Rubinstein-Taybi syndrome is characterised by mental retardation, growth retardation and a particular dysmorphology. The syndrome is rare, with a frequency of approximately one affected individual in 100 000 newborns. Mutations in two genes- CREBBP and EP300-have been identified to cause the syndrome. These two genes show strong homology and encode histone acetyltransferases (HATS), which are transcriptional co-activators involved in many signalling pathways.