How much do you really want to know about your genes?

If it had been possible to peer into your own DNA at the time Michael Szego was born, his life might have been very different. The 42-year-old would have learned as a child that he carries a genetic variant linked to a disorder called hypogonadism, leaving Szego and his parents to fret for years over how he would grow up.

Boys with hypogonadism don’t produce enough testosterone to fuel normal masculine development. Puberty can be delayed or impaired. The disorder can lead to sexual dysfunction, infertility and often depression. But Szego didn’t see his genome until 2015, when he was already a healthy father of three. By then, he could also see how easy the genome is to misinterpret. “If I got this report for my children, I’d be pretty worried,” says Szego, a bioethicist with the University of Toronto. He adds that if the result had been part of a prenatal test, “it might change my position about what their life might be like.”

There’s no longer any need to speak in hypotheticals. In Canada and the U.S., the first group of children are now growing up with their entire genomes mapped. As the technology to read DNA’s chemical code becomes faster and cheaper, hospitals and academic centres in countries all over the world are investigating what happens — medically, socially and psychologically — to both families and the health care system when you read a genomic road map of a human life at the start.

A genome, after all, is like no other piece of personal information. A chain of six billion nucleotides passed down from parents as 23 pairs of chromosomes, it holds a trove of secrets about a child’s past, present and future — literally millions of data points about a person’s health, appearance and behaviour. Theoretically, there could be much to gain: diseases detected before they develop, early interventions to improve health and extend lives. Everyone’s genetic map is dotted with potential and peril, but also plenty of biological minutiae. Will parents pay attention to every signpost? What if there are risks for conditions that may not strike for years, if at all? What if there’s something potentially lethal? How much direction do parents take from nature’s list of genetic traits when nurture accounts for so much of a child’s story? What do they do with information about her athletic or cognitive abilities, about whether she’s a risk taker or prone to alcoholism? And what happens to children who grow up glimpsing their genetic future?

Meanwhile, the science itself remains in its infancy — and there’s a gaping chasm between reading and comprehension. “Ninety percent of the genome is still not understood,” says Stephen Scherer, director at the Centre for Applied Genomics at Toronto’s Hospital for Sick Children and one of the field’s leading experts. The computational power to unwind and sequence a genome’s six billion units has progressed at a dizzying pace: The first genome map took 18 countries more than a decade to complete; today, machines at the Broad Institute of MIT and Harvard can spit one out every 12 minutes. But the ability to fathom what it all means — which quirks of code might make you sick, keep you healthy or simply reveal your Neanderthal ancestry — lags far behind.

Add in the unpredictable impact of lifestyle and the environment, and genetic road maps are fuzzy at best. Sure, researchers can spot landmarks where a single gene mutation will definitely wreak havoc, as well as dodgy areas that could be hazardous. But rarely can they accurately predict where a street leads and, especially, when it will end at the doorstep of big, common scourges like diabetes or cancer. The day when health care can be fully customized to our genes — that big dream destination of genomic medicine — appears to be a long way off.

Of course, the market seldom waits, and people’s appetite for do-it-yourself DNA tests has grown. Home kits that assess your health risks or ancestry, or your perfect diet or date, fuel a market expected to hit $350 million by the end of the decade. The popular consumer-testing company 23andMe has more than a million DNA samples, and AncestryDNA has a database of more than two million. This fall, a Silicon Valley start-up called Helix announced a service that offers access to our DNA through our smartphones, with a plan to sequence and store customers’ genomes while selling affordable pick-and-play testing apps that might charge, say, five bucks to find out if you have a sweet tooth, or $10 to learn if you really are lactose intolerant.

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Yet with all that remains to be understood about the genome, experts warn that the potential for misleading results, misdiagnosis and even genetic discrimination is growing right alongside consumer demand. As a recent report from the Mayo Clinic warns, “Genetic testing is a powerful tool, but it can also be a dangerous weapon.”

Szego says that his result, with its link to a disorder that could leave him sterile, is clear proof that more research is sorely needed. On paper, his genes suggest one story. In real life, his three children tell another story altogether. Maybe unidentified genetic traits protect him from hypogonadism; maybe the environment does; maybe the variant is nothing at all. “We just don’t know,” Szego says. “It shows you the limits of the data.”

Since the first disease gene was discovered in Canada in 1989, genetic tests have been developed for thousands of conditions, most often by studying the DNA of people with particular disorders. It’s largely a process of association: When researchers find a genetic abnormality in people with the disorder but don’t see that same glitch in others without it, the mutation is pegged as a likely culprit. But now it turns out that many of those associations have been wrong.

After combing through the genes of more than 60,000 people, an international research team reported in August that scores of mutations previously thought to be dangerous, or even deadly, are actually harmless. The report, from the Exome Aggregation Consortium (ExAC for short), reached its conclusion after finding these supposed disease genes are also relatively common in people who remain healthy. Until last year, in fact, it was estimated that each of us carries an average of 54 gene variants that are pathogenic. But it turns out that about 40 of them likely aren’t.

