Runs of homozygosity in European populations.

Estimating individual genome-wide autozygosity is important both in the identification of recessive disease variants via homozygosity mapping and in the investigation of the effects of genome-wide homozygosity on traits of biomedical importance. Approaches have tended to involve either single-point estimates or rather complex multipoint methods of inferring individual autozygosity, all on the basis of limited marker data. Now, with the availability of high-density genome scans, a multipoint, observational method of estimating individual autozygosity is possible. Using data from a 300,000 SNP panel in 2618 individuals from two isolated and two more-cosmopolitan populations of European origin, we explore the potential of estimating individual autozygosity from data on runs of homozygosity (ROHs). Termed F(roh), this is defined as the proportion of the autosomal genome in runs of homozygosity above a specified length. Mean F(roh) distinguishes clearly between subpopulations classified in terms of grandparental endogamy and population size. With the use of good pedigree data for one of the populations (Orkney), F(roh) was found to correlate strongly with the inbreeding coefficient estimated from pedigrees (r = 0.86). Using pedigrees to identify individuals with no shared maternal and paternal ancestors in five, and probably at least ten, generations, we show that ROHs measuring up to 4 Mb are common in demonstrably outbred individuals. Given the stochastic variation in ROH number, length, and location and the fact that ROHs are important whether ancient or recent in origin, approaches such as this will provide a more useful description of genomic autozygosity than has hitherto been possible.

3000 years of solitude: extreme differentiation in the island isolates of Dalmatia, Croatia.

Communities with increased shared ancestry represent invaluable tools for genetic studies of complex traits. "1001 Dalmatians" research program collects biomedical information for genetic epidemiological research from multiple small isolated populations ('metapopulation') in the islands of Dalmatia, Croatia. Random samples of 100 individuals from 10 small island settlements (n<2000 inhabitants) were collected in 2002 and 2003. These island communities were carefully chosen to represent a wide range of distinct and well-documented demographic histories. Here, we analysed their genetic make-up using 26 short tandem repeat (STR) markers, at least 5 cM apart. We found a very high level of differentiation between most of these island communities based on Wright's fixation indexes, even within the same island. The model-based clustering algorithm, implemented in STRUCTURE, defined six clusters with very distinct genetic signatures, four of which corresponded to single villages. The extent of background LD, assessed with eight linked markers on Xq13-21, paralleled the extent of differentiation and was also very high in most of the populations under study. For each population, demographic history was characterised and 12 "demographic history" variables were tentatively defined. Following stepwise regression, the demographic history variable that most significantly predicted the extent of LD was the proportion of locally born grandparents. Strong isolation and endogamy are likely to be the main forces maintaining this highly structured overall population.

The population history of the Croatian linguistic minority of Molise (southern Italy): a maternal view.

This study examines the mitochondrial DNA (mtDNA) diversity of the Croatian-speaking minority of Molise and evaluates its potential genetic relatedness to the neighbouring Italian groups and the Croatian parental population. Intermatch, genetic distance, and admixture analyses highlighted the genetic similarity between the Croatians of Molise and the neighbouring Italian populations and demonstrated that the Croatian-Italian ethnic minority presents features lying between Croatians and Italians. This finding was confirmed by a phylogeographic approach, which revealed both the prevalence of Croatian and the penetrance of Italian maternal lineages in the Croatian community of Molise. These results suggest that there was no reproductive isolation between the two geographically proximate, yet culturally distinct populations living in Italy. The gene flow between the Croatian-Italians and the surrounding Italian populations indicate, therefore, that ethnic consciousness has not created reproductive barriers and that the Croatian-speaking minority of Molise does not represent a reproductively isolated entity.

Y chromosome STR polymorphisms in a Serbian population sample.

Eight Y chromosome short tandem repeat (STR) polymorphisms (DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393) were analyzed in the sample of 114 unrelated males living in Serbia. A general STR allelic frequency pattern in Serbians corresponds to other European populations with the exception of loci DYS19, DYS389II and DYS385. Out of ninety identified haplotypes, 74 (64.91%) appeared in single copies. The most frequent haplotypes (DYS19-DYS385-DYS389I-DYS389II-DYS390-DYS391-DYS392-DYS393) 16-14/15-13-31-24-11-11-13 and 15-15/19-12-28-23-10-12-12 were found in four copies (3.51%). Total haplotype diversity was 0.9947+/-0.0021.

Population genetics of 8 Y chromosome STR loci in Macedonians and Macedonian Romani (Gypsy).

