The disclosure provides a non-human transgenic animal having at least one CREBBP gene locus into which a mutation has been introduced, wherein the mutated CREBBP gene encodes a mutant CREBBP consisting of an amino acid sequence having at least 90% identity with the amino acid sequence of SEQ ID NO: 5. The disclosure also provides a method of producing the transgenic animal comprising introducing a mutation into at least one CREBBP gene locus of a non-human animal. The disclosure further provides use of the transgenic animal as a model of Rubinstein-Taybi syndrome or advanced sleep phase syndrome.