Abstract
AIM
To explore the relationship between gene polymorphisms of vascular endothelial growth factor (VEGF) and retinopathy of prematurity (ROP).
METHODS
Literature materials related to gene polymorphisms of VEGF and ROP in PubMed, EMBASE, Cochrane and CBM database were retrieved. These materials were screened according to inclusion and exclusion standards. Patients diagnosed with ROP in clinic were regarded as control group and ROP patients who were in treatment were regarded as observation group. The indexes in two groups were matched except birth weight (BW), gender and gestational weeks. Meta5.1 was used to analyze the relationship between gene polymorphisms of VEGF and ROP.
RESULTS
Four random control tests (RCT) were included in this research, including 2611 patients. Meta analysis results showed that VEGF affected ROP, having statistical significance. The combined ratio was 0.44 (95%CI, 0.07, 0.80), 0.42 (95%CI, 0.09, 0.74) and 0.75 (95%CI, 0.02, 1.49), respectively. Carrying +405 allele might increase the premature infants' risk of having ROP.
CONCLUSION
ROP may be related to its carrying of +405 allele. Large-scale, multi-factor RCT researches are still needed in order to identify the relation between VEGF and ROP.
Keywords: polymorphisms of vascular endothelial growth factor, premature infant, retinopathy, Meta analysis
INTRODUCTION
Retinopathy of prematurity (ROP) refers to the retinopathy occurs in the infants with premature birth and low birth weight. The clinical manifestations of ROP are retinal ischemia, neovascularization, proliferative retinopathy, which are the main reasons for blindness of newborns in clinic[1]. However, there is significant difference on the prognosis of different ROP. ROP can gradually disappear soon after the born with no need of the treatment. But continued lesions occur in some patients, which need surgery or medicine. What reasons lead to the different prognosis, genetic susceptibility is one of the research focuses in clinic at present. Among these influencing factors, genetic polymorphism of vascular endothelial growth factor (VEGF) is closely related to genetic susceptibility[2]-[8]. Therefore, to explore the relationship between genetic polymorphisms of VEGF and ROP is helpful to the prognosis of ROP, which also provides reasonable foundations and plans for clinical treating of ROP. Four literatures on VEGF polymorphism were screened in this research. Meta analysis was conducted, emphatically investigating the relationship between polymorphism at +405G/C locus of ROP patients and ROP infants.
MATERIALS AND METHODS
Inclusion Standards
After screened in PubMed, EMBASE, Cochrane and CBM database, 28 related literatures on polymorphisms of VEGF and ROP infants were retrieved. After the screening, only 4 literatures met the standards. Literatures meeting the following conditions at the same time can be selected: 1) objects: patients diagnosed with ROP; 2) all the research hypothesis and methods were similar; 3) the detection results were expressed by mean±SD; 4) age, weight, gender and etc. should be taken into consideration at grouping and the bias caused by human factor should be excluded.
Exclusion Standards
1) experimental data with duplicate publication, comparison study with control before and after treatment and cohort study. 2) unserviceable literatures with poor research quality, little information and incomplete data, for example, case report. 3) the treatment efficacy was not evaluated by original literatures; 4) unreasonable research design of original literatures (such as unreasonable design in control group, incomplete sample materials, non-standard diagnosis or efficacy and etc. 5) literatures with duplicate publication.
Statistical Analysis
All the literature data including authors, publication time, cases of observation objects and etc. were input in Review Manager 5.0 software to conduct heterogeneity and Meta analysis. Funnel plot analysis were made for the number of the included literatures. The publication bias was detected. Clinical heterogeneity and statistical heterogeneity analysis were given to the included literatures. Fixed effect model was used for the analysis if the included researches had no heterogeneity (namely, P≥0.1, I2=0). On the contrary, random effect model was adopted for data analysis. Mantel-Haenszel (Fixed effect model), DerSimonian and Laird (random effect model) were used to calculate the combined effect value. Descriptive analysis was conducted if Meta analysis cannot achieve with the included literatures. OR value was used to express the effectiveness analysis statistics for all the measurement data and the corresponding 95%CI was calculated. P<0.05 means that statistical significance exists in the difference of the two treatment plans.
RESULTS
Retrieval results
Twenty-eight literatures were preliminarily retrieved. Twenty-four literatures were excluded after reading the titles and abstracts. After further judgment according to inclusion and exclusion standards, 4 literatures were finally included[9]-[12], the publication years of the literatures was between 2005 and 2008. The general features of the included researches were shown in Table 1.
Table 1. Polymorphism distribution at VEGF+405G/C locus.
| Author(s) and publication time | Genetype at + 405G/C locus | Control group (n) | Treatment group(n) |
| Huanglina(2008) | GG | 7 | 10 |
| GC | 9 | 9 | |
| CC | 49 | 1 | |
| ADAM Vannay(2005) | GG | 35 | 48 |
| GC | 48 | 46 | |
| CC | 17 | 6 | |
| Barkur S(2007) | GG | 41 | 41 |
| GC | 20 | 20 | |
| CC | 26 | 25 | |
| Przemko(2008) | GG | 456 | 361 |
| GC | 673 | 425 | |
| CC | -- | 290 |
Meta Analysis on VEGF+405G/C Polymorphism Locus and ROP
Genetype GG at+405G/C locus and ROP
After Meta analysis, heterogeneity test was given to 4 researches (P=0.60, I2=0), meaning that there was no heterogeneity. The results indicated that there was statistical significance of alleles at +405G/C locus, which can influence ROP (P<0.05, Figure 1).
