Observing low levels of CoQ10 in the muscle tissues of children with a diagnosis of chronic ataxia can be suggestive of potentially treatable causes of ataxia due to a deficit of CoQ10. Observing high levels of AFP in children with suspected chronic ataxia, along with a profile of low levels of IgA, IgE and IgG and a low lymphocyte count (CD4+ and CD8+), is suggestive of and supports an early diagnosis of Ataxia telangiectasia. The gene discussed is CD4; the disease is ataxia telangiectasia.