Fabio Rosa

An Overview of the Genetic Structure within the Italian Population from Genome-Wide Data

In spite of the common belief of Europe as reasonably homogeneous at genetic level, advances in high-throughput genotyping technology have resolved several gradients which define different geographical areas with good precision. When Northern and Southern European groups were considered separately, there were clear genetic distinctions. Intra-country genetic differences were also evident, especially in Finland and, to a lesser extent, within other European populations. Here, we present the first analysis using the 125,799 genome-wide Single Nucleotide Polymorphisms (SNPs) data of 1,014 Italians with wide geographical coverage. We showed by using Principal Component analysis and model-based individual ancestry analysis, that the current population of Sardinia can be clearly differentiated genetically from mainland Italy and Sicily, and that a certain degree of genetic differentiation is detectable within the current Italian peninsula population. Pair-wise FST statistics Northern and Southern Italy amounts approximately to 0.001 between, and around 0.002 between Northern Italy and Utah residents with Northern and Western European ancestry (CEU). The Italian population also revealed a fine genetic substructure underscoring by the genomic inflation (Sardinia vs. Northern Italy = 3.040 and Northern Italy vs. CEU = 1.427), warning against confounding effects of hidden relatedness and population substructure in association studies.

Polymorphisms in microRNA genes as predictors of clinical outcomes in colorectal cancer patients

Colorectal cancer (CRC) is one of the most frequently diagnosed malignancies worldwide. It is routinely cured by a 5-fluorouracil (5-FU)-based chemotherapy which improves outcomes in patients. We investigated the effect of single nucleotide polymorphisms (SNPs) in two microRNA (miRNA)-encoding genes that have been previously reported as important in prognosis in patients with stage III CRC and treated with 5-FU-based chemotherapy. Two SNPs (rs4919510 in miR-608 and rs213210 in miR-219-1) were genotyped in 1083 CRC patients recruited in the Czech Republic to evaluate their effect on clinical outcomes. Carriers of the variant T allele in rs213210 and receiving 5-FU chemotherapy were associated with a significantly worse survival [hazard ratio (HR) = 2.18; 95% confidence interval (CI): 1.20-3.98; adjusted P = 0.01] and an increased risk of relapse (HR = 1.94; 95% CI: 1.16-3.25; adjusted P = 0.01). After further stratification for tumor grading, stage III patients carrying the G allele of rs4919510 and undergoing adjuvant chemotherapy were at decreased risk of relapse (HR = 0.44; 95% CI: 0.20-0.94; adjusted P = 0.03). The present study confirms that variations in miRNA-encoding genes may be an important factor for modulating CRC prognosis and predicting therapy response.

Variation within 3' UTRs of base excision repair genes and response to therapy in colorectal cancer patients: a potential modulation of microRNAs binding

Purpose: Colorectal cancer is routinely treated with a 5-fluorouracil (5-FU)–based chemotherapy. 5-FU incorporates into DNA, and the base excision repair (BER) pathway specifically recognizes such damage. We investigated the association of single-nucleotide polymorphisms (SNP) in the 3′-untranslated regions (UTR) of BER genes, and potentially affecting the microRNA (miRNA) binding, on the risk of colorectal cancer, its progression, and prognosis. SNPs in miRNA-binding sites may modulate the posttranscriptional regulation of gene expression operated by miRNAs and explain interindividual variability in BER capacity and response to 5-FU. Experimental Design: We tested 12 SNPs in the 3′-UTRs of five BER genes for colorectal cancer susceptibility in a case–control study (1,098 cases and 1,459 healthy controls). Subsequently, we analyzed the role of these SNPs on clinical outcomes of patients (866 in the Training set and 232 in the Replication set). Results: SNPs in the SMUG1 and NEIL2 genes were associated with overall survival. In particular, SMUG1 rs2233921 TT carriers showed increased survival compared with those with GT/GG genotypes [HR, 0.54; 95% confidence interval (CI), 0.36–0.81; P = 0.003] in the Training set and after pooling results from the Replication set. The association was more significant following stratification for 5-FU–based chemotherapy (P = 5.6 × 10−5). A reduced expression of the reporter gene for the T allele of rs2233921 was observed when compared with the common G allele by in vitro assay. None of the genotyped BER polymorphisms were associated with colorectal cancer risk. Conclusions: We provide the first evidence that variations in miRNA-binding sites in BER genes 3′-UTR may modulate colorectal cancer prognosis and therapy response. Clin Cancer Res; 19(21); 6044–56. ©2013 AACR.

