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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Genet.</journal-id>
<journal-title>Frontiers in Genetics</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Genet.</abbrev-journal-title>
<issn pub-type="epub">1664-8021</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">774489</article-id>
<article-id pub-id-type="doi">10.3389/fgene.2021.774489</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Genetics</subject>
<subj-group>
<subject>Systematic Review</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Association Between Insulin-like Growth Factor-1 rs35767 Polymorphism and Type 2 Diabetes Mellitus Susceptibility: A Meta-Analysis</article-title>
<alt-title alt-title-type="left-running-head">Zeng et&#x20;al.</alt-title>
<alt-title alt-title-type="right-running-head">IGF1 rs35767 and T2DM Susceptibility</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Zeng</surname>
<given-names>Qiaoli</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<xref ref-type="fn" rid="fn1">
<sup>&#x2020;</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/940794/overview"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zou</surname>
<given-names>Dehua</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<xref ref-type="fn" rid="fn1">
<sup>&#x2020;</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/978440/overview"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zeng</surname>
<given-names>Qiaodi</given-names>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
<xref ref-type="fn" rid="fn1">
<sup>&#x2020;</sup>
</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Chen</surname>
<given-names>Xiaoming</given-names>
</name>
<xref ref-type="aff" rid="aff6">
<sup>6</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Wei</surname>
<given-names>Yue</given-names>
</name>
<xref ref-type="aff" rid="aff7">
<sup>7</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Guo</surname>
<given-names>Runmin</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<xref ref-type="aff" rid="aff6">
<sup>6</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1214689/overview"/>
</contrib>
</contrib-group>
<aff id="aff1">
<label>
<sup>1</sup>
</label>Department of Internal Medicine, Shunde Women and Children&#x2019;s Hospital (Maternity and Child Healthcare Hospital of Shunde Foshan), Guangdong Medical University, <addr-line>Foshan</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<label>
<sup>2</sup>
</label>Key Laboratory of Research in Maternal and Child Medicine and Birth Defects, Guangdong Medical University, <addr-line>Foshan</addr-line>, <country>China</country>
</aff>
<aff id="aff3">
<label>
<sup>3</sup>
</label>Shunde Women and Children&#x2019;s Hospital (Maternity and Child Healthcare Hospital of Shunde Foshan), Matenal and Child Research Institute, Guangdong Medical University, <addr-line>Foshan</addr-line>, <country>China</country>
</aff>
<aff id="aff4">
<label>
<sup>4</sup>
</label>State Key Laboratory for Quality Research of Chinese Medicines, Macau University of Science and Technology, Taipa, <addr-line>Macau (SAR)</addr-line> <country>China</country>
</aff>
<aff id="aff5">
<label>
<sup>5</sup>
</label>Department of Clinical Laboratory, People&#x2019;s Hospital of Haiyuan County, <addr-line>Zhongwei</addr-line>, <country>China</country>
</aff>
<aff id="aff6">
<label>
<sup>6</sup>
</label>Department of Endocrinology, Affiliated Hospital of Guangdong Medical University, <addr-line>Zhanjiang</addr-line>, <country>China</country>
</aff>
<aff id="aff7">
<label>
<sup>7</sup>
</label>Department of Ultrasound, Shunde Women and Children&#x2019;s Hospital (Maternity and Child Healthcare Hospital of Shunde Foshan), Guangdong Medical University, <addr-line>Foshan</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/721279/overview">Liangcai Zhang</ext-link>, Janssen Research and Development, United&#x20;States</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/156624/overview">Tonia Carter</ext-link>, Marshfield Clinic, United&#x20;States</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/398150/overview">Yanfang Chen</ext-link>, Wright State University, United&#x20;States</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Xiaoming Chen, <email>chenxiaoming@gdmu.edu.cn</email>; Yue Wei, <email>weiyue138@163.com</email>; Runmin Guo, <email>runmin.guo@gdmu.edu.cn</email>
</corresp>
<fn fn-type="equal" id="fn1">
<label>
<sup>&#x2020;</sup>
</label>
<p>These authors have contributed equally to this&#x20;work</p>
</fn>
<fn fn-type="other">
<p>This article was submitted to Statistical Genetics and Methodology, a section of the journal Frontiers in Genetics</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>22</day>
<month>11</month>
<year>2021</year>
</pub-date>
<pub-date pub-type="collection">
<year>2021</year>
</pub-date>
<volume>12</volume>
<elocation-id>774489</elocation-id>
<history>
<date date-type="received">
<day>12</day>
<month>09</month>
<year>2021</year>
</date>
<date date-type="accepted">
<day>25</day>
<month>10</month>
