Lack of transgenerational effects of ionizing radiation exposure from the Chernobyl accident

Effects of radiation exposure from the Chernobyl nuclear accident remain a topic of interest. We investigated germline de novo mutations (DNMs) in children born to parents employed as cleanup workers or exposed to occupational and environmental ionizing radiation after the accident. Whole-genome sequencing of 130 children (born 1987-2002) and their parents did not reveal an increase in the rates, distributions, or types of DNMs relative to the results of previous studies. We find no elevation in total DNMs, regardless of cumulative preconception gonadal paternal [mean = 365 milligrays (mGy), range = 0 to 4080 mGy] or maternal (mean = 19 mGy, range = 0 to 550 mGy) exposure to ionizing radiation. Thus, we conclude that, over this exposure range, evidence is lacking for a substantial effect on germline DNMs in humans, suggesting minimal impact from transgenerational genetic effects.

Abstract 941: Exome sequencing identified POT1, a telomere shelterin gene, as a major susceptibility gene for familial cutaneous malignant melanoma

Approximately 10% of cutaneous malignant melanoma (CMM) cases occur in a familial setting and known high-penetrance melanoma susceptibility genes (CDKN2A, CDK4, BAP1, and TERT) account for melanoma susceptibility in a small proportion of melanoma-prone families. To identify additional high-penetrance susceptibility genes for familial CMM, we performed whole exome sequencing in 101 CMM cases/obligate carriers in 56 unrelated melanoma-prone families recruited from the Romagna area in Italy. We identified a germline founder mutation in Protection Of Telomeres 1(POT1) (g.7:124493086 C>T, p.S270N) in five unrelated melanoma-prone families. The mutation was also found in a single sporadic CMM case from Romagna out of 1,824 Italian cases examined, but it was not seen in public databases, our internal exome databases of over 1000 subjects, and 878 Spanish CMM cases and 3,489 controls (2,038 Italian and 1,451Spanish) genotyped. POT1 is a component of the telomeric shelterin complex that plays a critical role in maintaining telomere integrity and regulating telomere length. The p.S270N mutation is highly conserved among vertebrates and predicted to be deleterious by most computational programs we evaluated. Carriers of the p.S270N mutation had increased length and heterogeneity as well as increased average number of fragile telomeres in peripheral blood mononuclear cell (PBMC) DNA compared to age-matched CMM cases (controls) without the mutation. Exome sequencing analysis of Italian families also identified two other rare missense substitutions in POT1 (g.7:124464052 C>G [p.Q623H] and g.7:124503540 C>T [p.R137H]) that were found in all cases sequenced in two families. Both missense mutations are absent from public databases and 3,489 genotyped controls, and are predicted to be deleterious by most algorithms. The carriers of these two mutations showed slightly but significantly increased telomere intensity signals and telomere fragility in PBMCs compared to age-matched controls. We further sequenced POT1 exons in 768 CMM cases and 768 controls collected from Italy and we found that CMM cases showed a significant increase in the burden of rare exonic variants compared to controls (OR=5.4, 95% CI=1.5-29.2, P=0.0021). Subsequently, we identified two novel recurrent germline missense mutations in POT1 (g.7:124499043 C>T, p.D224N and g.7:124469308 C>G, p.A532P) in American and French familial melanoma cases. Our findings suggest that POT1 is a major susceptibility gene for familial melanoma in several populations and that genes involved in telomere maintenance may play important roles in melanoma development.

Citation Format: Jianxin Shi, Xiaohong R. Yang, Bari Ballew, Melissa Rotunno, Donato Calista, Maria C. Fargnoli, Paola Ghiorzo, Brigitte Bressac-de Paillerets, Eduardo Nagore, NCI DCEG Cancer Sequencing Working Group, Xing Hua, Paula Hyland, Jinhu Yin, Haritha Vallabhaneni, Weihang Chai, Sarangan Ravichandran, Alexander Eggermont, Mark Lathrop, Ketty Peris, Giovanna Bianchi-Scarra, Giorgio Landi, Sharon Savage, Joshua Sampson, Ji He, Meredith Yeager, Lynn Goldin, Florence Demenais, Stephen Chanock, Margaret Tucker, Alisa Goldstein, Yie Liu, Maria T. Landi. Exome sequencing identified POT1, a telomere shelterin gene, as a major susceptibility gene for familial cutaneous malignant melanoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 941. doi:10.1158/1538-7445.AM2014-941

Characterization of T gene sequence variants and germline duplications in familial and sporadic chordoma

Chordoma is a rare bone cancer that is believed to originate from notochordal remnants. We previously identified germline T duplication as a major susceptibility mechanism in several chordoma families. Recently, a common genetic variant in T (rs2305089) was significantly associated with the risk of sporadic chordoma. We sequenced all T exons in 24 familial cases and 54 unaffected family members from eight chordoma families (three with T duplications), 103 sporadic cases, and 160 unrelated controls. We also measured T copy number variation in all sporadic cases. We confirmed the association between the previously reported variant rs2305089 and risk of familial [odds ratio (OR) = 2.6, 95% confidence interval (CI) = 0.93, 7.25, P = 0.067] and sporadic chordoma (OR = 2.85, 95% CI = 1.89, 4.29, P < 0.0001). We also identified a second common variant, rs1056048, that was strongly associated with chordoma in families (OR = 4.14, 95% CI = 1.43, 11.92, P = 0.0086). Among sporadic cases, another common variant (rs3816300) was significantly associated with risk when jointly analyzed with rs2305089. The association with rs3816300 was significantly stronger in cases with early age onset. In addition, we identified three rare variants that were only observed among sporadic chordoma cases, all of which have potential functional relevance based on in silico predictions. Finally, we did not observe T duplication in any sporadic chordoma case. Our findings further highlight the importance of the T gene in the pathogenesis of both familial and sporadic chordoma and suggest a complex susceptibility related to T.

Rare missense variants in POT1 predispose to familial cutaneous malignant melanoma

Although CDKN2A is the most frequent high-risk melanoma susceptibility gene, the underlying genetic factors for most melanoma-prone families remain unknown. Using whole-exome sequencing, we identified a rare variant that arose as a founder mutation in the telomere shelterin gene POT1 (chromosome 7, g.124493086C>T; p.Ser270Asn) in five unrelated melanoma-prone families from Romagna, Italy. Carriers of this variant had increased telomere lengths and numbers of fragile telomeres, suggesting that this variant perturbs telomere maintenance. Two additional rare POT1 variants were identified in all cases sequenced in two separate Italian families, one variant per family, yielding a frequency for POT1 variants comparable to that for CDKN2A mutations in this population. These variants were not found in public databases or in 2,038 genotyped Italian controls. We also identified two rare recurrent POT1 variants in US and French familial melanoma cases. Our findings suggest that POT1 is a major susceptibility gene for familial melanoma in several populations.