Question: What are the genetic changes related to Adams-Oliver syndrome ?
Answer: Mutations in the ARHGAP31, DLL4, DOCK6, EOGT, NOTCH1, or RBPJ gene can cause Adams-Oliver syndrome. Because some affected individuals do not have mutations in one of these genes, it is likely that other genes that have not been identified are also involved in this condition. Each of the known genes plays an important role during embryonic development, and changes in any one of them can impair this tightly controlled process, leading to the signs and symptoms of Adams-Oliver syndrome. The proteins produced from the ARHGAP31 and DOCK6 genes are both involved in the regulation of proteins called GTPases, which transmit signals that are critical for various aspects of embryonic development. The ARHGAP31 and DOCK6 proteins appear to be especially important for GTPase regulation during development of the limbs, skull, and heart. GTPases are often called molecular switches because they can be turned on and off. The DOCK6 protein turns them on, and the ARHGAP31 protein turns them off. Mutations in the DOCK6 gene lead to production of an abnormally short DOCK6 protein that is likely unable to turn on GTPases, which reduces their activity. Mutations in the ARHGAP31 gene also decrease GTPase activity by leading to production of an abnormally active ARHGAP31 protein, which turns off GTPases when it normally would not. This decline in GTPase activity leads to the skin problems, bone malformations, and other features characteristic of Adams-Oliver syndrome. The proteins produced from the NOTCH1, DLL4, and RBPJ genes are part of a signaling pathway known as the Notch pathway. Notch signaling controls how certain types of cells develop in the growing embryo, including those that form the bones, heart, muscles, nerves, and blood vessels. The Notch1 and DLL4 proteins fit together like a lock and its key to stimulate one part of the Notch pathway, which is important for development of blood vessels. The NOTCH1 and DLL4 gene mutations involved in Adams-Oliver syndrome likely impair Notch1 signaling, which may underlie blood vessel and heart abnormalities in some people with Adams-Oliver syndrome. Researchers suspect that the other features of the condition may be due to abnormal blood vessel development before birth. Signaling through Notch1 and other Notch proteins stimulates the RBP-J protein, produced from the RBPJ gene, to attach (bind) to specific regions of DNA and control the activity of genes that play a role in cellular development in multiple tissues throughout the body. The RBPJ gene mutations involved in Adams-Oliver syndrome alter the region of the RBP-J protein that normally binds DNA. The altered protein is unable to bind to DNA, preventing it from turning on particular genes. These changes in gene activity impair the proper development of the skin, bones, and other tissues, leading to the features of Adams-Oliver syndrome. Little is known about how mutations in the EOGT gene cause Adams-Oliver syndrome. The protein produced from this gene modifies certain proteins by transferring a molecule called N-acetylglucosamine to them. It is thought that the EOGT protein modifies Notch proteins, which stimulate the Notch signaling pathway. However, the impact of the modification on Notch signaling is unclear. At least three mutations in the EOGT gene have been identified in people with Adams-Oliver syndrome, but how the genetic changes contribute to the signs and symptoms of this disorder is still unknown.