RESUMO
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. 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]. Incidence of LX promoter haplotype among the patients was [58%] [p < 0.05]. Homo-zygosity 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]. 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