McArdle disease: a novel mutation in Jewish families from the Caucasus region

McArdle disease is caused by a myophosphorylase deficiency consequent to defects in the PYGM gene. A minority of the over-133 known mutations are associated with ethnicity, occurring mainly in patients from western Europe, the United States, and Japan. We identified a novel mutation, c.632delG, in three unrelated families of Jewish descent originating from the Caucasus region. This possibly ethnicity-associated mutation can significantly facilitate the diagnosis in Jews of the Caucasus and contribute to genetic consultations.

[The Dagestan gene pool: polymorphism of immunogenetic and biochemical markers in Kumyks]

This study is a part of long-term investigations devoted to the analysis of the gene pool of Dagestan ethnic groups. The phenotype (in %), gene, and haplotype frequencies in Kumyk ethnic group are reported. A total of 39 alleles and six haplotypes of 14 loci (AB0, Rhesus, P, Levis, Kell, HP, GC, C'3, TF, 6PGD, GLO1, ESD, ACP, and PGM1) of immunobiochemical genetic marker systems were examined. Rare haplotypes of the Rhesus system were identified, including CDE in the Karabudakhkent population with the frequency of 0.030, and Cde and cdE in the Dorgeli population with the frequencies of 0.034 and 0.38, respectively. Similarly to the other ethnic populations of Dagestan examined, Kukyk populations carried rare, albeit typically "Caucasoid" gene ACP1(c) of the AcP1 locus. The frequency of this allele in the two populations was similar, constituting 0.031 for Karabudakhkent and 0.032 for Dorgeli. In Kumyks, allele frequencies of the AB0, Rhesus, P, Lewis, Kell, HP, GC, C'3, TF, 6PGD, GLO1, ESD, ACP, but not PGM1, systems were similar to the mean allele frequencies at these loci observed in the other ethnic groups from the Dagestan, Caucasus, and the whole European historical ethnographic province. At the same time, the allele frequency values obtained were different from those for the populations of Kazakhstan, Central Asia, Siberia, and the Ruswsian Far East. Thus, the results obtained for classical genetic markers indicate that Kumyks are genetically closer to the indigenous populations of Dagestan than to Turkic-speaking populations. Analysis of the fit of the observed phenotype frequencies to the Hardy-Weinberg expectations showed that compared to other indigenous populations of Dagestan examined, in Kumyks the genetic state of the population upon random allele association was close to equilibrium. Probably, this state was determined by practical absence of the consanguineous marriages upon preservation of intra-aul endogamy.

[The Dagestan gene pool: analysis of the frequencies of classical genetic markers in Avars]

This study is part of long-term research in the gene pool of Dagestan ethnic groups. The phenotype (in percent), gene, and haplotype frequencies in three Avar populations are reported. A total of 37 alleles of 13 loci of immune and biochemical genetic marker systems (ABO, Rhesus, P, Lewis, HP, GC, C'3, TF, 6PGD, GLO1, ESD, ACP, and PGM1) have been studied. Rare haplotypes of the Rhesus system (CDE, Cde, and cdE) have been found in the populations studied. In two out of three local populations (Khunzakh and Kharakhi), a typically "Caucasoid" rare gene ACP1c of the AcP1 locus has proved to be relatively frequent (0.030 and 0.023, respectively). The frequencies of the allele variants P2, le, and Hp1 of loci of the P, Lewis, and HP systems, respectively, have been found to be lower than in other Caucasian ethnic groups and the total northern Eurasian population. The mean allele frequencies for the GC, C'3, TF, 6PGD, GLO1, and ESD systems in the populations studied are comparable wit those for both Caucasian ethnic groups and the total population of the European historical ethnographic province. Statistical analysis of the results has shown 11 cases of significant deviations of the observed phenotype frequencies from the Hardy-Weinberg equilibrium.

