Post-GWAS Validation of Target Genes Associated with HbF and HbA2 Levels.

Genome-Wide Association Studies (GWASs) have identified a huge number of variants associated with different traits. However, their validation through in vitro and in vivo studies often lags well behind their identification. For variants associated with traits or diseases of biomedical interest, this gap delays the development of possible therapies. This issue also impacts beta-hemoglobinopathies, such as beta-thalassemia and sickle cell disease (SCD). The definitive cures for these diseases are currently bone marrow transplantation and gene therapy. However, limitations regarding their effective use restrict their worldwide application. Great efforts have been made to identify whether modulators of fetal hemoglobin (HbF) and, to a lesser extent, hemoglobin A2 (HbA2) are possible therapeutic targets. Herein, we performed the post-GWAS in vivo validation of two genes, cyclin D3 (CCND3) and nuclear factor I X (NFIX), previously associated with HbF and HbA2 levels. The absence of Ccnd3 expression in vivo significantly increased g (HbF) and d (HbA2) globin gene expression. Our data suggest that CCND3 is a possible therapeutic target in sickle cell disease. We also confirmed the association of Nfix with γ-globin gene expression and present data suggesting a possible role for Nfix in regulating Kruppel-like transcription factor 1 (Klf1), a master regulator of hemoglobin switching. This study contributes to filling the gap between GWAS variant identification and target validation for beta-hemoglobinopathies.

Estimation of metabolic syndrome heritability in three large populations including full pedigree and genomic information.

Metabolic syndrome is a complex human disorder characterized by a cluster of conditions (increased blood pressure, hyperglycemia, excessive body fat around the waist, and abnormal cholesterol or triglyceride levels). Any of these conditions increases the risk of serious disorders such as diabetes or cardiovascular disease. Currently, the degree of genetic regulation of this syndrome is under debate and partially unknown. The principal aim of this study was to estimate the genetic component and the common environmental effects in different populations using full pedigree and genomic information. We used three large populations (Gubbio, ARIC, and Ogliastra cohorts) to estimate the heritability of metabolic syndrome. Due to both pedigree and genotyped data, different approaches were applied to summarize relatedness conditions. Linear mixed models (LLM) using average information restricted maximum likelihood (AIREML) algorithm were applied to partition the variances and estimate heritability (h2) and common sib-household effect (c2). Globally, results obtained from pedigree information showed a significant heritability (h2: 0.286 and 0.271 in Gubbio and Ogliastra, respectively), whereas a lower, but still significant heritability was found using SNPs data ([Formula: see text]: 0.167 and 0.254 in ARIC and Ogliastra). The remaining heritability between h2 and [Formula: see text] ranged between 0.031 and 0.237. Finally, the common environmental c2 in Gubbio and Ogliastra were also significant accounting for about 11% of the phenotypic variance. Availability of different kinds of populations and data helped us to better understand what happened when heritability of metabolic syndrome is estimated and account for different possible confounding. Furthermore, the opportunity of comparing different results provided more precise and less biased estimation of heritability.

Height-reducing variants and selection for short stature in Sardinia.

We report sequencing-based whole-genome association analyses to evaluate the impact of rare and founder variants on stature in 6,307 individuals on the island of Sardinia. We identify two variants with large effects. One variant, which introduces a stop codon in the GHR gene, is relatively frequent in Sardinia (0.87% versus <0.01% elsewhere) and in the homozygous state causes Laron syndrome involving short stature. We find that this variant reduces height in heterozygotes by an average of 4.2 cm (-0.64 s.d.). The other variant, in the imprinted KCNQ1 gene (minor allele frequency (MAF) = 7.7% in Sardinia versus <1% elsewhere) reduces height by an average of 1.83 cm (-0.31 s.d.) when maternally inherited. Additionally, polygenic scores indicate that known height-decreasing alleles are at systematically higher frequencies in Sardinians than would be expected by genetic drift. The findings are consistent with selection for shorter stature in Sardinia and a suggestive human example of the proposed 'island effect' reducing the size of large mammals.

