Monitoring Ig levels (IgA, IgE, IgG, IgM) and lymphocyte count in children with ataxia telangiectasia, can be useful to characterize an immunodeficiency profile and therefore prevent the risk of infections. Observing high levels of IgM in children with a suspect of ataxia telangiectasia is suggestive of a phenotype characterized by a higher risk of infection and earlier mortality. This evidence concerns the gene CD40LG and ataxia telangiectasia.