<year>2021</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2021 Zeng, Zou, Zeng, Chen, Wei and Guo.</copyright-statement>
<copyright-year>2021</copyright-year>
<copyright-holder>Zeng, Zou, Zeng, Chen, Wei and Guo</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these&#x20;terms.</p>
</license>
</permissions>
<abstract>
<p>
<bold>Background:</bold> Insulin-like growth factor-1 (IGF-1) has been demonstrated to increase fatty acid <italic>&#x3b2;</italic> oxidation during fasting, and play an important role in regulating lipid metabolism and type 2 diabetes mellitus (T2DM). The rs35767 (T &#x3e; C) polymorphism, a functional SNP was found in <italic>IGF-1</italic> promoter, which may directly affect <italic>IGF-1</italic> expression. However, the inconsistent findings showed on the <italic>IGF-1</italic> rs35767 polymorphism and T2DM&#x20;risk.</p>
<p>
<bold>Methods:</bold> We performed a comprehensive meta-analysis to estimate the association between the <italic>IGF-1</italic> rs35767 and T2DM risk among four genetic models (the allele, additive, recessive and dominant models).</p>
<p>
<bold>Results:</bold> A total 49,587 T2DM cases and 97,906 NDM controls were included in the allele model, a total 2256 T2DM cases and 2228 NDM controls were included in the other three genetic models (the additive; recessive and dominant models). In overall analysis, the <italic>IGF-1</italic> rs35767 was shown to be significantly associated with increased T2DM risk for the allele model (T vs. C: OR &#x3d; 1.251, 95% CI: 1.082&#x2013;1.447, <italic>p</italic>&#x20;&#x3d; 0.002), additive model (homozygote comparisons: TT vs. CC: OR &#x3d; 2.433, 95% CI: 1.095&#x2013;5.405, <italic>p</italic>&#x20;&#x3d; 0.029; heterozygote comparisons: TC vs. CC: OR &#x3d; 1.623, 95% CI: 1.055&#x2013;2.495, <italic>p</italic>&#x20;&#x3d; 0.027) and dominant model (TT &#x2b; CT vs. CC: OR &#x3d; 1.934, 95% CI: 1.148&#x2013;3.257, <italic>p</italic>&#x20;&#x3d; 0.013) with random effects model. After omitting Gouda&#x2019;s study could reduce the heterogeneity, especially in the recessive model (TT vs. CC &#x2b; CT: I<sup>2</sup> &#x3d; 38.7%, <italic>p</italic>&#x20;&#x3d; 0.163), the fixed effects model for recessive effect of the T allele (TT vs. CC &#x2b; CT) produce results that were of borderline statistical significance (OR &#x3d; 1.206, 95% CI: 1.004&#x2013;1.448, <italic>p</italic>&#x20;&#x3d; 0.045). And increasing the risk of T2DM in Uyghur population of subgroup for the allele&#x20;model.</p>
<p>
<bold>Conclusion:</bold> The initial analyses that included all studies showed statistically significant associations between the rs35767 SNP and type 2 diabetes, but after removing the Gouda et&#x20;al. study produced results that were mostly not statistically significant. Therefore, there is not enough evidence from the results of the meta-analysis to indicate that the rs35767 SNP has a statistically significant association with type 2 diabetes.</p>
</abstract>
<kwd-group>
<kwd>type 2 diabete mellitus</kwd>
<kwd>insulin-like growth factor-1</kwd>
<kwd>rs35767</kwd>
<kwd>susceptibility</kwd>
<kwd>meta-analysis</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<sec id="s1">
<title>1 Introduction</title>
<p>Diabetes is one of the most common chronic metabolic disorder diseases in the worldwide, over 90% of the diabetes patients are type 2 diabetes mellitus (T2DM), which is characterized by insulin resistance in peripheral tissues and dysregulated insulin secretion by pancreatic beta (<italic>&#x3b2;</italic>) cells (<xref ref-type="bibr" rid="B1">Banerjee and Vats, 2014</xref>; <xref ref-type="bibr" rid="B36">Song et&#x20;al., 2015</xref>). Substantial evidence suggests that insulin resistance, an inherited genetic defect, is the basis and major feature of T2DM (<xref ref-type="bibr" rid="B7">DeFronzo and Tripathy, 2009</xref>; <xref ref-type="bibr" rid="B2">Cai et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>). Insulin resistance is attributable to excess fatty acids and proinflammatory cytokines, which leads to impaired glucose transport and increases fat breakdown. Since there is an inadequate response or production of insulin, the body responds by inappropriately increasing glucagon, thus further contributing to hyperglycemia. Accumulated data have revealed that lipid abnormalities are associated with insulin resistance and contribute to T2DM (<xref ref-type="bibr" rid="B15">Johnson and Olefsky, 2013</xref>; <xref ref-type="bibr" rid="B29">Perry et&#x20;al., 2014</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>). Studies have also revealed lipid metabolism-related genes and their single-nucleotide polymorphisms (SNPs) associated with insulin resistance and the development of T2DM (<xref ref-type="bibr" rid="B32">Ruchat et&#x20;al., 2009</xref>; <xref ref-type="bibr" rid="B8">Dupuis et&#x20;al., 2010</xref>; <xref ref-type="bibr" rid="B4">Chistiakov et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B16">Langberg et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B27">Mannino et&#x20;al., 2013</xref>; <xref ref-type="bibr" rid="B20">Li et&#x20;al., 2014</xref>; <xref ref-type="bibr" rid="B38">Thankamony et&#x20;al., 2014</xref>; <xref ref-type="bibr" rid="B42">Yuan et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>).</p>
