IL1RAPL1 is an X-linked synaptic adhesion molecule localized at the postsynaptic membrane that plays critical roles in neuronal development and synapse formation 1. The protein regulates dendrite morphology through its extracellular domain, with IL1RAPL1 loss-of-function mutations resulting in increased dendritic branching and simplified neuronal arborization 2. IL1RAPL1 mediates IL-1β activity on dendrite formation 2 and regulates glutamatergic synapse formation and stabilization through the Mcf2l-RhoA-ROCK signaling pathway, affecting AMPA receptor trafficking 3. Mutations and deletions of IL1RAPL1 are associated with X-linked intellectual disability (ID), autism spectrum disorder (ASD), and dysmorphic features 45. Genetic variation in IL1RAPL1 correlates with cognitive abilities, particularly memory and concentration, with the protein highly expressed in hippocampus and other memory-associated brain regions 6. Rare variants in IL1RAPL1 have also been identified in patients with treatment-resistant schizophrenia 7. These findings establish IL1RAPL1 as essential for normal cognitive development through regulation of dendritic architecture and synaptic plasticity.