Genotyping of mannose-binding lectin (MBL2) codon 54 and promoter alleles in Egyptian infants with acute respiratory tract infections

Abstract

Background: MBL2 gene polymorphisms affect serum concentration of mannose-binding lectin and are associated with infectious conditions. Acute respiratory tract infections are among the most prevalent infections in childhood with the highest incidence among children younger than 2 years. This study aimed at correlation between the occurrence of acute respiratory tract infections and the prevalence of MBL2 gene codon (54) and promoter variants among the Egyptian infants in the study.
Subjects and methods: This case-control study included 25 neonates (0.21 ±0.19 months), 25 infants (9.65± 8.5 months) with acute respiratory tract infection and normal control group. CBC, CRP and chest X-ray were done. DNA was extracted from peripheral blood. Genotypes of MBL gene codon 54-exon 1(G54D) were identified by PCR-RFLP analysis. MBL2 promoter genotyping was performed by allele-specific polymorphisms at 550 (H/L) and 221(X/Y).
Results: Incidence of LX promoter haplotype among the patients was (58%) (p< 0.05). Homozygosity for codon (54) allele A (high expression activity) among patients was (72%) (p> 0.05). Heterozygote codon 54 A/B genotype appeared more in patients (18%) (p< 0.05). Mutant genotype (too low expression activity) was more in patients but the difference was insignificant. Collectively the mutant allele (glycine to aspartic acid, allele B) appeared in 28% of patients compared to 20% in control (p> 0.05). YA/XA heterozygote promoter genotype was more prevalent among patients group (44%) (p< 0.05). Low-expression promoters (XA/B) and (B/B) appeared more in the patients (20%) compared to (12%) among control group (p> 0.05). Among ICU neonates, LX promoter was the most  prevalent among all grades of respiratory distress (39.13%) followed by LY allele (34.78%). In the infants group, LY allele was (52.1%) with equal distribution of LY and HY (23.91% each).
Conclusion: Although there is a significantly increased incidence of LX promoter coding for low serum MBL concentrations among the ARTI patients; the YA/XA heterozygote promoter genotype was more prevalent over the homozygote mutant genotype. Also, the heterozygote codon 54 A/B genotype was more prevalent in the group of patients compared to the control. This may be an example of heterosis (heterozygote advantage) which may support the concept of balanced polymorphism.

Keywords: Mannose binding lectin; Respiratory distress; MBL2 gene; Polymorphism