In the current systematic review and meta-analysis that covered six case-control association studies, we found rs644242 in the PAX6 gene to have a suggestive association with both high and extreme myopia, whereas there was no association between SNPs rs667773, rs3026354, rs2071754, or rs3026393 and myopia. Interestingly, the ORs of rs644242 for extreme myopia (OR = 0.79 and 0.80 in the dominant and heterozygous models, respectively) were lower than for high myopia (OR = 0.87 and 0.85, respectively), indicating that the protective effect might be stronger for extreme myopia. Moreover, the allelic association was significant in extreme myopia (OR = 0.81; p = 0.01) but not in high myopia (OR = 0.90; p = 0.39), and the pooled OR for extreme myopia as compared with high myopia only was 0.93, adding evidence that the A allele of rs644242 is a stronger protective allele for extreme myopia. Because such a difference in ORs is small, a study on a much larger sample size, with more than 10,000 patients and 10,000 controls (assuming α = 0.05, power = 80%, and OR = 0.93 between extreme and high myopia), is needed to confirm the heterogeneity in the ORs. Moreover, to account for multiple testing, we adopted Bonferroni correction, which helps eliminate false-positive findings. After correction, the association of rs644242 with both high and extreme myopia could not withstand (p > 0.005). Therefore, further studies are warranted to consolidate the association between rs644242 and myopia.
Of note, family-based studies, which were not included in the meta-analysis, also showed an evident link between PAX6 and high myopia. In 2004, Hammond et al.35 first reported a significant linkage (with a maximum LOD of 6.1) of the PAX6 locus to refractive errors in a twins-based study, thus, PAX6 was suggested to be a susceptibility gene for myopia. Later, Hewitt et al.36 recruited four pedigrees known to have different mutations in the PAX6 gene and found them to be significantly associated with high myopia. Single-nucleotide polymorphisms rs3026390 and rs3026393 of PAX6 were also found to be associated with high myopia in the family-based study of Han et al.37 These familial studies, together with our meta-analysis of association studies, indicate that PAX6 is a susceptibility gene for high myopia and/or extreme myopia.
The PAX6 protein is a transcriptional factor that regulates the development of the eyeball. It is closely associated with developmental ocular disorders such as aniridia and foveal hyperplasia.32 In a case series of patients with PAX6 mutations, the patient carriers were not only associated with aniridia but also had other manifestations like high myopia.49 PAX6 plays a key role in oculogenesis. The dosage of PAX6 could influence the oculogenesis in mice.50 Insufficiency and overexpression of PAX6 can both influence embryonic eyeball development. Therefore, in mice, the extremely abnormal dosage of PAX6 could induce multiple ocular defects, such as microphthalmia and anophthalmia.50 However, because of the variances among different species, a human in embryonic stage suffering from overexpression or insufficiency of PAX6 has a high rate of stillbirth or a low survival rate after birth, resulting from multiple-organ defects.51 In animal studies, myopic models were related to an abnormal expression of PAX6 in the postnatal stage. Researchers found that the expression of PAX6 in the retina was elevated in hyperopic defocused baby monkeys,52 and the expression of PAX6 was reduced in chicken with form-deprivation myopia.53 In addition, chronic hyperinsulinemia was one pathogenesis of juvenile-onset myopia, and insulin was known to act as a strong stimulus of axial length in myopia chicken,54 whereas PAX6 could transactivate the insulin promoters; therefore, elevated insulin levels by overexpressed PAX6 might stimulate elongation of the eyeball.55 Despite all these findings in animal models, it should be noted that myopia is a complex disease resulting from the interaction of multiple genetic and environmental risk factors and usually develops after birth. PAX6 is only one of the associated genes for myopia, and as indicated in our study, the effect size of the PAX6 SNP in myopia is small. Therefore, the PAX6 gene may, if any, contribute to a small proportion of myopia pathogenesis. However, how the SNP rs644242 works to alter the function of PAX6 still needs further investigations.
