GRIN2B (NMDA Receptor)

**What it means:** GRIN2B (also known as NR2B) is a subunit of the **NMDA-type glutamate receptor**, which is critical for synaptic plasticity — the brain's ability to strengthen or weaken connections between neurons based on experience. This is the biological basis of **learning and memory**. **Why it matters for MHS:** MEF2C directly regulates GRIN2B expression. When MEF2C is deficient, GRIN2B levels drop, reducing NMDA receptor function and impairing synaptic plasticity. This could directly contribute to the cognitive impairments seen in MHS. Some researchers believe that enhancing NMDA receptor function could partially compensate for MEF2C deficiency.