Once informed, Counsyl says, couples can take steps like using in vitro fertilisation with genetic testing of the embryos, to avoid bearing children who would have the diseases, many of which are incurable and fatal in childhood.
Some genetic testing of prospective parents is done now, but only for a few diseases like cystic fibrosis and Tay-Sachs, and only for certain ethnic groups. Each test can cost hundreds or even thousands of dollars.

Counsyl’s  test, which analyses DNA from saliva samples, costs $349 for an individual or $698 for a couple. Similar tests from others are on the way, experts say. The trend shows that new technology could make possible widespread screening for the risk of passing on rare diseases, something that was simply not practical before.

Some experts caution that it is too soon to know how accurate Counsyl’s test actually is, in part because neither the company nor any outside reviewer has published papers on its approach and results. Others say the it overstates the case with its Universal Genetic Test, as there are thousands of genetic diseases, not just the 100 Counsyl tests detect.

Counsyl executives say the company operating quietly for a few months, has already administered thousands of the tests offered by more than 100 fertility clinics around the country, and  notes some insurers are paying for it.

“For the same price that we would be checking cystic fibrosis, they are checking cystic fibrosis but also 100 other diseases,” said Dr. R. Ian Hardy, medical director of the Fertility Centers of New England. Dr. Hardy said two couples at his clinic who had taken the Counsyl test had already found they could be at risk of having a child with a genetic disease.

The diseases Counsyl screens for are rare and caused by a mutation in a single gene. For most of the disorders, people with one mutated version of the gene and one normal version do not have the disease and often are not aware that they are carriers of the mutation. But if both parents have one mutated gene, each of their children will have a one in four chance of inheriting two mutated copies and having the disease.

Such screening could save countless parents from heartache, and society from the millions of dollars it can cost to care for even one severely ill person over a lifetime.

Counsyl executives say 35 to 40% of people tested are carriers for at least one disease in the test. In about 0.6-0.8% of cases, they say, both members of the couple are carriers for the same disease.

The company relies mainly on a so-called DNA chip,  simultaneously testing for thousands of genetic variants in a person’s DNA similar technology used by companies like 23andMe, which provide information to people about their own disease risks. Counsyl however has customised the technology to test the mutations involved in rare inherited diseases.

Balaji Srinivasan, (right) Counsyl chief technology officer, said the founders, who do not yet have children but intend to, saw themselves as social entrepreneurs on a campaign.

“The goal is not to maximize revenue but to bring the benefits to humanity,” he said. “Nothing is more relevant than making sure your child doesn’t die from a preventable disease.”

But there are other issues emerging. So many people would be carriers for at least one disease that genetic counsellors might be overloaded. Such testing is a step toward designer babies. There is also concern that having fewer babies born with these diseases means reduced effort to develop treatments.