Genetic and population structure of four Sardinian villages

The double-sided of human leukocyte antigen-G molecules in type 1 autoimmune hepatitis

The immunomodulatory effects of HLA-G expression and its role in cancers, human liver infections and liver transplantation are well documented, but so far, there are only a few reports addressing autoimmune liver diseases, particularly autoimmune hepatitis (AIH).

METHOD AND MATERIALS

We analyzed the genetic and phenotypic characteristics of HLA-G in 205 type 1 AIH patients (AIH-1) and a population of 210 healthy controls from Sardinia (Italy).

RESULTS

Analysis of the HLA-G locus showed no substantial differences in allele frequencies between patients and the healthy control population. The HLA-G UTR-1 haplotype was the most prevalent in both AIH-1 patients and controls (40.24% and 34.29%). Strong linkage was found between the HLA-G UTR-1 haplotype and HLA-DRB1*03:01 in AIH-1 patients but not controls (D' = 0.92 vs D' = 0.50 respectively; P = 1.3x10-8). Soluble HLA-G (sHLA-G) levels were significantly lower in AIH-1 patients compared to controls [13.9 (11.6 - 17.4) U/mL vs 21.3 (16.5 - 27.8) U/mL; P = 0.011]. Twenty-four patients with mild or moderate inflammatory involvement, as assessed from liver biopsy, showed much higher sHLA-G levels compared to the 28 patients with severe liver inflammation [33.5 (23.6 - 44.8) U/mL vs 8.8 (6.1 - 14.5) U/mL; P = 0.003]. Finally, immunohistochemistry analysis of 52 liver biopsies from AIH-1 patients did not show expression of HLA-G molecules in the liver parenchyma. However, a percentage of 69.2% (36/52) revealed widespread expression of HLA-G both in the cytoplasm and the membrane of plasma cells labeled with anti-HLA-G monoclonal antibodies.

CONCLUSION

This study highlights the positive immunomodulatory effect of HLA-G molecules on the clinical course of AIH-1 and how this improvement closely correlates with plasma levels of sHLA-G. However, our results open the debate on the ambiguous role of HLA-G molecules expressed by plasma cells, which are pathognomonic features of AIH-1.

Genetic Creutzfeldt-Jakob disease in Sardinia: a case series linked to the PRNP R208H mutation due to a single founder effect

In genetic prion diseases (gPrD), five genetic variants (E200K, V210I, V180I, P102L, and D178N) are responsible for about 85% of cases. The R208H is one of the several additional rare mutations and to date, only 16 cases carrying this mutation have been reported worldwide. To describe the phenotypic features of 5 affected patients belonging to apparently unrelated Sardinian (Italian) families with R208H gPrD, and provide evidence for a possible founder effect are the aims of this study. The R208H PRNP mutation has a much higher relative frequency in Sardinia than elsewhere in Italy (72% vs. 4.4% of gCJD cases). Our cohort shared similar phenotypic features to the previously described patients with R208H-129M haplotype with most patients showing the classical Creutzfeldt-Jakob disease (CJD) phenotype. The analysis of 10 controls and 5 patients by NGS sequencing identified 4 haplotypes, 3 associated with the wild type variant, and one (H1) shared by all patients carrying the 208His variant. This is the first report of a regional cluster for R208H mutation in gPrD and the first report of the presence of a common ancestor for this Sardinian R208H cluster, confirming the probable consequences of genetic isolation process even for rare diseases.

Reconstructing the genetic structure of the Kazakh from clan distribution data

Applying quasigenetic markers - non-biological traits which are nevertheless inherited in generations - is one of the research fields within human population genetics. For the West European, East European, and Caucasus populations, surnames are typical quasigenetic markers. For Central Asian populations, particularly Kazakh, the clan affiliation serves as a good marker: a set of papers demonstrated that many clans include mainly persons which biologically descent from a recent common ancestor. In this study, we analyzed a large (~4.2 million persons) dataset on quasigenetic markers - the geographic distribution of 50 Kazakh clans at the beginning of the 20th century, and compared the dataset with the direct data of the Y-chro-mosomal diversity in modern Kazakh populations. The analysis included three steps: the isonymy method, which is standard for quasigenetic markers, comparing frequencies of quasigenetic markers, and comparing the quasigenetic and genetic datasets. We constructed 50 maps of frequency of the distribution of each clan and revealed that these maps correlate with the maps of genetic distances. The Mantel test also demonstrated a significant correlation between geographic and quasigenetic distances (г = 0.60; p < 0.05). The analysis of inter-population variability revealed the largest diversity between geographic territories corresponding to the social-territorial groups of the Kazakh Khanate (zhuzes) rather than to other historical groups that existed on the territory of Kazakhstan in preceding and modern epochs. The same is evidenced by the principal components and multidimensional scaling plots, which grouped geographic populations into three clusters corresponding to three zhuzes. This indicates that the final structuring of the Kazakh gene pool might have occurred during the Kazakh Khanate period.

Spatial diffusion of surnames by long transhumance routes between highland and lowland: A study in Sardinia

RIASSUNTO.

High prevalence of diabetes-specific autoimmunity in first-degree relatives of Sardinian patients with type 1 diabetes

BACKGROUND

The incidence of type 1 diabetes mellitus (T1DM) in Sardinia is among the highest in the world (44.8 cases/100,000 person-years). Recommendations of the Immunology of Diabetes Society advise evaluating autoantibody positivity in first-degree relatives (FDRs) of patients with T1DM, for their higher risk to develop the disease. The aim of this study was to determine the prevalence of beta-cell autoimmunity in FDRs of T1DM patients in Sardinia.

METHODS

A total of 188 Sardinian families were recruited in collaboration between diabetes and pediatric units of university and district hospitals in Sardinia. The recruitment involved 188 patients with diagnosed T1DM and all their available FDRs (n = 447). Autoantibodies (Aabs) against GAD, IA2, insulin, and ZnT8 were measured in all subjects. Human leukocyte antigen (HLA) risk genotypes (HLA-DR and DQ loci) were analyzed in 43 Aabs-positive FDR.

