New discoveries in genetics always seem to work their way into fertility clinics before they are used in any other area of medicine. An announcement from a team in the Netherlands today is a case in point.

The team has developed a test that can identify embryos with genetic abnormalities that predispose them to developing two incurable cancer syndromes called neurofibromatosis type 1 (NF1) and Von Hippel-Lindau disease (VHL). Families with these diseases can use the test during assisted reproduction in a procedure called preimplantation genetic diagnosis to discover which of their embryos are free of the genetic mutations that cause them. These embryos can then be implanted in the mother’s womb. Indeed, the team reports that one set of healthy twins was born to a couple who used the test to screen for VHL-causing mutations.

Genetic testing has already been used to screen embryos for glitches in the BRCA1 gene that raise the risk of breast and ovarian cancer. The new test works slightly differently; the high-risk version of BRCA1 can be detected by looking for a mutation that is only a single DNA “letter” long. In contrast, the genetic mutations that often cause NF1 and VHL are called “microdeletions,” and are many DNA letters long. So it’s a bit more challenging to check all the possible microdeletions during preimplantation genetic diagnosis.

But this is exactly what the Dutch team has done. And although the team admits its process was “time-consuming,” team leader Joris Vermeesch of the University Hospital Leuven in Belgium says that his group is already developing genetic tests that could check much more quickly for many harmful microdeletions at once.

This technology is being driven by recent discoveries that more diseases are caused by microdeletions and other relatively large genetic rearrangements than was realized in the past. Already, doctors are using new technologies that can survey many possible genetic abnormalities at once to find mutations in patients whose symptoms previously couldn’t be traced back to any known cause. And fertility clinics have already begun rolling out similar tests for use in preimplantation genetic diagnosis.

These tests raise ethical issues, for they could allow parents to order “designer babies.” One fertility doctor has already said he would help parents use far less advanced technology to create kids with custom hair, skin and eye color, although he has since rescinded that offer. But the use of the tests to spare babies from incurable diseases, such as neurofibromatosis and Von Hippel-Lindau disease, seems an undeniable good.