Single gene sequencing of the ATM-gene (ataxia telangiectasia, mutated) uncovered a compound heterozygous mutation status (p.Tyr1284GInfsX9 in exon 28, p.Arg2032Lys in exon 43) in both affected siblings, confirming a diagnosis of ataxia-telangiectasia (Louis-Bar syndrome). Here, ATM is linked to Ataxia-telangiectasia.