Homozygous ATM mutation due to germline uniparental isodisomy in patient with T acute lymphoblastic leukemia and hepatosplenic T-cell lymphoma

Uniparental disomy has long been recognized as a significant cause of genetic disease in imprinting-associated conditions. More recently, it has increasingly been implicated as a potentially significant cause of autosomal recessive disease. Here we report a case of a patient with a history of leukemia and αβ hepatosplenic T-cell lymphoma who was diagnosed with ataxia telangiectasia via paired tumor-germline testing at age 20. Germline testing detected a homozygous pathogenic variant in the ATM gene. Parental testing identified this variant only in the mother, leading to suspicion for non-paternity or an atypical cause of autosomal recessive disease. Additional analysis of the proband's sample identified a 54 megabase region at chr11q13.4-q25 with alleles all derived from a single parent, consistent with uniparental isodisomy as causative of autosomal recessive ataxia telangiectasia in this case. This report provides further evidence that uniparental isodisomy should be considered in the potential etiology of autosomal recessive conditions, including in the setting of paired tumor-germline testing. Confirming the method of inheritance is particularly important in cases such as this one where being a heterozygous carrier has medical management implications for cancer screening for relatives as well as for cascade testing and family planning for relatives.