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18 November 2010

Mom's DNA explains foetal abnormalities in miscarriage

When looking for genetic causes of a miscarriage, parental karyotyping might provide a clue even when the foetal tissue appears normal, researchers say.

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When looking for genetic causes of a miscarriage, parental karyotyping might provide a clue even when the foetal tissue appears normal, researchers say.

Their suggestion is based on a single case, reported in Fertility and Sterility. The foetal tissue had a normal karyotype, but the mother's karyotype was abnormal. A second look at the foetal chromosomes - this time using fluorescence in situ hybridisation (FISH) to look for the known translocation segments - showed the same abnormality.

The researchers believe this one example is an indication that many more foetal genetic disorders can be found using this method, which could help pinpoint the cause of miscarriage and save costs on further testing.

Subtle kinds of abnormalities

"There are subtle kinds of abnormalities in foetal chromosomes that aren't detectable with standard karyotyping procedures," said lead author Dr Lawrence Grunfeld of the Mount Sinai School of Medicine in New York City. "But without doing the parental karyotyping, you wouldn't know to go back and look for those."

Dr Grunfeld believes that the number of miscarriages linked to genetic disorders - estimated by one study to be 80% of miscarriages - is actually much higher than what's currently assumed.

By finding these cases, he says "we won't wind up doing tests that can be very expensive and potentially dangerous for patients," such as testing for blood clots and prescribing blood thinners.

Fixing the problem

But fixing the problem of inefficient fetal karyotyping may not be that simple, said Dr William Hogge, who practices obstetrics and clinical genetics at the University of Pittsburgh Medical Centre.

The first issue, he said, is that there is no evidence that the abnormality seen in the case report - a fragment of chromosome 10 was found on chromosome 8 - caused the miscarriage.

"The abnormality might have been so small that it didn't have an effect on the miscarriage," said Dr Hogge, who was not involved with the study. "What would make this case stronger is if the patient was to have another loss and they found the same thing."

He added that many other factors could have influenced the miscarriage in this particular case - the woman, 32 years old, received ovulation induction and intrauterine inseminations, and the miscarriage was her second.

Genetic abnormalities rare

Additionally, according to Dr Hogge, subtle genetic abnormalities are so rare that it might not be worthwhile to increase the amount of testing.

"The number of abnormalities we find would certainly be higher if we do more karyotyping on the parents. But the question is whether or not it's higher enough to be cost-effective," he said. "I'm not sure it is."

Instead of doing more tests on parental chromosomes, he suggests doctors and researchers should be looking more at new technologies currently being developed, such as micro-array assays.

"This study makes a strong case for a different technology to do this. But it doesn't discuss the newer technologies that would do away with the traditional karyotyping. With micro-array technology we could detect the more common abnormalities, like trisomies, or the subtle rearrangements like the one seen here." (Reuters Health/ November 2010)

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