For the other three SNPs in our meta-analysis, rs2071754, rs3026354, and rs3026393, none was associated with high myopia in respective original studies.39–41,44 Our analysis also confirmed a lack of significant association. In addition, there are a group of SNPs that have been studied and some of them showed a significant association with high myopia. For example, rs662702 was found to be associated with extreme myopia in the study of Liang et al.39 Also, Han et al.37 had detected associations between SNPs rs3026390 and rs3026393 and high myopia in a family-based study, with the haplotypes with the T allele of rs3026393 demonstrating an increased transmission. However, no replication data have been reported for these associations. Therefore, whether they are genuine myopia-associated SNPs have yet to be further investigated.
In the current meta-analysis, we adopted a standard and stringent strategy for study inclusion. The test for heterogeneity and potential biases should render our interpretation more solid. Moreover, our study revealed several limitations in the understanding of PAX6 in myopia genetics. First, the results were generated from a limited number of studies, resulting in borderline pooled p values. Therefore, the association of PAX6 with high and extreme myopia should be validated in more study cohorts. Nevertheless, although the family-based studies could not be included in the meta-analysis, their findings did provide supportive evidence for a link between PAX6 and myopia.35,37,42 Second, a high heterogeneity in some models was detected, which was likely caused by various definitions of the control group and from the innate differences in minor allele frequencies across study populations. In this situation, our interpretation of the findings has been strengthened by the use of the random-effects model, yielding more conservative ORs. Third, the existing studies were mainly based on cohorts of Asians. It may restrict our conclusions within the Asian population and indicates the need for studies in other ethnic populations.
In conclusion, this systematic review and meta-analysis suggested an association of the PAX6 SNP rs644242 with extreme and high myopia. However, the association could not withstand Bonferroni correction and the effect size of PAX6 is small. Therefore, in view of the fact that myopia is a polygenic disease, PAX6 may, if any, confer a small effect on myopia development.
1. Pan CW, Ramamurthy D, Saw SM. Worldwide prevalence and risk factors for myopia. Ophthalmic Physiol Opt 2012; 32: 3–16.
2. Vitale S, Ellwein L, Cotch MF, Ferris FL 3rd, Sperduto R. Prevalence of refractive error in the United States, 1999-2004. Arch Ophthalmol 2008; 126: 1111–9.
3. Pan CW, Zheng YF, Anuar AR, Chew M, Gazzard G, Aung T, Cheng CY, Wong TY, Saw SM. Prevalence of refractive errors in a multiethnic Asian population: the Singapore epidemiology of eye disease study. Invest Ophthalmol Vis Sci 2013; 54: 2590–8.
4. Quek TP, Chua CG, Chong CS, Chong JH, Hey HW, Lee J, Lim YF, Saw SM. Prevalence of refractive errors in teenage high school students in Singapore. Ophthalmic Physiol Opt 2004; 24: 47–55.
5. Sun J, Zhou J, Zhao P, Lian J, Zhu H, Zhou Y, Sun Y, Wang Y, Zhao L, Wei Y, Wang L, Cun B, Ge S, Fan X. High prevalence of myopia and high myopia in 5060 Chinese university students in Shanghai. Invest Ophthalmol Vis Sci 2012; 53: 7504–9.
6. Coppe AM, Ripandelli G, Parisi V, Varano M, Stirpe M. Prevalence of asymptomatic macular holes in highly myopic eyes. Ophthalmology 2005; 112: 2103–9.
7. Hornbeak DM, Young TL. Myopia genetics: a review of current research and emerging trends. Curr Opin Ophthalmol 2009; 20: 356–62.
8. Saw SM, Gazzard G, Shih-Yen EC, Chua WH. Myopia and associated pathological complications. Ophthalmic Physiol Opt 2005; 25: 381–91.
9. Marcus MW, de Vries MM, Junoy Montolio FG, Jansonius NM. Myopia as a risk factor for open-angle glaucoma: a systematic review and meta-analysis. Ophthalmology 2011; 118: 1989–94 e2.
10. Ip JM, Rose KA, Morgan IG, Burlutsky G, Mitchell P. Myopia and the urban environment: findings in a sample of 12-year-old Australian school children. Invest Ophthalmol Vis Sci 2008; 49: 3858–63.