Eight Y chromosome short tandem repeat (STR) polymorphisms (DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393) were analyzed in Macedonians (n = 84) and Macedonian Romani ethnic group (n = 68). Observed allelic frequency distribution and locus diversity values in Macedonians correspond closer to neighboring southeastern European populations than (mostly) western European populations, whereas observed allelic frequency distribution and locus diversity values in Macedonian Romani, as expected based on their Asian (Indian) origin, differ from both neighboring southeastern and (mostly) western European populations. Sixty-six (78.57%) haplotypes appeared in single copies in Macedonians and 15 (22.06%) in Macedonian Romani. The most frequent Macedonian haplotypes (DYS19-DYS385-DYS389I-DYS389II-DYS390-DYS391-DYS392-DYS393) 16-14/15-13-31-24-11-11-13 and 13-16/18-13-30-24-10-11-13 were found in 7 and 6 copies, respectively. The most frequent Macedonian Romani haplotype 15-15/17-14-29-22-10-11-12 was found in 18 males. Total haplotype diversity was 0.9885 +/- 0.0058 (Macedonians) and 0.9008 +/- 0.0242 (Macedonian Romani).

Evaluation of Y-STR variation in Bosnian and Herzegovinian population.

Eight Y-STR polymorphisms (DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392 and DYS393) were analyzed in the samples of 181 unrelated males from Bosnia and Herzegovinia. Observed STR allelic frequency pattern and locus diversity values in Bosnians and Herzegovinians correspond closer to neighboring southeastern European populations than previously reported (mostly western) European populations. One hundred and five haplotypes were identified and 78 haplotypes (74.3%) appeared in single copies. The most frequent haplotypes (DYS19-DYS385-DYS389I-DYS389II-DYS390-DYS391-DYS392-DYS393) were 16-14/15-13-31-24-11-11-13 (7.7%), 16-14/15-13-30-24-11-11-13 (7.7%) and 15-14/15-13-31-24-11-11-13 (5.5%). Total haplotype diversity was 0.9820 +/- 0.0040.

Segregation analysis of systolic and diastolic blood pressure in Middle Dalmatia Island population.

A complex segregation analysis of systolic and diastolic blood pressure has been performed on pedigree data from rural populations inhabiting Middle Dalmatian islands of Brac, Hvar and Korcula and the Peljesac peninsula. The purpose of the performed analysis was to possibly elucidate a signal of a large-effect gene responsible for high prevalence of hypertension present in this population (the age-adjusted prevalence of developed hypertension being 31.82% in males and 28.23% in females). The analysis was performed on a sample of 389 two- and three-generation families consisting of 2 to 19 observed individuals (1126 examinees in total, 526 males and 600 females, aged 17 to 83). Since the examinees were randomly selected from census data encompassing 22.6% of the total population--the family relations having been established afterwards--the selected sample can be considered representative for the examined populations. By applying the usual transmission probability tests, the major gene model has been accepted for systolic as well as for diastolic blood pressure. The most parsimonious models showed that: (a) inheritance of blood pressure in the Middle Dalmatia population can be attributed to the effect of a major gene responsible for 34% (systolic) and 36% (diastolic) blood pressure variation; (b) alleles of that major gene act in co-dominant fashion; (c) allele frequency for high blood pressure (A2) is 18% (systolic) and 15% (diastolic blood pressure); and (d) the residual (non-major gene) familial correlation is negligible and can be constrained to zero. Since the results are also indicating heterogeneity within the sample in the genetic determination of the systolic blood pressure, the obtained results thus justify further search for the most promising subpopulation for incoming genetic epidemiological investigations of hypertension.

Y chromosomal heritage of Croatian population and its island isolates.

Y chromosome variation in 457 Croatian samples was studied using 16 SNPs/indel and eight STR loci. High frequency of haplogroup I in Croatian populations and the phylogeographic pattern in its background STR diversity over Europe make Adriatic coast one likely source of the recolonization of Europe following the Last Glacial Maximum. The higher frequency of I in the southern island populations is contrasted with higher frequency of group R1a chromosomes in the northern island of Krk and in the mainland. R1a frequency, while low in Greeks and Albanians, is highest in Polish, Ukrainian and Russian populations and could be a sign of the Slavic impact in the Balkan region. Haplogroups J, G and E that can be related to the spread of farming characterize the minor part (12.5%) of the Croatian paternal lineages. In one of the southern island (Hvar) populations, we found a relatively high frequency (14%) of lineages belonging to P*(xM173) cluster, which is unusual for European populations. Interestingly, the same population also harbored mitochondrial haplogroup F that is virtually absent in European populations--indicating a connection with Central Asian populations, possibly the Avars.

