In recent years, there has been an increase in both domestic and foreign research on MBL gene polymorphism and sepsis. However, there are certain limitations in this area. For example, the small quantity of samples increases the possibility of false-positives and false-negatives from various geographic regions and ethnicities, while the inconsistencies in the composition of the control population in the study, the various underlying diseases, the inconsistent research methods, and the different levels of MBL concentrations all have a different integration ability for various pathogens, particularly for children of different ages.
The MBL gene has different mutation frequencies in different population types. For example, the mutation frequency of Asp54 in a population from Hong Kong is 0.11, while it is 0.19 in a population from England, and is very rare among Africans. The mutation frequency of Glu57 in Caucasians is 0.02 and in African Gambians is 0.29, however, Cys52 has always maintained a low mutation frequency in the study population .
Liu. et al.  performed genotyping (GG, GA, AA, G, A) on the MBL2 gene rs1800450 polymorphism (codon 54A/B, G230A) in patients with sepsis and found that allele genes can significantly increase the risk of sepsis. The GA genotype is closely related to the onset of sepsis, while the AA genotype is not significantly related to the occurrence of sepsis. Furthermore, the frequency of the GA genotype and the A allele based on the MBL2 gene rs1800450 polymorphism was significantly increased and further ELISA testing demonstrated that the serum MBL level of the sepsis group was significantly lower than that of the control group, as was the MBL level of the rs1800450 genotype. There was also a significant downward trend, so it is inferred that the rs1800450A allele increases the risk of sepsis by reducing MBL levels. A 2015 study showed that the B allele of the A/B polymorphism is a risk factor for sepsis in Turks . Huh et al.  included a total of 266 sepsis patients and 398 healthy patients and detected three single nucleotide polymorphisms (54, -550, +4) in the MBL2 gene related to sepsis in a Korean population. Seemingly, a single nucleotide polymorphism has nothing to do with the occurrence of sepsis, but the homozygosity of promoter 54 (A/A) and promoter -550 (H/H) is associated with the degree of severity of sepsis, but is not related to the outcome of sepsis. Mills et al.  genotyped and analyzed four MBL2 mononucleotide polymorphisms (rs5030737, rs1800450, rs1800451, rs7096206) in 1,839 European patients with community-acquired pneumonia and peritonitis sepsis and found that, in this large cohort of adult patients, there was no obvious association between the MBL2 gene polymorphism and the susceptibility to sepsis.
When the MBL gene polymorphism is inconsistent with the research results of sepsis susceptibility, a meta-analysis is the best analysis method. Compared with traditional descriptive literature reviews, a meta-analysis is a quantitative analysis method with better accuracy and higher testing power .
The current study summarized the research articles on the association between MBL gene polymorphism and sepsis published before December 1, 2019, then conducted a meta-analysis to analyze the association between the MBL gene polymorphism and the risk of sepsis. The results suggested that allele O may increase the risk of sepsis overall and that, among the three models of the MBL +54A/B gene polymorphism, the MBL +54A/B gene polymorphism had a significant correlation with the risk of sepsis. In the adult group, the MBL A/O gene polymorphism was related to the risk of sepsis in the dominant and allele model, while the MBL+54A/B gene polymorphism was significantly related to the risk of sepsis in the recessive model. In the children group, none of the polymorphic sites were found to be significantly related to the occurrence of sepsis in any of the three models.
For data sets with ≥ 10 articles, funnel plots, Begg's tests, and Egger's tests were used to evaluate the possibility of publication bias. For the total and adult groups, the results demonstrated no publication bias in the unadjusted estimate of the association between the MBL A/O and -211Y/X gene polymorphism and sepsis.
In summary, the MBL gene polymorphisms that are closely related to the occurrence of sepsis are primarily A/O and +54A/B, Although not every model or population has consistent results; MBL -221Y/X and -550H/L have no obvious association with the occurrence of sepsis in different age groups or different models.
There are still some limitations to the current study. First, the populations included in the study came from different countries/regions, hospitals, and/or treatment levels. In addition, there were disparities in the detection methods of the genotypes in the studies, the sources of specimens were also different, and the control group settings were inconsistent, all of which might affect the correlation between the genetic polymorphism and the risk of sepsis. Finally, the current study only collected the English documents from the three major databases; documents in other languages or other databases would inevitably be missed, which would affect the results.
Conclusions The polymorphisms of MBL that are related to the occurrence of sepsis are primarily A/O and +54A/B, while -221Y/X and -550H/L have no clear relationship with the susceptibility of sepsis in various age groups or different models.