Dyskeratosis congenita: the first NIH clinical research workshop

Dyskeratosis congenita (DC) is a heterogeneous inherited bone marrow failure syndrome, characterized by abnormally short telomeres and mutations in telomere biology genes. The spectrum of telomere biology disorders is growing and the clinical management of these patients is complex. A DC-specific workshop was held at the NIH on September 19, 2008; participants included physicians, patients with DC, their family members, and representatives from other support groups. Data from the UK's DC Registry and the NCI's DC cohort were described. Updates on the function of the known DC genes were presented. Clinical aspects discussed included androgen therapy, stem cell transplant, cancer risk, and cancer screening. Families with DC met for the first time and formed a family support group (http://www.dcoutreach.com/). Ongoing, open collaboration between the clinical, scientific, and family communities is required for continued improvement in our understanding of DC and the clinical consequences of telomeric defects.

Secondary supratentorial primitive neuroectodermal tumor following treatment of childhood osteosarcoma

A 16-year-old Caucasian male was diagnosed with a primitive neuroectodermal tumor (PNET) 5 years following the diagnosis of nonmetastatic osteosarcoma of the left proximal humerus. The patient was initially treated with standard chemotherapy and limb salvage resection for osteosarcoma. Nine months after the completion of therapy, he developed lung metastases for which he underwent surgical resection and received additional chemotherapy. Almost 5 years after the osteosarcoma diagnosis, the patient was diagnosed with a supratentorial PNET, which represents the first known case reported in a patient with osteosarcoma.

The association between leukocyte telomere length and cigarette smoking, dietary and physical variables, and risk of prostate cancer

Telomeres consist of nucleotide repeats and a protein complex at chromosome ends that are essential to maintaining chromosomal integrity. Several studies have suggested that subjects with shorter telomeres are at increased risk of bladder and lung cancer. In comparison to normal tissues, telomeres are shorter in high-grade intraepithelial neoplasia and prostate cancer. We examined prostate cancer risk associated with relative telomere length as determined by quantitative PCR on prediagnostic buffy coat DNA isolated from 612 advanced prostate cancer cases and 1049 age-matched, cancer-free controls from the PLCO Cancer Screening Trial. Telomere length was analyzed as both a continuous and a categorical variable with adjustment for potential confounders. Statistically significant inverse correlations between telomere length, age and smoking status were observed in cases and controls. Telomere length was not associated with prostate cancer risk (at the median, OR = 0.85, 95% CI: 0.67, 1.08); associations were similar when telomere length was evaluated as a continuous variable or by quartiles. The relationships between telomere length and inflammation-related factors, diet, exercise, body mass index, and other lifestyle variables were explored since many of these have previously been associated with shorter telomeres. Healthy lifestyle factors (i.e., lower BMI, more exercise, tobacco abstinence, diets high in fruit and vegetables) tended to be associated with greater telomere length. This study found no statistically significant association between leukocyte telomere length and advanced prostate cancer risk. However, correlations of telomere length with healthy lifestyles were noted, suggesting the role of these factors in telomere biology maintenance and potentially impacting overall health status.

International osteosarcoma incidence patterns in children and adolescents, middle ages and elderly persons

Osteosarcoma incidence rates in the United States peak in adolescence and in the elderly. The international patterns of osteosarcoma incidence in children have been described, whereas those for young, middle age or elderly adults have not. Using the Cancer Incidence in Five Continents, International Agency for Cancer Research database we compared incidence rates for children and adolescents (age 0-24 years), the middle age group (25-59 years) and elderly (>or=60 years) persons by world regions and individual countries. Overall, worldwide osteosarcoma incidence rates were quite similar in the younger age groups. The greatest variation in incidence rates was observed in the elderly.

Osteosarcoma incidence and survival rates from 1973 to 2004: data from the Surveillance, Epidemiology, and End Results Program

BACKGROUND

Osteosarcoma, which is the most common primary bone tumor, occurs most frequently in adolescents, but there is a second incidence peak among individuals aged > 60 years. Most osteosarcoma epidemiology studies have been embedded in large analyses of all bone tumors or focused on cases occurring in adolescence. Detailed descriptions of osteosarcoma incidence and survival with direct comparisons among patients of all ages and ethnicities are not available.

