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Citation on PubMed or Free article on PubMed Central Genetic heterogeneity in Rubinstein-Taybi syndrome:ĭelineation of the phenotype of the first patients carrying mutations in EP300. Bartholdi D, Roelfsema JH, Papadia F, Breuning MH, Niedrist D, Hennekam RC,.Researchers predict that mutations in other genes can also cause the disorder. The cause of the condition is unknown in these cases. Nearly 30 to 40 percent of people with Rubinstein-Taybi syndrome do not have an identified mutation in the CREBBP or EP300 gene or a chromosome 16 deletion. However, a few studies indicate that some people with large deletions in the same region of chromosome 16 have characteristic features of Rubinstein-Taybi syndrome rather than a more severe condition. Some researchers suggest that these cases are a separate condition called chromosome 16p13.3 deletion syndrome. Researchers believe that the loss of multiple genes in this region probably accounts for the serious complications associated with severe Rubinstein-Taybi syndrome. Multiple genes, including the CREBBP gene, are missing as a result of this deletion. Several cases of severe Rubinstein-Taybi syndrome have resulted from a deletion of genetic material from the short (p) arm of chromosome 16. The signs and symptoms of this disorder caused by EP300 gene mutations are typically milder than those caused by mutations in the CREBBP gene. EP300 gene mutations result in the loss of one functional copy of the gene in each cell, which interferes with normal development and causes the typical features of Rubinstein-Taybi syndrome. It also appears to be important for development before and after birth. Like the CREBBP gene, this gene provides instructions for making a protein that helps control the activity of other genes. Mutations in the EP300 gene cause a small percentage of cases of Rubinstein-Taybi syndrome. Researchers have not determined how CREBBP gene mutations lead to other signs and symptoms of Rubinstein-Taybi syndrome. Abnormal brain development is thought to underlie intellectual disability in people with Rubinstein-Taybi syndrome. A reduction in the amount of this protein disrupts normal development before and after birth. Because one copy of the CREBBP gene is deleted or mutated in people with Rubinstein-Taybi syndrome, their cells make only half of the normal amount of CREB binding protein. This protein, called CREB binding protein, plays an important role in regulating cell growth and division and is essential for normal development before birth. The CREBBP gene provides instructions for making a protein that helps control the activity of many other genes. Mutations in the CREBBP gene cause about half of cases of Rubinstein-Taybi syndrome.