Dissecting metabolic syndrome components: data from an epidemiologic survey in a genetic isolate.

The metabolic syndrome (MetS) is a large-scale and expanding public-health and clinical threat worldwide. We investigated the determinants of MetS, assessed its prevalence and components and, estimated their genetic contribution, taking advantage of the special characteristics of Sardinian isolated populations. Inhabitants of 10 villages in Ogliastra region participated in a cross-sectional survey in 2002-2008 (n = 9,647). Blood samples, blood pressure (BP), anthropometry and, data from a standardized interview were collected. Prevalence of MetS was estimated by the direct method of standardization. Variables associated with the MetS were identified using multilevel logistic regression. Heritability was determined using variance component models. MetS Prevalence was 19.6% (95% CI 18.9-20.4%) according to NCEP-ATPIII, 24.8% (95% CI 24.0-25.6%) according to IDF and, 29% (95% CI 28.1-29.8%) according to AHA/NHLBI harmonized criteria, ranging from 9 to 26% among villages. The most prevalent combination was BP + HDL-cholesterol (HDL) + triglycerides (TRIG) (19%), followed by BP + HDL + waist circumference (WAIST) (17%) and, BP + HDL + TRIG + WAIST (13.6%). Heritability of MetS was 48% (p = 1.62 × 10(-25)), as the two most common combinations (BP + HDL + TRIG and BP + HDL + WAIST) showed heritability of 53 and 52%, respectively. The larger genetic components of the two most frequent combinations determining MetS deserve greater investigation in order to understand the underlying mechanisms. Besides, further studies are warranted to confirm these findings both in isolated and outbred populations.

Phylogeny and patterns of diversity of goat mtDNA haplogroup A revealed by resequencing complete mitogenomes.

We sequenced to near completion the entire mtDNA of 28 Sardinian goats, selected to represent the widest possible diversity of the most widespread mitochondrial evolutionary lineage, haplogroup (Hg) A. These specimens were reporters of the diversity in the island but also elsewhere, as inferred from their affiliation to each of 11 clades defined by D-loop variation. Two reference sequences completed the dataset. Overall, 206 variations were found in the full set of 30 sequences, of which 23 were protein-coding non-synonymous single nucleotide substitutions. Many polymorphic sites within Hg A were informative for the reconstruction of its internal phylogeny. Bayesian and network clustering revealed a general similarity over the entire molecule of sequences previously assigned to the same D-loop clade, indicating evolutionarily meaningful lineages. Two major sister groupings emerged within Hg A, which parallel distinct geographical distributions of D-loop clades in extant stocks. The pattern of variation in protein-coding genes revealed an overwhelming role of purifying selection, with the quota of surviving variants approaching neutrality. However, a simple model of relaxation of selection for the bulk of variants here reported should be rejected. Non-synonymous diversity of Hg's A, B and C denoted that a proportion of variants not greater than that allowed in the wild was given the opportunity to spread into domesticated stocks. Our results also confirmed that a remarkable proportion of pre-existing Hg A diversity became incorporated into domestic stocks. Our results confirm clade A11 as a well differentiated and ancient lineage peculiar of Sardinia.

Environmental and genetic contribution to hypertension prevalence: data from an epidemiological survey on Sardinian genetic isolates.

BACKGROUND AND OBJECTIVES: Hypertension represents a major cause of cardiovascular morbidity and mortality worldwide but its prevalence has been shown to vary in different countries. The reasons for such differences are still matter of debate, the relative contributions given by environmental and genetic factors being still poorly defined. We estimated the current prevalence, distribution and determinants of hypertension in isolated Sardinian populations and also investigated the environmental and genetic contribution to hypertension prevalence taking advantage of the characteristics of such populations. METHODS AND RESULTS: An epidemiological survey with cross-sectional design was carried out measuring blood pressure in 9845 inhabitants of 10 villages of Ogliastra region between 2002 and 2008. Regression analysis for assessing blood pressure determinants and variance component models for estimating heritability were performed. Overall 38.8% of this population had hypertension, its prevalence varying significantly by age, sex and among villages taking into account age and sex structure of their population. About 50% of hypertensives had prior cardiovascular disease. High blood pressure was independently associated with age, obesity related factors, heart rate, total cholesterol, alcohol consumption, low education and smoking status, all these factors contributing more in women than in men. Heritability was 27% for diastolic and 36% for systolic blood pressure, its contribution being significantly higher in men (57%) than in women (46%). Finally, the genetic correlation between systolic and diastolic blood pressure was 0.74, indicating incomplete pleiotropy. CONCLUSION: Genetic factors involved in the expression of blood pressure traits account for about 30% of the phenotypic variance, but seem to play a larger role in men; comorbidities and environmental factors remain of predominant importance, but seem to contribute much more in women.

