TCF4 and Pitt-Hopkins syndrome: In summary, this study of a TCF4 translocation and its consequence on TCF4 promoter usage and fusion transcript expression provides insight into the relative roles of TCF4 isoforms in ID, highlights the potential for some TCF4 isoforms to partially rescue the dysmorphisms and ID characteristic of PTHS, shows that the ID phenotype associated with TCF4 mutation can be relatively consistent over generations and from childhood through adulthood.