LMO1 polymorphisms and the risk of neuroblastoma: Assessment of meta‐analysis of case‐control studies

Abstract Neuroblastoma (NB), a neuroendocrine tumour, is one of the most prevalent cancers in children. The link between LMO1 polymorphisms and NB has been investigated by several groups, rendering inconclusive results. Here, with this comprehensive systematic review and up‐to‐date meta‐analysis, we aim to distinctively elucidate the possible correlation between LMO1 polymorphisms and NB susceptibility. Eligible studies were systematically researched and identified using PubMed, Web of Science and Scopus databases up to 10 February 2019. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the strength of the associations. Our findings revealed that rs110419 and rs2168101 polymorphisms were significantly associated with a decreased risk of NB in all genetic models. In addition, the rs4758051 variant appeared protective against NB in homozygous, dominant and allele genetic models, whereas the rs10840002 variant markedly decreased the risk of NB in the allele model. In contrast, the rs204938 polymorphism showed a positive association with NB susceptibility in allele genetic models. In summary, our meta‐analysis is the first to provide clear evidence of an association between specific polymorphisms of LMO1 and susceptibility to NB. Of note, additional larger well‐designed studies would be helpful to further evaluate and confirm this association.

prevalence varies worldwide, affecting approximately 8-14 individuals per million in the developed countries. 4 Possible risk factors suspected of aiding the development of NB in children include parental exposure to radiation sources, solders, wood dust and hydrocarbons. 5,6 Hence, degradation of environment may contribute to the occurrence of the cancer. Furthermore, with the advances in regenerative medicine and the use of novel biomaterials in implants such risks may increase. 7,8 Our group performed in the past years several meta-analyses, [9][10][11] which underlined the role of polymorphisms in various cancer-associated genes. Over the last decade, genome-wide association studies (GWAS) have identified several loci linked to NB susceptibility, [12][13][14][15][16][17][18][19][20][21][22] of which the LIM domain only 1 (LMO1) gene at 11p15.4 represents a promising candidate. 14 LMO1 was recognized as neuroblastoma oncogene. 14 It also acts as an oncogene in colorectal cancer (CRC) and lung cancer. LMO1 overexpression is a new predictive marker for anti-EGFR therapy. 23,24 However, no significant differences were observed for LMO1 gene expression level between tumour tissues and corresponding adjacent benign tissues in human breast cancer, hepatocellular carcinoma (HCC) and gastric cancer (GC), which suggests that LMO1 gene may display a more complex functional network in these cancers. 24 Sun et al 25 have found that the expression levels of LMO1 in gastric cancer tissues were higher than those in adjacent tissues and the overexpression of LMO1 could be as a markers of poor prognosis.
Deregulated expression of LMO1 may be involved in the development and maintenance of T-ALL (T-acute lymphoblastic leukaemia). 26 Thus far, several studies have investigated LMO1 polymorphisms and their impact on NB susceptibility, with varying and inconclusive results. 14,20,[27][28][29][30][31][32][33] In the current study, we performed an up-to-date meta-analysis to more precisely evaluate the association between specific LMO1 polymorphisms and NB susceptibility.

| Data extraction
Two investigators independently searched literature and extracted the appropriate data from eligible studies. Data collected from each study included: the first author, publication date, country, ethnicity of study participants, control-population source, genotyping methods of LOM1 polymorphisms, genotype distributions in cases and controls, and the result of the HWE test (Table 1).

| Statistical analysis
All analyses were performed using STATA 14.1 (Stata Corporation).
Departure from Hardy-Weinberg equilibrium (HWE) in controls was examined by the χ 2 test. The strength of the association between LMO1 polymorphisms and NB risk was assessed by pooled odds ratios (ORs) and their 95% confidence intervals (CIs). The Z-test was implemented to establish the statistical significance of the pooled ORs. We estimated the between-study heterogeneity by the Q-test and I 2 -test, with P < .10 indicating the presence of heterogeneity. In case of heterogeneity, a random-effect model was used; otherwise, a fixed-effect model was employed.
We determined publication bias using funnel plots for visual inspection and by conducting quantitative estimations using the Egger's test. Sensitivity analyses were carried out by sequentially ignoring a single study at a time to assess the impact of individual data sets on the pooled ORs.   Figure 2).  Table 2). In addition, the rs2168101 polymorphism

| Heterogeneity and publication bias
Between-study heterogeneity across studies included into pooled analysis is displayed in  Figure 4). Our meta-analysis, based on systematically collected studies, aimed to obtain an accurate summary of the estimates of the strength of association between specific LMO1 gene polymorphisms and NB susceptibility, and, to our best knowledge, is the first to do so. We found that rs110419, rs4758051, rs10840002 and rs2168101 polymorphisms were associated with reduced susceptibility to NB, while the rs204938 polymorphism increased the risk of the disease.

| Sensitivity analysis
He et al 30 reported that rs110419, rs10840002, rs4758051 and rs2168101 polymorphisms of the LMO1 gene were associated with a decreased risk of NB in an eastern Chinese subpopulation. In addition, the rs2168101 and rs3750952 polymorphisms were markedly associated with decreased NB susceptibility in children from North and South China. 28 Similarly, the LMO1 rs110419 A > G polymorphism was linked to a reduced NB risk in Southern Chinese children. 29 A significant association between the rs204926 variant and NB susceptibility has been reported, 32 and rs4758051 and rs10840002 polymorphisms were associated with decreased NB. 33 Furthermore, a significant association between the rs110419 polymorphism and risk of NB was observed in an Italian population as well as European American children. 27 Conversely, no significant associations between LMO1 polymorphisms and NB risk were observed in African Americans. 31 While some studies indicate that frequently occurring polymorphisms at the LMO1 locus are strongly connected to susceptibility to developing NB. 14 The observed differences in susceptibility, between populations, are likely due to the overall genetic background that modifies the LMO1 prone risk factors.
This meta-analysis has a few limitations that should be considered. First, we have only included studies published in the English language. Second, there was significant heterogeneity among studies. There was also variation in study sample size, populations and ethnicity of participants, (please see Table 1 for details). Third, our findings were obtained with a relatively limited sample size and consequently, our conclusions are preliminary in nature. Fourth, the assessments of gene-gene and gene/environment interactions were not performed despite some data suggest so.
In conclusion, our meta-analysis is the first to provide evidence of an association between specific genetic polymorphisms of the LMO1 gene and susceptibility to NB. Further validation by well-designed studies performed by international multicenter programme (addressing diverse ethnic populations) is needed to conclusively confirm the impact of specific LMOI polymorphisms on NB susceptibility and development. Unfortunately, at present we lack sufficient number of studies (studied populations) to reliably perform such analyses. Nevertheless, the presented analysis offers interesting insight into the analysed polymorphisms, as outlined above.

ACK N OWLED G EM ENTS
The authors would like to thank Science Impact (Winnipeg) for postediting the manuscript. JS and MJŁ thank you for the support from Polish National Science Centre, grants # 2016/21/B/ST7/02241.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript or in the decision to publish the results.