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New pre-conception carrier screening for genetic diseases

Analysis of a study published in a science journal   |   By Dr Philippa Brice   |   Published 18 January 2011
Study: Carrier Testing for Severe Childhood Recessive Diseases by Next-Generation Sequencing
By: Bell C.J. et al. (16 authors total)
In: Science Translational Medicine
Link: http://dx.doi.org/10.1126/scitranslmed.3001756
What this study set out to do:

Use next-generation sequencing technology to analyse selected genes, screening for multiple recessive variants that cause known genetic diseases, to create a carrier screening test.

How they went about it:

The researchers developed a screen to include the maximum possible number of genetic variants linked to serious and highly penetrant genetic diseases, to create a cost-effective, broad coverage test. Genotyping of so many regions (7717) within 437 target genes was made possible by the use of techniques to enrich the target DNA sequences combined with the new, very rapid sequencing approaches.

Outcome:

The screening method reportedly showed around 95% sensitivity (ability to detect mutations) and around 100% specificity (ie. virtually no cases of false identification of mutations) for a wide range of common genetic variants and mutation types. In a total of 104 different DNA samples tested, the number of recessive disease genes identified for each was between 0-7, with an average of 2.8. 

Conclusion:

A large-scale pre-conception genetic screening test of this type, if suitably validated, could be used in the general population to 'reduce the incidence of and ameliorate the suffering associated with severe recessive childhood disorders'. Identifying carrier status in two prospective parents would identify cases where both parents carry mutations associated with severe genetic diseases, and where children of the couple would be at risk of the disease. This would allow them to take steps to prevent  or reduce the chance of having an affected child, should they wish to do so - for example, by pre-implantation genetic diagnosis (PGD) or antenatal testing and selective termination of affected pregnancies.

Our view:

The authors are correct to point out that, although most severe genetic diseases are very rare and so few members of the population are carriers, the impact of the diseases on affected children is profound and the associated healthcare costs (and suffering) great. A cheap and comprehensive form of pre-conception screening could therefore be of significant value; however, this is still a long way off, since the volume and complexity of mutations underlying even the most severe genetic diseases are so large and there are many barriers to clinical validation. Another issue is that to be effective, a significant number of couples from the general population would have to access testing prior to starting families.

Further discussion:

However, the pace of technical development is very fast indeed in this, as so many areas involving DNA sequencing. This new test, if developed for clinical use, could outstrip existing techniques for pre-conception screening (see previous news) in offering cheaper testing for a much wider panel of diseases. Consideration of the wider implications of this type of testing for medical practice and society as a whole is urgently required.

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