Telomere Length and Telomerase Complex Mutations in Pediatric Acute Myeloid Leukemia

Abstract 1482

Inherited loss-of-function mutations in the telomerase complex gene TERT have recently been implicated as risk factors for acute myeloid leukemia (AML) in adults. The telomerase complex is expressed in highly proliferative cells, and is responsible for maintaining telomeres, which cap the ends of chromosomes and protect genomic DNA from eroding during cell division. Impaired telomerase function can result in extremely short telomeres, which limits the proliferative capacity of progenitor cells, and can also lead to chromosomal instability, thus predisposing to malignant transformation. In pediatric AML, the frequency of such mutations, and the association of telomere length with cytogenetic, molecular, and clinical characteristics and outcome, are unknown.

In a cohort of 168 pediatric AML patients, we determined the frequency of telomerase complex gene mutations and leukemic cell telomere length, and correlated this with prognostic cytogenetic characteristics (inv(16), t(8;21), MLL rearrangements, normal karyotype, other aberrations), molecular aberrations (CEBPA double mutations, NPM1 mutations, FLT3/ITD, WT1 mutations), clinical characteristics, and outcome.

No mutations were present in TERC. Three heterozygous variants in TERT, E327D, T726M, and A1062T, were identified in eight of 168 pediatric AML patients (carrier frequency 0.048). In three of six patients carrying A1062T, remission material was available, in which germ-line origin of the variant was confirmed. The variants E327D and T726M were absent, but A1062T was present in a cohort of 406 geographically matched controls (carrier frequency 0.049). Telomerase activity, as determined by TRAP assay in reconstitution experiments, of the novel E327D variant was unaffected, as was the previously published activity of T726M; the earlier reported activity of A1062T was reduced to 60%.

Telomere length of leukemic cells was not associated with age, sex, prognostic cytogenetic subgroup, complex karyotype, or expression levels of telomerase and shelterin complex genes. However, patients carrying the high-risk molecular aberration FLT3/ITD had significantly shorter telomeres than did patients with favorable NPM1 mutation or CEBPA double mutations. Telomere length was not associated with overall survival, event-free survival, or cumulative incidence of relapse.

We conclude that, in pediatric AML, telomerase complex mutations do not confer a risk for leukemia development, and although short telomeres correlate with the high-risk molecular aberration FLT3/ITD, telomere length of leukemic cells obtained at diagnosis does not correlate with adverse outcome in this pediatric AML cohort.