Dovepress Statistical analysis The sample size was estimated using Quanto software12 with type 1 error set at 0.05 and power set at 80%. The minor allele frequency applied for this estimation was based on the lowest frequency of the three investigated SNPs in Asians reported in the literature, which was the frequency of Y402H of 0.05.13 The prevalence of PCV was based on that of neovascular AMD in Thailand, 0.2%.14 PCV was estimated to be 23% of this prevalence15 or 0.05%. At least 85 participants were required in each study group using this estimation. The chi-square test was used for testing deviation of genotypic frequency from Hardy–Weinberg equilibrium. The Fisher’s exact test was used to test the allelic and genotypic associations of each SNP with PCV. Statistical significance was considered at P , 0.05. Logistic regression analysis was used to estimate the odds ratio of having PCV for participants with the homozygous risk genotype compared with those who had the heterozygous, and homozygous nonrisk genotypes. Bonferroni correction was used for assessing the P-values obtained from these analyses. For comparison with other Asian populations, data were compiled of association studies between the three SNPs and PCV in Asians published in the literature9,13,16–22 and calcu- lated the association, allele frequency, and genotype distribu- tion for each SNP using the same protocol. These compiled data gave sample sizes of 1291 PCVs and 2455 controls for Y402H, 713 PCVs and 1604 controls for I62V, and 747 PCVs and 1331 controls for A69S. Results A total of 97 patients with PCV and 102 normal controls were included for genetic analysis. No significant difference between these two groups was found for the demographic characteristics (Table 1). No significant deviation from the Hardy–Weinberg equilibrium was found for each SNP in either study group. The DNA sequencing results of all nine random blood samples confirmed the genotyping results of this study. Risk allele frequency In the cohorts used in this study, the frequency of the risk allele for each SNP, C, G, and T for Y402H, I62V, and A69S Table 1 Demographic characteristic of the study population PCV Controls P-value (n = 97) (n = 102) gender (male/female) 48/49 50/52 0.948a Mean age ± SD (years) 62.9 ± 8.9 62.2 ± 7.6 0.595b Age range (years) 42–87 50–86 Notes: aBy z-test; bby independent t-test. Abbreviations: PCV, polypoidal choroidal vasculopathy; SD, standard deviation. Clinical Ophthalmology 2012:6 CFH and ARMS2 and PCV respectively, were found to be similar to that in the compiled data. In addition, the frequency of the risk allele of each SNP was significantly higher in participants with PCV than in controls in both datasets (Table 2). Risk genotype Data in Table 3 show that the genotype distribution in this study’s Thai population was similar to that in the compiled Asian population. The only exception was found for the frequency of the homozygous risk genotype (CC) of Y402H in the PCV group, which was higher in the present study’s population (3.1%) than in the compiled Asian population (0.7%). These frequencies, however, were very low in both populations. Compared with having the homozygous nonrisk genotype (TT), having the heterozygous genotype Y402H (CT) signifi- cantly increased the chance (by approximately three times) of having PCV. Individuals with the homozygous risk allele of I62V (GG) and A69S (TT) were approximately 4–5 times as likely to have PCV as those with the homozygous nonrisk allele (Table 4). Discussion This study showed that both Y402H and I62V polymorphisms in the CFH and the A69S in the ARMS2 genes were strongly associated with PCV in the Thai population. The confirmed genotyping results by DNA sequencing of all nine random blood samples suggested that the dataset was homogenous and unbiased. The strong association of the three SNPs was also observed in the compiled data of previously published studies in other Asian populations. The I62V of CFH gene, rather than the Y402H, was initially believed to be the SNP associated with PCV in the Asian population.13,20 The results of this present study, in a Thai population, as well as those in the compiled data indicated that both I62V and Y402H SNPs were associated with PCV in Asians. This discordance might be due to the low frequency of Y402H in Asians compared with the higher frequency of I62V. There is no report on the association between I62V and PCV or AMD in Caucasians. Interestingly, the frequency of the risk alleles of the Y402H and A69S in Asian patients with PCV may be different from that in Caucasian patients with PCV. The frequencies of the risk allele C of the Y402H in PCVs, 15.0% in the present study and 10.3% in the compiled data, were much lower than that in a cohort of subjects with PCV of European descent in the United States, which was 49.1%.10 This is also true for the risk allele T of the A69S. These allele frequencies in submit your manuscript | www.dovepress.com Dovepress 467