<p>
<italic>Insulin-like growth factor-1</italic> (<italic>IGF-1</italic>) is a circulating growth factor which structure is highly homologous with pro-insulin. <italic>IGF-1</italic> is expresses in insulin-resistant tissue, it downregulates free fatty acid and increases fatty acid <italic>&#x3b2;</italic> oxidation during fasting (<xref ref-type="bibr" rid="B38">Thankamony et&#x20;al., 2014</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>). It plays an important role in regulating lipid metabolism and insulin sensitivity (<xref ref-type="bibr" rid="B33">Sepp&#xe4; et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B10">Gouda et&#x20;al., 2019</xref>), since it effects on glucose homeostasis and associated with insulin resistance (<xref ref-type="bibr" rid="B17">Li et&#x20;al., 2011</xref>; <xref ref-type="bibr" rid="B20">Li et&#x20;al., 2014</xref>; <xref ref-type="bibr" rid="B6">Dai et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B28">Ming et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B42">Yuan et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B41">Wei et&#x20;al., 2018</xref>; <xref ref-type="bibr" rid="B23">Liao et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B31">Regu&#xe9; et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>). Previous studies have been reported that people with a low <italic>IGF-1</italic> level are prone to have diabetes mellitus (<xref ref-type="bibr" rid="B3">Chen et&#x20;al., 2013</xref>; <xref ref-type="bibr" rid="B5">Colao et&#x20;al., 2013</xref>; <xref ref-type="bibr" rid="B34">Shankar and Li, 2013</xref>). Polymorphisms in the <italic>IGF-1</italic> gene can directly affect <italic>IGF-1</italic> expression. The rs35767 (T &#x3e; C) polymorphism, a functional SNP was found in <italic>IGF-1</italic> promoter, in which the promoter with C allele showed a higher transcriptional activity than promoter with T allele (<xref ref-type="bibr" rid="B37">Telgmann et&#x20;al., 2009</xref>). Therefore, rs35767 may contribute to insulin resistance involving lipid metabolism in&#x20;T2DM.</p>
<p>A significant association of <italic>IGF-1</italic> rs35767 with T2DM has been reported in several case-control studies (<xref ref-type="bibr" rid="B10">Gouda et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B11">Gulixiati&#xb7;Maimaitituersun. 2020</xref>; <xref ref-type="bibr" rid="B39">Wang. 2019;</xref> <xref ref-type="bibr" rid="B44">Zhang et&#x20;al., 2017</xref>; <xref ref-type="bibr" rid="B36">Song et&#x20;al., 2015</xref>). However, seven studies failed to replicate the results (<xref ref-type="bibr" rid="B8">Dupuis et&#x20;al., 2010</xref>; <xref ref-type="bibr" rid="B14">Hu et&#x20;al., 2010</xref>; <xref ref-type="bibr" rid="B9">Fujita et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B24">Liu et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B46">Zhao et&#x20;al., 2016</xref>; <xref ref-type="bibr" rid="B19">Li et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>). In veiw of the inconsistent results, whether <italic>IGF-1</italic> rs35767 is associated with T2DM remains to be determined. In this meta-analysis, we estimate the association of <italic>IGF-1</italic> rs35767 with T2DM among four different genetic models.</p>
</sec>
<sec id="s2">
<title>2 Materials and Methods</title>
<sec id="s2-1">
<title>2.1 Literature Search</title>
<p>The Google Scholar, PubMed and Chinese National Knowledge Infrastructure were comprehensively searched for related studies published before July 31, 2021, using the key terms: &#x201c;insulin-like growth factor 1 or <italic>IGF-1</italic> or <italic>IGF1</italic>,&#x201d; &#x201c;rs35767 or rs35767 (T &#x3e; C) or rs35767 (A &#x3e; G),&#x201d; &#x201c;polymorphism or SNP or mutation or variant&#x201d; and &#x201c;diabetes or type 2 diabetes or T2DM.&#x201d; All searches had no language limitations. Eligible studies were estimated by reading full texts, and excluded substandard studies.</p>
</sec>
<sec id="s2-2">
<title>2.2 Inclusion and Exclusion Criteria</title>
<p>The following inclusion criteria: 1) case-control or cohort studies that relate to the <italic>IGF-1</italic> rs35767 and T2DM risk; 2) sufficient raw data or adequate data for assessing odds ratios (ORs) with corresponding 95% confidence intervals (CIs); and 3) The diagnostic standard of T2DM conformed to the World Health Organization.</p>
<p>The following exclusion criteria: 1) not a case-control study; 2) irrelevant to <italic>IGF-1</italic> rs35767 and T2DM risk; 3) lacking detailed data; and 4) control subjects is not in Hardy-Weinberg equilibrium (HWE).</p>
</sec>
<sec id="s2-3">
<title>2.3 Data Extraction</title>
<p>Data were independently extracted by two authors from the eligible studies and collected the following data: first author, year of publication, origin, the numbers of T2DM cases and NDM controls, gender and age, BMI (kg/m<sup>2</sup>), the distributions number of genotype and alleles, ORs with 95% CI, or ability to calculate the OR and 95% CI. <italic>p</italic>-value for the HWE of NDM controls.</p>
