PSD-95 (DLG4)

**What it means:** PSD-95 (encoded by the DLG4 gene) is a **scaffolding protein** located at the synapse. It acts like the structural framework of a building, holding receptors, signaling molecules, and other components in the right place. Without PSD-95, the synapse loses its structural integrity. **In MHS:** MEF2C regulates PSD-95, and reduced PSD-95 means weaker, less organized synapses — another piece of the puzzle explaining why MHS patients have impaired cognitive function.