Finally, a working diagnosis of Mowat Wilson syndrome was changed to Pitt-Hopkins syndrome in a 2.5-year-old male with severe developmental delay, no speech, microcephaly, poor weight gain and a happy demeanour after a de novo mutation was identified in TCF4 [34] (c.1486G>C, p.(Gly496Arg)). This evidence concerns the gene TCF4 and Mowat-Wilson syndrome.