Diagnosis of Ataxia-Telangiectasia IgA and serum alpha-1 fetoprotein levels Genetic testing The following clinical findings suggest the diagnosis of ataxia-telangiectasia: Cerebellar ataxia (particularly when telangiectasias are present) Low levels of IgA (present in 80% of patients with this disorder) High levels of serum alpha-1 fetoprotein If karyotype analysis is done, chromosome breaks, consistent with a defect in DNA repair, are often identified.