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Evidence for non-invasive Down's Syndrome screening

Analysis of a study published in a science journal   |   By Dr Philippa Brice   |   Published 14 January 2011
Study: Non-invasive prenatal assessment of trisomy 21 by multiplexed maternal plasma DNA sequencing: large scale validity study
By: Chiu R.W.K. et al. (14 authors total)
In: British Medical Journal
Link: http://dx.doi.org/10.1136/bmj.c7401
What this study set out to do:

Test the performance of a technique for massively parallel genomic sequencing of blood from pregnant women to determine whether or not the fetus had Down’s Syndrome (trisomy 21). 

How they went about it:

Researchers were able to analyse very large numbers of small fetal DNA sequences present in the mother’s blood. Sequences from chromosome 21 were identified for each sample, with very high proportions of such sequences taken to indicate the presence of fetal trisomy 21; these results were compared with those from normal ‘gold-standard’ chromosomal analysis (karyotyping).

Outcome:

An approach tested in 314 women was found to correctly identify 96.6% of affected pregnancies, and 100% of unaffected ones. A second method tested in 753 women performed less well, correctly diagnosing 91.9% of affected pregnancies and 96.9% of unaffected ones.

Conclusion:

If used to screen pregnant women identified as high risk of having a fetus with trisomy 21, the optimal technique could prevent about 98% of referrals for invasive diagnostic testing.

Our view:

Invasive testing procedures cause miscarriage in about 1% of cases; it is also expensive to provide and frequently distressing for women. The ultimate goal for this technique would be a single, non-invasive and highly accurate prenatal diagnosis or exclusion of Down’s Syndrome in the fetus. Meanwhile, use as an interim screening measure could be hugely beneficial, potentially performing far better than current serum screening approaches and reducing by many thousands each year in the UK alone the number of invasive diagnostic tests. 

Further discussion:

Larger trials are now needed to see how well the technique performs and how it could operate within antenatal care. A limiting factor for use would be the currently very high cost of the genomic sequencing, although this is likely to fall rapidly. 

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