TCF4 and Pitt-Hopkins syndrome: Phenotypes produced by variants in TCF4 range from mild cognitive impairment to Pitt-Hopkins syndrome (PTHS), a neurodevelopmental disorder characterized by ID and characteristic facial features, in some cases accompanied by respiratory abnormalities, microcephaly, ophthalmological problems, epilepsy, or behavioural problems (autism spectrum disorder) [56,57,58,59,60,61].