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Further insight into the genetic causes of developmental delay

Analysis of a study published in a science journal   |   By Dr Sowmiya Moorthie   |   Published 18 August 2011
Study: A copy number variation morbidity map of developmental delay
By: Cooper G.M. et al. (18 authors total)
In: Nature Genetics
Link: http://dx.doi.org/doi:10.1038/ng.909
What this study set out to do:

Produce a detailed map of where rare copy number variants (CNVs) that cause developmental and intellectual disability lie on the genome to understand how they contribute to these conditions.  

How they went about it:

Analysed CNVs in 15,767 children with intellectual disability or developmental delay (cases) and compared the pattern with a CNV map produced from analyzing DNA of unaffected adults (controls). Deletions or duplications present in cases and controls were analysed in order to identify pathogenic CNVs.

Outcome:

Although CNVs were present in both cases and control samples, the frequency of rare CNVs was higher in the cases. Furthermore, there was an excess of large CNVs in the case samples and an increased disease risk with increasing CNV size. Comparison of deletions and duplications identified 59 pathogenic CNVs; 15 of these loci were either new or had previously been characterized as having a weak association with disease. They were also able to analyse CNVs and identify 940 candidate dosage-sensitive genes.

Conclusion:

The CNV morbidity map produced here combined with exome and genome sequencing can be used to more precisely identify the rare causal variants that lead to developmental delay, intellectual disability and autism spectrum disorders.

Our view:

Although CNVs are known to be associated with developmental disorders finding the causative CNVs is often problematic due to the rarity of each individual CNV and the fact that similar CNVs can lead to different phenotypes. Large studies such as these and the DDD project (see previous news) provide a means of identifying causal CNVs which could ultimately lead to improved diagnosis and information on medical care.

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