Antonia Velázquez

Genome-wide association study on differentiated thyroid cancer.

CONTEXT Genome-wide association studies (GWASs) of differentiated thyroid cancer (DTC) have identified associations with polymorphisms at 2q35 (DIRC3), 8p12 (NRG1), 9q22.33 (FOXE1), and 14q13.2 (NKX2-1). However, most of the inherited genetic risk factors of DTC remain to be discovered. OBJECTIVE Our objective was to identify additional common DTC susceptibility loci. DESIGN We conducted a GWAS in a high-incidence Italian population of 690 cases and 497 controls and followed up the most significant polymorphisms in 2 additional Italian series and in 3 low-incidence populations totaling 2958 cases and 3727 controls. RESULTS After excluding the most robust previously identified locus (9q22.33), the strongest association was shown by rs6759952, confirming the recently published association in DIRC3 (odds ratio [OR] = 1.21, P = 6.4 × 10(-10), GWAS and all replications combined). Additionally, in the combined analysis of the Italian series, suggestive associations were attained with rs10238549 and rs7800391 in IMMP2L (OR = 1.27, P = 4.1 × 10(-6); and OR = 1.25, P = 5.7 × 10(-6)), rs7617304 in RARRES1 (OR = 1.25, P = 4.6 × 10(-5)) and rs10781500 in SNAPC4/CARD9 (OR = 1.23, P = 3.5 × 10(-5)). CONCLUSIONS Our findings provide additional insights into the genetic and biological basis of inherited genetic susceptibility to DTC. Additional studies are needed to determine the role of the identified polymorphisms in the development of DTC and their possible use in the clinical practice.

Association studies of OGG1, XRCC1, XRCC2 and XRCC3 polymorphisms with differentiated thyroid cancer.

The role of the DNA repair genes OGG1, XRCC1, XRCC2 and XRCC3 on differentiated thyroid cancer (DTC) susceptibility was examined in 881 individuals (402 DTC and 479 controls). DNA repair genes were proposed as candidate genes, since the current data indicate that exposure to ionizing radiation is the only established factor in the development of thyroid cancer, especially when it occurs in early stages of life. We have genotyped DNA repair genes involved in base excision repair (BER) (OGG1, Ser326Cys; XRCC1, Arg280His and Arg399Gln), and homologous recombination repair (HRR) (XRCC2, Arg188His and XRCC3, ISV-14G). Genotyping was carried out using the iPLEX (Sequenom) technique. Multivariate logistic regression analyses were performed in a case-control study design. From all the studied polymorphism, only a positive association (OR=1.58, 95% CI 1.05-2.46, P=0.027) was obtained for XRCC1 (Arg280His). No associations were observed for the other polymorphisms. No effects of the histopathological type of tumor were found when the DTC patients were stratified according to the type of tumor. It must be emphasized that this study include the greater patients group, among the few studies carried out until now determining the role of DNA repair genes in thyroid cancer susceptibility.

Genotoxicity is modulated by ascorbic acid studies using the wing spot test in Drosophila

The ability of ascorbic acid (Vitamin C) to modulate the genotoxic action of several mutagens was investigated in the wing spot test of Drosophila melanogaster. In this assay, 3-day-old transheterozygous larvae for the multiple wing hairs (mwh, 3-0.3) and flare (flr, 3-38.8) genes were treated with three reference mutagenic compounds, namely cobalt chloride (CoCl2), 4-nitroquinoline 1-oxide (4-NQO) and potassium dichromate (K2Cr2O7). The results obtained show that the three reference mutagens tested were clearly genotoxic in the Drosophila wing somatic mutation and recombination test (SMART). None of the three concentrations tested of ascorbic acid (25, 75 and 250mM) induced significant increases in the frequency of the mutant clones recorded. When co-treatment experiments with ascorbic acid were carried out, different results were found. Thus, ascorbic acid was effective in reducing the genotoxicity of K2Cr2O7 virtually to the control level; on the contrary, it did not show any antigenotoxic effect on the genotoxicity of 4-NQO. Finally, co-treatments with CoCl2 and ascorbic acid show a significant increase in the frequency of mutant clones over the values obtained with CoCl2 alone.

Strong Association of Chromosome 1p12 Loci with Thyroid Cancer Susceptibility

Several genes directly related to thyroid cancer development have been described; nevertheless, the genetic pathways of this tumorigenesis process are unknown. Together with environmental factors, susceptibility genes could have an important role in thyroid cancer. Our previous studies suggest that the chromosome 1p12-13 is related to thyroid cancer incidence. Here, we extend the analysis with a case-control association study in a Spanish population. Thus, six single-nucleotide polymorphisms were genotyped, covering 2.4 Mb of the 1p12-13 region. A statistically significant association between thyroid cancer incidence and the rs2145418 and rs4658973 polymorphisms was found (P < 0.0001). No association was detected for the other four polymorphisms studied. The rs2145418 marker showed a significant odds ratio of 5.0 [95% confidence interval (95% CI), 2.85-8.83] and 9.2 (95% CI, 4.50-21.6) for heterozygous and homozygous G-variant alleles, respectively. For rs4658973, the odds ratios were 0.40 (95% CI, 0.26-0.62) and 0.07 (95% CI, 0.03-0.18) for heterozygous and homozygous G-variant alleles, respectively. These markers map into the 1p12 region, and no linkage disequilibrium was found between them, indicating an independent relation of these polymorphisms with thyroid cancer susceptibility. Our data provide evidence of a strong association of the chromosome 1p12 with thyroid cancer risk, and it is the first study describing susceptibility loci for thyroid cancer in this region. (Cancer Epidemiol Biomarkers Prev 2008;17(6):1499–504)

