Genetic Epidemiology of Telomere Maintenance and Cancer Etiology

先天性角化异常（Dyskeratosis congenita， DC） [CAS 10374]研究为DC患者及其家庭成员提供了全面的临床和分子评估，以更好地了解端粒生物学缺陷在该疾病中的作用。DC是一种遗传性骨髓衰竭综合征（IBMFS），其特征是指甲异常，网状色素沉着，口腔白斑，端粒非常短，再生障碍性贫血和癌症的风险显著升高。DC的家庭谱系表明存在多种遗传模式（例如x连锁，常染色体显性和常染色体隐性），尽管许多病例是散发的（即缺乏家族史）。我们发现了两种新的DC病因：(1)TINF2的种系突变首次证明了庇护蛋白保护复合物的破坏可导致人类疾病；(2) WRAP53引起dc的突变首次证明端粒酶错定位可导致人类疾病。所有参加NCIs IBMFS研究的DC家族都被评估了已知DC基因的突变：TINF2、DKC1、TERC、TERT、NOP10、NHP2和WRAP53。所有DC队列的参与者都被评估DC相关基因的突变。然而，近50%的病人是突变阴性的。我们正在进行的工作包括使用下一代测序技术来确定突变阴性家庭中DC的遗传原因。我们的DC研究已经被用来证明，外周血白细胞亚群中非常短的端粒（通过Flow-FISH）构成了这种疾病的诊断异常。对这些家族中癌症的分析表明，这种模式与范可尼贫血（即MDS、AML、头颈部鳞状细胞癌和肛肠癌）中观察到的模式惊人地相似。DC生物标本库是一个丰富的资源，用于了解端粒生物学异常的分子后果。我们也在探索一些与DC发病机制相关的新假说，包括表观遗传基因调控和染色体异常。临床表型和医学并发症的详细描述正在进行中。靶组织的端粒长度[CAS 10373]现已关闭。该研究评估了来自IBMFS患者血液、颊细胞和成纤维细胞的DNA的QPCR测量的个体内端粒长度，以及flow-FISH和QPCR之间的相关性。研究发现，一般来说，成纤维细胞端粒比血细胞或颊细胞端粒长，但组织类型之间存在显著的个体内相关性。这项初步研究为端粒生物学和癌症风险的更大规模方法学研究奠定了基础。我们也在研究端粒长度作为癌症危险因素[CAS 10371]。大量研究表明，短的替代组织TL是癌症的危险因素。我们之前的病例对照研究发现，短端粒与卵巢癌和胃癌的风险增加有关。然而，我们对TL和前列腺癌的队列研究并没有发现相同的关联。我们对替代组织中TL与癌症风险之间关系的荟萃分析表明，短TL与整体癌症相关，但这可能是由对特定癌症的更强影响驱动的。回顾性研究的ORs远高于前瞻性研究（2.9 vs 1.16），这表明反向因果偏倚和样本收集前的癌症治疗可能起作用。研究异质性和某些癌症部位的数据很少或没有数据也是这些分析的局限性。正在进行的工作包括许多TL和癌症的合作研究，旨在1)确定TL是否与特定癌症或癌症相关结果的风险相关，2)确定病例对照研究与队列研究中TL和癌症相关性的差异，以及3)使用这些研究作为种系(即，通过分析来自NCI CGEMS前列腺癌和乳腺癌GWAS的SNP数据，评估了与端粒长度相关的遗传变异[CAS 10371]。我们发现来自4个基因的13个SNP与TL相关，我们还与哈佛大学合作进行了TL的全基因组关联研究（GWAS），该研究证实了TERC中的一个SNP与TL相关，但与其他研究相似，其他位点的SNP与TL之间没有很强的相关性。启动了获得性严重再生障碍性贫血患者造血干细胞移植后端粒长度的研究[CAS 10508]，旨在了解端粒生物学在获得性严重再生障碍性贫血（SAA）患者造血干细胞移植（HSCT）后预后中的作用。与国家骨髓捐献计划（NMDP）和国际血液和骨髓移植研究中心（CIBMTR）合作，对对照者、供者和HSCT受者的移植前TL进行了测量。正在进行的分析包括TL与HSCT结果（如死亡、移植后恶性肿瘤和纤维化疾病）的关联。端粒生物学基因的群体遗传研究[CAS 10372]继续为其进化史提供重要的见解。这将提高对基因变异在其功能中的作用的理解，并有助于理解这些变异是癌症的危险因素。我们利用人类基因组多样性小组（Human Genome Diversity Panel）的SNP数据，对全球53个人群中的37个端粒生物学基因进行了评估，从而扩展了对7个基因的初步研究。本研究表明，端粒生物学基因作为一个群体，具有低至中等的单倍型多样性，高祖先等位基因频率，低分化。端粒酶基因（TERT）是一个显著的例外，具有低水平的连锁不平衡。有证据表明进化选择存在于五个基因中。正在进行的研究包括使用1000个基因组数据对5p15.33染色体位点的遗传变异进行详细研究。该基因座包括TERT和CLPTM1L，并包括在几种GWAS中与癌症风险相关的snp。

The Dyskeratosis congenita (DC) [CAS 10374] study provides comprehensive clinical and molecular evaluations to patients with DC and their family members, to better understand the role of telomere biology defects in this disorder. DC is an inherited bone marrow failure syndrome (IBMFS) characterized by abnormal nails, lacey reticular pigmentation, oral leukoplakia, very short telomeres, and significantly elevated risks of aplastic anemia and cancer. Family pedigrees in DC indicate that there are multiple modes of inheritance (e.g. X-linked, autosomal dominant and autosomal recessive), although many cases are sporadic (i.e., lack a family history). We have discovered two novel causes of DC: (1) Germline mutations in TINF2 provided the first evidence that disruption of the shelterin protein protection complex can cause human disease; (2) DC-causing mutations in WRAP53 were first proof that mislocalization of telomerase could cause human illness. All families with DC enrolled in the NCIs IBMFS study are evaluated for mutations in the known DC genes: TINF2, DKC1, TERC, TERT, NOP10, NHP2, and WRAP53.. All participants in the DC cohort are evaluated for mutations in the DC-associated genes. However, nearly 50% of our patients are mutation-negative. Our ongoing work includes use of next-generation sequencing technologies to identify the genetic causes of DC in mutation-negative families. Our DC studies have been used to demonstrate that very short telomeres (by Flow-FISH) in peripheral blood leukocyte subsets comprise a diagnostic abnormality for this disorder. Analysis of the cancers in these families demonstrates a pattern that is strikingly similar to that observed in Fanconi anemia (i.e., MDS, AML, squamous cell cancers of the head/neck and anorectal cancers). The DC Biospecimen Repository is a rich resource used to understand the molecular consequences of telomere biology abnormalities. We are also exploring several new hypotheses related to DC pathogenesis, including epigenetic gene regulation and chromosomal abnormalities. Detailed characterization of