Y chromosome STRs in Croatians.

Eight Y chromosome short tandem repeat (STR) polymorphisms (DYS19, DYS388, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393) were analyzed in the sample of 457 unrelated Croatian men. A general STR allelic frequency pattern in Croatians corresponds to other European populations with the exception of the loci DYS19 and DYS389II. The most frequent DYS19 allele was 16, while at the DYS389II the most frequent were alleles 30 and 31. The most frequent Y chromosome haplotype (16-13-13-31-24-11-11-13) was found in 33 individuals (7.22%). One hundred and seventy-four haplotypes (38.07%) were observed in single copies.

Y chromosome haplotypes in Albanian population from Kosovo.

Eight Y chromosome short tandem repeat (STR) polymorphisms (DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392, and DYS393) were analyzed in the sample of 117 unrelated Albanian males living in Kosovo. A general STR allelic frequency pattern in the Albanian population from Kosovo corresponds to other European populations. Fourty six haplotypes were observed in single copy. The most frequent haplotypes were (DYS19-DYS385-DYS389I-DYS389II-DYS390-DYS391-DYS392-DYS393) 14-11/11-13-29-24-11-13-13 (10.26%), 14-14/17-12-28-24-10-11-12 (9.40%), 13-16/18-13-30-24-10-11-13 (9.40%), and 14-17/17-13-31-24-10-11-13 (9.40%).

Ace Alu insertion polymorphism in Croatia and its isolates.

Alu elements are a family of interspersed repeats in the genome propagating by retroposition into new chromosomal locations. Alu insertion in Ace gene is known to be polymorphic (presence/absence of Alu element) in worldwide populations and as such serves as marker for population structure analyses. In this study we examined the distribution of genotypes and allele frequencies of this polymorphism in general Croatian population and its two isolates (the island of Hvar and the coastal region of the Middle Dalmatia) and related them to the level of endogamy as an indicator of inbreeding in these populations. Results showed that these three population groups are different with respect to Ace Alu polymorphism. The endogamy was highest on the island of Hvar. With the increase of endogamy a decrease in heterozigosity was observed. The same trend was observed for the frequency of insertion allele. Its frequencies in the village subpopulations of two studied isolates are subject to genetic drift due to small population sizes and high levels of endogamy. This in turn causes genetic differentiation among villages that is observed to be higher on the island of Hvar than in the coastal region. In the worldwide perspective, the Ace Alu insertion allele frequency of 50.6% in the general Croatian population falls within the range of other European populations.

Holistic anthropological research of Hvar Islanders, Croatia--from parish registries to DNA studies in 33 years.

The complexity of interactions between hereditary, environmental and cultural factors in determining human phenotypes is often underestimated in biomedical research. In this paper, we present 33 years of holistic anthropological research that was being conducted since 1971 in the island of Hvar, Croatia. During this period, detailed characterization of migrations, demography, isonymy, linguistic differences, anthropometric traits (head and body dimensions), physiological (cardio-respiratory) properties, quantitative and qualitative dermatoglyphic traits, radiogrammetric metacarpal bone dimensions and genetic traits (classical antigens, HLA diversity, DNA short tandem repeat -STR, mitochondrial DNA and Y-chromosome polymorphisms) was performed. The analysis of this large collection of data using both model-bound and model-free approaches showed that the complexity underlying human biological traits may be considerably greater than generally assumed, which has important implications for design of future studies into genetic determinants of complex traits.

Inbreeding and susceptibility to osteoporosis in Croatian island isolates.

The aim of this study was to investigate a recessive genetic component in susceptibility to osteoporosis (OP) by comparing its prevalence in isolated villages of three Croatian islands: Brac, Hvar and Korcula with different levels of inbreeding. A random sample of 20-30% adults from 14 villages was obtained, including a total of 1,389 examinees. The average inbreeding coefficient (F) of examinees from each village population was estimated using Wright's path method (based on genealogical information). The morphometry of the metacarpal bones was performed on hand-wrist radiographs of both hands in all examinees. OP was defined as values of cortical index smaller than 2 standard deviations based on distribution of values in examinees of the same sex under 45 years of age. Mean values of cortical index (CI) and prevalence of OP (both standardized by age and weighted for the sample size) in each village were correlated to the mean inbreeding coefficient (F). The coefficient of correlation (r) between F values and CI was -0.28 in males (p = 0.08) and -0.42 in females (p = 0.005), and between F and OP prevalence 0.32 in males (p < 0.001) and 0.43 in females (p < 0.001). These results indicate a trend of increased susceptibility to osteoporosis with increasing level of inbreeding in isolated communities of Croatian islands.