</sec>
<sec id="s2-4">
<title>2.4 Statistical Analysis</title>
<p>Statistical analyses using the STATA v.14.0 software (Stata Corporation, TX, United&#x20;States). Four genetic models were evaluated in this meta-analysis: the allele model (T vs. C); the additive model (homozygote comparisons: TT vs. CC; heterozygote comparisons: TC vs. CC); the recessive model (TT vs. CC &#x2b; CT) and the dominant model (TT &#x2b; CT vs. CC). Using Q-test and I<sup>2</sup> test to estimate the genetic heterogeneity. OR with corresponding 95% CIs were calculated by the random effectss model when <italic>p</italic>&#x20;&#x3c; 0.01 and I<sup>2</sup> &#x3e; 50% (<xref ref-type="bibr" rid="B13">He et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B45">Zhang et&#x20;al., 2016</xref>). Otherwise, the fixed effectss model were used. Sensitivity analyses were implemented to evaluate the stability of the overall effect by excluding a study at a time. The Hardy-Weinberg equilibrium for the NDM controls was assessed using Pearson&#x2019;s Chi-squared test. Using Bgger&#x2019;s test to evaluate publication bias (<xref ref-type="bibr" rid="B35">Shen et&#x20;al., 2015</xref>; <xref ref-type="bibr" rid="B22">Li et&#x20;al., 2016</xref>; <xref ref-type="bibr" rid="B25">Liu et&#x20;al., 2017</xref>; <xref ref-type="bibr" rid="B12">Han et&#x20;al., 2019</xref>).</p>
</sec>
</sec>
<sec id="s3">
<title>3 Results</title>
<sec id="s3-1">
<title>3.1 Study Inclusion and Characteristics</title>
<p>A total of 182 potential articles obtained through initial search. 51 duplicates were excluded. Then 131 studies were screened on title and abstract, 84 of them were excluded. The left 47 articles were evaluated by full-text reading, 35 of them were excluded cause that 22 were not case-control researchs, 10 were not related to rs35767 or T2DM, three did not provided sufficient data. 12 articles were included that there are six articles including five in English and one in Chinese just of the allele model data, and other six articles including four in English and two in Chinese of four genetic models data (the allele, additive, recessive and dominant models). Flow chart of researches selection in the meta-analysis was shown in <xref ref-type="fig" rid="F1">Figure&#x20;1</xref>. A total 49,587 T2DM cases and 97,906 NDM controls were included in the allele model, a total 2256 T2DM cases and 2228 NDM controls were included in the other three genetic models (the additive; recessive and dominant models). The characteristics of each study are shown in <xref ref-type="table" rid="T1">Table 1</xref> and <xref ref-type="sec" rid="s10">Supplementary Table S1</xref>.</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>Flow chart of researches selection in the meta-analysis.</p>
</caption>
<graphic xlink:href="fgene-12-774489-g001.tif"/>
</fig>
<table-wrap id="T1" position="float">
<label>TABLE 1</label>
<caption>
<p>Characteristics of each study included in this meta-analysis.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th rowspan="2" colspan="5" align="left"/>
<th align="center">Allele distribution</th>
<th align="left"/>
<th align="left"/>
<th align="left"/>
<th align="center">Genotype distribution</th>
<th align="left"/>
<th align="left"/>
<th align="left"/>
<th align="left"/>
<th align="left"/>
</tr>
<tr>
<th align="center">T2DM, n</th>
<th align="left"/>
<th align="center">NDM, n</th>
<th align="left"/>
<th align="center">T2DM, n</th>
<th align="left"/>
<th align="left"/>
<th align="center">NDM, n</th>
<th align="left"/>
<th align="left"/>
</tr>
<tr>
<th align="left">Authors</th>
<th align="center">Origin</th>
<th align="center">Gender</th>
<th align="center">T2DM/NDM, n</th>
<th align="center">ORs with 95% CI (T vs. C)</th>
<th align="center">C</th>
<th align="center">T</th>
<th align="center">C</th>
<th align="center">T</th>
<th align="center">CC</th>
<th align="center">CT</th>
<th align="center">TT</th>
<th align="center">CC</th>
<th align="center">CT</th>
<th align="center">TT</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left">
<xref ref-type="bibr" rid="B21">Li et al. (2021)</xref>
</td>
<td align="center">Chinese (Yunnan)</td>
<td align="center">M/F</td>
<td align="center">1194/1274</td>
<td align="center">0.928 (0.826&#x2212;1.042)</td>
<td align="center">1538</td>
<td align="center">850</td>
<td align="center">1597</td>
<td align="center">951</td>
<td align="center">513</td>
<td align="center">512</td>
<td align="center">169</td>
<td align="center">500</td>
<td align="center">597</td>
<td align="center">177</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B11">Gulixiati et al. (2020)</xref>
</td>
<td align="center">Chinese (Xinjiang)</td>
<td align="center">M/F</td>
<td align="center">220/229</td>
<td align="center">1.452 (1.092&#x2212;1.931)</td>
<td align="center">287</td>
<td align="center">153</td>
<td align="center">335</td>
