Copy number variations can be identified using newer genotyping arrays with higher single nucleotide polymorphisms (SNPs) density and copy number probes accompanied by newer algorithms. McCarroll et al. (2008) applied these to the HapMap II samples and identified 1316 copy number polymorphisms (CNPs). In our study, we applied the same approach to 859 samples from three Singapore populations and seven HapMap III populations. Approximately 50% of the 1291 autosomal CNPs were found to be polymorphic only in populations of non-African ancestry. Pairwise comparisons among the 10 populations showed substantial differences in the CNPs frequencies. Additionally, 698 CNPs showed significant differences with false discovery rate (FDR)<0.01 among the 10 populations and these loci overlap with known disease-associated or pharmacogenetic-related genes such as CFHR3 and CFHR1 (age related macular degeneration), GSTTI (metabolism of various carcinogenic compounds and cancers) and UGT2B17 (prostate cancer and graft-versus-host disease). The correlations between CNPs and genome-wide association studies-SNPs were investigated and several loci, which were previously unreported, that may potentially be implicated in complex diseases and traits were found; for example, childhood acute lymphoblastic leukaemia, age-related macular degeneration, breast cancer, response to antipsychotic treatment, rheumatoid arthritis and type-1 diabetes. Additionally, we also found 5014 novel copy number loci that have not been reported previously by McCarroll et al. (2008) in the 10 populations.
Recent genome-wide association studies (GWAS) have identified 38 obesity-associated loci among European populations. However, their contribution to obesity in other ethnicities is largely unknown.
Research on the role of copy number variations (CNVs) in the genetic risk of diseases in Asian populations has been hampered by a relative lack of reference CNV maps for Asian populations outside the East Asians. In this article, we report the population characteristics of CNVs in Chinese, Malay, and Asian Indian populations in Singapore. Using the Illumina Human 1M Beadchip array, we identify 1,174 CNV loci in these populations that corroborated with findings when the same samples were typed on the Affymetrix 6.0 platform. We identify 441 novel loci not previously reported in the Database of Genomic Variations (DGV). We observe a considerable number of loci that span all three populations and were previously unreported, as well as population-specific loci that are quite common in the respective populations. From this we observe the distribution of CNVs in the Asian Indian population to be considerably different from the Chinese and Malay populations. About half of the deletion loci and three-quarters of duplication loci overlap UCSC genes. Tens of loci show population differentiation and overlap with genes previously known to be associated with genetic risk of diseases. One of these loci is the CYP2A6 deletion, previously linked to reduced susceptibility to lung cancer.
We conducted a cross-sectional study of Malay participants aged 40-80 years (n = 2,932) to examine the associations between polymorphisms at newly identified, lipid-associated loci with blood lipid levels and prevalent cardiovascular disease (CVD) in a Malay population in Asia. A polymorphism adjacent to the TRIB1 locus (rs17321515) was associated with elevated total cholesterol and LDL-cholesterol (LDL-C) after adjustment for age and sex (both P values <0.007) and with increased risk of coronary heart disease and CVD [odds ratio (OR) 1.23, 95% confidence interval (95% CI) 1.03-1.46; and OR 1.2, 95% CI 1.02-1.42, respectively] under an additive model of inheritance. In addition, using recessive models of inheritance, polymorphisms on chromosome 19 adjacent to the CILP2 and PBX4 loci (rs16996148) and on chromosome 1 at the GALNT2 locus (rs4846914) were associated with elevated HDL-C (P = 0.005) and lower LDL-C (P = 0.048), respectively. Although novel, the former is consistent with the association between this polymorphism and lower blood triglycerides observed in the initial studies conducted in populations of European ancestry. Neither showed statistically significant association with CVD. These observations should form the basis of further investigation to identify the causative polymorphisms at this locus, and also to understand the mechanistic roles that this protein may play in lipoprotein metabolism in Asians and other populations.
The Singapore Genome Variation Project (SGVP) provides a publicly available resource of 1.6 million single nucleotide polymorphisms (SNPs) genotyped in 268 individuals from the Chinese, Malay, and Indian population groups in Southeast Asia. This online database catalogs information and summaries on genotype and phased haplotype data, including allele frequencies, assessment of linkage disequilibrium (LD), and recombination rates in a format similar to the International HapMap Project. Here, we introduce this resource and describe the analysis of human genomic variation upon agglomerating data from the HapMap and the Human Genome Diversity Project, providing useful insights into the population structure of the three major population groups in Asia. In addition, this resource also surveyed across the genome for variation in regional patterns of LD between the HapMap and SGVP populations, and for signatures of positive natural selection using two well-established metrics: iHS and XP-EHH. The raw and processed genetic data, together with all population genetic summaries, are publicly available for download and browsing through a web browser modeled with the Generic Genome Browser.
