June 30, 2009

Comprehensive Embryo Gene Test

British researchers say a genetic test that can determine whether an embryo has any inherited disease could be a less than a year away.

The new test would differ from current tests in that it would not require doctors to know the specific genetic mutation involved. It would allow doctors to check whether an embryo is in good overall genetic shape.

However, experts caution that there must be strict limits on how such tests are used.

The test uses karyomapping, a technique that searches for the inheritance of sections of DNA or chromosomes.  It allows doctors to search for an entire block of DNA that may contain a faulty gene, instead of having to know the precise genetic mutation passed down through generations of a family affected by certain conditions.

While current genetic testing of embryos is typically limited to just a few conditions, karyomapping could theoretically test for any one of the 15,000 known genetic defects.  The same test could also determine whether any chromosomes are missing or duplicated, which could indicate the embryo is not viable.

Furthermore, the new test can be conducted far faster than existing tests, taking just three days instead of many weeks.

Professor Alan Handyside from London's Bridge Center developed the $4,100 test.  In the small number of families tested, it has been 100% successful in identifying affected embryos, he said.

Researchers in the United States have also conducted the test in embryos at risk of cystic fibrosis.  In five cases where families had donated embryos for research, the test identified cystic fibrosis mutations.   Serious chromosome abnormalities were also found, suggesting the embryos would not have been viable.

The test could be used to help couples have successful IVF pregnancies with babies free from the condition in question.

Clinical trials of the new test are set to begin later this year, and British regulators will be working to assess the test's safety and effectiveness.

But ethical issues remain, since the test could be used to find conditions that are not serious or life threatening, causing some to worry about the potential for so-called "designer babies."

The developers of the test have applied for a license with Britain's Human Fertility and Embryology Authority (HFEA), which has the power to set conditions for use of the test.

Professor Handyside said the test would be useful in finding genetic causes of autism.   It could also be used to test for conditions such as Huntington's disease and spinal muscular atrophy.

"What we're mapping is inheritance from the father and the mother across the entire genome," he told BBC News.

"The potential criticism of this work is we could find all kinds of changes in the embryo.

"But we wouldn't get a license to do this for all conditions.

"We are limited in the number of embryos we can test so something has to be very likely to turn up," he said.

Professor Tony Ruthford, who chairs the British Fertility Society, acknowledged the technology could open a "Pandora's box."

"The issue here is we may find out a lot of genetic information and how is that going to be used or stored," he told BBC News, adding, however, that UK regulations on what can be tested are very strict," he told BBC News.

"We're not mad Frankenstein's working away in our laboratories to create designer babies," he said.

"We are only allowed to look for major diseases which cause handicaps."


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