<td align="center">123</td>
<td align="center">93</td>
<td align="center">101</td>
<td align="center">26</td>
<td align="center">120</td>
<td align="center">65</td>
<td align="center">14</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B10">Gouda et al. (2019)</xref>
</td>
<td align="center">Egyptian</td>
<td align="center">F</td>
<td align="center">180/165</td>
<td align="center">5.103 (3.641&#x2212;7.153)</td>
<td align="center">72</td>
<td align="center">288</td>
<td align="center">185</td>
<td align="center">145</td>
<td align="center">12</td>
<td align="center">48</td>
<td align="center">120</td>
<td align="center">60</td>
<td align="center">65</td>
<td align="center">40</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B39">Wang et al. (2019)</xref>
</td>
<td align="center">Chinese (Tianjin)</td>
<td align="center">M/F</td>
<td align="center">367/367</td>
<td align="center">1.322 (1.065&#x2212;1.641)</td>
<td align="center">460</td>
<td align="center">274</td>
<td align="center">506</td>
<td align="center">228</td>
<td align="center">146</td>
<td align="center">168</td>
<td align="center">53</td>
<td align="center">176</td>
<td align="center">154</td>
<td align="center">37</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B44">Zhang et al. (2017)</xref>
</td>
<td align="center">Chinese (Hebei)</td>
<td align="center">M/F</td>
<td align="center">244/142</td>
<td align="center">1.388 (1.025&#x2212;1.879)</td>
<td align="center">280</td>
<td align="center">208</td>
<td align="center">185</td>
<td align="center">99</td>
<td align="center">77</td>
<td align="center">126</td>
<td align="center">41</td>
<td align="center">56</td>
<td align="center">73</td>
<td align="center">13</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B36">Song et al. (2015)</xref>
</td>
<td align="center">Chinese (Xinjiang)</td>
<td align="center">M/F</td>
<td align="center">51/51</td>
<td align="center">1.900 (1.006&#x2212;3.587)</td>
<td align="center">67</td>
<td align="center">33</td>
<td align="center">81</td>
<td align="center">21</td>
<td align="center">21</td>
<td align="center">25</td>
<td align="center">4</td>
<td align="center">34</td>
<td align="center">13</td>
<td align="center">4</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B19">Li et al. (2019)</xref>
</td>
<td align="center">Chinese (Tianjin)</td>
<td align="center">F</td>
<td align="center">80/1160</td>
<td align="center">1.043 (0.727&#x2212;1.494)</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B46">Zhao et al. (2016)</xref>
</td>
<td align="center">Chinese (Xinjiang)</td>
<td align="center">M/F</td>
<td align="center">130/135</td>
<td align="center">1.480 (0.980-2.230)</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B9">Fujita et al. (2012)</xref>
</td>
<td align="center">Japanese</td>
<td align="center">M/F</td>
<td align="center">2632/2050</td>
<td align="center">0.990 (0.912-1.075)</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B17">Liu et al. (2011)</xref>
</td>
<td align="center">Chinese (Beijing, Shanghai)</td>
<td align="center">M/F</td>
<td align="center">424/1899</td>
<td align="center">0.935 (0.795-1.099)</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B14">Hu et al. (2010)</xref>
</td>
<td align="center">Chinese (Shanghai)</td>
<td align="center">M/F</td>
<td align="center">3410/3412</td>
<td align="center">1.027 (0.956-1.103)</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
</tr>
<tr>
<td align="left">
<xref ref-type="bibr" rid="B8">Dupuis et al. (2010)</xref>
</td>
<td align="center">European</td>
<td align="center">M/F</td>
<td align="center">40655/87022</td>
<td align="center">0.962 (0.890-1.038)</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
<td align="center">&#x2212;</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>n, Number; M, Male; F, Female; T2DM, type 2 diabetes mellitus; NDM, Non-diabetic subject;OR, odds ratio; CI, confidence interval; (-), not applicable.</p>
</fn>
</table-wrap-foot>
</table-wrap>
</sec>
<sec id="s3-2">
<title>3.2&#x20;Meta-Analysis</title>
<p>The association between the <italic>IGF-1</italic> rs35767 polymorphism and T2DM were evaluated using ORs and 95% CI in the allele model (12 studies, 49587 T2DM cases and 97906 NDM controls) and the additive; recessive and dominant models (6 studies, 2256 T2DM cases and 2228 NDM controls).</p>
