Head-up tilt induced syncope and adenosine A2A receptor gene polymorphism

High adenosine plasma levels and high expression of adenosine A(2A) receptors are observed in patients with unexplained syncope and a positive head-up tilt test (HUT). This study aimed to evaluate the single nucleotide polymorphism (SNP) (c.1364 T > C) which is the most commonly found polymorphism in the A(2A) receptor gene, in patients with unexplained syncope undergoing HUT. One hundred and five patients with unexplained syncope who underwent HUT were included. Fifty-two had a positive test. Receptor genotype determinations were performed in patients and in 121 healthy subjects. Genotype (TT, CC, TC) was determined from DNA leucocytes. The distribution of the polymorphism showed significant (P < 0.0001) difference when the results of HUT were analysed. Fifty-two per cent of patients with a positive HUT had a CC genotype and 34.6% a TC genotype, whereas 13.2% of the patients with a negative HUT had a CC genotype and 71.7% a TC genotype. Patients with a CC genotype had a higher incidence of spontaneous syncopal episodes. In patients with unexplained syncope, a significant association between high incidence of syncopal episodes, positive HUT, and the presence of the CC variant in the adenosine A(2A) receptor gene was elicited.