Germline Mutation

**What it means:** A germline mutation is present in **every cell** of the body because it was in the original genetic material passed to the embryo. It's different from a "somatic" mutation, which only affects certain cells (like a cancer mutation that develops later in life). "Germline" refers to the reproductive cells (sperm/eggs) — if a mutation is in the germline, it can be passed from parent to child. **In the MEF2C context:** The MUSC mouse models (Mef2c-Het mice) use a germline heterozygous loss-of-function mutation — meaning the mice were bred so that every cell has one normal copy and one broken copy of Mef2c, mimicking the human condition.