RESULTS

The prevalence of Aabs (any type of autoantibody, single or multiple) in FDR was 11.9% (53/447). Of those with autoantibodies, 62.3% (33/53) were positive to only 1 autoantibody, 22.6% (12/53) had 2 autoantibodies, 7.55% (4/53) had 3 autoantibodies, and 7.55% (4/53) had all 4 autoantibodies. Typing of HLA-DR and DQ loci showed that 89% of FDR carried moderate- to high-risk genotypes, with only 5 FDR with low-risk genotypes.

CONCLUSIONS

The prevalence of T1DM autoantibodies in FDRs of T1DM patients was very high (11.9%) in the Sardinian population, higher than in other populations from the United States and Europe, and similar to that observed in Finland. Autoantibody positivity strongly associated with HLA risk. This study provides evidence of the high risk of T1DM in FDR of T1DM patients in Sardinia and warrants longitudinal follow-up to estimate the risk of progression to T1DM in high-risk populations.

Constructional apraxia in frontotemporal dementia associated with the C9orf72 mutation: broadening the clinical and neuropsychological phenotype

In our study we analysed clinical and neuropsychological data in a cohort of 57 Sardinian patients with FTD (55 apparently unrelated and two belonging to the same family), who underwent genetic screening for the C9orf72 mutation. Eight out of 56 patients were found positive for the C9orf72 mutation representing 14% of the entire cohort and 31.6% of the familial cases (6/19). C9orf72 mutated patients differed from the other FTD cases of the cohort for a younger age of onset, higher frequency of familial history for FTD and higher prevalence of delusional psychotic symptoms and hallucinations. In the neuropsychological assessment, C9orf72 mutated patients differed from non-mutated for the high frequency of visuospatial dysfunction regarding constructional apraxia (p = 0.02). In conclusion, our study confirms that Sardinian FTD patients have peculiar genetic characteristics and that C9orf72 mutated patients have a distinctive clinical and neuropsychological profile that could help differentiate them from other FTD patients. In our cohort we found that constructional apraxia, rarely reported in FTD, can properly discriminate between C9orf72 mutated and non-mutated patients and contribute to broaden the neuropsychological profile in frontotemporal dementia associated with this mutation.

Amyotrophic lateral sclerosis in Sardinia, insular Italy, 1995-2009

Recent genetic studies suggest a Sardinian type of amyotrophic lateral sclerosis (ALS). Thus, ALS incidence, prevalence and survival were investigated in a large population of Sardinians aimed to disclose population-specific patterns and their temporal changes. This is a population-based incidence and prevalence study in northern and central Sardinia, insular Italy (over 700,000 population). Incidence rates were computed for the time interval 1995-2009 and by quinquennia. Prevalence was computed for prevalence days 31 December 2004 and 2009. Onset-based survival for 1995-2009 is also reported. All ALS patients (El Escorial Criteria) in the study area were retrospectively included. The ALS crude incidence from 2005-2009 was 2.5 (95 % CIs: 0.1, 4.9), 3.4 in men and 1.6 in women. Onset occurred most often between the age of 65-74 years in men and 55-64 years in women. The ALS incidence tended to increase over the period 1995-2009. The mean age at onset was 61.7 years with no difference based on gender, varying significantly from 59.9 years in 1995-1999 to 63.9 years in 2005-2009. On December 31, 2009, the ALS crude prevalence was 10.8 per 100,000 (95 % CIs: 8.6, 13.1), 13.8 in men and 8.0 in women, whereas it was 6.3 per 100,000 (95 % CIs: 4.1, 8.6) on December 31, 2004 (M:F ratio of 0.95). Mean survival from onset was 37.0 months, with no difference based on gender, and a tendency to decrease during the period 1995-2009, in relation to type and age of onset. The population-based incidence and prevalence data of ALS in Sardinians indicate an increase of the disease occurrence over the past 40 years, providing support for a population-specific variant of ALS in Sardinia.

ALS/FTD phenotype in two Sardinian families carrying both C9ORF72 and TARDBP mutations

BACKGROUND

In the isolated population of Sardinia, a Mediterranean island, ∼25% of ALS cases carry either a p.A382T mutation of the TARDBP gene or a GGGGCC hexanucleotide repeat expansion in the first intron of the C9ORF72 gene.

OBJECTIVE

To describe the co-presence of two genetic mutations in two Sardinian ALS patients.

METHODS

We identified two index ALS cases carrying both the p.A382T missense mutation of TARDBP gene and the hexanucleotide repeat expansion of C9ORF72 gene.

RESULTS

The index case of Family A had bulbar ALS and frontemporal dementia (FTD) at 43. His father, who carried the hexanucleotide repeat expansion of C9ORF72 gene, had spinal ALS and FTD at 64 and his mother, who carried the TARDBP gene p.A382T missense mutation, had spinal ALS and FTD at 69. The index case of Family B developed spinal ALS without FTD at 35 and had a rapid course to respiratory failure. His parents are healthy at 62 and 63. The two patients share the known founder risk haplotypes across both the C9ORF72 9p21 locus and the TARDBP 1p36.22 locus.

CONCLUSIONS

Our data show that in rare neurodegenerative causing genes can co-exist within the same individuals and are associated with a more severe disease course.

Large proportion of amyotrophic lateral sclerosis cases in Sardinia due to a single founder mutation of the TARDBP gene

OBJECTIVE

To perform an extensive screening for mutations of amyotrophic lateral sclerosis (ALS)-related genes in a consecutive cohort of Sardinian patients, a genetic isolate phylogenically distinct from other European populations.

DESIGN

Population-based, prospective cohort study.

PATIENTS

A total of 135 Sardinian patients with ALS and 156 healthy control subjects of Sardinian origin who were age- and sex-matched to patients.

INTERVENTION

Patients underwent mutational analysis for SOD1, FUS, and TARDBP.

RESULTS

Mutational screening of the entire cohort found that 39 patients (28.7%) carried the c.1144G>A (p.A382T) missense mutation of the TARDBP gene. Of these, 15 had familial ALS (belonging to 10 distinct pedigrees) and 24 had apparently sporadic ALS. None of the 156 age-, sex-, and ethnicity-matched controls carried the pathogenic variant. Genotype data obtained for 5 ALS cases carrying the p.A382T mutation found that they shared a 94-single-nucleotide polymorphism risk haplotype that spanned 663 Kb across the TARDBP locus on chromosome 1p36.22. Three patients with ALS who carry the p.A382T mutation developed extrapyramidal symptoms several years after their initial presentation with motor weakness.

