title: Specific genetic influences on nighttime blood pressure.
abstract: OBJECTIVE
  Nighttime blood pressure (BP) has been shown to be superior to daytime BP in predicting hypertension related target organ damage and cardiac mortality. In our Georgia Cardiovascular Twin Study, we showed that apart from the genes that also influence daytime BP, specific genetic determinants explained 44% and 67% of the nighttime systolic BP (SBP) and diastolic BP (DBP) heritabilities, respectively. Here, we determined whether these results could be confirmed in a much larger twin cohort of young adults with 24-hour ambulatory BP measurements.
  
  
  METHODS
  Ambulatory BP was available in 703 white twins (308 pairs and 87 singletons, aged 18-34 years, 50% males) from the Prenatal Programming Twin Study. A bivariate quantitative genetic twin model was used to analyze daytime and nighttime BP. We conducted a meta-analysis to compare and integrate results from the 2 twin cohorts.
  
  
  RESULTS
  Model fitting showed no sex differences for any of the measures. Heritabilities were 0.60 and 0.51 for SBP and 0.54 and 0.46 for DBP at daytime and nighttime. The specific heritability due to novel genetic effects emerging during the nighttime was 0.21 for SBP and 0.26 for DBP, which comprised 41% and 57% of the total nighttime heritability for SBP and DBP, respectively. Meta-analysis confirmed absence of cohort differences with very similar combined results.
  
  
  CONCLUSIONS
  In addition to genes that influence both daytime and nighttime BP, a large part of the heritability is explained by genes that specifically influence BP at night.
authors.affiliation: Georgia Prevention Center, Institute of Prevention and Public Health, Georgia Regents University, Augusta, Georgia;
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Xu
authors.affiliation: Georgia Prevention Center, Institute of Prevention and Public Health, Georgia Regents University, Augusta, Georgia;
authors.forename: Shaoyong
authors.initials: S
authors.lastname: Su
authors.affiliation: College of Nursing, Medical University of South Carolina, Charleston, South Carolina;
authors.forename: Frank A
authors.initials: FA
authors.lastname: Treiber
authors.affiliation: Department for Human Genetics, University Hospital Gasthuisberg, KU Leuven, Leuven, Belgium;
authors.forename: Robert
authors.initials: R
authors.lastname: Vlietinck
authors.affiliation: Hypertension and Cardiovascular Rehabilitation Unit, Department of Cardiovascular Diseases, KU Leuven, Leuven, Belgium;
authors.forename: Robert
authors.initials: R
authors.lastname: Fagard
authors.affiliation: Department for Human Genetics, University Hospital Gasthuisberg, KU Leuven, Leuven, Belgium;
authors.forename: Catherine
authors.initials: C
authors.lastname: Derom
authors.affiliation: Research School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, Maastricht, The Netherlands; Cluster of Genetics and Cell Biology, Department of Complex Genetics, Maastricht University Medical Centre, Maastricht, The Netherlands;
authors.forename: Marij
authors.initials: M
authors.lastname: Gielen
authors.affiliation: Medical Research Council Epidemiology Unit, Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, United Kingdom; Department of Biomedical Kinesiology, Faculty of Kinesiology and Rehabilitation Sciences, University Hospital Gasthuisberg, KU Leuven, Leuven, Belgium; Genetics of Obesity and Related Metabolic Traits Program, Institute for Personalized Medicine, Child Health and Development Institute, Department of Preventive Medicine, Mount Sinai School of Medicine, New York;
authors.forename: Ruth J F
authors.initials: RJ
authors.lastname: Loos
authors.affiliation: Unit of Genetic Epidemiology and Bioinformatics, Department of Epidemiology, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Harold
authors.initials: H
authors.lastname: Snieder
authors.affiliation: Georgia Prevention Center, Institute of Prevention and Public Health, Georgia Regents University, Augusta, Georgia; xwang@gru.edu.
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000235:genetics*; D018660:Blood Pressure Monitoring, Ambulatory; D002940:Circadian Rhythm / Q000235:genetics*; D005260:Female; D005838:Genotype; D040941:Heredity; D006801:Humans; D008297:Male; D010641:Phenotype; D011446:Prospective Studies; D013997:Time Factors; D014427:Twins / Q000235:genetics*; D055815:Young Adult
keywords: heritability; meta-analysis; nighttime blood pressure; twin study.