In children who are positive to mutations associated to Joubert syndrome (JS), Friedreich ataxia (FA) or ataxia telangiectasia (AT), the characterization of the specific gene should be performed for JS, the size of the GAA expansion of the FXN gene should be investigated for FDRA, and the type of mutation of the ATM gene should be defined for AT, to predict the severity and progression of the disease and the possible presence of associated symptoms. The gene discussed is FXN; the disease is Ataxia-telangiectasia.