TCF4 and Intellectual disability: Haploinsufficiency of TCF4 causes a rare neurodevelopmental Pitt-Hopkins syndrome, TCF4 has been linked to schizophrenia and mild to moderate intellectual disability, and has been shown to regulate neurogenesis, synaptic plasticity, memory and DNA methylation (Zweier et al., 2007; Blake et al., 2010; Kennedy et al., 2016; Jung et al., 2018; Page et al., 2018; Li et al., 2019).