Scientists have discovered that a common cause of sudden heart death has been misunderstood because researchers didn’t appropriately account for racial differences in their studies.
The findings, published online Wednesday in the New England Journal of Medicine,have implications far beyond this particular inherited disease, called hypertrophic cardiomyopathy, or HCM. Researchers say the results also sound a cautionary note for many other illnesses that have been identified through genetic markers.
HCM gained attention in the 1980s after several seemingly healthy athletes, including the rising basketball talent, Hank Gathers, suddenly died from it. Scientists had figured out that the propensity for developing HCM is passed along as a genetic trait; the condition affects about one in 500 Americans.
Tarika Mingo, a psychiatric social worker in New York City, first realized something was wrong with her own heart several years ago, when she became so short of breath during gentle activity that she nearly passed out. In 2014 her doctors accurately diagnosed her with HCM. They performed open-heart surgery and reduced her risk of sudden death. She still feels the effect of the disease, however.
The diagnosis also sent reverberations through her family. That’s because the likelihood of developing HCM follows a simple, inherited pattern: If your parent has the disease, your likelihood of developing it is 50:50. So she urged her entire family to get checked out. Mingo’s 16-year-old son shows no signs of having inherited the condition, but her 29-year-old sister has some ominous symptoms.
As part of the diagnosis, doctors turn to genetic testing. But, while the inheritance of this disease follows a simple pattern, the genes that control it reveal a much more complicated story than geneticists realized until very recently.
And that applies to many other genetic traits that are now commonly diagnosed in medical labs.
In HCM, it turns out, any one of about a dozen genes can be damaged in ways that lead to the illness, and there are many different possible mutations in each of these genes. So there are many ways the disease can be passed down.
What’s more, some of the variants that researchers originally flagged as disease-causing mutations have actually turned out to be benign.
Dr. Isaac Kohane at Harvard Medical School says a postdoctoral fellow working with him, Arjun Manrai, came across this serious problem of misdiagnosis quite by accident.
They were studying the genetic variants related to HCM. While the disease is observed to occur in about one in 500 people, “we saw that the variants that were ostensibly causing disease seemed to add up to much more than one in 500,” he says.
In fact, the supposedly risky gene variants appeared in one out of 10 or one out of 20 people of African descent — an impossibly high number.