Myopia is thought to be a complicated multigenic disease. Genetic research on myopia remains to be a huge challenge. Therefore, the research on how genetic polymorphisms affect myopia is useful for elucidating the connection between myopia and genetics. As mentioned above, some studies had explored the effect of FGF10 polymorphism on myopia but they did not reach a consensus. The inconsistent conclusions may due to the difference in study designs, ethnicity, source of control, age range, sex ratios and so on. It may be difficult for an individual study with a small sample size to determine whether a genetic variant causes high myopia, but meta-analysis, which pools all eligible data, can produce more comprehensive outcome.
Our Meta-analysis was based on the pooled ORs from 6 eligible case-control studies consisting of 4339 cases and 4652 controls. The findings indicated a significant correlation in the Chinese population between FGF10 rs339501 and myopia, high myopia, or extreme myopia though they did not show a correlation between this allele and myopia in the overall population. These significant results mainly fell on the recessive and homozygote models, and especially for the high myopia, of whom the pooled results in allelic and dominant models were also significant. Additionally, the allelic model for the association between SNP rs339501 and myopia was also significant. Therefore, according to these findings, the G allele of SNP rs339501 might enhance the risk of myopia in the Chinese population. Chinese and Japanese people are of Asian descent, and both live in east Asia areas that have similar natural growth environment, thus their genetic research outcomes should be similar in theory. While studies in The Japanese population have found that the A allele of SNP rs339501 would increase the risk of myopia which was in contrary to studies based on the Chinese population. In order to reach more representative and comprehensive conclusions, The subgroup analysis' outcomes should be interpreted with caution. Additionally, more large and well-designed trials using standardized unbiased methods and including other ethnic groups are expected to further clarify this association.
Heterogeneity may limit the interpretation of pooled estimates. We found that Yoshida’s study [18] is the main source of the heterogeneity. Even though, none of the individual studies had a significant effect on the pooled data while being excluded, which suggested the stability of our Meta-analysis. In subgroup analysis, only Yoshida’s study [18] focused on Japanese population while others included Chinese population, thus the subgroup analysis happened to reduce the heterogeneity in the Chinese subgroup and found that Chinese populations with the rs339501 variants to G allele may have somewhat higher risks of developing myopia. The results indicated that rs339501 variants may have more effects on the development of myopia for Chinese in comparison to Japanese. However, considering there’s only one study included Japanese, and the cases were limited to the patients with extreme myopia, the pooled results in total may not be universal. Subgroup analysis also revealed some statistically significant results and some OR values which were below 2.00 would make us wonder if these associations were meaningful. Given that myopia is a mild disease that doesn’t cause much harm to our body as cancer. Also, it is universal in population, and affected jointly by gene and environment. The relatively lower ORs in these models seem to be reasonable.
FGF10 is abundant in the retina and sclera of mice [15, 25]. In the lens-induced myopia model of tree shrew, the expression of FGF10 was increased in retina after 6 hours of lens-wearing [26]. And in FDM mice, FGF10 mRNA levels were increased in the sclera of the occluded eyes [15]. Scleral remodeling is an important mechanism in the incidence and progression of myopia [27], numerous genes are related to scleral remodeling, including glycosaminoglycans (GAGs) [28], Matrix metalloproteinases (MMPs) [29], Tissue inhibitors of metalloproteinases (TIMPs) [29] and transforming growth factor-β (TGF-β) [30]. According to previous studies, MMP and TIMPs involved in scleral remodeling were mainly MMP2 and TIMP2 [31, 32] and FGF10 played a key role in controlling the extension process of lacrimal bud through regulation of GAGs, MMPs and TIMPs [33,34]. In addition, it is reported that all the FGF members would inhibit the TGF-β signaling, when they are bound to the FGF receptors [35]. As a result, it is hypothesized that FGF10 might play a role in myopia scleral remodeling by controlling the production of MMP2, TIMP2, or GAGs. SNP rs339501 is located in CHR5:44365531 (GRCh38), coding transcript intron variant of FGF10, and it is a transcription factor binding site as well as a sequence variant located within a regulatory region which may regulates the activity of transcription factors [36]. Based on the ChIP-seq data, some transcription factors (e.g., CEBPB, HIF-1A and FOS) can bind at the region where rs339501 is located [37]. However, the experimental studies exploring the effect of these transcription factors on FGF10 has not been conducted. Also, some genome-scale pathogenicity scores (e.g. DANN, CADD and FATHMM-MKL) indicated that this variant is likely pathogenic [37].
Advantages and Limitations
This is, to the best of our knowledge, the first meta-analysis to examine the relationship between FGF10 rs339501 and myopia. During the searching process, we did not use the language limitation which minimized the bias within our research. Also, among the included studies, we found no evidence of publication bias during the analysis. Additionally, the heterogeneity among the studies in each subgroup was successfully minimized by the subgroup analysis carried out in our study (most were reduced from over 50% to under 50% as mentioned above).
However, there were several limitations in our study which shouldn’t be neglected. First, the study population were only from China and Japan which meant that our results might not be applied for other ethnic groups. More studies focusing on other population should be conducted. Second, since we only used pooled estimates of a single variable, our results were not very exact. If we had had access to individual data, we could have adjusted our results for factors like age, gender, and other covariates. Third, our analysis did not take into account the potential for gene-gene or or other interactions between polymorphisms, necessitating additional research into the haplotypic effects of genes and multiple polymorphisms in more genes.