METHODS

Frequency, incidence, and survival rates for 3482 patients with osteosarcoma from the National Cancer Institute's population-based Surveillance, Epidemiology, and End Results (SEER) Program between 1973 and 2004 were investigated by age (ages 0-24 years, 25-59 years, and 60 to > or = 85 years), race, sex, pathology subtype, stage, and anatomic site.

RESULTS

There were large differences in incidence and survival rates by age. There was a high percentage of osteosarcoma with Paget disease and osteosarcoma as a second or later cancer among the elderly. There was a high percentage of osteosarcoma among patients with Paget disease and osteosarcoma as a second or later cancer among the elderly. Tumor site differences among age groups were noted. Survival rates varied by anatomic site and disease stage and did not improve significantly from 1984 to 2004.

CONCLUSIONS

This comprehensive, population-based description of osteosarcoma, identified important differences in incidence, survival, pathologic subtype, and anatomic site among age groups, and quantified the impact of osteosarcoma in patients with Paget disease or as a second cancer on incidence and mortality rates. These findings may have implications in understanding osteosarcoma biology and epidemiology.

Structure and function of the human Gly1619Arg polymorphism of M6P/IGF2R domain 11 implicated in IGF2 dependent growth

The mannose 6-phosphate/IGF 2 receptor (IGF2R) is comprised of 15 extra-cellular domains that bind IGF2 and mannose 6-phosphate ligands. IGF2R transports ligands from the Golgi to the pre-lysosomal compartment and thereafter to and from the cell surface. IGF2R regulates growth, placental development, tumour suppression and signalling. The ligand IGF2 is implicated in the growth phenotype, where IGF2R normally limits bioavailability, such that loss and gain of IGF2R results in increased and reduced growth respectively. The IGF2R exon 34 (5002A>G) polymorphism (rs629849) of the IGF2 specific binding domain has been correlated with impaired childhood growth (A/A homozygotes). We evaluated the function of the Gly1619Arg non-synonymous amino acid modification of domain 11. NMR and X-ray crystallography structures located 1619 remote from the ligand binding region of domain 11. Arg1619 was located close to the fibronectin type II (FnII) domain of domain 13, previously implicated as a modifier of IGF2 ligand binding through indirect interaction with the AB loop of the binding cleft. However, comparison of binding kinetics of IGF2R, Gly1619 and Arg1619 to either IGF2 or mannose 6-phosphate revealed no differences in 'on' and 'off' rates. Quantitative PCR, (35)S pulse chase and flow cytometry failed to demonstrate altered gene expression, protein half-life and cell membrane distribution, suggesting the polymorphism had no direct effect on receptor function. Intronic polymorphisms were identified which may be in linkage disequilibrium with rs629849 in certain populations. Other potential IGF2R polymorphisms may account for the correlation with childhood growth, warranting further functional evaluation.

Dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome characterized clinically by the triad of abnormal nails, reticular skin pigmentation, and oral leukoplakia, and is associated with high risk of developing aplastic anemia, myelodysplastic syndrome, leukemia, and solid tumors. Patients have very short germline telomeres, and approximately half have mutations in one of six genes encoding proteins that maintain telomere function. Accurate diagnosis of DC is critical to ensure proper clinical management, because patients who have DC and bone marrow failure do not respond to immunosuppressive therapy and may have increased morbidity and mortality associated with hematopoietic stem cell transplantation.

Cancer genetic association studies in the genome-wide age

Genome-wide association studies of hundreds of thousands of SNPs have led to a deluge of studies of genetic variation in cancer and other common diseases. Large case-control and cohort studies have identified novel SNPs as markers of cancer risk. Genome-wide association study SNP data have also advanced understanding of population-specific genetic variation. While studies of risk profiles, combinations of SNPs that may increase cancer risk, are not yet clinically applicable, future, large-scale studies will make individualized cancer screening and prevention possible.

