Rubinstein-Taybi syndrome (RTS) is a well-defined syndrome characterized by 
facial abnormalities, broad thumbs, broad big toes, and growth and mental 
retardation as the main clinical features. RTS was shown to be associated with 
disruption of the CREB-binding protein gene CBP (CREBBP), either by gross 
chromosomal rearrangements or by point mutations. Translocations and inversions 
involving chromosome band 16p13.3 form the minority of CBP mutations, whereas 
microdeletions occur more frequently (about 10%). Most deletion studies in RTS 
are performed by FISH analysis, and five cosmids must be used to cover the whole 
of the CBP gene, which spreads over 150 kb. Here we report the design of gene 
dosage assays by real-time quantitative PCR that are targeted on three exons 
located respectively at the 5' end (exon 2), in the middle (exon 12), and at the 
3' end (exon 30) of the CBP gene. This technique proved to be efficient and 
powerful in finding deletions and complementary to the other available 
techniques, since it allowed us to identify deletions at the 3' end of the gene 
that had been missed by FISH analysis, and to refine some deletion breakpoints. 
Our results therefore suggest that real-time quantitative PCR is a useful 
technique to be included in the deletion search in RTS patients.