Rubinstein-Taybi syndrome (RSTS) is a multiple congenital anomaly syndrome characterized by mental retardation, postnatal growth deficiency, microcephaly, broad thumbs and halluces, and dysmorphic facial features. The classic facial appearance is striking, with highly arched eyebrows, long eyelashes, downslanting palpebral fissures, broad nasal bridge, beaked nose with the nasal septum, highly arched palate, mild micrognathia, and characteristic grimacing or abnormal smile. About 50 to 70% of patients have RSTS1 due to mutation in the CREBBP gene. RSTS2 is much less common, and about 3% of patients have mutations in the EP300 gene. RSTS2 appears to be associated with a milder phenotype than RSTS1. Patients with RSTS2 have less severe facial dysmorphism and better cognitive function, but may have more severe microcephaly and malformation of facial bone structures compared to those with RSTS1. [From OMIM]