analyses of the association between certain observable traits – everything from having black hair to developing Alzheimer’s disease – and specific genetic variations in the form of Single Nucleotide Polymorphisms (SNPs – pronounced ‘snips’).
SNPs begin as mutations: accidental changes in the sequence of the ‘letters’ that form the DNA code of each gene. Some mutations are incompatible with life and quickly disappear from the gene pool, but mutations that confer some type of survival advantage in the particular environment in which they arose will persist and spread through the population.
Unfortunately, these SNPs can also confer disadvantages in other environments. For example, SNPs that increase an individual’s propensity to store body fat will help that individual to survive famine and get their genes into the next generation. But in our modern environment of caloric overabundance, those same SNPs will increase the individual’s likelihood of becoming obese and developing type 2 diabetes.
However, when all the data were crunched, Wishart’s team found that 202 out of 219 conditions had SNP heritability values of under 15% – that is, inherited alterations in DNA contributed less than 15% of the risk of diseases such as diabetes (both type 1 and type 2), Alzheimer’s disease and many cancers (including breast, pancreatic, gastric, oesophageal and bowel), schizophrenia and major mood disorders.
Furthermore, when they compared the ability of GWAS to predict disease to non-genetic tests such as measuring metabolites, chemicals, proteins, or the microbiome, they found that the latter were far more accurate:
“Non-genetic factors were generally better at predicting disease than genetic factors.”
There were some notable exceptions, however: coeliac disease, Dupuytren’s disease, age-related macular degeneration and progressive supranuclear palsy are all largely determined by SNPs.
But in general, the environment in which your genes are placed – including diet, lifestyle, and exposure to chemicals and pathogen – is a far more significant determinant of your risk for developing various diseases and conditions than the individual variations in those genes.
I vividly remember the buzz that surrounded the Human Genome Project, which succeeded in sequencing the human genome in the early 2000s. Scientists – including my cellular and molecular biochemistry lecturer at UNE – were agog with excitement over the potential that cracking our genetic code held for improving disease prediction, diagnosis and management.
But 20 years on, few of these promised benefits have materialised. It turned out that the human genome contained far fewer genes than was initially anticipated (less than 25 000, while the worm Caenorhabditis elegans has around 20 000, and rice plants up to 50 000), and that the vast majority of heritable human diseases are influenced by a multitude of different genes.
And then there’s epigenetic influences: factors which modify the expression of genes without altering the genes themselves, and which are also heritable.
Developing individualised treatment regimes which are precisely tailored to this level of genetic and epigenetic complexity is virtually impossible.
So while there’s no doubt that the Human Genome Project and its intellectual progeny, including GWAS, are monumental scientific achievements that have contributed significantly to our understanding of ourselves both as individuals and as a species, when it comes to managing our health, there’s nothing new under the sun.
To thrive now and prevent disease in the future, we need what humans have always needed: clean air and water, nutritious food that’s appropriate for our species (we’re primates, after all), regular physical activity, restorative sleep, satisfying social connection and meaningful occupation.
The bottom line: Take the money you were going to stump up for a mail order DNA tests and spend it on kale and a gym membership.
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