A unique consanguineous family with 2 genomic instability disorders, Fanconi anemia and ataxia telangiectasia, revealed exceptional combinations of null mutations in the FANCA and ATM genes. Two siblings with Fanconi anemia had novel homozygous consecutive microdeletions (c.1361-1370delCCTCCTTTGG, c.1374delC) adjoined to upstream 65 nucleotide direct tandem repeats and deletion hotspot motifs in the FANCA gene. The sibling with ataxia telangiectasia revealed a homozygous p.Arg2993Stop (c.8977C>T) null mutation in the ATM gene. All patients were also heterozygous for the opposite mutations without any additional clinical or laboratory manifestations. Double heterozygote parents did not present any clinical symptoms suggestive of the 2 disorders.