Association of beta(2)-adrenergic receptor gene polymorphisms and nocturnal asthma in Saudi patients

Background and objectives: Two polymorphisms of beta(2)-adrenergic receptor (β(2)-AR) gene, namely the substitution from arginine (Arg) to glycine (Gly) at codon 16 and from glutamine (Gln) to glutamic (Glu) at codon 27, are linked with functional changes in the β(2)-AR in the respiratory system even though they are not deemed to be susceptibility genes for asthma per se. The objective of this study was to investigate this association in a subset of asthmatic patients, namely those with nocturnal asthma.

Methods: The β(2)-AR gene polymorphisms at codon 16 and 27 were assessed in 40 patients clinically diagnosed with nocturnal asthma and 96 normal controls. Genomic DNA was obtained from whole blood and genotyping was carried out by a PCR based restriction fragment length polymorphism technique.

Results: There was a statistically significant difference in genotype frequencies at codon 16 (Arg/Gly) between nocturnal asthmatic patients and normal control subjects (P < 0.05). However, there was no statistically significant difference in allele frequencies between the two groups. In addition, there was a significant association between Arg16-Gly genotype with nocturnal asthma compared to homozygous Gly16 (codominant model P = 0.0033, OR = 3.69: 95% CI: 1.49-9.12). However, there were no statistically significant differences in genotype and allele frequencies at codon 27 (Gln/Glu) between the normal control and nocturnal asthmatic groups (χ(2) = 1.81, P = 0.41). The results also indicate that linkage disequilibrium existed between the β(2)-AR codon 16 and β(2)-AR codon 27 polymorphism (|D´| = 0.577). The data for all haplotypes did not show a statistically significant association.

Conclusion: We present the genotype and allele frequencies of β(2)-AR gene polymorphisms in normal Saudi subjects and nocturnal asthmatic patients. There was a significant difference in genotype frequencies at codon 16 (Arg/Gly). However, our study indicates a poor association of individual single nuceotide polymorphisms with nocturnal asthma.