Microdeletion (5q14.3)

**What it means:** A microdeletion is a small chunk of DNA that's been deleted — typically too small to see under a microscope but large enough to remove several genes. "5q14.3" is the specific chromosomal location. It's different from a point mutation (a single letter change) because it removes a whole stretch of DNA. **In MHS:** Some MHS patients have a 5q14.3 microdeletion (not just a MEF2C point mutation). This means they lose MEF2C AND neighboring genes, which can make their phenotype more severe than someone with just a MEF2C point mutation. This is why MEF2C deficiency has two broad categories of genetic cause.