CONCLUSIONS

The TARDBP p.A382T missense mutation accounts for approximately one-third of all ALS cases in this island population. These patients share a large risk haplotype across the TARDBP locus, indicating that they have a common ancestor.

Plasmodium falciparum malaria and the immunogenetics of ABO, HLA, and CD36 (platelet glycoprotein IV)

Plasmodium falciparum malaria has long been a killer of the young, and has selected for polymorphisms affecting not only erythrocytes, but the immunogenetics of three histocompatibility systems: ABO, human leukocyte antigen (HLA), and CD36. The ABO system is important because the original allele, encoding glycosylation with the A sugar, acts as an adhesion ligand with infected red blood cells (iRBC), thereby promoting vasoocclusion. The prevalence of blood group O, which reduces this cytoadhesion, has increased in endemic areas. Other adaptations which could mitigate A-mediated rosetting include weaker A expression and increased soluble A secretion. The role of the HLA system in malaria has been harder to verify. Although HLA-B53 and DRB1*04 may be associated with clinical outcome, HLA studies are challenged by numerous comparisons in this most polymorphic of systems, and confounded by increasingly heterogeneous populations. Certain HLA markers may also reflect linkage artefact with other malaria-relevant polymorphisms. HLA may be less important because the parasite predominantly invades a compartment which does not express HLA. Adhesion of iRBCs is also mediated by CD36, expressed on platelets, monocytes, and microvascular endothelium. CD36 on monocytes is involved in clearing iRBC, while CD36 on platelets and the endothelium may play a role in tissue sequestration. The genetics of CD36 expression are complex, and recent research is fraught with inconsistent results. The solution may lie in examining genotype-phenotype correlations, zygosity effects on differential tissue expression, or other mechanisms altering CD36 tissue expression. Carefully designed prospective studies should bridge the gap between in-vitro observations and clinical outcomes.

The Sardinian way to type 1 diabetes

Sardinia and Finland are the "hottest" areas for type 1 diabetes mellitus (T1DM) worldwide. Its genetic and epidemiological background make Sardinia an ideal region for investigating environmental, immunological, and genetic factors related to the etiopathogenesis of T1DM. Consequently, in 1990, the Insulin-Dependent Diabetes Mellitus Sardinia Project was launched in order to map the geographical distribution of T1DM in the island and to investigate preclinical phases of T1DM in a large cohort of people genetically at risk. The final goal would be to design models of prediction and to formulate safe preventive measures, especially addressed to the general population living in areas at high risk.

Genetics of susceptibility to Plasmodium falciparum: from classical malaria resistance genes towards genome-wide association studies

Plasmodium falciparum represents one of the strongest selective forces on the human genome. This stable and perennial pressure has contributed to the progressive accumulation in the exposed populations of genetic adaptations to malaria. Descriptive genetic epidemiology provides the initial step of a logical procedure of consequential phases spanning from the identification of genes involved in the resistance/susceptibility to diseases, to the determination of the underlying mechanisms and finally to the possible translation of the acquired knowledge in new control tools. In malaria, the rational development of this strategy is traditionally based on complementary interactions of heterogeneous disciplines going from epidemiology to vaccinology passing through genetics, pathogenesis and immunology. New tools including expression profile analysis and genome-wide association studies are recently available to explore the complex interactions of host-parasite co-evolution. Particularly, the combination of genome-wide association studies with large multi-centre initiatives can overcome the limits of previous results due to local population dynamics. Thus, we anticipate substantial advances in the interpretation and validation of the effects of genetic variation on malaria susceptibility, and thereby on molecular mechanisms of protective immune responses and pathogenesis.

HLA-B27 and ankylosing spondylitis geographic distribution as the result of a genetic selection induced by malaria endemic? A review supporting the hypothesis

The geographic distribution of HLA-B27 shows a latitude-related gradient inverse to that of malaria endemic. An apparent exception occurs in New Guinea, a region where malaria is present, but where HLA-B27 frequency shows, however, an orographic gradient antithetic to that of malaria incidence. We therefore suggest that Plasmodium falciparum may have exerted a negative selection on this gene. This might be due to a higher susceptibility to severe forms of malaria, associated with HLA-B27 or other close gene(s). In addition, we suggest here that the same selective pressure that has contributed to reduce the HLA-B27 frequency in some regions has favoured the fixing of newly generated B27 subtypes included in more advantageous HLA haplotypes. In some cases, as for B*2709 in Sardinia and B*2706 in Southeast Asia, these haplotypes may harbour factors that protect from Ankylosing Spondylitis, an autoimmune disease strongly associated with HLA-B27, thus offering a novel, powerful tool to dissect disease pathogenesis, and to identify additional genetic factors of susceptibility.

Lasker's coefficient of isonymy between and within 16 Sardinian villages in the periods 1825-1849, 1875-1899, and 1925-1949

Coefficients of relationship by isonymy, based on the frequency of common surnames, were used to estimate the biological affinity between (R(ib)) and within (R(iw)) 16 Sardinian villages in the periods 1825-1849, 1875-1899, and 1925-1949. The database for the surname analysis consisted of 13,515 marriages registered in the parishes of villages, all belonging to the Sardinian linguistic area. The values of R(ib) and R(iw) tend to decrease in time. In all three periods, the R(ib) values generally decrease as the geographical distance between villages increases. The negative values of the Bravais-Pearson coefficient of correlation between the matrix of R(ib) values and the matrices of geographical distances (calculated both in a straight line and from road distances) are significant for each period (modified Mantel test), with slightly higher correlation coefficients for road distances. Moreover, the plots of isonymic relationships obtained by nonmetric multidimensional scaling for 1825-1849 and 1925-1949 show that the biological relationships between neighboring villages increase in the latter period. The positive values of the Bravais-Pearson coefficients of correlation between R(iw) and altitude are significant in all three periods, while the correlation between R(iw) and population size is not significant, even when altitude is controlled for. Since altitude is considered an indicator of isolation, the results obtained with the coefficient of relationship by isonymy within villages also support the isolation-by-distance model. R(ib) values provided a reliable picture of the biological relationships between 16 Sardinian villages, while R(iw) values illustrated the biological affinity within the communities for a period of 100 years, from 1825-1849 to 1925-1949.