Central corneal thickness (CCT) is a risk factor of glaucoma, the most common cause of irreversible blindness worldwide. The identification of genetic determinants affecting CCT in the normal population will provide insights into the mechanisms underlying the association between CCT and glaucoma, as well as the pathogenesis of glaucoma itself. We conducted two genome-wide association studies for CCT in 5080 individuals drawn from two ethnic populations in Singapore (2538 Indian and 2542 Malays) and identified novel genetic loci significantly associated with CCT (COL8A2 rs96067, p(meta) = 5.40 × 10⁻¹³, interval of RXRA-COL5A1 rs1536478, p(meta) = 3.05 × 10⁻⁹). We confirmed the involvement of a previously reported gene for CCT and brittle cornea syndrome (ZNF469) [rs9938149 (p(meta) = 1.63 × 10⁻¹⁶) and rs12447690 (p(meta) = 1.92 × 10⁻¹⁴)]. Evidence of association exceeding the formal threshold for genome-wide significance was observed at rs7044529, an SNP located within COL5A1 when data from this study (n = 5080, P = 0.0012) were considered together with all published data (reflecting an additional 7349 individuals, p(Fisher) = 1.5 × 10⁻⁹). These findings implicate the involvement of collagen genes influencing CCT and thus, possibly the pathogenesis of glaucoma.
CONTEXT:
Novel type 2 diabetes mellitus (T2DM) susceptibility loci, identified through genome-wide association studies (GWAS), have been replicated in many European and Japanese populations. However, the association in other East Asian populations is less well characterized.
OBJECTIVE:
To examine the effects of SNPs in CDKAL1, CDKN2A/B, IGF2BP2, HHEX, SLC30A8, PKN2, LOC387761, and KCNQ1 on risk of T2DM in Chinese, Malays, and Asian-Indians in Singapore.
DESIGN:
We genotyped these candidate single-nucleotide polymorphisms (SNPs) in subjects from three major ethnic groups in Asia, namely, the Chinese (2196 controls and 1541 cases), Malays (2257 controls and 1076 cases), and Asian-Indians (364 controls and 246 cases). We also performed a metaanalysis of our results with published studies in East Asians.
RESULTS:
In Chinese, SNPs in CDKAL1 [odds ratio (OR) = 1.19; P = 2 x 10(-4)], HHEX (OR = 1.15; P = 0.013), and KCNQ1 (OR = 1.21; P = 3 x 10(-4)) were significantly associated with T2DM. Among Malays, SNPs in CDKN2A/B (OR = 1.22; P = 3.7 x 10(-4)), HHEX (OR = 1.12; P = 0.044), SLC30A8 (OR = 1.12; P = 0.037), and KCNQ1 (OR = 1.19-1.25; P = 0.003-2.5 x 10(-4)) showed significant association with T2DM. The combined analysis of the three ethnic groups revealed significant associations between SNPs in CDKAL1 (OR = 1.13; P = 3 x 10(-4)), CDKN2A/B (OR = 1.16; P = 9 x 10(-5)), HHEX (OR = 1.14; P = 6 x 10(-4)), and KCNQ1 (OR = 1.16-1.20; P = 3 x 10(-4) to 3 x 10(-6)) with T2DM. SLC30A8 (OR = 1.06; P = 0.039) showed association only after adjustment for gender and body mass index. Metaanalysis with data from other East Asian populations showed similar effect sizes to those observed in populations of European ancestry.
CONCLUSIONS:
SNPs at T2DM susceptibility loci identified through GWAS in populations of European ancestry show similar effects in Asian populations. Failure to detect these effects across different populations may be due to issues of power owing to limited sample size, lower minor allele frequency, or differences in genetic effect sizes.
Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. We conducted a genome-wide association study (GWAS) followed by replication in a combined total of 10,503 PACG cases and 29,567 controls drawn from 24 countries across Asia, Australia, Europe, North America, and South America. We observed significant evidence of disease association at five new genetic loci upon meta-analysis of all patient collections. These loci are at EPDR1 rs3816415 (odds ratio (OR) = 1.24, P = 5.94 × 10(-15)), CHAT rs1258267 (OR = 1.22, P = 2.85 × 10(-16)), GLIS3 rs736893 (OR = 1.18, P = 1.43 × 10(-14)), FERMT2 rs7494379 (OR = 1.14, P = 3.43 × 10(-11)), and DPM2-FAM102A rs3739821 (OR = 1.15, P = 8.32 × 10(-12)). We also confirmed significant association at three previously described loci (P < 5 × 10(-8) for each sentinel SNP at PLEKHA7, COL11A1, and PCMTD1-ST18), providing new insights into the biology of PACG.