EEF2 and neurodevelopmental disorder: Importantly, human patients deficient in diphthamide-modified eEF2 display symptoms of a neurodevelopmental disorder known as diphthamide deficiency syndrome (DDS) [18,19,20,21,22] and diphtheria toxin (DT) from Corynebacterium diphtheriae attacks the diphthamide décor on eEF2 by ADP-ribosylation to block mRNA translation in infected host cells [23].