Our study focuses on a rare genetic change in the GRIA3 gene, which plays a key role in excitatory brain pathways. This gene encodes a protein that is part of the AMPA receptor. We discovered a new variant in a child with severe developmental problems, epilepsy, and movement disorders. Interestingly, this mutation does not fit neatly into the usual “loss” or “gain” of function categories—it shows features of both. This mixed effect may explain why the child’s symptoms are especially severe. Our findings highlight the complexity of brain disorders and may guide future diagnosis and treatment strategies. (By Dr. Carme Fons, https://jmg.bmj.com/content/early/2025/09/10/jmg-2025-110855 )