Frequencies of mtDNA haplogroups in southeastern Europe--Croatians, Bosnians and Herzegovinians, Serbians, Macedonians and Macedonian Romani.

Mitochondrial DNA polymorphisms were analyzed in of 1,610 randomly chosen adult men from 11 different regions from southeastern Europe (Croatians, Bosnians and Herzegovinians, Serbians, Macedonians and Macedonian Romani). MtDNA HVS-I region together with RFLP sites diagnostic for main Euroasian and African mtDNA haplogroups were typed to determine haplogroup frequency distribution. The most frequent haplogroup in studied populations was H with the exception of Macedonian Romani among whom the most frequent were South Asian (Indian) specific variants of haplogroup M. The multidimensional scaling plot showed two clusters of populations and two outliers (Macedonian Romani and the most distant from mainland Croatian island of Korcula). The first cluster was formed by populations from three Croatian islands (Hvar, Krk and Brac) and the second cluster was formed by Macedonians, Serbians, Croatians from mainland and coast, Herzegovinians, Bosnians, Slovenians, Poles and Russians. The present analysis does not address a precise evaluation of phylogenetic relations of studied populations although some conclusions about historical migrations could be noticed. More extended conclusions will be possible after deeper phylogenetic and statistical analyses.

Effects of isolation and inbreeding on human quantitative traits: an example of biochemical markers of hemostasis and inflammation.

Isolation is a known force in evolutionary biology and one of the main factors in speciation. One of the main consequences of severe isolation is reduced mate choice, which results in the occurrence of inbreeding as a result of isolation. We investigated the effects of individual genome-wide heterozygosity measured as the multilocus heterozygosity (MLH) on biochemical markers of hemostasis and inflammation in 1,041 individuals from the island of Vis, Croatia, where inbreeding is prevalent and a wide range of variation in the genome-wide heterozygosity is expected. Assessment of individual genome-wide heterozygosity was based on genome-wide scans using 800 microsatellite (STR) and 317,503 single nucleotide (SNP) polymorphic markers in each examinee. In addition, for each examinee we defined a personal genetic history (PGH) based on genealogical records. The association between PGH and MLH and fibrinogen, D-dimer (Dd), von Willebrand factor (vWF), tissue plasminogen activator (tPA), and C-reactive protein (CRP) was performed with a mixed model, controlling for possible confounding effects. PGH was a significant predictor only for tPA (P < 0.001), whereas neither of the two MLH measures exhibited significant association with any of the investigated traits. The effects of individual genome-wide heterozygosity are most likely expressed in highly polygenically determined traits or in traits that are mediated by rare and recessive genetic variants. Weak associations between PGH and MLH and markers of hemostasis and inflammation suggest that their genetic control may not be highly polygenic and that they could be promising targets for genetic association studies.

SLC2A9 is a newly identified urate transporter influencing serum urate concentration, urate excretion and gout.

Uric acid is the end product of purine metabolism in humans and great apes, which have lost hepatic uricase activity, leading to uniquely high serum uric acid concentrations (200-500 microM) compared with other mammals (3-120 microM). About 70% of daily urate disposal occurs via the kidneys, and in 5-25% of the human population, impaired renal excretion leads to hyperuricemia. About 10% of people with hyperuricemia develop gout, an inflammatory arthritis that results from deposition of monosodium urate crystals in the joint. We have identified genetic variants within a transporter gene, SLC2A9, that explain 1.7-5.3% of the variance in serum uric acid concentrations, following a genome-wide association scan in a Croatian population sample. SLC2A9 variants were also associated with low fractional excretion of uric acid and/or gout in UK, Croatian and German population samples. SLC2A9 is a known fructose transporter, and we now show that it has strong uric acid transport activity in Xenopus laevis oocytes.

An mtDNA perspective of French genetic variation.

BACKGROUND: The French has been insufficiently characterized so far for mitochondrial DNA (mtDNA) diversity. AIMS: The study aimed to enhance the information available for the French mtDNA pool and to explore the potential microgeographical differentiation of two French regions selected for their linguistic and historical idiosyncrasies. SUBJECTS AND METHODS: A total of 868 samples from 12 different locations in France were collected. They were sequenced for the hypervariable segment I (HVS-I) and typed for haplogroup defining markers from the coding region either by restriction fragment length polymorphism (RFLP) or by a new protocol based on the 5' nuclease allelic discrimination. The mtDNA gene pools of French Basques and Bretons were compared in terms of frequency and composition with relevant neighbouring populations. RESULTS: The French Basques' mtDNA pool shares some common features with that of the Spanish Basques, such as the high frequency of haplogroup H. However, the French Basques exhibit a number of distinct features, most notably expressed in the prevalence of haplogroups linked with the Neolithic diffusion in Europe. In Brittany, Finistère shows closer affinities with Britain and Scandinavia than the two other departments of Brittany. CONCLUSION: The mtDNA haplogroup composition of the French does not differ significantly from the surrounding European genetic landscape. At a finer grain, microgeographical differentiation can be revealed, as shown for the French Basque country and for Brittany.

