ESHG 2010 abstracts

Some excerpts from this year's European Society of Human Genetics meeting:

P10.31 - Pigmentation gene MC1R shows strong genetic patterning in Eurasia

We present a comprehensive analysis of allele/haplotype frequencies from five functional SNPs (rs1805005, rs2228479, rs1805007, rs1805008, and rs885479) in MC1R throughout Eurasia, including from 12,151 individuals from 141 regional populations, focussing on novel genotype data from 38 Central Asian populations.

P10.39 - Genetic variation in Bulgarians: a mitochondrial DNA perspective

The structure and diversity of the Bulgarian mitochondrial DNA (mtDNA) gene pool is still almost unknown. In the present study, we have evaluated the extent and nature of mtDNA variation in the largest Bulgarian sample to date, comprising 855 healthy unrelated subjects from across the country.

P10.41 - Mitochondrial genome diversity in Ulchi, the tungusic-speaking tribe of the Russian Far East

The present report is based on the study of mtDNA variation in Ulchi (n=74), a Tungusic-speaking tribe of hunters and fishermen dispersed along the lakes and reaches of the Lower Amur. MtDNA analysis revealed 39 distinct mtDNA haplotypes belonging to 21 Eurasian haplogroups C2-C3, D3-D8, D11, G1-G2, M7-M9, Z, B, F, N9, Y and U4, with overall N macrohaplogroup derivatives frequency 53%, M - 43%, and R - 4%.

P10.62 - Genetic structure of Western Caucasus populations on the base of uniparental polymorphisms

We have analyzed 52 markers in coding region of the mtDNA and 48 markers in the non-recombining part of the Y-chromosome in 592 individuals representing five populations from western Caucasus (Abkhazians, Adyghes, Abazins, Georgians, and Circassians). Y-chromosome haplogroups G-M201 and J2 (J-M172) account for more than 50% of all haplogroup diversity in the studied populations. Haplogroup G-M201 in the Western Caucasus populations is represented only by subclade G2a (G-P15) with the insignificantly low exception in the Adyghe population where G1a (G-P20) amounts to less than 1%. In contrast to high frequency of J2 haplogroup J1 exhibit moderate occurrence and vary from 2 to 6 %. Haplogroup R1a (R-SRY10831.2) is also present in all studied populations.

Light-pigmented Caucasoids from prehistoric Siberia

This sample was previously tested for Y-chromosome and mtDNA polymorphisms.

The pigmentation-related loci tested can be seen in the labels of my post, which should lead you to some earlier studies on them.

Most individuals were found to be most similar to European than to East Asian or African individuals based on these loci, although some (2 from Andronovo) of them were more similar to East Asians or intermediate (1 from Tagar) between East Asians and Europeans.

Interestingly, 1 of the Andronovo Mongoloids (S07) was previously found to belong to Y chromosome haplogroup C(xC3), while the Caucasoid-Mongoloid individual from Tagar (S32) belonged to haplogroup R1a1.

It should be noted that the use of the term "European individual ancestry" does not mean that these individuals were from Europe, as no test to distinguish between European and Asian Caucasoids was performed, and we know from literary descriptions and occasional archaeological remains about the ancient presence of light-pigmented Caucasoids in Siberia.

From the paper:

The genotype for rs12913832 was obtained for 23 out of the 25 samples, and most had the G/G genotype (n=15), which indicates that at least 60% of ancient specimens were probably blue- or green-eyed individuals. The remaining samples had the A/G (n=5) or A/A (n=3) genotypes, which are predictive of brown eye color phenotype.

International Journal of Legal Medicine doi:10.1007/s00414-009-0348-5

Pigment phenotype and biogeographical ancestry from ancient skeletal remains: inferences from multiplexed autosomal SNP analysis

Caroline Bouakaze et al.

