title: Dipping and variability of blood pressure and heart rate at night are heritable traits.
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.
authors.affiliation: Department of Endocrinology, University Hospital MAS, Malmö, Sweden. cristiano.fava@endo.mas.lu.se
authors.forename: Cristiano
authors.initials: C
authors.lastname: Fava
authors.forename: Philippe
authors.initials: P
authors.lastname: Burri
authors.forename: Peter
authors.initials: P
authors.lastname: Almgren
authors.forename: Guido
authors.initials: G
authors.lastname: Arcaro
authors.forename: Leif
authors.initials: L
authors.lastname: Groop
authors.forename: U
authors.initials: U
authors.lastname: Lennart Hulthén
authors.forename: Olle
authors.initials: O
authors.lastname: Melander
mesh_terms: D000328:Adult; D000367:Age Factors; D001794:Blood Pressure / Q000235:genetics* / Q000502:physiology; D018660:Blood Pressure Monitoring, Ambulatory; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000235:genetics* / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D019655:Quantitative Trait, Heritable; D012737:Sex Factors; D035781:Siblings; D013223:Statistics as Topic