A family based linkage analysis of HLA and 5-HTTLPR gene polymorphisms in Sardinian children with autism spectrum disorder

Autism spectrum disorders (ASD) are characterized by a broad range in clinical presentation. Although a definite genetic cause has not yet been fully demonstrated, family based studies suggest that a multigenic pattern may be responsible for susceptibility, but most results are conflicting and have yet to be replicated. The purpose of this investigation was to analyze the linkage of the human leukocyte antigen (HLA) and the human serotonin transporter coding (5-HTTLPR) genes with ASD in a group of 37 families of Sardinian ethnicity in insular Italy. In 50% of these families, ASD is linked to HLA, and in the other 50% it is linked to 5-HTTLPR polymorphic genes; in other words, linkage to one or the other was evident in all cases. Despite a very homogenous genetic pattern being generally reported for Sardinians, the linkage observed with HLA and 5-HTTLPR genetic regions indicated a statistically defined heterogeneity (p=0.002). No allelic HLA or 5-HTTLPR polymorphisms were specifically associated with ASD, suggesting these loci as markers of other genes mapped in their close proximity that may be more directly involved and thus may merit further analytical studies.

Genes, environment, and susceptibility to multiple sclerosis

Multiple sclerosis (MS) is a chronic disease of the central nervous system affecting young adults and thus representing a major burden also for their families and communities. The etiology of MS is obscure and its pathogenesis is yet incompletely depicted. Increased evidences indicate a strong genetic contribution to MS susceptibility, although others support the view that it is also influenced by environmental factors, possibly related to still unidentified pathogens. MS appears to be more heterogeneous than previously believed at the immunological level, and new pathological studies indicate a series of subset of conditions under the common denominator MS. The use of genetically homogeneous and geographically isolated populations at high MS risk, such as that of Sardinia, insular Italy, becomes in principle a vital requirement to reduce biological variables and the intrinsic complexity of the disease. This review will focus on recent findings on the peculiarity of Sardinian MS concerning epidemiological, genetic, and environmental aspects. Epidemiological studies reveal a clear heterogeneous distribution of MS cases in the Northern province of Sassari which may not be uniquely assigned to genetic variations. Furthermore, a different immunogenetic profile, including the association with other immunomediated diseases, and a progressive change in clinical phenotype, including age at onset, are present in this island which gives us unexpected variations at the level of patients' cohort and territorial distribution, especially when the northern province is compared to the southern one. This renders MS etiopathogenesis more complex than formerly thought even in this selected and genetically stable population.

Multiple sclerosis complexity in selected populations: the challenge of Sardinia, insular Italy

Several lines of evidence indicate a genetic contribution to multiple sclerosis (MS) both in terms of predisposition to the disease and of immunological mechanisms which are known to play crucial roles in MS pathogenesis. The presence of high- and low-risk areas for MS in neighbouring regions supports the theory that MS predisposition is influenced by a complex interaction of genetic and environmental factors. Therefore, the use of genetically homogeneous and geographically isolated populations becomes an increasing requirement to reduce biasing biological variables. Sardinians fulfil these conditions well because of their different phylogeny from Europeans and the unique selective pressures which shaped their genome. Sardinians display amongst the highest MS prevalence rates world-wide and increasing MS incidence rates over time. Also, MS in Sardinia is linked to distinct human leucocyte antigen (HLA) alleles and associated to different patterns of cytokine production from lymphoid cells of different HLA subtypes. In this context, recent findings and future perspectives on the peculiarities of Sardinian MS concerning genetic, immunological and epidemiological aspects are presented. So far, our results indicate that variations at the level of territorial distribution and HLA-association are present which render MS heterogeneous even in this ethnically homogeneous population.

Autosomal recessive hypercholesterolaemia in Sardinia, Italy, and mutations in ARH: a clinical and molecular genetic analysis

BACKGROUND

Autosomal recessive hypercholesterolaemia (ARH) is caused by mutations in a putative adaptor protein called ARH. This recessive disorder, characterised by severe hypercholesterolaemia, xanthomatosis, and premature coronary artery disease, is rare except on the island of Sardinia, Italy. Our aim was to ascertain why ARH is more common on Sardinia than elsewhere.

METHODS

We obtained detailed medical histories, did physical examinations, measured concentrations of lipoproteins, and harvested genomic DNA from 28 Sardinians with ARH from 17 unrelated families. We sequenced the coding regions and consensus splice sites of ARH in probands from these families, and from 40 individuals of non-Sardinian origin who had an autosomal recessive form of hypercholesterolaemia of unknown cause.

FINDINGS

Two ARH mutations, a frameshift mutation (c432insA) in exon 4 (ARH1) and a nonsense mutation (c65G-->A) in exon 1 (ARH2), were present in all of the 17 unrelated families with ARH. Three of the ARH alleles contained both mutations, as a result of an ancient recombination between ARH1 and ARH2. No regional clustering of the three mutant alleles within Sardinia was apparent. Furthermore, four Italians from the mainland with autosomal recessive hypercholesterolaemia were homozygous for ARH1.

INTERPRETATION

The small number, high frequency, and dispersed distribution of ARH mutations on Sardinia are consistent with these mutations being ancient and maintained in the Sardinian population because of geographic isolation.

Genetic factors and the founder effect explain familial MS in Sardinia

OBJECTIVE

To estimate the presence of familial aggregation and determine the contribution of genetic factors to familial clustering of MS in patients coming from Sardinia, a Mediterranean island considered a genetically homogeneous, isolated area having high disease incidence and prevalence.

METHODS

Recurrence risk in siblings of 901 Sardinian patients and factors influencing risk (patient and sibling sex, patient age at onset, sibling birth cohort, and presence of affected relatives other than siblings) were examined. The presence of distant familial relationships among patients was evaluated by tracing the extended pedigrees of all patients with MS born in one Sardinian village.

