Mutations in TCF4 cause Pitt-Hopkins Syndrome (PTHS). These mutations cause TCF4 proteins to not bind to DNA properly and control the differentiation of the nervous system. It has been suggested that TCF4 loss-of-function leads to decreased Wnt signaling and, consequently, a reduced neural progenitor proliferation. In most cases that have been studied, the mutations were de novo, meaning it was a new mutation not found in other family members of the patient. Common symptoms of Pitt-Hopkins Syndrome include a wide mouth, gastrointestinal problems, developmental delay of fine motor skills, speech and breathing problems, epilepsy, and other brain defects.