1. ¹Department of Endocrinology, University Hospital MAS, Malmö, Sweden
2. ²Department of Internal Medicine, University Hospital of Verona, Verona, Italy

Correspondence: Dr. Cristiano Fava, Department of Internal Medicine C, Hospital "GB Rossi" of Verona, P.zza LA Scuro 10, 37134 Verona, Italy E-mail: cristiano.fava@endo.mas.lu.se

^*This study was supported by grants from the Swedish Medical Research Council, the Swedish Heart and Lung Foundation, the Medical Faculty of Lund University, Malmö University Hospital, the Albert Påhlsson Research Foundation, the Crafoord foundation, the Ernhold Lundströms Research Foundation, and the Region Skane.

Received 24 February 2005; Revised 5 May 2005; Accepted 5 May 2005.

Abstract

Background: Blunted nocturnal blood pressure dipping (NBPD) as well as high variability in blood pressure (BPV) and low variability in heart rate (HRV), are associated with increased cardiovascular morbidity and mortality. The aim of this study was to determine whether these traits are heritable.

Methods: We studied 260 healthy siblings without antihypertensive drugs from 118 Swedish families. The BPV and HRV were defined as the standard deviation of BP and heart rate values recorded during 24 h, daytime (6 AM to 10 PM), and night-time (10 PM to 6 AM). The NBPD was defined as the ratio between night-time and daytime BP. Heritability was estimated with a maximal likelihood method implemented in the Solar software package with and without adjustment for significant covariates.

Results: At night, significant heritability was found for systolic (33%, P < .05), diastolic (36%, P < .05), and mean (42%, P < .01) BPV. After covariate adjustment the corresponding heritability values were 23% (P = .08), 29% (P < .05), and 37% (P < .05). Daytime BPV was not heritable. The heritability of NBPD was 38% (P < .05) for systolic, 9% (P = .29) for diastolic, and 36% (P < .05) for mean BP, but after adjustment only systolic NBPD was significant (29%, P < .05). Heart rate was highly heritable both during daytime (57%, P < .001) and night-time (58%, P < .001), but the variability of heart rate, after adjustment, was only significant at night (37%, P < .05).

Conclusions: Our data suggest that BPV and HRV are partially under genetic control and that genetic loci of importance for these traits could be mapped by linkage analysis.