Haplotype affinities resolve a major component of goat (Capra hircus) MtDNA D-loop diversity and reveal specific features of the Sardinian stock.

Goat mtDNA haplogroup A is a poorly resolved lineage absorbing most of the overall diversity and is found in locations as distant as Eastern Asia and Southern Africa. Its phylogenetic dissection would cast light on an important portion of the spread of goat breeding. The aims of this work were 1) to provide an operational definition of meaningful mtDNA units within haplogroup A, 2) to investigate the mechanisms underlying the maintenance of diversity by considering the modes of selection operated by breeders and 3) to identify the peculiarities of Sardinian mtDNA types. We sequenced the mtDNA D-loop in a large sample of animals (1,591) which represents a non-trivial quota of the entire goat population of Sardinia. We found that Sardinia mirrors a large quota of mtDNA diversity of Western Eurasia in the number of variable sites, their mutational pattern and allele frequency. By using bayesian analysis, a distance-based tree and a network analysis, we recognized demographically coherent groups of sequences identified by particular subsets of the variable positions. The results showed that this assignment system could be reproduced in other studies, capturing the greatest part of haplotype diversity.We identified haplotype groups overrepresented in Sardinian goats as a result of founder effects. We found that breeders maintain diversity of matrilines most likely through equalization of the reproductive potential. Moreover, the relevant amount of inter-farm mtDNA diversity found does not increase proportionally with distance. Our results illustrate the effects of breeding practices on the composition of maternal gene pool and identify mtDNA types that may be considered in projects aimed at retrieving the maternal component of the oldest breeds of Sardinia.

A population-based study of an Italian genetic isolate reveals that mean platelet volume is not a risk factor for thrombosis.

INTRODUCTION: Several studies revealed that mean platelet volume (MPV) was larger in the acute phase of arterial and venous thrombosis and predicted a poor clinical outcome. It has been suggested that MPV is a risk factor for thrombosis. However, it is unclear whether increased platelet size is a cause or a consequence of thrombosis. It was the objective of this study to verify whether MPV is a risk factor for arterial and venous thrombosis. METHODS: We search for associations between platelet parameters and thrombosis by a population-based study in 11,084 inhabitants of an Italian genetic isolate characterized by wide variability of platelet parameters. To validate this methodology of investigation, we also evaluated whether it was able to identify several well known thrombotic risk factors in the study population. RESULTS: Statistical analysis confirmed that male gender, ageing, hypertension, high total cholesterol, low HDL cholesterol, diabetes, obesity and smoking were risk factors for arterial thrombosis, while alcohol consumption had a protective effect. Female gender, ageing, pregnancy, estroprogestinic treatment, obesity, varicose veins were associated with venous thrombosis. At variance, MPV and platelet count were unrelated to previous thrombotic events. However, MPV was negatively correlated with the time since the last thrombotic event. CONCLUSIONS: This study indicated that an epidemiologic study of a population isolate is appropriate for the identification of thrombotic risk factors, but it failed to identify such a role for MPV. Thus, we suggest that the increased MPV previously described in subjects with acute thrombosis was a consequence instead of a cause of thrombosis.

Epidemiology of osteoporosis in an isolated Sardinian population by using quantitative ultrasound.

