SLC33A1 and Global developmental delay: Loss-of-function mutations or gene duplication events in AT-1/SLC33A1 are associated with severe disease phenotypes spanning from spastic paraplegia (heterozygous mutation) to developmental delay and premature death (homozygous mutations)9–11 and intellectual disability with autistic-like traits and progeria-like dysmorphic features (gene duplication)12,13.