Genetic Variants Associated with Increased Risk of Malignant Pleural Mesothelioma: A Genome-Wide Association Study

Asbestos exposure is the main risk factor for malignant pleural mesothelioma (MPM), a rare aggressive tumor. Nevertheless, only 5–17% of those exposed to asbestos develop MPM, suggesting the involvement of other environmental and genetic risk factors. To identify the genetic risk factors that may contribute to the development of MPM, we conducted a genome-wide association study (GWAS; 370,000 genotyped SNPs, 5 million imputed SNPs) in Italy, among 407 MPM cases and 389 controls with a complete history of asbestos exposure. A replication study was also undertaken and included 428 MPM cases and 1269 controls from Australia. Although no single marker reached the genome-wide significance threshold, several associations were supported by haplotype-, chromosomal region-, gene- and gene-ontology process-based analyses. Most of these SNPs were located in regions reported to harbor aberrant alterations in mesothelioma (SLC7A14, THRB, CEBP350, ADAMTS2, ETV1, PVT1 and MMP14 genes), causing at most a 2–3-fold increase in MPM risk. The Australian replication study showed significant associations in five of these chromosomal regions (3q26.2, 4q32.1, 7p22.2, 14q11.2, 15q14). Multivariate analysis suggested an independent contribution of 10 genetic variants, with an Area Under the ROC Curve (AUC) of 0.76 when only exposure and covariates were included in the model, and of 0.86 when the genetic component was also included, with a substantial increase of asbestos exposure risk estimation (odds ratio, OR: 45.28, 95% confidence interval, CI: 21.52–95.28). These results showed that genetic risk factors may play an additional role in the development of MPM, and that these should be taken into account to better estimate individual MPM risk in individuals who have been exposed to asbestos.

Sardinians genetic background explained by runs of homozygosity and genomic regions under positive selection

The peculiar position of Sardinia in the Mediterranean sea has rendered its population an interesting biogeographical isolate. The aim of this study was to investigate the genetic population structure, as well as to estimate Runs of Homozygosity and regions under positive selection, using about 1.2 million single nucleotide polymorphisms genotyped in 1077 Sardinian individuals. Using four different methods - fixation index, inflation factor, principal component analysis and ancestry estimation - we were able to highlight, as expected for a genetic isolate, the high internal homogeneity of the island. Sardinians showed a higher percentage of genome covered by RoHs>0.5 Mb (FRoH%0.5) when compared to peninsular Italians, with the only exception of the area surrounding Alghero. We furthermore identified 9 genomic regions showing signs of positive selection and, we re-captured many previously inferred signals. Other regions harbor novel candidate genes for positive selection, like TMEM252, or regions containing long non coding RNA. With the present study we confirmed the high genetic homogeneity of Sardinia that may be explained by the shared ancestry combined with the action of evolutionary forces.

Bulky DNA Adducts in White Blood Cells: A Pooled Analysis of 3,600 Subjects

Background: Bulky DNA adducts are markers of exposure to genotoxic aromatic compounds, which reflect the ability of an individual to metabolically activate carcinogens and to repair DNA damage. Polycyclic aromatic hydrocarbons (PAHs) represent a major class of carcinogens that are capable of forming such adducts. Factors that have been reported to be related to DNA adduct levels include smoking, diet, body mass index (BMI), genetic polymorphisms, the season of collection of biologic material, and air pollutants. Methods: We pooled 11 studies (3,600 subjects) in which bulky DNA adducts were measured in human white blood cells with similar 32P-postlabeling techniques and for which a similar set of variables was available, including individual data on age, gender, ethnicity, batch, smoking habits, BMI, and season of blood collection, and a limited set of gene variants. Results: Lowest DNA adduct levels (P = 0.006) were observed in the spring (median = 0.50 adducts per 108 nucleotides), followed by summer (0.64), autumn (0.70), and winter (0.85). The same pattern emerged in multivariate analysis but only among never smokers (P = 0.02). Adduct levels were significantly lower (P = 0.001) in northern Europe (the Netherlands and Denmark; mean = 0.60, median = 0.40) than in southern Europe (Italy, Spain, France, and Greece; mean = 0.79, median = 0.60). Conclusions: In this large pooled analysis, we have found only weak associations between bulky DNA adducts and exposure variables. Seasonality (with higher adducts levels in winter) and air pollution may partly explain some of the interarea differences (north vs. south Europe), but most inter-area and interindividual variations in adduct levels still remain unexplained. Impact: Our study describes the largest pooled analysis of bulky DNA adducts so far, showing that interindividual variation is still largely unexplained, though seasonality seems to play a role. Cancer Epidemiol Biomarkers Prev; 19(12); 3174–81. ©2010 AACR.

Functional Annotation and Identification of Candidate Disease Genes by Computational Analysis of Normal Tissue Gene Expression Data

Background High-throughput gene expression data can predict gene function through the “guilt by association” principle: coexpressed genes are likely to be functionally associated. Methodology/Principal Findings We analyzed publicly available expression data on normal human tissues. The analysis is based on the integration of data obtained with two experimental platforms (microarrays and SAGE) and of various measures of dissimilarity between expression profiles. The building blocks of the procedure are the Ranked Coexpression Groups (RCG), small sets of tightly coexpressed genes which are analyzed in terms of functional annotation. Functionally characterized RCGs are selected by means of the majority rule and used to predict new functional annotations. Functionally characterized RCGs are enriched in groups of genes associated to similar phenotypes. We exploit this fact to find new candidate disease genes for many OMIM phenotypes of unknown molecular origin. Conclusions/Significance We predict new functional annotations for many human genes, showing that the integration of different data sets and coexpression measures significantly improves the scope of the results. Combining gene expression data, functional annotation and known phenotype-gene associations we provide candidate genes for several genetic diseases of unknown molecular basis.

