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CHORI Scientists Validate Efficacy of Non-invasive Maternal Urine Analysis for the Prenatal Diagnosis of SLOS

Smith-Lemli-Opitz Syndrome (SLOS) is a devastating autosomal recessive disorder resulting in malformation and mental retardation, with a previously estimated incidence of approximately 1 per 10,000-20,000 births. The costs of this disorder are huge over a lifetime, both in terms of the financial burden as well as the stress on the family and care-givers. While the gold standard for prenatal diagnosis has been to test amniotic fluid obtained via amniocentesis, CHORI scientist Cedric Shackleton, PhD, hopes to change that with his maternal urine or serum analysis.

“Amniocentesis as a procedure is expensive, has an estimated 1 to 2 percent fatality risk, and the cost of chemical analysis on the sample at the end of the day is exactly the same,” says Dr. Shackleton. “Compare that with our test, which is completely non-invasive, has zero risk and simply relies on is a bodily function we all do several times a day.”

The latest study published by Dr Shackleton and his colleagues in the American Journal of Medical Genetics compares the efficacy of his maternal urine test with the classic amniotic fluid test in the largest collection of data to date on prenatal SLOS diagnosis.

"This was a great opportunity to establish the verity of our test against the gold standard," Dr. Shackleton explains of the study, which utilized samples taken from a group of about 700 women identified as "at risk" for SLOS during an initial screening for Down Syndrome conducted in over 1 million American women.

"From this 700 or so, we found 5 patients using our new test - the same 5 that were found using the classic amniotic fluid test," says Dr. Shackleton, adding that all the testing was of course blinded. "We had no idea which samples were the positives when doing our testing."

While Dr. Shackleton and his colleagues identified the analyte in maternal urine that is a marker for SLOS nearly 6 years ago taking that research from the bench to clinical practice has been slow and painstaking. Though the test is already licensed with two different companies, big business can often be hampered by profit margins, and is also accompanied by state and federal paperwork that doesn't always get processed as quickly as scientists like Dr. Shackleton would like. Dr. Shackleton hopes the latest study, however, will provide an impetus for reducing any remaining hurdles.

In addition, the current study also found a much lower incidence of SLOS than was expected, about 1 per 100,000 viable pregnancies. This suggests that the risk of SLOS may not be high enough to justify screening in all pregnant women, although improvements in analytical instrumentation may cut the cost of analyses, allowing screening to be undertaken on a wider population.

In the mean time, however, even if screening is only conducted in high risk populations, with the results from the latest study in, it looks as though the switch from the invasive to the non-invasive test is all but inevitable.

As Dr. Shackleton says, "This particular study was essentially the rubber stamp for our test."

He is quick to point out, however, that the test has only come this far with the collaboratory efforts of his fellow scientists and the genetic testing community.

It is thanks to Dr. Shackleton and his colleagues' hard work in the laboratory that multiple women in the real world will now be able to allay any fears of SLOS with a simple urine sample without the unnecessary risks and discomfort of amniocentesis.

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Monday, May 16, 2011 11:33 PM

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