Nucleotide diversity and population differentiation of the melanocortin 1 receptor gene, MC1R

Background

The melanocortin 1 receptor gene (MC1R) is responsible for normal pigment variation in humans and is highly polymorphic with numerous population-specific alleles. Some MC1R variants have been associated with skin cancer risk.

Results

Allele frequency data were compiled on 55 single nucleotide polymorphisms from seven geographically distinct human populations (n = 2306 individuals). MC1R nucleotide diversity, π, was much higher (10.1 × 10^-4) than in other genes for all subjects. A large degree of population differentiation, determined by F_ST, was also present, particularly between Asia and all other populations, due to the p.R163Q (c.488 G>A) polymorphism. The least amount of differentiation was between the United States, Northern Europe, and Southern Europe. Tajima's D statistic suggested the presence of positive selection in individuals from Europe.

Conclusion

This study further quantifies the degree of population-specific genetic variation and suggests that positive selection may be present in European populations in MC1R.

Parathyroid tumor development involves deregulation of homeobox genes

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant syndrome caused by mutations in the MEN1 tumor suppressor gene. Loss of the functional second copy of the MEN1 gene causes individuals to develop multiple endocrine tumors, primarily affecting the parathyroid, pituitary, and pancreas. While it is clear that the protein encoded by MEN1, menin, suppresses endocrine tumors, its biochemical functions and direct downstream targets remain unclear. Recent studies have suggested that menin may act as a scaffold protein to coordinate gene transcription, and that menin is an oncogenic cofactor for homeobox (HOX) gene expression in hematopoietic cancer. The role of HOX genes in adult cell differentiation is still obscure, but growing evidence suggests that they may play important roles in the development of cancer. Therefore, we hypothesized that specific HOX genes were regulated by menin in parathyroid tumor development. Utilizing quantitative TaqMan RT-PCR, we compared expression profiles of the 39 HOX genes in human familial MEN1 (fMEN1) parathyroid tumors and sporadic parathyroid adenomas with normal samples. We identified a large set of 23 HOX genes whose deregulation is specific for fMEN1 parathyroid tumors, and only 5 HOX genes whose misexpression are specific for sporadic parathyroid tumor development. These findings provide the first evidence that loss of the MEN1 tumor suppressor gene is associated with deregulation of specific HOX gene expression in the development of familial human parathyroid tumors. Our results strongly reinforce the idea that abnormal expression of developmental HOX genes can be critical in human cancer progression.

TINF2, a component of the shelterin telomere protection complex, is mutated in dyskeratosis congenita

Patients with dyskeratosis congenita (DC), a heterogeneous inherited bone marrow failure syndrome, have abnormalities in telomere biology, including very short telomeres and germline mutations in DKC1, TERC, TERT, or NOP10, but approximately 60% of DC patients lack an identifiable mutation. With the very short telomere phenotype and a highly penetrant, rare disease model, a linkage scan was performed on a family with autosomal-dominant DC and no mutations in DKCI, TERC, or TERT. Evidence favoring linkage was found at 2p24 and 14q11.2, and this led to the identification of TINF2 (14q11.2) mutations, K280E, in the proband and her five affected relatives and TINF2 R282H in three additional unrelated DC probands, including one with Revesz syndrome; a fifth DC proband had a R282S mutation. TINF2 mutations were not present in unaffected relatives, DC probands with mutations in DKC1, TERC, or TERT or 298 control subjects. We demonstrate that a fifth gene, TINF2, is mutated in classical DC and, for the first time, in Revesz syndrome. This represents the first shelterin complex mutation linked to human disease and confirms the role of very short telomeres as a diagnostic test for DC.