[The dagestan gene pool: the genetic structure of the nine largest ethnic groups: analysis based on data on the ABO and Rhesus blood groups]

Detailed analysis of the population structure of Dagestan ethnic groups based on data on the ABO and Rhesus blood groups has been carried out. A total of 32101 representatives of the nine largest ethnic groups of Dagestan (from 682 auls in 46 raions) have been examined. This allows a comprehensive genetic landscape of the Dagestan population to be drawn. Comparison of the ethnic groups studied with other Caucasian ethnic groups makes it possible to determine the position of the Dagestan gene pool in the total structure of the Caucasian gene pool.

Culture creates genetic structure in the Caucasus: autosomal, mitochondrial, and Y-chromosomal variation in Daghestan

BACKGROUND

Near the junction of three major continents, the Caucasus region has been an important thoroughfare for human migration. While the Caucasus Mountains have diverted human traffic to the few lowland regions that provide a gateway from north to south between the Caspian and Black Seas, highland populations have been isolated by their remote geographic location and their practice of patrilocal endogamy. We investigate how these cultural and historical differences between highland and lowland populations have affected patterns of genetic diversity. We test 1) whether the highland practice of patrilocal endogamy has generated sex-specific population relationships, and 2) whether the history of migration and military conquest associated with the lowland populations has left Central Asian genes in the Caucasus, by comparing genetic diversity and pairwise population relationships between Daghestani populations and reference populations throughout Europe and Asia for autosomal, mitochondrial, and Y-chromosomal markers.

RESULTS

We found that the highland Daghestani populations had contrasting histories for the mitochondrial DNA and Y-chromosome data sets. Y-chromosomal haplogroup diversity was reduced among highland Daghestani populations when compared to other populations and to highland Daghestani mitochondrial DNA haplogroup diversity. Lowland Daghestani populations showed Turkish and Central Asian affinities for both mitochondrial and Y-chromosomal data sets. Autosomal population histories are strongly correlated to the pattern observed for the mitochondrial DNA data set, while the correlation between the mitochondrial DNA and Y-chromosome distance matrices was weak and not significant.

CONCLUSION

The reduced Y-chromosomal diversity exhibited by highland Daghestani populations is consistent with genetic drift caused by patrilocal endogamy. Mitochondrial and Y-chromosomal phylogeographic comparisons indicate a common Near Eastern origin of highland populations. Lowland Daghestani populations show varying influence from Near Eastern and Central Asian populations.

Genetic structure of Dagestan populations: a study of 11 Alu insertion polymorphisms

We examined genetic variation in nine populations of Dagestan using 11 autosomal Alu insertion polymorphisms to investigate the genetic structure of indigenous groups and to assess their genetic relationship with world populations. Genetic differentiation among mountain inhabitants (Gsr = 2%) is comparable to that for European populations. Traces of genetic drift are detectable only for endogamous and small Ando-Dido-speaking ethnic groups, and they coincide with the most linguistically diverse region of Dagestan. Multidimensional scaling analyses among West Eurasian populations revealed that mountain inhabitants of Dagestan are closely related to Anatolian and Cyprus Turks. Thus our frequency data are consistent with the available Y-chromosome data, according to which the Middle East and the Caucasus share a considerable portion of the gene pool. Overall, our results corroborate the initially suggested genetic contribution of Middle Eastern populations to Caucasus populations.

Ethnogenomic diversity of Caucasus, Daghestan

Autosomal short-tandem repeats (STRs) were typed in ethnic populations of Kubachians, Dargins, Avars, Lezgins, Kumiks, and Nogais of the Caucasus (Daghestan, Russia) at the University of Utah. Daghestan ethnic populations demonstrated differences in STR allele frequency distributions, but these differences were much lower among these ethnic groups compared to worldwide ethnic groups. The observed genetic diversity was low while F(ST) values were high, both of which provided supporting evidence for small population sizes and high levels of isolation among the ethnic groups. An analysis of genetic distance from the three major continents, encompassing Daghestan populations and groups, reveals three distinct clusters: all populations of African affiliation, European and Daghestan populations except the Nogais, and Asian populations with ethnic Nogais.

