Constitutional Telomerase-Associated Gene Variants In Pediatric Acute Myeloid Leukemia (AML) and In Association With Chemotherapy-Related Toxicities
Authors: Gramatges M. Monica , Sasa Ghadir S. , Gerbing Robert B. , Jo Eunji , Alonzo Todd A. , Ahern Charlotte H , Meshinchi Soheil , Bertuch Alison A. 
Published: October 2019

Abstract

Background
The telomerase enzyme complex maintains telomeric DNA, the TTAGGG repeats localized to chromosome ends. Constitutional telomerase mutations are associated with short age-adjusted telomeres and a spectrum of disorders including familial pulmonary fibrosis and liver disease, aplastic anemia, myelodysplastic syndrome (MDS), and dyskeratosis congenita (DC). Notably, DC confers a 90% lifetime risk for bone marrow failure, a 200-fold risk for AML, a 2500-fold risk for MDS, and is associated with chemosensitivity in affected individuals. Exposure to intensive chemotherapy may accelerate telomere shortening and promote manifestations of a telomere biology disorder phenotype in individuals with underlying defects in telomere maintenance. Therefore, we investigated the incidence of constitutional telomerase variants in pediatric AML and their role in therapy-related adverse events (AE’s). We hypothesized that constitutional telomerase variants would be (1) more frequent in AML cases compared with controls, (2) associated with characteristics of telomere biology disorders, and (3) in addition to telomere length, would further characterize AML cases with specific AE’s.

Methods
We sequenced the exons and flanking intronic regions of the telomerase subunits TERT, DKC1, and TERC, as well as TINF2, a critical component in recruiting telomerase to telomeres, in a local pediatric AML/MDS cohort (n=104), a distinct Children’s Oncology Group (COG) AML AAML0531 study cohort (n=115), and a cohort of healthy controls racially and ethnically matched to our local AML/MDS cohort (n=254). We reviewed medical records in the local cohort for characteristics suggestive of DC, including first degree family history of cancer, liver, or pulmonary disease, delay in chemotherapy >60 days due to cytopenias(s), persistent liver or pulmonary disease, persistent cytopenias after AML therapy, history of second cancer, and specific skin, nail, and mucosal abnormalities. For the COG cohort, we compared the number of variants and remission relative telomere length (RTL), measured by qPCR, in subjects with time to absolute neutrophil count (ANC) recovery at least 1 SD above the mean for at least 2 chemotherapy courses (n=53) to those with time to ANC recovery within 1 SD above the mean for all 5 chemotherapy courses (n=62). A relationship between variants, telomere length, and specific grade 3 or 4 AE’s was also explored.

Results
In the local AML/MDS cohort, 13 variants resulting in missense changes or deletions were found in 21/101 subjects (20.8%). When compared with population databases, the number of novel variants in this cohort (8/13) far exceeded the expected number (p<0.0001), and remained significantly high after comparison to local controls (p<0.0001). Retrospective medical record review demonstrated a significant association between presence of a variant and 2 or more features of DC (p=0.047). When evaluated by logistic regression, the total number of DC features was predictive but not statistically significant (p=0.052). However, skin, nail, and mucosal abnormalities were significantly predictive of a variant (p=0.039).
Within the COG AML cohort, no significant difference was noted in the number of variants with respect to ANC recovery, nor was the presence of a variant predictive of specific severe AE’s. RTL’s were divided into quartiles, and the shortest quartile compared to the remaining quartiles relative to time to ANC recovery and AE’s for each chemotherapy cycle. Though no association was noted with specific AE’s, in the fourth chemotherapy cycle we observed a significant association between the shortest RTL quartile and delays in ANC recovery (p=0.03), an effect also seen in the fifth chemotherapy cycle, though not significant (p=0.08).

Conclusions
Cases of pediatric AML demonstrate a propensity for novel constitutional variants in telomerase-related genes. Moreover, presence of a variant is associated with characteristics specific to defects in telomere biology. Shorter telomeres are associated with significant delays in time to ANC recovery in later cycles of AML chemotherapy, presumably reflecting a stress in capacity for hematopoietic reconstitution. Prospective evaluation of the effects of telomerase variants and telomere shortening over time, as well as correlative functional analyses, may provide valuable insight to therapy-related AE’s in pediatric AML.

Disclosures:
No relevant conflicts of interest to declare.