11. Rose KA, Morgan IG, Ip J, Kifley A, Huynh S, Smith W, Mitchell P. Outdoor activity reduces the prevalence of myopia in children. Ophthalmology 2008; 115: 1279–85.
12. Saw SM, Chua WH, Hong CY, Wu HM, Chan WY, Chia KS, Stone RA, Tan D. Nearwork in early-onset myopia. Invest Ophthalmol Vis Sci 2002; 43: 332–9.
13. Farbrother JE, Kirov G, Owen MJ, Guggenheim JA. Family aggregation of high myopia: estimation of the sibling recurrence risk ratio. Invest Ophthalmol Vis Sci 2004; 45: 2873–8.
14. Liang CL, Yen E, Su JY, Liu C, Chang TY, Park N, Wu MJ, Lee S, Flynn JT, Juo SH. Impact of family history of high myopia on level and onset of myopia. Invest Ophthalmol Vis Sci 2004; 45: 3446–52.
15. Zejmo M, Forminska-Kapuscik M, Pieczara E, Filipek E, Mrukwa-Kominek E, Samochowiec-Donocik E, Domanska O, Smuzynska M. Etiopathogenesis and management of high myopia. Part II. Med Sci Monit 2009; 15: RA252–5.
16. Jacobi FK, Pusch CM. A decade in search of myopia genes. Front Biosci (Landmark Ed) 2010; 15: 359–72.
17. Verhoeven VJ, Hysi PG, Wojciechowski R, Fan Q, Guggenheim JA, Hohn R, MacGregor S, Hewitt AW, Nag A, Cheng CY, Yonova-Doing E, Zhou X, et al. Genome-wide meta-analyses of multiancestry cohorts identify multiple new susceptibility loci for refractive error and myopia. Nat Genet 2013; 45: 314–8.
18. Paluru PC, Nallasamy S, Devoto M, Rappaport EF, Young TL. Identification of a novel locus on 2q for autosomal dominant high-grade myopia. Invest Ophthalmol Vis Sci 2005; 46: 2300–7.
19. Jacobi FK, Zrenner E, Broghammer M, Pusch CM. A genetic perspective on myopia. Cell Mol Life Sci 2005; 62: 800–8.
20. Ho DW, Yap MK, Ng PW, Fung WY, Yip SP. Association of high myopia with crystallin beta A4 (CRYBA4) gene polymorphisms in the linkage-identified MYP6 locus. PLoS One 2012; 7: e40238.
21. Hawthorne F, Feng S, Metlapally R, Li YJ, Tran-Viet KN, Guggenheim JA, Malecaze F, Calvas P, Rosenberg T, Mackey DA, Venturini C, Hysi PG, Hammond CJ, Young TL. Association mapping of the high-grade myopia MYP3 locus reveals novel candidates UHRF1BP1L, PTPRR, and PPFIA2. Invest Ophthalmol Vis Sci 2013; 54: 2076–86.
22. Gong B, Liu X, Zhang D, Wang P, Huang L, Lin Y, Lu F, Ma S, Cheng J, Chen R, Li X, Lin H, Zeng G, Zhu X, Hu J, Yang Z, Shi Y. Evaluation of MMP2 as a candidate gene for high myopia. Mol Vis 2013; 19: 121–7.
23. Nakanishi H, Yamada R, Gotoh N, Hayashi H, Yamashiro K, Shimada N, Ohno-Matsui K, Mochizuki M, Saito M, Iida T, Matsuo K, Tajima K, Yoshimura N, Matsuda F. A genome-wide association analysis identified a novel susceptible locus for pathological myopia at 11q24.1. PLoS Genet 2009; 5: e1000660.
24. Shi Y, Qu J, Zhang D, Zhao P, Zhang Q, Tam PO, Sun L, Zuo X, Zhou X, Xiao X, Hu J, Li Y, et al. Genetic variants at 13q12.12 are associated with high myopia in the Han Chinese population. Am J Hum Genet 2011; 88: 805–13.
25. Shi Y, Gong B, Chen L, Zuo X, Liu X, Tam PO, Zhou X, Zhao P, Lu F, Qu J, Sun L, Zhao F, et al. A genome-wide meta-analysis identifies two novel loci associated with high myopia in the Han Chinese population. Hum Mol Genet 2013; 22: 2325–33.
