Genetic polymorphisms of the β₂-Adrenergic receptor in the severity of bronchial asthma

Background: Genetic and environmental factors are known to affect the incidence and severity of asthma. Stimulation of β₂-Adrenergic Receptor (β₂AR) results in smooth muscle relaxation, leading to decrease in resistance of airflow. The gene encoding the β₂AR has recently been sequenced. The β₂AR genotype at the polymorphic loci of codons 16, 27, 34, and 164 was known to cause changes in the amino acids. The relationships between the structure of the β₂AR and its functions are being elucidated. Purpose: The gene encoding the β₂AR was carried out to assess the frequency of polymorphisms in bronchial asthma, to determine whether these polymorphisms have any relation to the severity, or nocturnal symptoms in bronchial asthma. Methods: The subjects studied were 103 patients with bronchial asthma, which consisted of 30 mild episodic, 32 mild persistent, 17 moderate, and 24 severe asthma patients. The polymorphisms of the β₂AR gene were detected by mutated allele specific amplification (MASA) method at the codons 16, 27, 34, and 164. Results: The most frequent polymorphism was arginine 16 to glycine. The other two polymorphisms, valine 34 to methionine and glutamine 27 to glutamic acid occurred in 11 and 6 patients respectively. The polymorphism of threonine 164 to isoleucine was not found in our enrolled patients. The homozygous polymorphism of β₂AR gene was found in only arginine 16 to glycine (12.6%). The heterozygous polymorphisms of β₂AR gene were in arginine 16 to glycine, valine 34 to methionine, and glutamine 27 to glutamic acid, as 65.1%, 10.7%, and 5.8% respectively in asthma patients. The presence of arginine 16 to glycine heterozygous or/and homozygous polymorphism was associated in severe asthma (p = 0.015), but there was no association between the other three polymorphisms and the severity of asthma The frequency of the β₂AR gene polymorphisms was no relation in nocturnal asthma as compared with non-nocturnal asthma. Conclusion: The arginine 16 to glycine polymorphism of the β₂AR gene is the most frequently found asthma patients and association with severe asthma. But there was no association between the polymorphism of the β₂AR gene and nocturnal asthma.