This study aimed at estimating the prevalence of osteoporosis and osteopenia in a Sardinian isolated population using hand quantitative ultrasound and at investigating the associated factors. The authors utilized a subset of data from a large population-based epidemiologic survey carried out in the Ogliastra region of Sardinia between 2003 and 2008. The sample consists of 6,326 men and women aged ≥30 years, who underwent quantitative ultrasound at the phalanges, bioelectrical impedance, anthropometric measurements, blood tests, and a standardized epidemiologic questionnaire collecting sociodemographic, lifestyle, medical, physiologic, and pharmacologic data. The T-score thresholds for amplitude-dependent speed of sound of -3.2 standard deviations and between -3.2 and -1 standard deviations were used to diagnose osteoporosis and osteopenia, respectively. Prevalence of osteoporosis was 17.0% in women and 5.2% in men. Logistic regression analysis revealed that factors associated with osteoporosis were age, anthropometric and bioimpedance measures, alkaline phosphatase levels, and menopause in women. High education, exercise, and beer consumption seem to be protective factors, whereas a family history of osteoporosis is a risk factor. Results show that osteoporosis in this population is comparable with that found in different countries, suggesting that quantitative ultrasound could be used more widely to detect high-risk individuals for preventing osteoporotic fractures.

Analysis of 12,517 inhabitants of a Sardinian geographic isolate reveals that predispositions to thrombocytopenia and thrombocytosis are inherited traits.

BACKGROUND: Thrombocytopenia is a common finding in several diseases but almost nothing is known about the prevalence of thrombocytopenia in the general population. We examined the prevalence of thrombocytopenia and determinants of platelet count in a healthy population with a wide age range. DESIGN AND METHODS: We performed a cross-sectional study on 12,517 inhabitants of ten villages (80% of residents) in a secluded area of Sardinia (Ogliastra). Participants underwent a complete blood count evaluation and a structured questionnaire, used to collect epidemiological data. RESULTS: We observed a platelet count lower than 150 × 109/L in 3.2% (2.8%-3.6%) of females and 4.8% (4.3%-5.4%) of males, with a value of 3.9% (3.6%-4.3%) in the entire population. Thrombocytopenia was mild (platelet count: 100 × 109/L-150 × 109/L), asymptomatic and not associated with other cytopenias or overt disorders in most cases. Its standardized prevalence was quite different in different villages, with values ranging from 1.5% to 6.8%, and was negatively correlated with the prevalence of a mild form of thrombocytosis, which ranged from 0.9% to 4.5%. Analysis of platelet counts across classes of age revealed that platelet number decreased progressively with aging. As a consequence, thrombocytopenia was nearly absent in young people and its prevalence increased regularly during lifetime. The opposite occurred for thrombocytosis. CONCLUSIONS: Given the high genetic differentiation among Ogliastra villages with "high" and "low" platelet counts and the substantial heritability of this quantitative trait (54%), we concluded that the propensity to present mild and transient thrombocytosis in youth and to acquire mild thrombocytopenia during aging are new genetic traits.

History, geography and population structure influence the distribution and heritability of blood and anthropometric quantitative traits in nine Sardinian genetic isolates.

Isolated founder populations which exhibit great genetic and environmental homogeneity provide an attractive setting for the study of quantitative traits (QTs). Geneticists have repeatedly turned to population isolates and the past successes have prompted increased interest among medical researchers. We studied nine small isolated villages of a secluded area of Sardinia (Ogliastra), all of them characterized by a few founders, high endogamy rates, slow population expansion and a distinct genetic makeup. Anthropometric and blood parameters, 43 QTs in all, were analysed in about 9000 voluntary subjects for whom extended genealogical information was available. We explored the distribution and examined mean differences of each trait among villages by analysis of variance (ANOVA). A heritability analysis with the variance component (VC) method was performed. Results show significant differences in the distribution of most traits between groups of villages located in two distinct geographical areas already identified by a previous population structure analysis, thus supporting the existence of differentiation among sub-populations in the same region. Heritability estimates range between 30 and 89%, demonstrating that genetic effects substantially contribute to phenotypic variation of all investigated traits and that this population provides excellent research conditions for gene-mapping projects. Results suggest that history, geographic location and population structure may have influenced the genetic and phenotypic features of these isolates. Our findings may be useful for the ongoing linkage and association studies in these isolates and suggest that a thorough characterization of population is valuable to better identify genes or variants that may be rare in the population at large and peculiar to single villages.