26. Fan Q, Wojciechowski R, Kamran Ikram M, Cheng CY, Chen P, Zhou X, Pan CW, Khor CC, Tai ES, Aung T, Wong TY, Teo YY, Saw SM. Education influences the association between genetic variants and refractive error: a meta-analysis of five Singapore studies. Hum Mol Genet 2014; 23: 546–54.
27. Fan Q, Zhou X, Khor CC, Cheng CY, Goh LK, Sim X, Tay WT, Li YJ, Ong RT, Suo C, Cornes B, Ikram MK, et al. Genome-wide meta-analysis of five Asian cohorts identifies PDGFRA as a susceptibility locus for corneal astigmatism. PLoS Genet 2011; 7: e1002402.
28. Khor CC, Miyake M, Chen LJ, Shi Y, Barathi VA, Qiao F, Nakata I, Yamashiro K, Zhou X, Tam PO, Cheng CY, Tai ES, et al. Genome-wide association study identifies ZFHX1B as a susceptibility locus for severe myopia. Hum Mol Genet 2013; 22: 5288–94.
29. Kiefer AK, Tung JY, Do CB, Hinds DA, Mountain JL, Francke U, Eriksson N. Genome-wide analysis points to roles for extracellular matrix remodeling, the visual cycle, and neuronal development in myopia. PLoS Genet 2013; 9: e1003299.
30. Stambolian D, Wojciechowski R, Oexle K, Pirastu M, Li X, Raffe LJ, Cotch MF, Chew EY, Klein B, Klein R, Wong TY, Simpson CL, et al. Meta-analysis of genome-wide association studies in five cohorts reveals common variants in RBFOX1, a regulator of tissue-specific splicing, associated with refractive error. Hum Mol Genet 2013; 22: 2754–64.
31. Shi Y, Li Y, Zhang D, Zhang H, Li Y, Lu F, Liu X, He F, Gong B, Cai L, Li R, Liao S, et al. Exome sequencing identifies ZNF644 mutations in high myopia. PLoS Genet 2011; 7: e1002084.
32. Simpson TI, Price DJ. Pax6; a pleiotropic player in development. Bioessays 2002; 24: 1041–51.
33. Zhang X, Friedman A, Heaney S, Purcell P, Maas RL. Meis homeoproteins directly regulate Pax6 during vertebrate lens morphogenesis. Genes Dev 2002; 16: 2097–107.
34. Tsonis PA, Fuentes EJ. Focus on molecules: Pax-6, the eye master. Exp Eye Res 2006; 83: 233–4.
35. Hammond CJ, Andrew T, Mak YT, Spector TD. A susceptibility locus for myopia in the normal population is linked to the PAX6
gene region on chromosome 11: a genomewide scan of dizygotic twins. Am J Hum Genet 2004; 75: 294–304.
36. Hewitt AW, Kearns LS, Jamieson RV, Williamson KA, van Heyningen V, Mackey DA. PAX6 mutations may be associated with high myopia. Ophthalmic Genet 2007; 28: 179–82.
37. Han W, Leung KH, Fung WY, Mak JY, Li YM, Yap MK, Yip SP. Association of PAX6 polymorphisms with high myopia in Han Chinese nuclear families. Invest Ophthalmol Vis Sci 2009; 50: 47–56.
38. Ng TK, Lam CY, Lam DS, Chiang SW, Tam PO, Wang DY, Fan BJ, Yam GH, Fan DS, Pang CP. AC and AG dinucleotide repeats in the PAX6 P1 promoter are associated with high myopia. Mol Vis 2009; 15: 2239–48.
39. Liang CL, Hsi E, Chen KC, Pan YR, Wang YS, Juo SH. A functional polymorphism at 3’UTR of the PAX6
gene may confer risk for extreme myopia in the Chinese. Invest Ophthalmol Vis Sci 2011; 52: 3500–5.
40. Jiang B, Yap MK, Leung KH, Ng PW, Fung WY, Lam WW, Gu YS, Yip SP. PAX6 haplotypes are associated with high myopia in Han chinese. PLoS One 2011; 6: e19587.
