Imagine your DNA is a library of instruction manuals (genes). A transcription factor is like a foreman who walks through the library, finds the right manual, and tells the workers: "Okay, start reading this one now."
Specifically, transcription factors are proteins that bind to specific DNA sequences and turn genes "on" or "off" — they control whether a gene's instructions are copied (transcribed) into RNA, which then gets translated into protein.
Why MEF2C matters as one: MEF2C is a "master regulator" transcription factor — it doesn't just control one gene, it controls dozens or hundreds of downstream genes. When MEF2C is deficient, it's not just one gene that's affected — the entire regulatory network goes off-balance. This explains why MHS affects so many systems simultaneously.