Ataxia-Telangiectasia is caused by the lack of functional ATM protein. ATM regulates the activation of chemical reactions that promote cell survival. The details of ATM function in the control of these reactions are poorly understood. Preliminary experiments indicated the presence of defects in glucose usage, leading to the discovery that Ataxia-Telangiectasia patients cells accumulate glycogen, the storage form of glucose. We will test the hypothesis that ATM controls the chemical reactions required for the correct use of glucose. Glucose usage defects could lead to glycogen accumulation, which might be toxic for brain cells. We will study the molecular reactions controlled by ATM that promote correct glucose usage and assess possible toxicity of glycogen accumulation to understand how these defects occur and how we can correct them. The information resulting from this study could help Ataxia-Telangiectasia managing clinicians to better understand how to treat the disease.