Gene duplications in AT-1/SLC33A1 have been identified in patients with autistic-like features, intellectual disability, and dysmorphic features; heterozygous mutations in AT-1/SLC33A1 are associated with a familial form of spastic paraplegia, while homozygous mutations are associated with developmental delay and premature death3–7. The gene discussed is SLC33A1; the disease is Global developmental delay.