MEF2 (the family, not just MEF2C)

**What it means:** MEF2C is one member of a family of four related transcription factors: MEF2A, MEF2B, MEF2C, and MEF2D. They all share a similar DNA-binding domain (the "MADS-box"), which is why they're grouped together. **Why MEF2C is special:** MEF2C is uniquely important for brain development. MEF2A is mostly heart-related, MEF2D is also in the brain but has different targets, and MEF2B is the least studied. The specificity of MEF2C for neuronal development is why its deficiency causes such specific and severe neurological symptoms — it's not just that "any MEF2 protein could do the job." MEF2C has unique targets that the others can't compensate for.