The role of telomere biology in bone marrow failure and other disorders

Telomeres, consisting of nucleotide repeats and a protein complex at chromosome ends, are essential in maintaining chromosomal integrity. Dyskeratosis congenita (DC) is the inherited bone marrow failure syndrome (IBMFS) that epitomizes the effects of abnormal telomere biology. Patients with DC have extremely short telomere lengths (<1st percentile) and many have mutations in telomere biology genes. Interpretation of telomere length in other IBMFSs is less straightforward. Abnormal telomere shortening has been reported in patients with apparently acquired hematologic disorders, including aplastic anemia, myeolodysplasia, paroxysmal nocturnal hemoglobinuria, and leukemia. In these disorders, the shortest-lived cells have the shortest telomeres, suggestive of increased hematopoietic stress. Telomeres are also markers of replicative and/or oxidative stress in other complex disease pathways, such as inflammation, stress, and carcinogenesis. The spectrum of related disorders caused by mutations in telomere biology genes extends beyond classical DC to include marrow failure that does not respond to immunosuppression, idiopathic pulmonary fibrosis, and possibly other syndromes. We suggest that such patients be categorized as having an inherited disorder of telomere biology. Longitudinal studies of patients with very short telomeres but without classical DC are necessary to further understand the long-term sequelae, such as malignancy, osteonecrosis/osteoporosis, and pulmonary and liver disease.

Genetic variation in five genes important in telomere biology and risk for breast cancer

Telomeres, consisting of TTAGGG nucleotide repeats and a protein complex at chromosome ends, are critical for maintaining chromosomal stability. Genomic instability, following telomere crisis, may contribute to breast cancer pathogenesis. Many genes critical in telomere biology have limited nucleotide diversity, thus, single nucleotide polymorphisms (SNPs) in this pathway could contribute to breast cancer risk. In a population-based study of 1995 breast cancer cases and 2296 controls from Poland, 24 SNPs representing common variation in POT1, TEP1, TERF1, TERF2 and TERT were genotyped. We did not identify any significant associations between individual SNPs or haplotypes and breast cancer risk; however, data suggested that three correlated SNPs in TERT (−1381C>T, −244C>T, and Ex2-659G>A) may be associated with reduced risk of breast cancer among individuals with a family history of breast cancer (odds ratios 0.73, 0.66, and 0.57, 95% confidence intervals 0.53–1.00, 0.46–0.95 and 0.39–0.84, respectively). In conclusion, our data do not support substantial overall associations between SNPs in telomere pathway genes and breast cancer risk. Intriguing associations with variants in TERT among women with a family history of breast cancer warrant follow-up in independent studies.

Analysis of Genes Critical for Growth Regulation Identifies Insulin-like Growth Factor 2 Receptor Variations with Possible Functional Significance as Risk Factors for Osteosarcoma

BACKGROUND

Osteosarcoma, the most common malignant primary bone tumor, typically occurs during the adolescent growth spurt. Germ-line genetic variation in genes critical in growth regulation could confer altered risk of osteosarcoma.

METHODS

Fifty-two common single nucleotide polymorphisms (SNP) in 13 genes were genotyped in a prospective case-control study of osteosarcoma (104 osteosarcoma cases and 74 orthopedic controls). Genotype data analyzed with contingency tables suggested the strongest association with insulin-like growth factor 2 receptor (IGF2R) SNPs. Additional SNPs were genotyped to capture IGF2R common haplotypes and resequencing was done across the IGF2R block associated with osteosarcoma risk. Percentage methylation was determined by pyrosequencing of the IGF2R variant allele located in a CpG island.

RESULTS

IGF2R Ex16+88G>A (rs998075) and IVS16+15C>T (rs998074) SNPs were associated with increased risk for osteosarcoma compared with orthopedic controls (haplotype odds ratio, 2.04; 95% confidence interval, 1.29-3.24). Follow-up genotyping showed that IGF2R IVS15+213C>T was also associated with increased osteosarcoma risk. Resequence analysis identified two additional SNPs linked to the risk-associated SNPs; linkage disequilibrium was strongest in a 1-kb pair region around them. The Ex16+88G>A SNP is located within a CpG island and alters methylation at that site.

