Very rare, homozygous loss-of-function variants in SLC6A7, together with MPPE1 (Metallophosphoesterase 1) mutations, have been identified in a complex neurodevelopmental disorder characterized by severe developmental delay, generalized dystonia with episodic status dystonicus, chorea, epilepsy, and cataracts [12]. This evidence concerns the gene MPPE1 and Global developmental delay.