Novel Genome-Wide Association Study-Based Candidate Loci for Differentiated Thyroid Cancer Risk

CONTEXT Genome-wide association studies (GWASs) on differentiated thyroid cancer (DTC) have identified robust associations with single nucleotide polymorphisms (SNPs) at 9q22.33 (FOXE1), 14q13.3 (NKX2-1), and 2q35 (DIRC3). Our recently published GWAS suggested additional susceptibility loci specific for the high-incidence Italian population. OBJECTIVE The purpose of this study was to identify novel Italian-specific DTC risk variants based on our GWAS and to test them further in low-incidence populations. DESIGN We investigated 45 SNPs selected from our GWAS first in an Italian population. SNPs that showed suggestive evidence of association were investigated in the Polish and Spanish cohorts. RESULTS The combined analysis of the GWAS and the Italian replication study (2260 case patients and 2218 control subjects) provided strong evidence of association with rs10136427 near BATF (odds ratio [OR] =1.40, P = 4.35 × 10(-7)) and rs7267944 near DHX35 (OR = 1.39, P = 2.13 × 10(-8)). A possible role in DTC susceptibility in the Italian populations was also found for rs13184587 (ARSB) (P = 8.54 × 10(-6)) and rs1220597 (SPATA13) (P = 3.25 × 10(-6)). Only the associations between rs10136427 and rs7267944 and DTC risk were replicated in the Polish and the Spanish populations with little evidence of population heterogeneity (GWAS and all replications combined, OR = 1.30, P = 9.30 × 10(-7) and OR = 1.32, P = 1.34 × 10(-8), respectively). In silico analyses provided new insights into the possible functional consequences of the SNPs that showed the strongest association with DTC. CONCLUSIONS Our findings provide evidence for novel DTC susceptibility variants. Further studies are warranted to identify the specific genetic variants responsible for the observed associations and to functionally validate our in silico predictions.

Analysis of genomic damage in the mutagen-sensitive mus-201 mutant of Drosophila melanogaster by arbitrarily primed PCR (AP-PCR) fingerprinting

DNA repair mechanisms are important to maintain the stability of the genome. In Drosophila melanogaster, the mus-201 gene is required in the excision repair process. To study the contribution of the mus-201 gene in the stability of the Drosophila genome, we have used the arbitrarily primed PCR fingerprinting method (AP-PCR). We have analysed the changes in the genomic DNA fingerprints from the progeny of wild-type males crossed with mus-201 repair-deficient or repair-proficient females. After induction of DNA damage with 2-acetylaminofluorene (2-AAF) in the wild-type parental males, quantitative and qualitative differences in the AP-PCR fingerprints were detected between the two crosses, and the estimate of the genomic damage detected by AP-PCR has clearly shown that the mus-201 repair deficiency is associated with an increase of genomic damage. The predominant type of alterations detected by AP-PCR under the mus-201 repair-deficient conditions agree with the results obtained in microsatellite PCR analysis, suggesting that the role of the mus-201 gene, necessary in excision repair, is not associated to the mismatch repair process. The work reported here demonstrates that the AP-PCR is a suitable technique to analyse genetic alterations in D. melanogaster and, consequently, can be used to compare the susceptibility to genomic damage of different DNA repair mutants.

Common Variants of the Thyroglobulin Gene Are Associated with Differentiated Thyroid Cancer Risk

BACKGROUND Genetic factors are important in thyroid cancer susceptibility. Recently, it has been reported that there are associations of certain chromosome regions with thyroid cancer. In this case-control study, we sought to determine whether there is an association between differentiated thyroid cancer (DTC) and variants in regions of chromosome 8q. METHODS We used a case-control association design in a population of 877 individuals (398 patients with sporadic DTC and 479 healthy controls). The iPLEX technology was applied to analyze seven single-nucleotide polymorphisms (SNPs) in chromosome 8q: two SNPs that map at 8q24, previously reported as risk markers in different types of cancer, two SNPs in the thyrotropin-releasing hormone receptor gene (TRHR), and three SNPs in the thyroglobulin gene (TG). Risk assessment was done by unconditional regression analysis. RESULTS The two SNPs that map at 8q24, rs6983267 and rs1447295, and the two TRHR polymorphisms showed no association with DTC. No association was also found for the exon 33 TG polymorphism. The two TG polymorphisms in the exon 10-12 cluster, however, were associated with an increased risk of DTC (dominant model odds ratio = 1.80, 95% confidence interval = 1.30-2.50, p < 0.001). CONCLUSIONS In this study, we show for the first time that the TG gene is a susceptibility factor for thyroid cancer. Although these conclusions are based on a large population, additional studies are warranted to support these data.