the clinical phenotype and medical complications is ongoing. Telomere Length in Target Tissues [CAS 10373] is now closed. It evaluated intra-individual telomere length measured by QPCR of DNA derived from blood, buccal cells, and fibroblasts from IBMFS patients as well as the correlation between flow-FISH and QPCR. It found that in general, fibroblast telomeres were longer than blood or buccal cell telomeres but that there was significant intra-individual correlation between tissue types. This pilot study forms the basis for larger methodological studies of telomere biology and cancer risk. We are also investigating Telomere Length as Cancer Risk Factor [CAS 10371]. Numerous studies suggest that short surrogate tissue TL is a cancer risk factor. Our previous case-control studies found that short telomeres are associated with increased risk of ovarian and gastric cancer. However, our cohort study of TL and prostate cancer did not find the same association. Our meta-analysis on the association between TL in surrogate tissues and cancer risk which suggests short TL and overall cancer are associated but this may be driven by stronger effects in specific cancers. The ORs derived from retrospective studies were much higher than for prospective studies (2.9 versus 1.16), which suggests reverse causation bias and possible contribution of cancer therapy prior to sample collection. Study heterogeneity and minimal or no data on certain cancer sites were also limitations of these analyses. Ongoing work includes many collaborative studies of TL and cancer designed to 1) determine if TL is associated with risk of specific cancers or cancer-related outcomes, 2) determine differences in TL and cancer associations in case-control versus cohort studies, and 3) use these studies as building blocks for germline (i.e., surrogate) and somatic tissue studies aimed at better understanding the contribution of telomere biology to cancer etiology Genetic Variants That Correlate With Telomere Length [CAS 10371] have been evaluated through analyses of SNP data derived from the NCI CGEMS GWAS of prostate and breast cancer. We found that 13 SNPs from 4 genes were associated with TL. We also collaborated with Harvard University on a genome-wide association study (GWAS) of TL. That study confirmed a SNP in TERC as associated with TL, but, similar to other studies, did not find strong associations between SNPs at other sites and TL. A new project, Telomere length after HSCT in patients with acquired severe aplastic anemia [CAS 10508] was initiated which seeks to understand the role of telomere biology in outcomes after hematopoictic stem cell transplant (HSCT) for acquired severe aplastic anemia (SAA). Pre-transplant TL has been measured in controls, donors, and HSCT recipients in collaboration with the National Marrow Donor Program (NMDP) and the Center for International Blood and Marrow transplant research (CIBMTR). Ongoing analyses include the association of TL with HSCT outcomes such as death, post-transplant malignancies, and fibrotic diseases. Population genetic studies of telomere biology genes [CAS 10372] continue to provide important insight into their evolutionary history. This will improve understanding of the role of genetic variation in their function and aid in understanding these variants as cancer risk factors. We expanded on our initial study of seven genes by evaluating 37 telomere biology genes in 53 worldwide populations utilizing SNP data from the Human Genome Diversity Panel. This study showed that, as a group, telomere biology genes have low to moderate haplotype diversity, high ancestral allele frequencies, and low differentiation. The telomerase gene (TERT) was a notable exception with low levels of linkage disequilibrium. Evidence suggestive of evolutionary selection was present in five genes. Ongoing studies include detailed studies of genetic variation in the 5p15.33 chromosomal locus using 1000 Genomes data. This locus includes TERT and CLPTM1L and includes SNPs which have been associated with cancer risk in several GWAS.