Abstract

In the present study, a multiplexed genotyping assay for ten single nucleotide polymorphisms (SNPs) located within six pigmentation candidate genes was developed on modern biological samples and applied to DNA retrieved from 25 archeological human remains from southern central Siberia dating from the Bronze and Iron Ages. SNP genotyping was successful for the majority of ancient samples and revealed that most probably had typical European pigment features, i.e., blue or green eye color, light hair color and skin type, and were likely of European individual ancestry. To our knowledge, this study reports for the first time the multiplexed typing of autosomal SNPs on aged and degraded DNA. By providing valuable information on pigment traits of an individual and allowing individual biogeographical ancestry estimation, autosomal SNP typing can improve ancient DNA studies and aid human identification in some forensic casework situations when used to complement conventional molecular markers.

Link

Interaction between loci affecting human pigmentation in Poland

Annals of Human Genetics doi:10.1111/j.1469-1809.2009.00504.x

Interactions Between HERC2, OCA2 and MC1R May Influence Human Pigmentation Phenotype

Wojciech Branicki et al.

Abstract

Human pigmentation is a polygenic trait which may be shaped by different kinds of gene–gene interactions. Recent studies have revealed that interactive effects between HERC2 and OCA2 may be responsible for blue eye colour determination in humans. Here we performed a population association study, examining important polymorphisms within the HERC2 and OCA2 genes. Furthermore, pooling these results with genotyping data for MC1R, ASIP and SLC45A2 obtained for the same population sample we also analysed potential genetic interactions affecting variation in eye, hair and skin colour. Our results confirmed the association of HERC2 rs12913832 with eye colour and showed that this SNP is also significantly associated with skin and hair colouration. It is also concluded that OCA2 rs1800407 is independently associated with eye colour. Finally, using various approaches we were able to show that there is an interaction between MC1R and HERC2 in determination of skin and hair colour in the studied population sample.

Link

More ASHG 2008 abstracts

The previous batch is here.

Analysis of East Asia Genetic Substructure: Population Differentiation and PCA Clusters Correlate with Geographic Distribution

Accounting for genetic substructure within European populations has been important in reducing type 1 errors in genetic studies of complex disease. As efforts to understand complex genetic disease are expanded to other continental populations an understanding of genetic substructure within these continents will be useful in design and execution of association tests. In this study, population differentiation(Fst) and Principal Components Analyses(PCA) are examined using >200K genotypes from multiple populations of East Asian ancestry(total 298 subjects). The population groups included those from the Human Genome Diversity Panel[Cambodian(CAMB), Yi, Daur, Mongolian(MGL), Lahu, Dai, Hezhen, Miaozu, Naxi, Oroqen, She, Tu, Tujia, Naxi, and Xibo], HapMap(CHB and JPT), and East Asian or East Asian American subjects of Vietnamese(VIET), Korean(KOR), Filipino(FIL) and Chinese ancestry. Paired Fst(Wei and Cockerham) showed close relationships between CHB and several large East Asian population groups(CHB/KOR, 0.0019; CHB/JPT, 00651; CHB/VIET, 0.0065) with larger separation with FIL(CHB/FIL, 0.014). Low levels of differentiation were also observed between DAI and VIET(0.0045) and between VIET and CAMB(0.0062). Similarly, small Fsts were observed among different presumed Han Chinese populations originating in different regions of mainland of China and Taiwan. For example, the four For PCA, the first two PCs showed a pattern of relationships that closely followed the geographic distribution of the different East Asian populations.corner groups were JPT, FIL, CAMB and MGL with the CHB forming the center group, and KOR was between CHB and JPT. Other small ethnic groups were also in rough geographic correlation with their putative origins. These studies have also enabled the selection of a subset of East Asian substructure ancestry informative markers(EASTASAIMS) that may be useful for future genetic association studies in reducing type 1 errors and in identifying homogeneous groups.