RESULTS

Twenty-three brothers and 36 sisters of the 2,971 siblings were affected with MS. Recurrence risk was greater in siblings of index patients with onset age less than 30 years (p < 0.01, increased risk 2.33 times) and having a relative with MS other than a sibling or parent (p < 0.01, increased risk 2.90 times). Pedigree analysis of patients from the village of L. showed that all 11 patients descended from 3 pairs of ancestors, whereas no cases occurred in the remaining 2,346 inhabitants. In descendants from the 3 couples, MS prevalence was dramatically greater than the regional average and 1.5 times greater than that observed in siblings of affected cases.

CONCLUSIONS

Data from this study indicate that MS familial aggregation in Sardinians is influenced by genetic factors and that founder effect and the isolation of Sardinia can be considered causes of the enrichment of "etiologic" MS genes.

Multiple sclerosis distribution in northern Sardinia: spatial cluster analysis of prevalence

BACKGROUND

A heterogeneous geographic distribution of MS has been reported among different ethnic groups, and also within small communities. Epidemiologic studies conducted over the past two decades using repeated assessments clearly show that Sardinia is at high risk for MS, with a prevalence of 150 per 100,000 in 1997.

OBJECTIVE

To present spatial analysis of the disease prevalence to disclose possible "hot" or "cold" spots of disease, further allowing correlations with risk factors.

METHODS

A spatial analysis of the whole province of Sassari, in northern Sardinia, at a microgeographic level (i.e., in the 89 administrative communes and 6 linguistic areas) was conducted. Because of the small number of cases per commune and to overcome random variability, a hierarchical Bayesian approach was adopted. The distribution of prevalent cases by commune of residence on December 31, 1997 and from age 5 to 15 years was analyzed.

RESULTS

A clustering pattern was found in the southwestern communes of the province based on geographic distribution by both prevalence and residence at age 5 to 15 years. A west-to-east gradient also was observed.

CONCLUSIONS

This study highlights a hot spot of MS in the southwestern part of Sassari province, bordering with the commune of Macomer, where MS was once hypothesized as having occurred as an epidemic. Interestingly, these areas of MS clustering comprise the Common Logudorese linguistic domain. The Catalan area, linguistically and genetically distant from the remaining Sardinian domains, does not show such high estimates. Because MS is not a single-source infectious disease, this study may help test the hypothesis that a widely and evenly spread environmental (infectious?) agent may produce disease in subgroups of genetically more susceptible individuals in areas at higher inbreeding rates, wherein a disease mode of inheritance could be better investigated.

Association between the ancestral haplotype HLA A30B18DR3 and multiple sclerosis in central Sardinia

Association and linkage studies have established the importance of the major histocompatibility complex (MHC) in the susceptibility for multiple sclerosis (MS). We carried out a case-control study to investigate the ancestral haplotype A30B18DR3 and MS in the Nuoro population of Sardinia, which is isolated and genetically distinct from other populations in the Mediterranean basin and characterized by genetic homogeneity, high level of inbreeding, low migration, high prevalence of MS, high frequency of the relevant haplotype, and high past malaria prevalence. Cases and controls were serologically typed for the currently recognized HLA-A, B, and DR antigens. We used a log-linear approach to fit a wide class of models. We tested our hypothesis comparing different models via a likelihood ratio test. We overcame the complication due to unknown gametic phase using expectation-maximization (EM) algorithm as the estimation method. We estimated confidence intervals for odds ratio by using a profile likelihood approach. We found that: (1) the ancestral haplotype A30B18DR3 was associated to MS after allowing for a possible stratification in cases and controls; (2) DR3 allele was conditional independent on disease status, given A30B18 haplotype; (3) there was a tendency for ORs for the high-risk haplotypes to be higher in the high malaria strata; however, this indication did not achieve statistical significance (P = 0.11).

The increasing incidence and prevalence of MS in a Sardinian province

OBJECTIVE

To verify incidence rates and their temporal trend in a homogeneous, ethnically, and genetically distinct population of central Sardinia (the Nuoro province).

BACKGROUND

Intensive epidemiologic studies carried out in Sardinia since the 1970s have suggested that the prevalence and incidence of MS are much higher in this Mediterranean island compared with those found on mainland Italy.

METHODS

The study area had a population of approximately 274, 000 people in the 1991 census. The authors adopted a complete enumerative approach by reviewing all possible sources of case collection available in the investigative area.

RESULTS

Based on 469 MS patients, the mean annual incidence for 1955 to 1995 was 4.18 per 100,000 (or 4.3 per 100,000 if age- and sex-adjusted to the European population). The incidence, averaging 1.95 per 100,000 during 1955 to 1959, rose progressively over time, reaching rates of 6.6 in the quinquiennium 1985 to 1989 and 6.4 per 100,000 in 1990 to 1995. On December 31, 1994, the crude prevalence, based on 415 MS patients alive in the study area, was 151.9 per 100,000 (156.6 if adjusted to the European population).

CONCLUSION

These incidence and prevalence rates are the highest to date that have been estimated for a large community in southern Europe, and they constitute some of the highest rates in the world. Based on other surveys, these results reinforce the position of Sardinia as a higher and rising prevalence area for MS compared with other Mediterranean populations. Genetic and social-historic data strengthen the hypothesis of the environmental role and genetic factors among Sardinians in determining the notable difference in MS frequency between Sardinians and other Mediterraneans.

The immunogenetics of resistance to malaria

The genetic basis of susceptibility to malaria has been studied extensively using a variety of approaches. The protective role of several erythrocytic variants is now well established. More recently, there has been growing evidence that genes determining a variety of immune responses influence susceptibility to malaria. Some of these genes may specifically affect susceptibility to particular strains of malaria parasite. The recent adoption of genetic linkage approaches supplements the established strategy of assessing candidate gene polymorphisms in case-control studies. Immunogenetic associations with severe malaria have already suggested new approaches for intervention, and the highly polygenic nature of susceptibility to this disease suggests that the identification and analysis of new susceptibility and resistance loci should be worthwhile.

HLA-B35 frequency variations correlate with malaria infection in Sardinia

The hypothesis of a possible selective role of malaria in HLA allele frequency variations was investigated in Sardinia by typing completely 1,039 individuals for HLA: 536 from six lowland villages exposed to malaria until 1948, and 503 from six highland villages with no history of malaria. Another 1,928 individuals from 136 villages scattered all over the island were studied to establish if the HLA allele frequencies among villages correlated with the malaria incidence and/or altitude above sea level. Only the HLA-B35 allele yielded significantly higher frequencies in the lowland versus the highland villages (P<1 x 10(-5)). The observed B35 variance was 9.5 times higher than expected in the absence of selection, showing an adaptive origin. The highly significant positive correlation found between HLA-B35 frequency and malaria in 136 villages suggests that malaria has been the selective factor for HLA-B35 in Sardinia.

