β2‐adrenergic receptor gene polymorphisms in myasthenia gravis (MG)
The β2‐adrenergic receptor (β2‐AR) belongs to the group of G‐protein coupled receptors and is present mainly on skeletal and cardiac muscle cells and lymphocytes. The gene encoding β2‐AR (ADRB2) displays a moderate degree of heterogeneity in the human population. The distribution of polymorphisms at amino acid positions 16, 27 and 164 is changed in asthma, hypertension and obesity. We have earlier reported a decreased density of the β2‐AR on peripheral blood mononuclear cells and the presence of β2‐AR antibodies in patients with MG. Since certain polymorphisms affect the function of the β2‐AR, it was of interest to analyse these in MG. Using allele‐specific polymerase chain reaction amplification, we revealed an over‐representation of homozygosity for Arg16 and a lower prevalence of homozygosity for Gly16 in MG patients compared with healthy individuals. The increased frequency of homozygosity for Arg16 was due to a contribution from patients with generalized MG but not from patients with only ocular disease. Homozygosity for Glu27 was negatively associated with both the presence of β2‐AR antibodies and severity of disease. Moreover, acetylcholine receptor (AChR) antibodies were more often present in patients being homozygous for Gln27. Our results imply that homozygosity for Arg16 confers susceptibility to generalized MG, and that certain polymorphisms at amino acid position 27 are associated with subgroups of patients.