Clinical and Molecular Characterization of Germline Telomerase Reverse Transcriptase (TERT) Variants in Children with Acute Myeloid Leukemia (AML),
Authors: Gramatges M. Monica , Sasa Ghadir S. , Plon Sharon E , Bertuch Alison A. 
Published: October 2019

Abstract
Abstract 3571
Telomerase is an enzyme complex principally composed of a reverse transcriptase, TERT, and an RNA template, TERC. Telomerase maintains telomeric DNA, the TTAGGG repeats protecting chromosome ends. Defects in telomerase impair DNA replication efficiency, leading to early cell senescence. Germline telomerase mutations characterize a spectrum of telomere biology disorders including idiopathic pulmonary fibrosis, liver disease, aplastic anemia, myelodysplasia, and dyskeratosis congenita, a diagnosis that confers a 200-fold risk for AML and a 90% lifetime risk for bone marrow failure. These disorders have a variable and often subtle clinical phenotype, but pronounced telomere shortening is a universal finding. Though germline telomerase single nucleotide polymorphisms occur in 2–3% of the general population, enrichment of specific variants has been noted in adults with hematologic malignancies (Hills et al, Ann NY Acad Sci, 2009). For example, germline hypomorphic telomerase variants were found in 6.5% of a large adult AML cohort, with a single TERT variant, p.A1062T, occurring three times more frequently in cases than controls (p=0.0009), suggesting cancer susceptibility may be associated with variation in telomerase related genes (Calado et al, PNAS, 2009). In this project, we are exploring the role of telomerase in pediatric AML development and treatment-related toxicities. We hypothesize that AML populations are enriched for telomere biology disorders, and exposure to intensive chemotherapy regimens or stem cell transplant (SCT), resulting in further telomere shortening, will accelerate disease phenotype manifestation.
We have performed an exploratory analysis to determine if (1) the frequency of telomerase variants observed in a pediatric AML population approaches the frequency reported for adult patients and (2) presence of these variants is associated with a telomere biology disorder phenotype. We are sequencing the exons and flanking intronic regions of TERT in a local cohort of pediatric AML samples (n=100) and confirming missense variants to be germline by analysis of matched remission samples. Analysis of the first 57 subjects demonstrates germline heterozygous single nucleotide variants (SNV's) resulting in missense changes in 6/57 subjects (10.5%). Of the four missense variants found, 1 was novel and is being characterized by telomerase activity, processivity, and phylogeny, and 3 have previously been associated with reduced telomerase activity in vitro. None of these variants were found within 57 sex and race-matched local controls. These initial 57 cases have also been reviewed for evidence characteristic of a telomere biology disorder. Amongst individuals with variants, additional diagnoses included bronchiolitis obliterans and myelodysplastic syndrome, and three of the six died shortly after SCT. These findings suggest that, as in adults, presence of TERT hypomorphic variants may be a susceptibility locus in pediatric AML. AML falls within a spectrum of telomere biology disorders associated with pathologic variants in telomerase-related genes; however, children newly diagnosed with AML are not routinely screened for these disorders, despite the potential risk with these disorders for severe chemotherapy-related toxicities and morbidity with SCT. Our results suggest that further investigation of the disease phenotypes associated with these variants is warranted.Table 1:TERT SNV's in a Cohort of 57 Pediatric AML Patients and Associated Clinical FindingsMissense changeReference ID (dbSNP)ExonRegion in TERTIn vitro telomerase activity*Population hetero-zygosity +/− SEPatient IDClinical correlation after chart reviewp.A279T GCC/ACCrs617481812N terminus81–100%0.017 +/− 0.089233Chronic rash, nail abnormalities, chronic skin/oral GVHD post SCT1038Chronic rash, early death post SCTp.H412Y CAC/TACrs340947202N terminus CP motif36–85%0.01 +/− 0.071652Severe prolonged neutropenia & thrombocytopenia post chemo, MDSp.R962C CGC/TGCNOVEL12C terminus E1 motifUnknownNot applicable990Biphenotypic leukemia, early death post SCTp.A1062T GCC/ACCrs3571994015C terminus60%0.011 +/− 0.075242Bronchiolitis obliterans pre-SCT, early death post SCT453Unknown*Telomerase activity reported in Alder et al, PNAS, 2008 and Du et al, Blood, 2009 for p.A279T and p.H412Y, and reported in Calado et al, PNAS, 2009 for p.A1062T

Disclosures:
No relevant conflicts of interest to declare.