Figure 1. Meta analysis on genetype GG at +405G/C locus and ROP.
Potential publication bias
The influence of genetype GG at +405G/C locus on ROP was taken as the analysis index and inverted funnel plot was drawn. Due to the small amount of the included research and unobvious distribution trends, the inverted funnel plot showed trend symmetry, indicating that the publication bias was not big (Figure 2).
Figure 2. Bias analysis for the influence of genetype GG at +405G/C locus on ROP.
Potential publication bias
The influence of genetype GC at +405G/C locus on ROP was taken as the analysis index and inverted funnel plot was drawn. Due to the small amount of the included research and unobvious distribution trends, the inverted funnel plot showed trend symmetry, indicating that the publication bias was not big (Figure 3).
Figure 3. Bias analysis for the influence of genetype GC at +405G/C locus on ROP.
Genetype GC at +405G/C locus and ROP
After Meta analysis, heterogeneity test was given to 4 researches (P=0.92, I2=0), with no heterogeneity. The results indicated that there was correlation between genetype GC at +405G/C locus and ROP. Statistical significance of alleles at +405G/C locus was existed, which can influence ROP (P<0.05, Figure 4).
Figure 4. Results of Meta analysis on genetype GC at +405G/C locus and ROP.
Genetype CC at +405G/C locus and ROP
After Meta analysis, heterogeneity test was given to 4 researches (P=0.94, I2=0), meaning that there was no heterogeneity. The results indicated that there was correlation between genetype CC at +405G/C locus and ROP. P<0.05 meant that there existed statistical significance of alleles at +405G/C locus, which can influence ROP (Figure 5).
Figure 5. Meta analysis on genetype CC at +405G/C locus and ROP.
Potential publication bias
The influence of genetype CC at +405G/C locus on ROP was taken as the analysis index and inverted funnel plot was drawn. Due to the small amount of the included research and unobvious distribution trends, the inverted funnel plot showed trend symmetry, indicating that the publication bias was not big (Figure 6).
Figure 6. Bias analysis for the influence of genetype CC at +405G/C locus on ROP.
DISCUSSION
As we all know, the occurrence and development of ROP is directly related to VEGF[13]. VEGF plays an important role in neovascularization and vessel leakage during ROP disease course. The development of ROP mainly divides into two stages. The first stage: relative high-oxygen environment inhibits the normal secretion of VEGF, making retinal vascularization stop; the second stage: due to the stagnation of normal retinal vascularization, the tissue is relatively short of oxygen, promoting high-expression of VEGF and stimulating abnormal neovascularization from retina to vitreous cavity. At the same time, fibroplasia occurs. A lot of case-control studies verified that single nucleotide polymorphisms of VEGF are related to many kinds of diseases such as breast cancer, oral carcinoma, senile dementia, kidney disease and etc. Similarly, many researches also detect that single nucleotide polymorphisms of VEGF are related to the changes of protein expression during ROP threshold lesions. Cooke et al[2] pointed out in their case-control researches that VEGF-634G allele in 5′non-transcribed domain of VEGF is the independent risk factor in ROP threshold period. The risk of homozygous G allele developing into ROP threshold is twice times than other genetypes. On the contrary, Vanny et al[3] put forward the opposite opinion that VEGF-634C allele is more common in patients during ROP threshold lesions and C allele is the severe independent risk factor of ROP. But other researchers did not repeat these results[11]-[15].
Researches in recent years show that up-regulation of VEGF gene may play an important role in the occurrence and development of ROP[16],[17]. The retinal growth of premature infants and low birth weight babies is not mature. As a result, a large amount of avascular area exists. Due to the following features[18], VEGF is regarded as the most important factor promoting neovascularization: 1) VEGF has signal peptide that is essential to extracellular transport and promotes division and hyperplasia of endothelial cells; 2) VEGF enhances the permeability of microvascular endothelial cells. Macromolecular substance such as fibrinogen and etc. can enter into extracellular matrix and form fibrin gel, which supports endothelial cell growth of neovascularization[19]; 3) superfluous VEGF is produced under oxygen deficient condition[20]. But pathological retinal neovascularization is usually companied with non-perfusion of capillary; 4) the expression level of VEGF receptor in retinal endothelial cells increases under oxygen deficient condition. Retinal vessel system of premature infants is gradually mature after the birth. Therefore, its growth process can be observed by funduscope and fluorescence angiography technology.
The risk and influencing factors of VEGF on ROP were explored in this research. Through the analysis of VEGF expression during retinal growth of premature infants, we hope to further explore the effects and mechanisms of VEGF in angiogenesis of premature infants. Thus, in the clinical judgment of ROP prognosis, the combination of genetic polymorphism detection of VEGF gene at +405G/C locus and comprehensive consideration of other related factors may be helpful, providing theoretical foundation for making correct clinical treatment plans.
Footnotes
Foundation item: National Natural Science Foundation of China (No.60971110)
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