Worldwide Population Structure using SNP Microarray Genotyping

We genotyped 348 individuals sampled from 24 populations world-wide using the Affymetrix 250k NspI microarray chip. For context, we added matching genotypes from 210 HapMap individuals for a total of 250,823 loci genotyped in 543 individuals from 28 populations. We included populations from India and Daghestan to provide detail between the genetic poles of Western Europe, East Asia, and sub-Sahara Africa. With so many markers, principal components analyses reveal genetic differentiation between almost all identified populations in our sample. Northern and southern European populations (FST = 0.004, p <0.01) are statistically distinguishable, as are upper and lower caste groups in India (FST = 0.005, p <0.01). All individuals are accurately classified into continental groups, and even between closely-related populations, genetic- and self-classifications conflict for only a minority of individuals (e.g. ~2% between upper and lower Indian castes; k-means clustering.) As expected, the HapMap CHB+JPT, CEU, and YRI samples are most similar to our east Asian, west European, and African samples, respectively. The HapMap CEU samples and our northern European ancestry samples were both collected from Utah. Although individual samples cannot be reliably classified into their collection of origin, the groups are statistically distinguishable despite their high similarity (FST = 0.0005, n.s.). Our Japanese group is also statistically distinguishable from the HapMap JPT group (FST = 0.006, p <0.01), and in this comparison, most samples can be correctly classified. With such large numbers of genotypes, significant differences can be found even between very similar population samplings. Our results provide guidelines for researchers in selecting suitable control populations for case-control studies.

Frequency distribution and selection in 4 pigmentation genes in Europe

Pigmentation is one of the more obvious forms of variation in humans, particularly in Europeans where one sees more within group variation in hair and eye pigmentation than in the rest of the world. We studied 4 genes (SLC24A5, SLC45A2, OCA2 and MC1R) that are believed to contribute to the pigment phenotypes in Europeans. SLC24A5 has a single functional variant that leads to lighter skin pigmentation. Data on 83 populations worldwide (including 55 from our lab) show the variant (at rs1426654) has almost reached fixation in Europe, Southwest Asia, and North Africa, has moderate to high frequencies (.2-.9) throughout Central Asia, and has frequencies of .1-.3 in East and South Africa. The variant is essentially absent elsewhere. SLC45A2 also has a single functional variant (at rs16891982) associated with light skin pigmentation in Europe. Data on 84 populations worldwide show the light skin allele is nearly fixed in Northern Europe but has lower frequencies in Southern Europe, the Middle East and Northern Africa. In Central Asia the frequency of the SLC45A2 variant declines more quickly than the SLC24A5 variant. It is absent in both East and South Africa. In OCA2 we typed 4 SNPs (rs4778138, rs4778241, rs7495174, rs12913832) with a haplotype associated with blue eyes in Europeans. This haplotype shows a Southeastern to Northwestern pattern in Europe with frequencies of .25 (.05 homozygous) in the Adygei to .85 (.75 homozygous) in the Danes. In MC1R we typed 5 SNPs (rs3212345, rs3212357, rs3212363, C_25958294_10, rs7191944) that cover the entire MC1R gene and found a predominantly European haplotype that ranges in frequency from .35 to .65 in Europe, reaching its highest levels in Southwest Asia and Northwestern Europe. Extended Haplotype Heterozygosity (EHH) and normalized Haplosimilarity (nHS) show evidence of selection at SLC24A5 in not only our European and Southwest Asian populations but also our East African populations. Neither SLC45A2 or OCA2 showed evidence of selection in either test. MC1R did not show evidence of selection for our European specific haplotype but we did see some evidence both upstream and downstream in our nHS test in Europe.

Using principal components analysis to identify candidate genes for natural selection.

Genetic markers that differentiate populations are excellent candidates for natural selection due to local adaptation, and may shed light into physiological pathways that underlie disorders with varying frequencies around the world. Principal Components Analysis (PCA) has emerged as a powerful tool for the characterization and analysis of the structure of genomewide datasets. In prior work, we described an algorithm that can be used to select small subsets of genetic markers (SNPs) that correlate well with population structure, as captured by PCA. Our method can be used to detect SNPs that differentiate individuals from different geographic regions, or even neighboring subpopulations. We set out to explore the nature and properties of the genes where population-differentiating SNPs reside, by analyzing the publicly available Human Genome Diversity Panel dataset (650,000 SNPs for 1,043 individuals, 51 populations). Applying our SNP selection algorithms, we chose small subsets of SNPs that almost perfectly reproduce worldwide population structure as identified by PCA. We determined SNP panels both for population differentiation within seven geographic regions, as well as around the globe. We then explored the hypothesis that the selected SNPs attained their current worldwide allele frequency patterns as a response to the pressure of natural selection. Comparing our lists to recently published reports, we found a significant overlap with other genomewide scans for selection, thus validating our hypothesis. For example, EDAR (involved in the development of hair follicles) harbors the most differentiating SNPs in our world-wide panels. SNPs located in genes that are involved in skin and eye pigmentation (OCA2, MYO5C, HERC1, HERC2) are also among the top population differentiating markers. In East Asia, SNPs residing at the ADH cluster appear among the most important SNPs for population structure, while, in Europe, the same is true for genes that are involved in immune response to pathogens (CR1, DUOX2, TLR, and HLA). Finally, a comprehensive gene ontology analysis is presented.

