Researchers have identified 107 mutations in the RNA helicase DDX3X that cause cortical malformations in the developing brain. As the DDX3X gene is carried by the X chromosome, the associated developmental problems are more likely to occur in females. In severe cases, the functional changes in DDX3X resulted in a smaller or missing corpus callosum. Almost all of the mutations occurred de novo, meaning they happened during early development rather than being inherited from a parent. Researchers say the malfunction can now be considered to be a development disability syndrome.