Ataxia-Telangiectasia Mutated

Gene function: Encodes ATM kinase, key in double-strand DNA break repair.
Mutations: Heterozygous carriers have moderately increased breast cancer risk (~2x); homozygous mutations cause ataxia-telangiectasia (rare).
Clinical relevance:
- Associated with ER+ breast cancer.
- Carriers get enhanced screening (MRI/mammogram).
- May predict sensitivity to PARP inhibitors and ATR inhibitors (under clinical trials).
- Patients are more radiosensitive → radiation therapy planning may need caution.