Telomere-lengthening germline variants predispose to a syndromic papillary thyroid cancer subtype.

Papillary thyroid cancer (PTC) is the most common endocrine malignancy. 10% to 15% of individuals show familial clustering with three or more affected members, but the factors underlying this risk are unknown. In a group of recently studied individuals with POT1 pathogenic variants and ultra-long telomere length, PTC was the second most common solid tumor. We tested whether variants in POT1 and four other telomere-maintenance genes associated with familial cancer underlie PTC susceptibility. Among 470 individuals, we identified pathogenic or likely pathogenic variants in three genes encoding telomere-binding proteins: POT1, TINF2, and ACD. They were found in 4.5% and 1.5% of familial and unselected cases, respectively. Individuals harboring these variants had ultra-long telomere length, and 15 of 18 (83%) developed other cancers, of which melanoma, lymphoma, and sarcoma were most common. Among individuals with PTC and melanoma, 22% carried a deleterious germline variant, suggesting that a long telomere syndrome might be clinically recognizable. Successive generations had longer telomere length than their parents and, at times, developed more cancers at younger ages. Tumor sequencing identified a single oncogenic driver, BRAF p.Val600Glu, in 10 of 10 tumors studied, but no telomere-maintenance mechanism, including at the TERT promoter. These data identify a syndromic subset of PTCs with locus heterogeneity and telomere lengthening as a convergent mechanism. They suggest these germline variants lower the threshold to cancer by obviating the need for an acquired telomere-maintenance mechanism in addition to sustaining the longevity of oncogenic mutations.

Familial Clonal Hematopoiesis in a Long Telomere Syndrome.

BACKGROUND: Telomere shortening is a well-characterized cellular aging mechanism, and short telomere syndromes cause age-related disease. However, whether long telomere length is advantageous is poorly understood. METHODS: We examined the clinical and molecular features of aging and cancer in persons carrying heterozygous loss-of-function mutations in the telomere-related gene POT1 and noncarrier relatives. RESULTS: A total of 17 POT1 mutation carriers and 21 noncarrier relatives were initially included in the study, and a validation cohort of 6 additional mutation carriers was subsequently recruited. A majority of the POT1 mutation carriers with telomere length evaluated (9 of 13) had long telomeres (>99th percentile). POT1 mutation carriers had a range of benign and malignant neoplasms involving epithelial, mesenchymal, and neuronal tissues in addition to B- and T-cell lymphoma and myeloid cancers. Five of 18 POT1 mutation carriers (28%) had T-cell clonality, and 8 of 12 (67%) had clonal hematopoiesis of indeterminate potential. A predisposition to clonal hematopoiesis had an autosomal dominant pattern of inheritance, as well as penetrance that increased with age; somatic DNMT3A and JAK2 hotspot mutations were common. These and other somatic driver mutations probably arose in the first decades of life, and their lineages secondarily accumulated a higher mutation burden characterized by a clocklike signature. Successive generations showed genetic anticipation (i.e., an increasingly early onset of disease). In contrast to noncarrier relatives, who had the typical telomere shortening with age, POT1 mutation carriers maintained telomere length over the course of 2 years. CONCLUSIONS: POT1 mutations associated with long telomere length conferred a predisposition to a familial clonal hematopoiesis syndrome that was associated with a range of benign and malignant solid neoplasms. The risk of these phenotypes was mediated by extended cellular longevity and by the capacity to maintain telomeres over time. (Funded by the National Institutes of Health and others.).

Somatic reversion impacts myelodysplastic syndromes and acute myeloid leukemia evolution in the short telomere disorders.

BACKGROUNDGermline mutations in telomerase and other telomere maintenance genes manifest in the premature aging short telomere syndromes. Myelodysplastic syndromes and acute myeloid leukemia (MDS/AML) account for 75% of associated malignancies, but how these cancers overcome the inherited telomere defect is unknown.METHODSWe used ultra-deep targeted sequencing to detect somatic reversion mutations in 17 candidate telomere lengthening genes among controls and patients with short telomere syndromes with and without MDS/AML, and we tested the functional significance of these mutations.RESULTSWhile no controls carried somatic mutations in telomere maintenance genes, 29% (16 of 56) of adults with germline telomere maintenance defects carried at least 1 (P < 0.001), and 13% (7 of 56) had 2 or more. In addition to TERT promoter mutations, which were present in 19%, another 13% of patients carried a mutation in POT1 or TERF2IP. POT1 mutations impaired telomere binding in vitro and some mutations were identical to ones seen in familial melanoma associated with longer telomere length. Exclusively in patients with germline defects in telomerase RNA (TR), we identified somatic mutations in nuclear RNA exosome genes RBM7, SKIV2L2, and DIS3, where loss-of-function upregulates mature TR levels. Somatic reversion events in 6 telomere-related genes were more prevalent in patients who were MDS/AML-free (P = 0.02, RR 4.4, 95% CI 1.2-16.7), and no patient with MDS/AML had more than 1 reversion mutation.CONCLUSIONOur data indicate that diverse adaptive somatic mutations arise in the short telomere syndromes. Their presence may alleviate the telomere crisis that promotes transformation to MDS/AML.FUNDINGThis work was supported by the NIH, the Commonwealth Foundation, the S&R Foundation Kuno Award, the Williams Foundation, the Vera and Joseph Dresner Foundation, the MacMillan Pathway to Independence Award, the American Society of Hematology Scholar Award, the Johns Hopkins Research Program for Medical Students, and the Turock Scholars Fund.