Genetic testing doesn't always give yes-or-no results, but sometimes offers up a question mark in the form of a variant of unknown significance, the Guardian reports.
For instance, it notes that AnneMarie Ciccarella sought BRCA testing because of a strong family history of disease, but rather than learning she had a pathogenic or a benign variant, she learned that she had two variants whose impact on disease risk was uncertain. "I thought you could have a mutated gene or not, and with all the cancer in my family, I believed I would carry a mutation. I didn’t know there was this huge third category," she tells the Guardian. She later learned that Myriad Genetics reclassified one of her variants as benign — but no other group had.
Another family, meanwhile, pursued genetic testing to figure out the source of a young boy's seizure and panel testing uncovered a VUS in SCN1A, the Guardian says, adding that the boy died. When his parents went to have another child, they learned that the boy's VUS had been reclassified as pathogenic for Dravet syndrome and that some of the seizure medication he'd received might've made things worse. (A legal case is ongoing.)
"To get a better handle on all the variation in humans, scientists are going to need to sequence tens of millions of people," the Guardian adds. "And the only way to ever get these kinds of large numbers is by sharing data. But regardless of how good the databases get, and how many people have their genomes sequenced, uncertainty will never completely go away."