[Genetic subdivision of Dagestan ethnic populations]

Relationships between ethnic and genetic differentiation with respect to 54 microsatellites have been analyzed in five Daghestan ethnic groups. To detect the microsatellites, human chromosomes 3, 17, and 18 were screened with a step of 10 cM (Weber/CHLC 9.0 markers) at the Mammalian Genotyping Service (National Institute of Health, United States). Comparison of the polymorphism of these loci in Daghestan populations with average worldwide data has revealed generally low heterozygosity in Daghestan populations, which is accounted for by traditional endogamous and consanguineous marriages throughout the history of these populations. The inbreeding coefficient in Daghestan ethnic groups varies from 0.005 to 0.0134 and is close to the worldwide maximum known to date. For some DNA loci, significant differences between the offsprings of consanguineous and exogamous marriages with respect to allele sizes and their variance have been found. The Daghestan ethnic populations studied differ from one another in both the frequencies of common alleles and the presence of rare alleles that are unique for each ethnic group of Daghestan and have not been found in any other population in the world.

[Mapping genes of complex diseases in genetic isolates of Dagestan]

Original results of the analysis of genetic linkage between some genomic markers and two complex clinical phenotypes, schizophrenia and mental retardation, in pedigrees from Dagestan genetic isolates are described. Interpopulation differences in the epidemiology of the complex phenotypes were studied and in their genetic linkage was demonstrated. These differences are evidently related to the genetic structure of the isolates determined by their genetic history. The MR epidemiological index characterizing the lifetime morbid risk of schizophrenia varies in the Dagestan isolates studied from 0 to 4.95%, which is almost five times higher than the average worldwide population rate, 1%. Comparative genetic mapping permitted determination of the most probable genetic linkages and associations of loci from chromosomal regions 17p11.1-12, 3q13.3, and a locus from 22q with schizophrenia and locus 12q23 with mental retardation. There is evidence that this approach is effective for detailed study of the relationship between the genetic (allele and locus) and clinical heterogeneity of complex diseases, which favors successful identification of the genes determining them. The study of linkage disequilibrium (LD) in genetic isolates of Daghestan populations (which have a common genetic background) may be an effective methodological approach for revealing the numerous contradictory results of mapping of the same genes of complex disease performed by different researchers in different regions of the world.

[Mitochondrial DNA variation in Russian populations of Stavropol krai, Orel and Saratov oblasts]

Mitochondrial DNA (mtDNA) polymorphism was examined in three Russian populations from the European part of Russia (Stavropol krai, Orel oblast, and Saratov oblast). This analysis showed that mitochondrial gene pool of Russians was represented by the mtDNA types belonging to haplogroups H, V, HV*, J, T, U, K, I, W, and X. A mongoloid admixture (1.5%) was revealed in the form of mtDNA types of macrohaplogroup M. Comparative analysis of the mtDNA haplogroup frequency distribution patterns in six Russian populations from the European part of Russia indicated the absence of substantial genetic differences between them. However, in Russian populations from the southern and central regions the frequency of haplogroup V (average frequency 8%) was higher than in the populations from more northern regions. Based on the data on mtDNA HVS1 sequence variation, it was shown that the diversity of haplogroup V in Russians (h = 0.72) corresponded to the highest h values observed in Europe. The reasons for genetic differentiation of the Russian population (historical, ecological, and adaptive) are discussed.

Population-genetics approach to the genetics of human behaviour

Invariant values of inheritance factors within and between different populations can show the existence of and measure the degree of genetic determination of behavioural characters. The absence of inbred depression of quantitative behavioural characters in isolated populations of highland inhabitants of Daghestan is demonstrated by means of comparative analysis of the mean population values of psychophysiological characters in outbred, moderately isolated, and extremely isolated (and inbred) populations. The absence of pronounced adverse effects of inbred marriages, known as the 'Daghestan phenomenon', is explained by the antiquity of the native populations and the severe ecological conditions under which these populations live which have led to elimination of carriers of hereditary diseases and other detrimental phenotypes.