 Ataxia telangiectasia A-T is a rare devastating human recessive disorder characterized by progressive cerebellar ataxia, immunodeficiency, chromosomal instability, and cancer susceptibility. The underlying mechanism and process of neurodegeneration leading to loss of cerebellar neurons and neurological function is largely unknown. Laboratory diagnostic approaches to neurodegeneration in A-T are hampered by sampling issues. It is dangerous, impractical, and not ethically to directly sample brain tissue by surgical biopsy. In contrast cerebrospinal fluid CSF, a fluid that is in direct contact with brain tissue, is relatively easy to sample in a safe procedure lumbar puncture. The aim of the proposal is to investigate oxidative stress, low grade inflammation and tissue break down in the brain of A-T patients by analyzing CSF. In addition the alterations in protein expression related to A-T will be quantified by liquid chromatographymass spectrometry LCMS-based proteomic analysis of CSF from healthy individuals and A-T patients to determine candidate proteins new biomarkers which relative expression levels could be used as surrogate marker of disease progression. 