Lack of influence of apolipoprotein E4 on lipoprotein levels in the island population of Sardinia

BACKGROUND

In this study, the apolipoprotein E (apoE) genotypes as well as plasma lipid and lipoprotein levels have been determined for the first time in 633 healthy and unrelated inhabitants on the island of Sardinia (291 men and 342 women, age range 6-89 years), randomly selected in the four districts of Sardinia among healthy people having parents and grandparents born in the same geographic area. This island lies in the centre of the western Mediterranean sea with a well-recognized peculiar and preserved genetic background. The epsilon 3 allele frequency (0.897) is higher than that previously reported in southern and mainland Italy and is one of the highest in Europe and among Caucasians; epsilon 2 allele frequency (0.040) is the lowest in Europe; epsilon 4 (0.063) is unusually low and, most interestingly, does not change in the different age groups, i.e. does not decrease in old subjects.

RESULTS

Lipid and lipoprotein analysis confirm that total cholesterol and low-density lipoprotein (LDL)-cholesterol levels are lower than those described in mainland Italy; moreover, in this large Sardinian series, accurately selected, epsilon 4 allele did not influence total cholesterol (P = 0.270), LDL-cholesterol (P = 0.667) and high-density lipoprotein (HDL)-cholesterol (P = 0.549) as in other populations. In contrast, subjects carrying the epsilon 2 allele were found to have significantly lower total cholesterol (P = 0.001) and LDL-cholesterol (P = 0.001) levels than epsilon 3 carriers.

CONCLUSION

The low epsilon 4 frequency and the lack of influence of this allele on lipid metabolism is a unique characteristic and, to date, has been described only in Sardinia among Caucasians; it might contribute to the low prevalence of coronary artery disease in this island.

A new lease of life for an old enzyme

We review here some recent data about glucose-6-phosphate dehydrogenase (G6PD), the first and key regulatory enzyme of the pentose phosphate pathway. New evidence has been presented to suggest that malaria is a selective agent for G6PD deficiency, which is the most common enzymopathy in man, and that G6PD deficiency, generally considered to be a mild and benign condition, is significantly disadvantageous in certain environmental conditions. At the molecular level, the enzyme structure has recently been elucidated and mechanisms regulating G6PD gene expression have been determined. A G6PD knock-out mutation introduced in mouse cells makes them exquisitely sensitive to oxidative stress, indicating that this ubiquitous metabolic enzyme has a major role in the defence against oxidative stress, even in eukaryotic nucleated cells, which have several alternative routes for providing the same protection. Because of the high prevalence of G6PD deficiency in many populations, it is expected that these findings will prompt further studies to ascertain the putative role of G6PD deficiency in conditions such as carcinogenesis and ageing.

The genetic structure of a province as revealed by surnames and HLA genes: potential utility in transplantation policy

The combined use of surnames, which simulate selectively neutral genetic markers, and HLA genes may constitute a useful tool for the genetic survey of a small area. We found a coincidence between HLA genetic structure and surname "selectively neutral' pattern, in an Italian province, although HLA genes indicate a more pronounced genetic isolation for one particular subregion of the province. The patchiness of HLA allele distribution that is sometimes created by drift and/or selection can be used as the basis both of anthropological and of epidemiological studies. The creation of genetic maps of relatively small areas may also constitute a tool for the selection of bone marrow donors.

Genetic analysis of Sardinia: I. data on 12 polymorphisms in 21 linguistic domains

(1) The microgeographic structure of Sardinia, well documented from a historical and linguistic point of view, further supported by archaeological evidence, can also be dissected at the genetic level: gene frequencies show heterogeneities which are statistically significant. (2) Dendrogram analyses performed with different methods lead to the same result: even if gene frequencies cluster linguistically defined geographic domains in agreement with historical and archaeological evidence, no phylogenetic tree can be inferred, very likely because the assumptions which allow a phylogenetic tree to be a valid model of evolution (mainly constant evolutionary rates and independence between branches) do not apply to the genetic history of Sardinia. (3) Evidence of a qualitative association between distribution of genes and distribution of languages or dialects seems to emerge also at the microgeographic level of our analysis. More linguistic and genetic data are planned to be considered.

Strong association between microsatellites and an HLA-B, DR haplotype (B18-DR3): implication for microsatellite evolution

The HLA haplotype B18-DR3 has a widespread geographical distribution, but has its greatest frequencies in Southern Europe, probably vestigial of the earliest populations of this region, particularly in the Pays Basque and Sardinia. This haplotype is of medical significance, being that most implicated as a factor of risk in insulin-dependent diabetes mellitus. In this study, the closely linked microsatellite markers (TNFa,b,c) in the region of the tumor necrosis factor (TNF) genes have been used in an attempt to subtype this haplotype in the two populations and/or in healthy and diabetic populations. A total of 79 HLA-B18-DR3 haplotypes were analyzed: 54 in Basques (12 from healthy individuals and 42 from diabetics or their first-degree relatives) and 25 in Sardinians (13 from healthy and 12 from diabetic individuals). The TNF haplotype a1-b5-c2 is completely associated with B18-DR3 in both populations. The homogeneity of the B18-DR3 haplotype in two ethnically pure populations implies stability in evolution, which suggests that the mutation rate of these microsatellite markers must be less than is usually assumed (i. e., approximately 5 x 10(-4) per site per generation). Such markers should be powerful tools for studying genetic drift and admixture of populations, but it remains to be established whether this stability is a rule for all microsatellites in HLA haplotypes or whether it is restricted to some microsatellites and/or some HLA haplotypes. The population genetics of those microsatellites associated with HLA B18-DR3 was also studied in a random sample of the Basque population.