Genetic architecture of hand quantitative ultrasound measures: a population-based study in a Sardinian genetic isolate.

It is now recognized that quantitative ultrasound (QUS) measures may predict osteoporotic fracture risk independently of bone mineral density. Although many studies have examined genetic and environmental components of bone mineral density and calcaneal QUS measures, few of them were addressed to phalangeal QUS phenotypes, and none to graphic trace parameters. This study aims to evaluate the relative contribution of genetics in the expression of phalangeal QUS traits in the adult healthy population of a Sardinian genetic isolate. Our sample includes 6056 men and women aged 30-103 years, from 43 extended pedigrees recruited in 10 villages of Ogliastra region in occasion of a large epidemiologic survey. Amplitude-dependent speed of sound (AD-SoS), fast wave amplitude (FWA), signal dynamic (SDy), bone transmission time (BTT) and ultrasound bone profile index (UBPI) were obtained from the non-dominant hand using the IGEA DBM Sonic Bone Profiler. These phenotypes were first regressed on age, anthropometric and bioimpedance measures, serum calcium, phosphorus and alkaline phosphatase, alcohol and caffeine consumption, smoking status, exercise and also months since menopause and estrogens use in women. Adjusted QUS parameters were then analyzed by univariate and bivariate variance component models to obtain heritability estimates and genetic and environmental correlations. QUS parameters were correlated to age, anthropometric and bioimpedance measures, serum phosphorus, alkaline phosphatase and to reproductive history and menopause in women. All phenotypes demonstrated substantial heritabilities ranging from 0.29+/-0.03 for SDy to 0.55+/-0.03 for FWA. Proportion of variance due to all covariates ranged from 36% for SDy to 59% for BTT. Many significant genetic and environmental correlations were found between the different QUS measures. In this study, genetic factors appear to play a relevant role in determining hand QUS measures even when taking into account various important environmental factors. Furthermore, the modest genetic correlations may imply the existence of partially unique sets of genes affecting different QUS traits, thus suggesting that QUS parameters measure different properties of bone tissue.

Identification of a novel gene and a common variant associated with uric acid nephrolithiasis in a Sardinian genetic isolate.

Uric acid nephrolithiasis (UAN) is a common disease with an established genetic component that presents a complex mode of inheritance. While studying an ancient founder population in Talana, a village in Sardinia, we recently identified a susceptibility locus of approximately 2.5 cM for UAN on 10q21-q22 in a relatively small sample that was carefully selected through genealogical information. To refine the critical region and to identify the susceptibility gene, we extended our analysis to severely affected subjects from the same village. We confirm the involvement of this region in UAN through identical-by-descent sharing and autozygosity mapping, and we refine the critical region to an interval of approximately 67 kb associated with UAN by linkage-disequilibrium mapping. After inspecting the genomic sequences available in public databases, we determined that a novel gene overlaps this interval. This gene is divided into 15 exons, spanning a region of approximately 300 kb and generating at least four different proteins (407, 333, 462, and 216 amino acids). Interestingly, the last isoform was completely included in the 67-kb associated interval. Computer-assisted analysis of this isoform revealed at least one membrane-spanning domain and several N- and O-glycosylation consensus sites at N-termini, suggesting that it could be an integral membrane protein. Mutational analysis shows that a coding nucleotide variant (Ala62Thr), causing a missense in exon 12, is in strong association with UAN (P=.0051). Moreover, Ala62Thr modifies predicted protein secondary structure, suggesting that it may have a role in UAN etiology. The present study underscores the value of our small, genealogically well-characterized, isolated population as a model for the identification of susceptibility genes underlying complex diseases. Indeed, using a relatively small sample of affected and unaffected subjects, we identified a candidate gene for multifactorial UAN.