MicroRNA expression in relation to different dietary habits: a comparison in stool and plasma samples

MicroRNAs (miRNAs), a class of small non-coding RNAs, are fundamental for the post-transcriptional regulation of gene expression. Altered expression of miRNAs has been detected in cancers, not only in primary tissue but also in easily obtainable specimens like plasma and stools. miRNA expression is known to be modulated by diet (micro and macronutrients, phytochemicals) and possibly by other lifestyle factors; however, such influence has not yet been exhaustively explored in humans. In the present study, we analysed the expression levels of a panel of seven human miRNAs in plasma and stool samples of a group of 24 healthy individuals characterised by different dietary habits (eight vegans, eight vegetarians and eight subjects with omnivorous diet, all groups with similar age and sex distribution). The dual aim of the study was to identify possible differences in miRNA expression due to diet (or other lifestyle factors recorded from questionnaires) and to compare results in both types of specimens. miR-92a was differentially expressed in both plasma and stool samples and with the same trend, among the three groups with different diets (P = 0.0002 and P = 0.02, respectively, with expression levels of vegans>vegetarians>omnivores). miR-92a was also associated with low body mass index (P = 0.04 and P = 0.05, respectively) in both types of specimens, and with several dietary factors. Other analysed miRNAs (miR-16, miR-21, mir-34a and miR-222) were associated with dietary and lifestyle factors, but not consistently in both stool and plasma. Our pilot study provides the first evidence of miRNA modulation by diet and other factors, that can be detected consistently in both plasma and stools samples.

The Italian genome reflects the history of Europe and the Mediterranean basin

Recent scientific literature has highlighted the relevance of population genetic studies both for disease association mapping in admixed populations and for understanding the history of human migrations. Deeper insight into the history of the Italian population is critical for understanding the peopling of Europe. Because of its crucial position at the centre of the Mediterranean basin, the Italian peninsula has experienced a complex history of colonization and migration whose genetic signatures are still present in contemporary Italians. In this study, we investigated genomic variation in the Italian population using 2.5 million single-nucleotide polymorphisms in a sample of more than 300 unrelated Italian subjects with well-defined geographical origins. We combined several analytical approaches to interpret genome-wide data on 1272 individuals from European, Middle Eastern, and North African populations. We detected three major ancestral components contributing different proportions across the Italian peninsula, and signatures of continuous gene flow within Italy, which have produced remarkable genetic variability among contemporary Italians. In addition, we have extracted novel details about the Italian population’s ancestry, identifying the genetic signatures of major historical events in Europe and the Mediterranean basin from the Neolithic (e.g., peopling of Sardinia) to recent times (e.g., ‘barbarian invasion’ of Northern and Central Italy). These results are valuable for further genetic, epidemiological and forensic studies in Italy and in Europe.

Double-strand break repair and colorectal cancer: gene variants within 3′ UTRs and microRNAs binding as modulators of cancer risk and clinical outcome

Genetic variations in 3′ untranslated regions of target genes may affect microRNA binding, resulting in differential protein expression. microRNAs regulate DNA repair, and single-nucleotide polymorphisms in miRNA binding sites (miRSNPs) may account for interindividual differences in the DNA repair capacity. Our hypothesis is that miRSNPs in relevant DNA repair genes may ultimately affect cancer susceptibility and impact prognosis. In the present study, we analysed the association of polymorphisms in predicted microRNA target sites of double-strand breaks (DSBs) repair genes with colorectal cancer (CRC) risk and clinical outcome. Twenty-one miRSNPs in non-homologous end-joining and homologous recombination pathways were assessed in 1111 cases and 1469 controls. The variant CC genotype of rs2155209 in MRE11A was strongly associated with decreased cancer risk when compared with the other genotypes (OR 0.54, 95% CI 0.38–0.76, p = 0.0004). A reduced expression of the reporter gene was observed for the C allele of this polymorphism by in vitro assay, suggesting a more efficient interaction with potentially binding miRNAs. In colon cancer patients, the rs2155209 CC genotype was associated with shorter survival while the TT genotype of RAD52 rs11226 with longer survival when both compared with their respective more frequent genotypes (HR 1.63, 95% CI 1.06-2.51, p = 0.03 HR 0.60, 95% CI 0.41–0.89, p = 0.01, respectively). miRSNPs in DSB repair genes involved in the maintenance of genomic stability may have a role on CRC susceptibility and clinical outcome.