Importantly however, complete haploinsufficiency of TCF4 is known to result in Pitt-Hopkins syndrome (OMIM # 610954); a severe neurodevelopmental disorder associated with profound intellectual disability, absence of speech, behavioural issues and ventilation abnormalities (Amiel et al., 2007; Brockschmidt et al., 2007). This evidence concerns the gene TCF4 and Pitt-Hopkins syndrome.