Apolipoprotein E polymorphism in Italy investigated in native plasma by a simple polyacrylamide gel isoelectric focusing technique. Comparison with frequency data of other European populations

A new polyacrylamide gel isoelectric focusing (PAGIEF) technique has been developed that allows rapid and reliable identification of Apolipoprotein E (APOE) phenotypes directly from plasma or serum without any prior treatment. This method was used to determine the APOE phenotypes in samples from Central and Southern Italy, Sicily, and Sardinia. The frequencies observed for the APOE*2, APOE*3, and APOE*4 alleles in Central and Southern Italy (Sicily included) were similar (0.066, 0.851, 0.083 and 0.056, 0.858, 0.085 respectively) though lower APOE*4 frequencies were found in the more southern regions. The Sardinian population showed APOE gene frequencies (APOE*2 = 0.050, APOE*3 = 0.898, APOE*4 = 0.052) to be significantly different from those of the rest of Italy owing to the low APOE*4 frequency, the lowest among Caucasian populations. The frequencies were compared with those found in other European populations. A clear cut North-South decreasing cline was found for APOE*4 allele frequencies and an opposite trend was found for APOE*3 frequencies. The overall dispersion of European populations as determined by the three APOE allele frequencies was graphically represented using coordinate analysis. The tendency of the APOE*4 frequency to decline with latitude both at the Italian and at the European level was discussed with reference to similar trends observed for dietary habits (saturated fat intake).

Genetic data on Alghero population (Sardinia): contrast between biological and cultural evidence

Data on 20 genetic polymorphisms (61 alleles) in the Algehero population on the northwestern coast of Sardinia are presented and discussed in relation to its linguistic peculiarity inside the island. Since the Aragonese (Spain) conquest of Sardinia in the 13th century, the Catalan language, the same as that spoken in Northeastern Spain and certain districts of Southern France, has been used in Alghero even until today. Analysis for heterogeneity of gene frequency distributions indicates that the genetic information obtained on Alghero is adequate to discriminate Sardinians from other neighbouring populations. Genetic variation between populations measured through genetic distances and principal-component analysis shows that the present-day population of Alghero is much closer genetically to Sardinians than to Catalonians. Our genetic results do not support any interpretation of the linguistic affinities between Alghero and Catalonia at present as indicative of biological kinship.

Impact of malaria on genetic polymorphism and genetic diseases in Africans and African Americans

The high mortality from malaria in sub-Sahara Africa selected multiple genes that give the population a selective advantage. Identification of the genetic basis for resistance may suggest unusual approaches to development of malarial vaccines and antimalarial drugs. Some of these genes may be deleterious, although of selective advantage within the African setting, and need to be identified for counseling for disease prevention.

HLA structure of the Sardinian population: a haplotype study of 551 families

A study on the HLA structure of the Sardinian population was carried out on 551 healthy unrelated families representing all of the island districts. Altogether 2202 HLA-A, B, Cw, DR individual haplotypes and 853 different haplotypes were determined. Cavalli-Sforza and Edwards' genetic distance index for the total of 62 tested alleles showed a modest heterogeneity between one district and another (0.09-0.16). The genetic distance between Sardinians and the rest of the Italian population was 0.23 (0.22-0.26) and progressively increased in comparisons with caucasoids (0.26), negroids (0.34) and mongoloids (0.41). Sixty-three two-locus haplotypes with a high positive linkage disequilibrium were observed in our family sample. The percentages of two-locus haplotypes in LD shared with other populations turned out to be 45% with caucasoids, 20% with negroids and 10% with mongoloids. The distribution of the A, B, Cw, DR haplotypes is shown with 673 of them represented only once or twice, and 10 (1.2%) 14-322 times each. Of the latter, 8 are extended haplotypes, 6 of which characterize the Sardinian population. The analysis of our data suggests that the present-day Sardinian population is the result of a superposition of different populations, mainly consisting of caucasoids on a pre-caucasoid paleo-Mediterranean substratum.

Gm and Km allotypes in four Sardinian population samples

Serum samples of 683 unrelated male and female individuals of four Sardinian population samples (Sassari, Nuoro, Oristano and Cagliari) were typed for G 1 m (1,2,3,17), G 3 m (5,6,10,11,13,14,15,16,21,26), and Km (1). Phenotype, haplotype (Gm), and allele frequencies (Km), respectively, show a remarkable variability between these four population samples. Comparisons with other Italian populations reveal the considerable genetic difference of the Sardinians, which is in particular caused by the presence of the haplotype Gm1,3;5,10,11,13,14,26 in them. This haplotype is quite uncommon in Europeans and may reflect gene flow from Eastern populations (Phoenicians?) who came to this island in ancient-history times.

Common west African HLA antigens are associated with protection from severe malaria

A large case-control study of malaria in West African children shows that a human leucocyte class I antigen (HLA-Bw53) and an HLA class II haplotype (DRB1*1302-DQB1*0501), common in West Africans but rare in other racial groups, are independently associated with protection from severe malaria. In this population they account for as great a reduction in disease incidence as the sickle-cell haemoglobin variant. These data support the hypothesis that the extraordinary polymorphism of major histocompatibility complex genes has evolved primarily through natural selection by infectious pathogens.

Fertility and malaria in Sardinia

Using data from the 1961 Italian census, the study of fertility in Sardinia when malaria was endemic shows differential fertility between women living in areas with differing degrees of malaria. Cultural factors measured by women's level of education are negatively correlated with fertility, just as the 'urban' character of the area in which the women lived has a lowering effect on the fertility rate. The hypothesis of differential mortality according to social class, affecting lower-class women and in particular the more prolific among them, seems to be supported by data analysed through time. The subdivision of Sardinian towns and villages into those with a 'low' and a 'high' malaria rate was made on the basis of the classification given by Fermi in a period corresponding to the overall period of fertility of the women considered. Hypotheses about a greater acquired immunity and a higher frequency of heterozygotes for malarial genes, like thalassaemia and G-6-PD deficiency, in the area where malaria was more intense, are proposed to explain the higher fitness of women living in this area. The comparison between frequencies of heterozygotes for thalassaemia and G-6-PD deficiency, obtained by Siniscalco et al. for Sardinian villages in the two different malaria-infested areas, shows a significant difference when the areas are examined as a whole, but a great variability (principally for G-6-PD deficiency) between villages. Changes in ecological factors could have modified the geographical distribution of malaria today, compared with the distribution that may have determined the frequencies of heterozygotes many years ago.