<p>In overall analysis, A random effects model were used to analyze the allele, additive, recessive and dominant models. The <italic>IGF-1</italic> rs35767 was shown to be significantly associated with increased T2DM risk for the allele model (T vs. C: OR &#x3d; 1.251, 95% CI: 1.082&#x2013;1.447,<italic>p</italic>&#x20;&#x3d; 0.002), additive model (homozygote comparisons: TT vs. CC: OR &#x3d; 2.433, 95% CI: 1.095&#x2013;5.405, <italic>p</italic>&#x20;&#x3d; 0.029; heterozygote comparisons: TC vs. CC: OR &#x3d; 1.623, 95% CI: 1.055&#x2013;2.495, <italic>p</italic>&#x20;&#x3d; 0.027) and dominant model (TT &#x2b; CT vs. CC: OR &#x3d; 1.934, 95% CI: 1.148&#x2013;3.257, <italic>p</italic>&#x20;&#x3d; 0.013). The results showed no significant difference for the recessive model (TT vs. CC &#x2b; CT: OR &#x3d; 1.876, 95% CI: 0.989&#x2013;3.559, <italic>p</italic>&#x20;&#x3d; 0.054) (<xref ref-type="fig" rid="F2">Figure&#x20;2</xref>).</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>Meta-analysis with a random effects model for the association between the <italic>IGF-1</italic> rs35767 and T2DM susceptibility. <bold>(A)</bold> Allele model, T vs. C. <bold>(B)</bold> Additive model (homozygote comparisons): TT vs. CC.<bold>(C)</bold> Additive model (heterozygote comparisons): TC vs. CC. <bold>(D)</bold> Recessive model, TT vs. CC &#x2b; CT.<bold>(E)</bold> Dominant model, TT &#x2b; CT vs. CC. OR: odds ratio, CI: confidence interval, I-squared: measure to quantify the degree of heterogeneity in meta-analyses.</p>
</caption>
<graphic xlink:href="fgene-12-774489-g002.tif"/>
</fig>
</sec>
<sec id="s3-3">
<title>3.3 Sensitivity Analysis</title>
<p>Aiming to estimate the influence of each study on the overall OR below four genetic models and analysis the sources of high heterogeneity, sensitivity meta-analysis was performed with random effects model. The results were showed in <xref ref-type="fig" rid="F3">Figure3</xref>, omitting Gouda&#x2019;s study could reduce the heterogeneity, especially in the recessive model (TT vs. CC &#x2b; CT: I<sup>2</sup> &#x3d; 38.7%, <italic>p</italic>&#x20;&#x3d; 0.163), the fixed effects model for recessive effect of the T allele (TT vs. CC &#x2b; CT) produce results that were of borderline statistical significance (OR &#x3d; 1.206, 95% CI: 1.004&#x2013;1.448, <italic>p</italic>&#x20;&#x3d; 0.045); In addtion, other three modal show moderate degree of heterogeneity (T vs. C: I<sup>2</sup> &#x3d; 64.9%, <italic>p</italic>&#x20;&#x3d; 0.002; TT vs. CC: I<sup>2</sup> &#x3d; 70.3%, <italic>p</italic>&#x20;&#x3d; 0.009; TC vs. CC: I<sup>2</sup> &#x3d; 84.0%, <italic>p</italic>&#x20;&#x3d; 0.000; TT &#x2b; CT vs. CC: I<sup>2</sup> &#x3d; 85.8%, <italic>p</italic>&#x20;&#x3d; 0.000, respectively), the result showed no significant association between <italic>IGF-1</italic> rs35767 and T2DM risk with random effects model (T vs. C: OR &#x3d; 1.065, 95% CI: 0.983&#x2013;1.153, <italic>p</italic>&#x20;&#x3d; 0.126; TT vs. CC: OR &#x3d; 1.603, 95% CI: 0.996&#x2013;2.578, <italic>p</italic>&#x20;&#x3d; 0.052; TC vs. CC: OR &#x3d; 1.407, 95% CI: 0.937&#x2013;2.112, <italic>p</italic>&#x20;&#x3d; 0.099; TT &#x2b; CT vs. CC: OR &#x3d; 1.469, 95% CI: 0.978&#x2013;2.207, <italic>p</italic>&#x20;&#x3d; 0.064, respectively) (<xref ref-type="fig" rid="F4">Figure&#x20;4</xref>). Since there are not sufficient evidence to draw the conclusion that the rs35767 SNP is associated with&#x20;T2DM.</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>Sensitivity analysis by iteratively removing one study at a time. <bold>(A)</bold> Allele model, T vs. C. <bold>(B)</bold> Additive model (homozygote comparisons): TT vs. CC. <bold>(C)</bold> Additive model (heterozygote comparisons): TC vs. CC. <bold>(D)</bold> Recessive model, TT vs. CC &#x2b; CT. <bold>(E)</bold> Dominant model, TT &#x2b; CT vs. CC.</p>
</caption>
<graphic xlink:href="fgene-12-774489-g003.tif"/>
</fig>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>Meta-analysis for the association between the <italic>IGF-1</italic> rs35767 and T2DM susceptibility after omitting Gouda&#x2019;s study. <bold>(A)</bold> Allele model, T vs. C (random effects model). <bold>(B)</bold> Additive model (homozygote comparisons): TT vs. CC. (random effects model). <bold>(C)</bold> Additive model (heterozygote comparisons): TC vs. CC (random effects model) <bold>(D)</bold> Recessive model, TT vs. CC &#x2b; CT (fixed effects model) <bold>(E)</bold> Dominant model, TT &#x2b; CT vs. CC (random effects model). OR: odds ratio, CI: confidence interval, I-squared: measure to quantify the degree of heterogeneity in meta-analyses.</p>
</caption>
<graphic xlink:href="fgene-12-774489-g004.tif"/>
</fig>
</sec>
<sec id="s3-4">
<title>3.4&#x20;Subgroup-Analyses</title>
<p>As high heterogeneity was observed, we performed subgroup-analysis according to origin to evaluate the association between rs35767 and T2DM susceptibility in the allele model. The results suggested that rs35767 was significantly related to the risk of T2DM in <italic>XinJiang</italic>, China subgroup (T vs. C: OR &#x3d; 1.508, 95% CI: 1.210&#x2013;1.878, <italic>p</italic>&#x20;&#x3d; 0.000) with fixed effects model; a random effects model were used to analyze the other provinces, China, rs35767 was shown no significant association with T2DM risk (T vs. C: OR &#x3d; 1.051, 95% CI: 0.943&#x2013;1.173, <italic>p</italic>&#x20;&#x3d; 0.369); and not a significantly associatied in the other countries subgroup (excluding Gouda et&#x20;al. Literature) (T vs. C: OR &#x3d; 0.975, 95% CI: 0.922&#x2013;1.031, <italic>p</italic>&#x20;&#x3d; 0.376) with fixed effects model (<xref ref-type="fig" rid="F5">Figure&#x20;5</xref>).</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>The association between the <italic>IGF-1</italic> rs35767 and T2DM susceptibility in the subgroup for the allele model (T vs. C) <bold>(A)</bold> <italic>XinJiang</italic>, China (fixed effects model) <bold>(B)</bold> <italic>Other provinces</italic>, China (random effects model) <bold>(C)</bold> Other countries (fixed effects model). OR: odds ratio, CI: confidence interval, I-squared: measure to quantify the degree of heterogeneity in meta-analyses.</p>