SLC24A5 in Greeks

Since two subjects were heterozygous for the Thr(111) allele, its overall frequency in Greeks is 99.4%, within the range of 98.7% and 100% reported for European Americans.

Exp Dermatol. 2008 Jul 7.

A study of a single variant allele (rs1426654) of the pigmentation-related gene SLC24A5 in Greek subjects.

Dimisianos G, Stefanaki I, Nicolaou V, Sypsa V, Antoniou C, Poulou M, Papadopoulos O, Gogas H, Kanavakis E, Nicolaidou E, Katsambas AD, Stratigos AJ.

Department of Medical Genetics, University of Athens, Agia Sophia Children's Hospital, Athens, Greece.

The SLC24A5 gene, the human orthologue of the zebrafish golden gene, has been shown to play a key role in human pigmentation. In this study, we investigate the prevalence of the variant allele rs1426654 in a selected sample of Greek subjects. Allele-specific polymerase chain reaction was performed in peripheral blood samples from 158 attendants of a dermatology outpatient service. The results were correlated with pigmentary traits and MC1R genotype. The vast majority of subjects (99%) were homozygous for the Thr(111) allele. Only two subjects from the control group (1.26%) were heterozygous for the alanine and threonine allele. Both of these Thr(111)/Ala(111) heterozygotes carried a single polymorphism of MC1R (one with the V92M variant and another with the V60L variant). Following reports of the rs1426654 polymorphism reaching fixation in the European population, our study of Greek subjects showed a prevalence of the Thr(111) allele, even among subjects with darker skin pigmentation or phototype.

Link

TPCN2 and ASIP and hair/skin color

Nature Genetics, Published online: 18 May 2008 | doi:10.1038/ng.160

Two newly identified genetic determinants of pigmentation in Europeans

Patrick Sulem et al.

We present results from a genome-wide association study for variants associated with human pigmentation characteristics among 5,130 Icelanders, with follow-up analyses in 2,116 Icelanders and 1,214 Dutch individuals. Two coding variants in TPCN2 are associated with hair color, and a variant at the ASIP locus shows strong association with skin sensitivity to sun, freckling and red hair, phenotypic characteristics similar to those affected by well-known mutations in MC1R.

Link

New alleles for hair and skin pigmentation

Gnxp points me to this new paper on hair and skin color pigmentation alleles.

PLoS Genet 4(5): e1000074. doi:10.1371/journal.pgen.1000074

A Genome-Wide Association Study Identifies Novel Alleles Associated with Hair Color and Skin Pigmentation

Jiali Han et al.

Abstract

We conducted a multi-stage genome-wide association study of natural hair color in more than 10,000 men and women of European ancestry from the United States and Australia. An initial analysis of 528,173 single nucleotide polymorphisms (SNPs) genotyped on 2,287 women identified IRF4 and SLC24A4 as loci highly associated with hair color, along with three other regions encompassing known pigmentation genes. We confirmed these associations in 7,028 individuals from three additional studies. Across these four studies, SLC24A4 rs12896399 and IRF4 rs12203592 showed strong associations with hair color, with p = 6.0×10⁻⁶² and p = 7.46×10⁻¹²⁷, respectively. The IRF4 SNP was also associated with skin color (p = 6.2×10⁻¹⁴), eye color (p = 6.1×10⁻¹³), and skin tanning response to sunlight (p = 3.9×10⁻⁸⁹). A multivariable analysis pooling data from the initial GWAS and an additional 1,440 individuals suggested that the association between rs12203592 and hair color was independent of rs1540771, a SNP between the IRF4 and EXOC2 genes previously found to be associated with hair color. After adjustment for rs12203592, the association between rs1540771 and hair color was not significant (p = 0.52). One variant in the MATP gene was associated with hair color. A variant in the HERC2 gene upstream of the OCA2 gene showed the strongest and independent association with hair color compared with other SNPs in this region, including three previously reported SNPs. The signals detected in a region around the MC1R gene were explained by MC1R red hair color alleles. Our results suggest that the IRF4 and SLC24A4 loci are associated with human hair color and skin pigmentation.

