Germline versus somatic mutation

What it is

A germline mutation is a genetic change that is inherited and present in all of a person's cells (and can be passed to children), while a somatic mutation arises in specific cells during a person's life and is present only in the tumor. Most of the mutations driving gliomas are somatic.

Understanding Germline versus somatic mutation

This distinction is important for understanding heritability and risk. The mutations that drive most gliomas (such as IDH mutations) are somatic — they occur in glial cells during life, are found only in the tumor, and are not inherited or passed to children. In contrast, germline mutations (such as an inherited TP53 mutation in Li-Fraumeni syndrome) are present in every cell and indicate an inherited cancer-predisposition with implications for relatives. When a glioma is being evaluated, most testing examines the tumor's somatic mutations to classify and treat it; germline (inherited) testing is considered separately when an inherited syndrome is suspected. Recognizing whether a mutation is germline or somatic clarifies whether it has implications for family members. Understanding germline versus somatic mutations clarifies the difference between inherited and tumor-specific genetic changes.

Why it matters

Understanding germline versus somatic mutations helps patients and families see that most glioma mutations are tumor-specific (not inherited) — while germline mutations, when present, indicate inherited risk relevant to relatives.