</caption>
<graphic xlink:href="fgene-12-774489-g005.tif"/>
</fig>
</sec>
<sec id="s3-5">
<title>3.5 Publication Bias</title>
<p>The funnel plot was showed to be visually symmetrical (<xref ref-type="sec" rid="s10">Supplementary Figure S1</xref>, <xref ref-type="sec" rid="s10">Supplementary Figure S2</xref>, <xref ref-type="sec" rid="s10">Supplementary Figure S3</xref>). Begg&#x2019;s and Egger&#x2019;s tests were performed to detect publication bias. There was no significant publication bias appeared in all genetic models in overall analysis <italic>via</italic> Begg&#x2019;s test (all <italic>p</italic>&#x20;&#x3e; 0.05, <xref ref-type="sec" rid="s10">Supplementary Table S2</xref>), but for Egger&#x2019;s test, there was publication bias in the additive model (heterozygote comparisons) (Egger&#x2019;s test, <italic>p</italic>&#x20;&#x3d; 0.006, <xref ref-type="sec" rid="s10">Supplementary Table S2</xref>). We did not determine publication bias for Begg&#x2019;s test after omitting Gouda&#x2019;s study and subgroup analysis in all genetic models (all <italic>p</italic>&#x20;&#x3e; 0.05, <xref ref-type="sec" rid="s10">Supplementary Table S3</xref>, <xref ref-type="sec" rid="s10">Supplementary Table S4</xref>). However, for Egger&#x2019;s test, there were publication bias in the allele model (Egger&#x2019;s test, <italic>p</italic>&#x20;&#x3d; 0.039, <xref ref-type="sec" rid="s10">Supplementary Table S3</xref>) and additive model (heterozygote comparisons) (Egger&#x2019;s test, <italic>p</italic>&#x20;&#x3d; 0.031, <xref ref-type="sec" rid="s10">Supplementary Table&#x20;S4</xref>).</p>
</sec>
</sec>
<sec id="s4">
<title>4 Discussion</title>
<p>Previous studies have showed the inconsistent findings of association between <italic>IGF-1</italic> rs35767 and the risk of T2DM. Gouda et&#x20;al. revealed that the TT, TT &#x2b; CT genotypes of rs35767 were associated with an increased risk of T2DM in pregnant Egyptian women respectively (<xref ref-type="bibr" rid="B10">Gouda et&#x20;al., 2019</xref>). This results were successfully replicated in a Chinese Han population (Wang. 2019). Zhang et&#x20;al. found that the A allele of rs35767 contributed to the risk of developing T2DM in a Chinese Han population (<xref ref-type="bibr" rid="B44">Zhang.et&#x20;al., 2017</xref>). More recently, two studies documented that the association of the rs35767 in <italic>IGF-1</italic> was associated with T2DM in a Uyghur population in China (GulixiatiMaimaitituersun. 2020; <xref ref-type="bibr" rid="B36">Song et&#x20;al., 2015</xref>). However, some studies did not find evidence of an association between rs35767 and T2DM (<xref ref-type="bibr" rid="B8">Dupuis et&#x20;al., 2010</xref>; <xref ref-type="bibr" rid="B14">Hu et&#x20;al., 2010</xref>; <xref ref-type="bibr" rid="B9">Fujita et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B24">Liu et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B46">Zhao et&#x20;al., 2016</xref>; <xref ref-type="bibr" rid="B19">Li et&#x20;al., 2019</xref>; <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>). It is worth noting that the four largest studies with the most statistical power (Dupuis et&#x20;al., Hu et&#x20;al., Fujita et&#x20;al., and <xref ref-type="bibr" rid="B21">Li et&#x20;al., 2021</xref>) did not report statistically significant associations between the rs35767 SNP and T2DM, whereas five small studies (Song et&#x20;al., Zhang et&#x20;al., Wang et&#x20;al., Gouda et&#x20;al., and Gulixiati et&#x20;al.) all reported statistically significant associations. Compared the subjects selected for the studies between the larger and smaller studies, we found that in the Gouda et&#x20;al. study, the mean body mass index (BMI) of subjects with T2DM was 34.26&#x20;&#xb1; 5.7, which is very different from a mean BMI of 26.96&#x20;&#xb1; 4.57 for control subjects without T2DM. There were a significant difference concerning BMI between T2DM and control groups. This study included only pregnant women, was observed to be very influential on the initial analyses.</p>
<p>Previous studies have been reported that people with a low <italic>IGF-1</italic> level are prone to have diabetes mellitus (<xref ref-type="bibr" rid="B5">Colao et&#x20;al., 2013</xref>; <xref ref-type="bibr" rid="B34">Shankar and Li, 2013</xref>). The functional SNP rs35767 (T &#x3e; C) in <italic>IGF-1</italic> promoter, with C allele showed a higher transcriptional activity than promoter with T allele (<xref ref-type="bibr" rid="B37">Telgmann et&#x20;al., 2009</xref>). In terms of mechanism, the higher transcriptional activity of the C allele <italic>IGF-1</italic> promoter was contributed by the C/EBPD transcription activator, which bound exclusively to the C allele, but not to the T allele (<xref ref-type="bibr" rid="B3">Chen et&#x20;al., 2013</xref>; <xref ref-type="bibr" rid="B37">Telgmann et&#x20;al., 2009</xref>). Therefore, there may have low <italic>IGF-1</italic> expression level when promoter with rs35767&#xa0;T allele, which contribute to the development of T2DM. In our meta-analysis, we found that T allele, TT genotype, TT &#x2b; CT genotype of rs35767 increased T2DM risk in overall analysis, as well as increasing the risk of T2DM in Uyghur population. After omitting Gouda&#x2019;s study, the result showed TT genotype were of borderline statistical significance.</p>