41. Miyake M, Yamashiro K, Nakanishi H, Nakata I, Akagi-Kurashige Y, Tsujikawa A, Moriyama M, Ohno-Matsui K, Mochizuki M, Yamada R, Matsuda F, Yoshimura N. Association of paired box 6 with high myopia in Japanese. Mol Vis 2012; 18: 2726–35.
42. Mutti DO, Cooper ME, O’Brien S, Jones LA, Marazita ML, Murray JC, Zadnik K. Candidate gene and locus analysis of myopia. Mol Vis 2007; 13: 1012–9.
43. Simpson CL, Hysi P, Bhattacharya SS, Hammond CJ, Webster A, Peckham CS, Sham PC, Rahi JS. The roles of PAX6 and SOX2 in myopia: lessons from the 1958 British Birth Cohort. Invest Ophthalmol Vis Sci 2007; 48: 4421–5.
44. Tsai YY, Chiang CC, Lin HJ, Lin JM, Wan L, Tsai FJ. A PAX6
gene polymorphism is associated with genetic predisposition to extreme myopia. Eye (Lond) 2008; 22: 576–81.
45. Dai L, Li Y, Du CY, Gong LM, Han CC, Li XG, Fan P, Fu SB. Ten SNPs of PAX6, Lumican, and MYOC genes are not associated with high myopia in Han Chinese. Ophthalmic Genet 2012; 33: 171–8.
46. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials 1986; 7: 177–88.
47. Harbord RM, Egger M, Sterne JA. A modified test for small-study effects in meta-analyses of controlled trials with binary endpoints. Stat Med 2006; 25: 3443–57.
48. Boehringer S, Epplen JT, Krawczak M. Genetic association studies of bronchial asthma–a need for Bonferroni correction? Hum Genet 2000; 107: 197.
49. Bredrup C, Knappskog PM, Rodahl E, Boman H. Clinical manifestation of a novel PAX6 mutation Arg128Pro. Arch Ophthalmol 2008; 126: 428–30.
50. Schedl A, Ross A, Lee M, Engelkamp D, Rashbass P, van Heyningen V, Hastie ND. Influence of PAX6
gene dosage on development: overexpression causes severe eye abnormalities. Cell 1996; 86: 71–82.
51. Glaser T, Jepeal L, Edwards JG, Young SR, Favor J, Maas RL. PAX6
gene dosage effect in a family with congenital cataracts, aniridia, anophthalmia and central nervous system defects. Nat Genet 1994; 7: 463–71.
52. Zhong XW, Ge J, Deng WG, Chen XL, Huang J. Expression of pax-6 in rhesus monkey of optical defocus induced myopia and form deprivation myopia. Chin Med J (Engl) 2004; 117: 722–6.
53. Bhat SP, Rayner SA, Chau SC, Ariyasu RG. Pax-6 expression in posthatch chick retina during and recovery from form-deprivation myopia. Dev Neurosci 2004; 26: 328–35.
54. Cordain L, Eaton SB, Brand Miller J, Lindeberg S, Jensen C. An evolutionary analysis of the aetiology and pathogenesis of juvenile-onset myopia. Acta Ophthalmol Scand 2002; 80: 125–35.
55. Sander M, Neubuser A, Kalamaras J, Ee HC, Martin GR, German MS. Genetic analysis reveals that PAX6 is required for normal transcription of pancreatic hormone genes and islet development. Genes Dev 1997; 11: 1662–73.
56. Chen KC, Hsi E, Hu CY, Chou WW, Liang CL, Juo SH. MicroRNA-328 may influence myopia development by mediating the PAX6
gene. Invest Ophthalmol Vis Sci 2012; 53: 2732–9.
57. Callaerts P, Halder G, Gehring WJ. PAX-6 in development and evolution. Annu Rev Neurosci 1997; 20: 483–532.
58. Zayats T, Guggenheim JA, Hammond CJ, Young TL. Comment on: A PAX6
gene polymorphism is associated with genetic predisposition to extreme myopia. Eye 2008; 22: 598–9.