CONCLUSION

This pilot study of germ-line genetic variation in growth pathway genes and osteosarcoma identified a haplotype block in IGF2R associated with increased risk of osteosarcoma. The presence of a SNP in this block results in loss of methylation at a CpG island, providing corroborative evidence of a possible functional variant. Our analysis of the IGF2R haplotype structure will be applicable to future studies of IGF2R and disease risk.

Germ-line genetic variation of TP53 in osteosarcoma

BACKGROUND

Osteosarcoma (OS) has been well described in individuals with germ-line TP53 mutations (Li-Fraumeni Syndrome) but typically occurs sporadically in adolescents and young adults. Single nucleotide polymorphisms (SNPs), the most common germ-line genetic variation, have been associated with risk for other types of cancer. We hypothesized that genetic variation in TP53 could be associated with OS risk based on its critical role in cell growth and effect of somatic mutations in OS tumors.

PROCEDURE

Twelve common SNPs in TP53 were genotyped in a case-control study of sporadic OS. These SNPs spanned the TP53 locus and captured common haplotypes. Genotype data were analyzed using contingency tables for additive, dominant, and recessive genetic models. PHASEv2.1 and HaploStats were used to evaluate haplotypes.

RESULTS

The recessive model suggested an increased risk of OS when two copies of TP53-34 C>G variant (IVS2+38, rs1642785) were present, P = 0.041, odds ratio (OR) 6.70 (95% confidence interval [CI] 1.06-41.6). The TP53-01 variant C>G (Pro72Arg, rs1042522) may also be associated with increased risk for OS, P = 0.028, OR 7.5 (95% CI 1.20-46.3). Common TP53 haplotypes as well as the remaining 10 SNPs were not associated with risk for OS.

CONCLUSIONS

These data do not indicate a strong link between variation in TP53 and OS risk, although they provide preliminary evidence of an increased risk of OS associated with variants at IVS2+38 and Pro72Arg. The findings warrant replication in further studies.

Very short telomere length by flow fluorescence in situ hybridization identifies patients with dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome in which the known susceptibility genes (DKC1, TERC, and TERT) belong to the telomere maintenance pathway; patients with DC have very short telomeres. We used multicolor flow fluorescence in situ hybridization analysis of median telomere length in total blood leukocytes, granulocytes, lymphocytes, and several lymphocyte subsets to confirm the diagnosis of DC, distinguish patients with DC from unaffected family members, identify clinically silent DC carriers, and discriminate between patients with DC and those with other bone marrow failure disorders. We defined "very short" telomeres as below the first percentile measured among 400 healthy control subjects over the entire age range. Diagnostic sensitivity and specificity of very short telomeres for DC were more than 90% for total lymphocytes, CD45RA+/CD20- naive T cells, and CD20+ B cells. Granulocyte and total leukocyte assays were not specific; CD45RA- memory T cells and CD57+ NK/NKT were not sensitive. We observed very short telomeres in a clinically normal family member who subsequently developed DC. We propose adding leukocyte subset flow fluorescence in situ hybridization telomere length measurement to the evaluation of patients and families suspected to have DC, because the correct diagnosis will substantially affect patient management.

Teleconferencing in the management of head and neck cancer

Teleconferencing can be used as part of the integrated management of head and neck cancer. An audit of the participants' views would suggest that the meeting is used in the management of complex head and neck issues.

Genetic association studies in cancer: good, bad or no longer ugly?

For some time, investigators have appreciated that genetic association studies in cancer are complex because of the multi-stage process of cancer and the daunting challenge of analysing genetic variants in population and family studies. Because of recent technological advances and annotation of common genetic variation in the human genome, it is now possible for investigators to study genetic variation and cancer risk in many different settings. While these studies hold great promise for unravelling multiple genetic risk factors that contribute to the set of complex diseases called cancer, it is also imperative that study design and methods of interpretation be carefully considered. Replication of results in sufficiently large, well-powered studies is critical if genetic variation is to realise the promise of personalised medicine--namely, using genetic data to individualise medical decisions. In this regard, the plausibility of validated genetic variants can only be realised by the study of gene-gene and gene-environment interactions. The genetic association study in cancer has come a long way from the days of restriction fragment length polymorphisms, and now promises to scan an entire genome 'agnostically' in search of genetic markers for a disease or outcome. Moreover, the application and interpretation of these studies should be conducted cautiously.

