Defects in ATM gene → failure to detect DNA damage → failure to halt progression of cell cycle and perform non-homologous end-joining → mutations accumulate

- Autosomal recessive

Triad:- Cerebellar defects (ataxia)- Spider angiomas (telangiectasia)- IgA deficiency

Findings:- ↑ AFP- ↓ IgA, IgG, and IgE- Lymphopenia, cerebellar atrophy- ↑ risk of lymphoma and leukemia