Modifying effects of the R389G β₁-adrenoceptor polymorphism on resting heart rate and blood pressure in patients with obstructive sleep apnoea

OSA (obstructive sleep apnoea) stimulates sympathetic nervous activity and elevates resting HR (heart rate) and BP (blood pressure). In the present study in a cohort of 309 untreated OSA patients, the resting HR and BP during the daytime were correlated with AHI (apnoea/hypopnea index) and compared with patients with R389R (n=162), R389G (n=125) and G389G (n=22) genotypes of the β₁-adrenoreceptor R389G polymorphism. We analysed the impact of the genotype on the decline of HR and BP in a subgroup of 148 patients (R389R, n=86; R389G, n=54; G389G, n=8) during a 6-month follow-up period under CPAP (continuous positive airway pressure) therapy during which cardiovascular medication remained unchanged. In untreated OSA patients, we found an independent relationship between AHI and resting HR (β=0.096, P<0.001), systolic BP (β=0.09, P=0.021) and diastolic BP (β=0.059, P=0.016). The resting HR/BP, however, did not differ among carriers with the R389R, R389G and G389G genotypes. CPAP therapy significantly reduced HR [−2.5 (−1.1 to −4.0) beats/min; values are mean difference (95% confidence intervals)] and diastolic BP [−3.2 (−1.5 to −5.0) mmHg]. The decline in HR was more significantly pronounced in the R389R group compared with the Gly³⁸⁹ carriers [−4.1 (−2.3 to −5.9) beats/min (P<0.001) compared with −0.2 (2.1 to −2.6) beats/min (P=0.854) respectively; Student's t test between groups, P=0.008]. Diastolic BP was decreased significantly (P<0.001) only in Gly³⁸⁹ carriers (R389G or G389G) compared with R389R carriers [−5.0 (−2.3 to −7.6) mmHg compared with −2.0 (0.4 to −4.3) mmHg respectively]. ANOVA revealed a significant difference (P=0.023) in HR reduction between the three genotypes [−4.1 (±8.4) beats/min for R389R, −0.5 (±9.3) beats/min for R389G and +1.9 (±7.2) beats/min for G389G]. In conclusion, although the R389G polymorphism of the β₁-adrenoceptor gene did not influence resting HR or BP in untreated OSA patients, it may modify the beneficial effects of CPAP therapy on these parameters.