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One in 100 babies worldwide is born with a disease caused by a single gene, according to the World Health Organization. Two genetics companies—Counsyl and GoodStart Genetics—are now using low-cost sequencing as a way to provide a more comprehensive look at parents’ genes than has previously been available. The companies hope to better inform prospective parents about hidden single-gene diseases and potentially reduce their incidence.

Although most of these individual single-gene disease are rare, collectively they account for about 20 percent of infant deaths. When a disease gene is recessive, as is the case with sickle-cell anemia, Tay-Sachs, or cystic fibrosis, parents are unlikely to know they are carriers. If both parents carry a broken copy, they will have a 25 percent chance of having a child with the condition.

Doctors do screen prospective or expecting parents for a handful of diseases, but these tests are limited. Traditionally, the tests look for specific mutations for a particular disease, while the condition could be caused by many different mutations that are passed from generation to generation. “Generally, these tests top out at around 100 mutations,” says Gregory Porreca, a co-founder and vice president of research and technology at GoodStart Genetics. The reason is that every additional mutation will add cost, but the problem is that disease-causing mutations can be missed. For example, a traditional cystic fibrosis test would miss out on hundreds of disease-causing mutations—Porreca says that about 550 disease-causing mutations in the cystic fibrosis gene have been reported in the scientific literature. “With sequencing, you can look for all of them,” he says.

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