title: Genetic influences on daytime and night-time blood pressure: similarities and differences.
abstract: OBJECTIVE
  To examine whether the genetic influences on blood pressure (BP) during night-time are different from those during daytime and the extent to which they depend on ethnicity or sex.
  
  
  METHODS
  Ambulatory BP was measured in 240 European-American and 190 African-American twins (mean +/- SD age, 17.2 +/- 3.4). Individuals with night-time BP falls more than 10% of the daytime values were defined as dippers. A bivariate analysis of the daytime and the night-time BP levels, as well as a liability-threshold model of dippers vs. nondippers were used.
  
  
  RESULTS
  Bivariate model fitting showed no ethnic or sex differences for any of the measures, with heritabilities of 0.70 and 0.68 for SBP and 0.70 and 0.64 for DBP at daytime and at night-time. The genetic influences on daytime and night-time were not significantly different for SBP or DBP. The bivariate analysis also indicated that about 56 and 33% of the heritabilities of night-time SBP and DBP could be attributed to genes that also influenced daytime levels. The specific heritabilities due to genetic effects only influencing night-time values were 0.30 for SBP and 0.43 for DBP. The heritabilities of systolic and diastolic dipping were 0.59 and 0.81, respectively.
  
  
  CONCLUSIONS
  Independent of ethnicity and sex, an overlap exists between genes that influence daytime and night-time BP, as well as a significant genetic component that is specific to the night-time BP. These findings suggest that different genes or sets of genes contribute to BP regulation at daytime and night-time.
authors: Department of Pediatrics, Medical College of Georgia, Georgia Prevention Institute, Augusta, GA 30912, USA. xwang@mcg.edu
authors: Xiaoling
authors: X
authors: Wang
authors: Xiuhua
authors: X
authors: Ding
authors: Shaoyong
authors: S
authors: Su
authors: Weili
authors: W
authors: Yan
authors: Gregory
authors: G
authors: Harshfield
authors: Frank
authors: F
authors: Treiber
authors: Harold
authors: H
authors: Snieder
mesh_terms: D000293:Adolescent; D001741:Black or African American / Q000208:ethnology / Q000235:genetics; D001794:Blood Pressure / Q000235:genetics*; D018660:Blood Pressure Monitoring, Ambulatory; D002320:Cardiovascular Physiological Phenomena / Q000235:genetics*; D002940:Circadian Rhythm / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation; D005796:Genes; D006801:Humans; D008297:Male; D019655:Quantitative Trait, Heritable; D012737:Sex Factors; D014481:United States / Q000208:ethnology; D044465:White People / Q000208:ethnology / Q000235:genetics