Effects of genome-wide heterozygosity on a range of biomedically relevant human quantitative traits.

The dramatic changes in human population structure over the last 200 years have resulted in significant levels of outbreeding, which, in turn, is predicted to lead to increased levels of individual genetic diversity (genome-wide heterozygosity, h). To investigate possible effects of these large demographic changes on global health, we studied the effect of h, measured as relative heterozygosity, h(R), on 15 disease-related traits in four groups of individuals with widely differing ancestral histories (ranging from outbred to inbred) from the Dalmatian islands in Croatia. Higher levels of h(R), estimated using 1184 STR/indel markers, were found in the outbred group (P < 0.0001) and were associated with lower blood pressure (BP) and total/LDL cholesterol (P = 0.01 and 0.01, respectively) after controlling for other factors, with BP showing a strong sex effect (males P > 0.5 and females P = 0.002). These findings, if replicated, suggest that h(R) be considered as a genetic risk factor in genetic epidemiological studies on common disease traits. They are consistent with the well-known effects of heterosis (hybrid vigour) described when outcrossing animals and plants. Outbreeding resulting from urbanization and migration from traditional population subgroups may be leading to increasing h(R) and may have beneficial effects on a range of traits associated with human health and disease. Other traits, such as age at menarche, IQ and lifespan, which have been changing during the decades of urbanization, may also have been influenced by demographic factors.

Review of Croatian genetic heritage as revealed by mitochondrial DNA and Y chromosomal lineages.

The aim of this review is to summarize the existing data collected in high-resolution phylogenetic studies of mitochondrial DNA and Y chromosome variation in mainland and insular Croatian populations. Mitochondrial DNA polymorphisms were explored in 721 individuals by sequencing mtDNA HVS-1 region and screening a selection of 24 restriction fragment length polymorphisms (RFLPs), diagnostic for main Eurasian mtDNA haplogroups. Whereas Y chromosome variation was analyzed in 451 men by using 19 single nucleotide polymorphism (SNP)/indel and 8 short tandem repeat (STR) loci. The phylogeography of mtDNA and Y chromosome variants of Croatians can be adequately explained within typical European maternal and paternal genetic landscape, with the exception of mtDNA haplogroup F and Y-chromosomal haplogroup P* which indicate a connection to Asian populations. Similar to other European and Near Eastern populations, the most frequent mtDNA haplogroups in Croatians were H (41.1%), U5 (10.3%), and J (9.7%). The most frequent Y chromosomal haplogroups in Croatians, I-P37 (41.7%) and R1a-SRY1532 (25%), as well as the observed structuring of Y chromosomal variance reveal a clearly evident Slavic component in the paternal gene pool of contemporary Croatian men. Even though each population and groups of populations are well characterized by maternal and paternal haplogroup distribution, it is important to keep in mind that linking phylogeography of various haplogroups with known historic and prehistoric scenarios should be cautiously performed.

Genetic variation at nine short tandem repeat loci among islanders of the eastern Adriatic coast of Croatia.

We have analyzed the extent of genetic variation at nine autosomal short tandem repeat loci (D3S1358, VWA, FGA, TH01, TPOX, CSF1PO, D5S818, D13S317, D7S820) among six populations from Croatia: five distributed in the islands of the eastern Adriatic coast and one from the mainland. The purpose is to investigate the usefulness of these loci in detecting regional genetic differentiation in the studied populations. Significant heterogeneity among the island and mainland populations is revealed in the distributions of allele frequencies; however, the absolute magnitude of the coefficient of gene differentiation is small but significant. The summary measures of genetic variation, namely, heterozygosity, number of alleles, and allele size variance, do not indicate reduced genetic variation in the island populations compared to the mainland population. In contrast to the two measures of genetic variation, allele size variance and within-locus heterozygosity, the imbalance index (beta) indicates evidence of recent expansion of population sizes in all islands and in the mainland. High mutation rates of the studied loci together with local drift effects are likely explanations for interisland genetic variation and the observed lack of reduced genetic diversity among the island populations.