Link

Allele for light pigmentation has been positively selected in Europeans

A new paper shows that a polymorphism on the AIM1 locus which is associated with human pigmentation has been under strong positive selection in Europeans, reaching almost fixation in tested European populations (0.89 in South Africans and 0.96 in Germans), while being rare elsewhere. The derived allele is associated with lighter overall pigmentation. This contrasts to the situation with the MC1R locus in which the ancestral variant is maintained by selection in Negroids, but multiple unrelated mutations outside Africa have resulted in lighter-skinned phenotypes. Unlike the MC1R where relaxation of selection constraints were observed in non-Africans, the new AIM1 polymorphism has been positively selected.

The time of the common ancestor of alleles bearing the haplotype is estimated to be 10,965 years, although the 95% confidence interval is wide from 1,328 to 39,609 years. We should probably not speculate on what triggered the selection based on this very uncertain dating, but the repopulation of Europe after the last glaciation may be a candidate. As humans spread to higher latitudes, they may have been subjected to higher selective pressures for light pigmentation. It would be interesting to determine the frequency of the polymorphism in different Caucasoid populations and determine the most likely ancestral populations.


Molecular Biology and Evolution (published online)

Evidence for Recent Positive Selection at the Human AIM1 Locus in a European Population

Mikiko Soejima et al.

Abstract

Two missense polymorphisms (E272K and L374F) of the AIM1 locus, encoding a melanocyte differentiation antigen, were shown to have a clear association with human ethnicities. These two nonpathogenic SNPs may be associated with human pigmentation variation. In this study, we investigated sequence variation in the coding region and exon-flanking sequence and found low genetic variation only in subjects of European descent. All four statistical tests applied to the 7.55-kb region surrounding the L374F polymorphism detected statistically significant deviations from selective neutrality in Europeans. In addition, haplotype analysis revealed that one haplotype carrying 374F was overrepresented in this population, and the low rate of variation, with some features of selective sweeps, was shown to be statistically significant. These results suggest that positive selection recently has been acting or has acted on at least this region of the melanogenic gene and that an advantageous haplotype spread rapidly in Europe.

Link

ASIP gene and skin color

Human Genetics (Online First)

The 8818G allele of the agouti signaling protein (ASIP) gene is ancestral and is associated with darker skin color in African Americans

Carolina Bonilla et al.

Abstract Skin color, a predictor of social interactions and risk factor for several types of cancer, is due to two contrasting forms of melanin, the darker eumelanin and lighter phaeomelanin. The lighter pigment phaeomelanin is the product of the antagonistic function of the agouti signaling protein (ASIP) on the α-melanocyte stimulating hormone receptor (MC1R). Studies have shown that a single-nucleotide polymorphism (SNP) in the 3primeUTR of the ASIP gene is associated with dark hair and eyes; however, little is known about its role in inter-individual variation in skin color. Here we examine the relationship between the ASIP g.8818A>G SNP and skin color (M index) as assessed by reflectometry in 234 African Americans. Analyses of variance (ANOVA) were performed to evaluate the effects of ASIP genotypes, age, individual ancestry, and sex on skin color variation. Significant effects on M index variation were observed for ASIP genotypes (F(2,236)=4.37, P=0.01), ancestry (F(1,243)=37.2, P<0.001), p="0.05).">A polymorphism exhibits a dominant effect leading to lighter skin color and that variation in the ASIP gene may have been one of several factors contributing to reductions in pigmentation in some populations. Further study is needed to reveal how interactions between ASIP and several other genes, such as MC1R and P, predict human pigmentation.

Link