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The disturbing implication is that people have been misdiagnosed with genetic disorders or risks they don’t have, suffering through groundless anxiety and possibly treatments they never needed. This fall, doctors at the Mayo Clinic reported a case in which a commercial test wrongly informed more than two dozen members of an extended family that they had a potentially fatal heart condition; one family member had a defibrillator surgically implanted in his chest based on the faulty news. Further investigation at the Mayo Clinic revealed the family’s gene variant is harmless.

Part of the problem researchers face is that they long underestimated how much normal variation there is in the genes of healthy people, especially because the vast majority of studies have focused on subjects of European descent. Most studies hunting around for disease genes have also concentrated on abnormalities within the normal sequence of a gene. But other types of changes could be just as crucial, Scherer says, including extra copies of genes or genes that are missing entirely.

In September, Scherer kicked off a massive project that aims to sequence the genomes of 10,000 people a year in Toronto, where it’s hoped the city’s ethnically diverse population will offer a wider lens on human DNA. Before that, in 2012, Scherer launched the Personal Genome Project Canada, which is assembling a public online database of people’s DNA, along with their medical histories and lifestyle information, for researchers around the world to study. (Similar versions are under way in the U.S. and U.K.) So far, about 1,000 people have signed up and 50 have had their DNA sequenced, including Szego, who happens to be the project’s lead ethicist.

Szego’s result is not the only surprise to emerge from Canada’s genome project. In another case, one man was found to carry the genetic variant for early-onset Alzheimer’s — but at 70 years old, he still doesn’t have it. “We would have expected that variant to lead to Alzheimer’s 100 percent of the time,” says Jill Davies, the project’s Toronto-based genetic counsellor. “The question is, what makes him resilient?”

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It may be years before researchers have an answer. But they believe the only path out of this dark age of DNA is to collect and study more of it — including from children, whose contribution may shed light on the impact of genes and the environment over a lifetime.

While the current state of DNA sequencing seems underwhelming and often confusing, experts predict that it will one day lead to personalized medicine. It’s also likely to soon become a standard screening tool for newborns, since it will be less expensive to sequence a whole genome than to test one gene at a time after something goes wrong.

Yet aside from when it’s used to diagnose a specific disorder, genetic testing in children has always raised thorny ethical issues. The controversy stems from the idea that casting a wide net into a child’s genome can turn up information about all sorts of unrelated conditions, such as future heart health or cancer risks, and therefore robs an adult of the right to decide for herself what she might want to learn from her DNA. Parents may want to know if their young daughter is susceptible to depression, but that daughter, once she’s grown, may not.

For adults, the American College of Medical Genetics and Genomics recommends that doctors share the results of incidental or secondary findings only if they are “medically actionable,” meaning that the knowledge could lead to an intervention to improve the risk of disease. Discovering a gene linked to colon cancer, for example, might convince someone to undergo more frequent screening or cut red meat from his diet. (To date, the college has identified 56 genes that it considers to be medically actionable.)

With children, most health experts feel that doctors should tell parents only if they stumble upon a medically actionable condition that could develop in childhood, like muscular dystrophy or a sleep disorder. But with whole-genome sequencing on the horizon, researchers are examining how parents react when the option is there to learn much more — and discovering that many of them are ambivalent about the information.

In the U.S., the National Institutes of Health is funding four pilot projects to investigate the benefits and risks of sequencing children’s genomes, including risks related to privacy and discrimination. But in the study focused on newborns, parent participation has been low. At Brigham and Women’s Hospital in Boston, more than 2,400 parents have been approached to take part in baby sequencing, but so far, only 7 percent have agreed.

Toronto researchers, who are exploring the consequences of sequencing children’s whole genomes, have had more luck. At Sick Kids, several of the invited parents described a moral obligation to learn as much as they can, even when the conditions might not strike until adulthood. “Faced with the choice ... parents felt they had no choice,” Sick Kids researchers wrote in a study published in the Journal of Medical Ethics. While some parents expressed concern about whether a child could “live a happy and productive life” with “a guillotine hanging over his head of all these possible things that [could] go wrong,” others felt screening gave them valuable tools to “look for early signs of anything that could possibly affect her later in life.”

Researchers feel a similar obligation to provide parents with information about medically actionable conditions. Co-author Cheryl Shuman, the hospital’s director of genetic counselling, says the Sick Kids approach is unique among medical centres. When a child carries a mutation linked to an adult disease, such as those involved in heart disease or breast cancer, it was most often passed down from one of the parents, she says. With parents informed, they can choose to be tested themselves and act to maintain their own health, since “having healthy parents is in the best interests of the child,” Shuman says. Parents weren’t quite so certain: The study found “a significant minority” of them refused to learn about risks lurking in their own DNA.

How parents will respond to any of this is another unknown in the field. It may be that their ambivalence can never be resolved. But the work at Sick Kids, Shuman says, will shape guidelines to help parents decide whether they want that genetic road map of their children, and what they should choose to learn from it. Having those guidelines is crucial, Shuman adds, since genome sequencing is poised to become routine. “But it shouldn’t be a life-altering piece of information,” she says. “Our genes don’t define us or determine our destiny.”

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