Genetic variation, nucleotide diversity, and linkage disequilibrium in seven telomere stability genes suggest that these genes may be under constraint

To maintain chromosomal integrity and to protect the ends of chromosomes against recognition as damaged DNA, end-to-end fusion, or recombination, a coordinated set of genes is required to stabilize the telomere. We surveyed common genetic variation in seven genes that are vital to telomere stability (TERT, POT1, TNKS, TERF1, TINF2, TERF2, and TERF2IP) and validated single nucleotide polymorphisms (SNPs) in four different ethnic groups (n=118 total). Overall, our data show limited degrees of nucleotide diversity in comparison with data from other gene families. We observed that these genes are highly conserved in sequence between species, and that for nearly all of the coding SNPs the most common allele is ancestral (i.e., it is observed in primate sequences). Our findings support the hypothesis that genetic variation in a pathway that is critical for telomere stability may be under constraint. These data establish a foundation for further investigation of these genes in population-genetics, evolution, and disease-association studies.

Genetic variation in telomeric repeat binding factors 1 and 2 in aplastic anemia

OBJECTIVE

Abnormal telomere shortening has been observed in a subset of individuals with aplastic anemia (AA). We hypothesized that genetic variation in two genes critical in telomere biology, TERF1 and TERF2, could be a risk factor for AA.

METHODS

The proximal promoter and all coding regions of TERF1 and TERF2 were sequenced in 47 individuals with acquired AA. Regions with genetic variation were sequenced in an additional 95 AA patients and 289 healthy controls. Single nucleotide polymorphism (SNP) frequencies were analyzed using co-dominant and dominant models and haplotypes determined. Functional studies evaluated telomerase activity, telomere and telomeric overhang lengths, and TRF2 protein expression in select patients.

RESULTS

Two nonsynonymous amino acid changes were detected, one in exon 9 of TERF1 and another in exon 6 of TERF2. These sequence variants resulted in conservative amino acid changes and were not predicted to alter TRF1 or TRF2 protein expression or function. SNP and haplotype analyses in acquired AA patients suggested that one variant allele, in intron 9 of TERF1, and haplotype could be associated with increased risk for aplastic anemia (OR 1.59, 95% confidence interval 1.06-2.39, p = 0.033). TERF2 SNPs and haplotypes were not significantly associated with aplastic anemia.

CONCLUSIONS

It is possible that a common genetic variant in TERF1 is associated with risk for AA but additional studies are required. Highly penetrant, non-synonymous, or insertion-deletion mutations in TERF1 and TERF2 were not identified and therefore are not likely to be major genetic risk factors for the development of AA.

Telomere stability genes are not mutated in osteosarcoma cell lines

Osteosarcoma (OS), the most common primary bone tumor in adolescents and young adults, is characterized by a high degree of chromosomal abnormalities. Because telomeres are important for maintaining chromosomal integrity, it is plausible that germ-line or somatic mutations in the genes responsible for stabilizing the telomere complex could contribute to OS. We performed bi-directional sequence analysis in five OS cell lines and targeted all exons and proximal promoter regions in eight genes important in telomere stability: telomerase, the RNA component of telomerase (TERC), telomeric repeat binding factor 1, telomeric repeat binding factor 2, TERF1 interacting nuclear factor 2, human Rap1, protection of telomeres 1 and tankyrase. In this pilot study, we did not identify either somatic mutations or novel germ-line mutations in the five cell lines studied. However, we did confirm common genetic polymorphisms; an analysis of heterozygous sites suggests that loss of heterozygosity in OS is not present across these eight genes.