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IS IT ALL IN YOUR GENES?

How much our genes put our health at risk is complicated and varies from person to person— even within the same family.

With heart attacks, stroke, cancer and Type 2 diabetes twining through the branches of her family tree, 32-year-old Amanda Seabrook of London, Ont., wonders whether she or her four-year-old son, Forest, could be doomed to develop those health problems. When it comes to teasing out why the conditions seem to run in her family, Amanda says it’s hard to tell whether it’s strictly hereditary or whether the conditions are caused by some behaviour everyone in her family has in common. For instance, both obesity and inactivity are risk factors for Type 2 diabetes; in Amanda’s family, there’s little of the former, but a whole lot of the latter.

Just how much our genes put our health at risk is a complicated question—and the answer varies from one disease to another, as well as from person to person, even within the same family. While scientists once believed they would be able to trace each disease to a single gene, it turns out that’s only the case for a handful of conditions, such as cystic fibrosis, Huntington’s disease and retinoblastoma (a rare childhood eye cancer).

Diseases that run in families are usually passed down through multiple genes. Heart disease, for example, is linked to LDL (“lousy”) cholesterol, explains Dr. Rob Hegele, director of the Blackburn Cardiovascular Genetics Laboratory and professor of medicine at Western University in London, Ont. About one in 250 people inherits a defect in one gene that causes sky-high LDL, making that person extremely prone to early heart disease. A slightly larger group inherits a mutation in a different gene that gives them ultralow LDL levels, reducing their heart-attack risk by 90 percent. For the rest of us, the combined effect of 32 genes controls LDL levels. “For example, someone who gets 16 genes that slightly raise cholesterol and 16 that slightly lower it will have average cholesterol,” Dr. Hegele explains. Other risk factors for heart disease, Type 2 diabetes and cancers likely follow similar patterns.

Fortunately, a healthy lifestyle can offset the impact of inherited risk. Plus, many of the steps that protect against one of these diseases also help prevent the others.

CANCER“Breast cancer is always on my mind,” says Jenny Marino, 45, of Guelph, Ont., whose mother died from the disease at 52. “I really started thinking about it when I had my daughter, Bella, who’s now 10.” your risk Your chances of inheriting an abnormal gene that may cause cancer, even the most common cancers—lung, breast, prostate and colorectal—are small. A genetic link accounts for just five to 10 percent of all breast cancers, according to the Canadian Cancer Society. “Both genetic and epigenetic ‘errors’ are commonly observed in cancer, suggesting that genetics does not provide the full story,” says Martin Hirst, head of epigenomics— which studies how chemical modifications to DNA and proteins impact genes—at the BC Cancer Agency in Vancouver.