<p>In overall analysis, high heterogeneity among studies were detected in four genetic models, which might be a result of the difference in ethnicity, country, genetic background and environmental factors (e.g., dietary, life style, climates) (<xref ref-type="bibr" rid="B30">Qin et&#x20;al., 2010</xref>). Then omittied Gouda&#x2019;s study, the heterogeneity was reduced. We found that the subjects of Gouda&#x2019;s study were pregnant Egyptian women, but participants of other studies were both male and female. Thus gender ratio may also had a certain impact on heterogeneity. The subgroup-analyses were detected by origin in allele model, the subgroup of Uyghur in Xinjiang, China have no heterogeneity, but other subgroups still had high heterogeneity. It is noteworthy that a previous study in Xinjiang found that 19.6% of Uyghur had diabetes, exceptionally higher than that in Kazakh (7.3%) and Han Chinese (9.1%) (<xref ref-type="bibr" rid="B18">Li et&#x20;al., 2012</xref>; <xref ref-type="bibr" rid="B36">Song et&#x20;al., 2015</xref>). The marriage pattern and unique life style might be responsible for the observation. One hand, the practice of endogamy in Uyghur population might also be a reason (<xref ref-type="bibr" rid="B40">Wang et&#x20;al., 2003</xref>; <xref ref-type="bibr" rid="B26">Mamet et&#x20;al., 2005</xref>). On the other hand, The most Uyghurs have different dietary habits from Han Chinese. They have more meat, high carbohydrate diets with a higher salt (more than 20&#xa0;g per day) and less unsaturated fatty acids compared with Han Chinese (<xref ref-type="bibr" rid="B43">Zhai et&#x20;al., 2007</xref>).</p>
<p>There still have several limitations in our meta-analysis. Firstly, there were limited studies which estimated <italic>IGF-1</italic> rs35767 and T2DM risk, only six articles had four gene models data, and the other six articles had only one allele model data. Secondly, the results did not adjustment the potential risk factors, including gender, body mass index, age, drinking and smoking status, and environmental factors. Thirdly, some results showed relatively obvious heterogeneity, but research the source of heterogeneity needs to more larger sample. Finally, some groups results existed potential publication bias in Egger&#x2019;s test. Therefore, the results of the article should be interpreted carefully.</p>
</sec>
<sec id="s5">
<title>5 Conclusion</title>
<p>This is the first time to perform a meta-analysis to systematically summarize the association between the <italic>IGF-1</italic> rs35767 and T2DM susceptibility. Overall, there is not enough evidence from the results of the meta-analysis to indicate that the rs35767 SNP has a statistically significant association with T2DM. Further more studies are necessary to verify the results.</p>
</sec>
</body>
<back>
<sec id="s6">
<title>Data Availability Statement</title>
<p>The original contributions presented in the study are included in the article/<xref ref-type="sec" rid="s10">Supplementary Material</xref> further inquiries can be directed to the corresponding authors.</p>
</sec>
<sec id="s7">
<title>Author Contributions</title>
<p>QZ, DZ, and QdD were suitable for the study design, literature searches, statistical analysis, and manuscript preparation. The study was supervised by XC, YW, and RG.</p>
</sec>
<sec id="s8">
<title>Funding</title>
<p>Support for this work includes funding from the National Natural Science Foundation of China (81873649); Doctoral scientific research Initiate funding project of Shunde Women and Children&#x2019;s Hospital of Guangdong Medical University (Maternity and Child Healthcare Hospital of Shunde Foshan) (2020BSQD007); Guangdong Medical University Research Foundation (GDMUM2020008 and GDMUM2020012); Medical Research Project of Foshan Health Bureau (20210188 and 20210289).</p>
</sec>
<sec sec-type="COI-statement" id="s9">
<title>Conflict of Interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="disclaimer" id="s20">
<title>Publisher&#x2019;s Note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
<sec id="s10">
<title>Supplementary Material</title>
<p>The Supplementary Material for this article can be found online at: <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fgene.2021.774489/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/fgene.2021.774489/full&#x23;supplementary-material</ext-link>
</p>
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