The absence of 21-OH A and C4 B genes is a constant characteristic of the "Sardinian" HLA extended haplotype A30 Cw5 B18 BfF1 DR3 DRw52 DQw2

The genomic DNA of 25 unrelated individuals with HLA haplotype A30 Cw5 B18 BfF1 DR3 D w52 DQw2 was digested with the restriction enzyme Taq I and hybridized with cDNA probes for C4 and 21-OH genes. Eighteen individuals and a non-Sardinian reference cell (DUCAF) were homozygous for the entire extended haplotype, six individuals were heterozygous for the HLA-A locus and homozygous for the rest of the same haplotype. All of the 18 homozygous individuals, four of the six heterozygous subjects and the DUCAF cell revealed the absence of two fragments at 3.2 and 2.4 kb corresponding to the 21-OH A gene, and the absence of fragments corresponding to the C4 B "long" or "short" gene. The contemporary absence of the 21-OH A and C4 B genes seems to be a constant characteristic of this extended haplotype in the Sardinian population and suggests that this and other extended haplotypes bearing C4 A or C4 B null alleles could be ancestral haplotypes which never duplicated at these loci.

The "Sardinian" HLA-A30,B18,DR3,DQw2 haplotype constantly lacks the 21-OHA and C4B genes. Is it an ancestral haplotype without duplication?

The C4 and 21-OH loci of the class III HLA have been studied by specific DNA probes and the restriction enzyme Taq 1 in 24 unrelated Sardinian individuals selected from completely HLA-typed families. All 24 individuals had the HLA extended haplotype A30,Cw5,B18, BfF1,DR3,DRw52,DQw2, named "Sardinian" in the present paper because of its frequency of 15% in the Sardinian population. Eighteen of these were homozygous for the entire haplotype, and six were heterozygous at the A locus and blank (or homozygous) at all the other loci. In all completely homozygous cells and in four heterozygous cells at the A locus, the restriction fragments of the 21-OHA (3.2 kb) and C4B (5.8 kb or 5.4 kb) genes were absent, and the fragments of the C4A (7.0 kb) and 21-OHB (3.7 kb) genes were present. It is suggested that the "Sardinian" haplotype is an ancestral haplotype without duplication of the C4 and 21-OH genes, practically always identical in its structure, also in unrelated individuals. The diversity of this haplotype in the class III region (about 30 kb less) may be at least partially responsible for its misalignment with most haplotypes, which have duplicated C4 and 21-OH genes, and therefore also for its decreased probability to recombine. This can help explain its high stability and frequency in the Sardinian population. The same conclusion can be suggested for the Caucasian extended haplotype A1,B8,DR3 that always seems to lack the C4A and 21-OHA genes.

Mitochondrial DNA polymorphism in four Sardinian villages

Polymorphism of mitochondrial DNA has been studied in two highland (Desulo, Tonara) and in two lowland (Galtellì, Orosei) Sardinian isolates, formerly subjected to different selective pressure due to malaria, and in 103 individuals from Northern Italy (Bergamo area), where malaria never appeared to be endemic. Two mitochondrial restriction endonuclease patterns (morphs) never described before have been found, one in the Bergamo and Orosei samples, and the other one only in Orosei. Four new mitochondrial types (mitotypes) due to different combinations of morphs have been identified; two of them have been found only in Sardinia, but with such a low frequency that they cannot be defined as typical Sardinian mitotypes. One mitotype (BamHI-morph 3, MspI-morph 4, AvaII-morph 9 and HaeII-morph 1) showed a significantly higher frequency in the highland rather than in the lowland Sardinian villages or in the Bergamo area. Since this mitotype has been found at a relatively high frequency in Central and Southern Italy, while it has been reported to be rare in Caucasians of Central European origin and absent in other ethnic groups (Africans, Chinese, Japanese and Israeli Jews), we suggest it may represent an ancient Mediterranean type. The analysis of these data suggests that drift or other evolutive forces different from malaria might be the major cause of mitochondrial DNA variation in Sardinia.

A genetic history of Italy

Statistical techniques for displaying the geographical distribution of many genes in few synthetic images have been used to represent the various patterns of gene frequencies in Europe and in the world (Menozzi et al. 1978; Piazza et al. 1981 a). It has also been shown that such synthetic displays are particularly useful in detecting clines of genetic differentiation associated with movements of populations like those accompanying the Neolithic expansion of farmers from the Near East or, in more recent times, the putative diffusion of Indo-European-speaking populations (Ammerman & Cavalli-Sforza, 1984; Gimbutas, 1973). In this paper we use the same combination of statistical and graphical techniques to study the genetic structure of Italy, a European country whose unity of people and cultures was quite a recent event. The possibility of studying genetic differentiation in a small geographical area is tested and trends of genetic differences are tentatively interpreted in terms of historic and linguistic knowledge. The few demographic pieces of information taken from historical sources and compared with linguistic records support the hypothesis that the genetic structure of Italy still reflects the ethnic stratification of pre-Roman times.

Surnames in Ferrara: distribution, isonymy and levels of inbreeding

The distributions of surnames in populations of small and large towns are almost exactly linearized by a log-log transformation. This indicates probable fit of genetic models to most such distributions, even when the number of surnames is very large. Genetic parameters can then be conveniently calculated from surname distributions. It was found that inbreeding indicators calculated from isonymy are negatively correlated with the size of the towns from which the names were extracted. It was also found that the levels of inbreeding at present observed in Ferrara have little effect on the frequency of homozygotes for the beta-thalassaemia gene.

Failure to relate mononuclear phagocyte system function to HLA-A, B, C, DR, DQ antigens in membranous nephropathy

Nineteen patients with idiopathic membranous nephropathy were typed for HLA pattern and analyzed for the Fc receptor function of splenic macrophages by detecting in vivo the clearance of IgG-sensitized 51Cr-labelled autologous erythrocytes. Seven out of 19 patients were found to have a macrophage dysfunction. This defect was not related to any HLA-A, B, C, DR, DQ antigen tested nor to the levels of IgG-containing immune complexes, as detected by a Clq solid phase test, nor to the magnitude of proteinuria. Since HLA-B8 and HLA-DR3 antigens were significantly more frequent in patients than in the control group, the factors that may impair the macrophage system in individuals predisposed to this nephropathy are discussed.