Thyroid cancer GWAS identifies 10q26.12 and 6q14.1 as novel susceptibility loci and reveals genetic heterogeneity among populations.

Thyroid cancer is the most heritable cancer of all those not displaying typical Mendelian inheritance. However, most of the genetic factors that would explain the high heritability remain unknown. Our aim was to identify additional common genetic variants associated with susceptibility to this disease. In order to do so, we performed a genome‐wide association study in a series of 398 cases and 502 controls from Spain, followed by a replication in four well‐defined Southern European case‐control collections contributing a total of 1,422 cases and 1,908 controls. The association between the variation at the 9q22 locus near FOXE1 and thyroid cancer risk was consistent across all series, with several SNPs identified (rs7028661: OR = 1.64, p = 1.0 × 10−22, rs7037324: OR = 1.54, p = 1.2 × 10−17). Moreover, the rare alleles of three SNPs (rs2997312, rs10788123 and rs1254167) at 10q26.12 showed suggestive evidence of association with higher risk of the disease (OR = 1.35, p = 1.2 × 10−04, OR = 1.26, p = 5.2 × 10−04 and OR = 1.38, p = 5.9 × 10−05, respectively). Finally, the rare allele of rs4075570 at 6q14.1 conferred protection in the series studied (OR = 0.82, p = 2.0 × 10−04). This study suggests that heterogeneity in genetic susceptibility between populations is a key feature to take into account when exploring genetic risk factors related to this disease.

Thyroid Cancer Susceptibility and THRA1 and BAT-40 Repeats Polymorphisms

Although genetic and environmental factors have been identified in the etiology of thyroid cancer, the specific genetic implications in sporadic thyroid tumors are poorly understood but, as in other common cancers, low-penetrance susceptibility genes are believed to be crucial in the tumorigenesis processes. Here, we have carried out a case-control study to investigate whether there is an association between THRA1 CA repeat or BAT-40 A repeat polymorphisms and thyroid cancer risk. The THRA1 repeat resides in the thyroid hormone receptor-α1 gene, which is associated with thyroid cancer and whose expression depends on the THRA1 repeat size. We also analyzed the BAT-40 repeat that maps to chromosome 1, a region known to be involved in thyroid cancer. This repeat is located in the 3-β-hydroxysteroid dehydrogenase gene that is associated with prostate cancer susceptibility. The THRA1 repeat was genotyped in 212 thyroid cancer patients and 141 controls of a Spanish population. From these individuals, 207 patients and 138 controls were also analyzed for the BAT-40 marker. No significant difference in the THRA1 allele distribution between patients and controls was found, although short alleles (<128 bp) might have some protective effect on thyroid cancer risk of carriers (odds ratio, 0.50; 95% confidence interval, 0.22-1.13; P = 0.094). By contrast, the BAT-40 allele distribution in patients was significantly different with respect to control (P = 0.035). Essentially, the difference were found in the genotypes involving the 111- to 115-bp allele range, which seem to be associated with a protective effect on thyroid cancer susceptibility in the studied population (odds ratio, 0.18; 95% confidence interval, 0.01-0.57; P = 0.02). Therefore, our results indicate that the BAT-40 containing region and to a less extend the thyroid hormone receptor-α1 gene are related to thyroid cancer susceptibility. To our knowledge, this is the first study reporting the identification of genetic factors for thyroid cancer susceptibility.

Additional data in support of the quadruplicated white-ivory reversion system to test for somatic genotoxicity in Drosophila melanogaster

Cyclophosphamide, ethyl methanesulfonate, propyleneimine and tritiated water were tested in a new short-term somatic mutation bioassay, previously described by Green and coworkers (1986), to evaluate the suitability of the quadruplicated white-ivory system of Drosophila melanogaster for genotoxicity testing of chemicals. A 2.9-kb tandemly duplicated sequence of w+ within a w+ gene is responsible for the white-ivory phenotype. Reversion of wi to w+ is, in general, associated with the loss of the appended 2.9 kb or other alterations affecting this duplicated region. The appearance of light (white or nearly white) phenotypes could be due to the loss of some wi copies. Thus, in the eyes of adult males resulting from treated larvae, we can detect 2 types of sectors (red and light) on the orange-yellow background. Our results indicate that the genetic system used in this somatic assay is sensitive to the genotoxic effects of the 4 compounds tested. All 4 compounds tested were positive. Tritiated water had weak effects, cyclophosphamide was characterized by small revertant clones and ethyl methanesulfonate and propyleneimine by large clone size. From the available data, we feel that the wi system can be considered of potential value for genotoxicity testing.