Genetics and Cardiovascular Reactivity in Young Twins
Condition: Cardiovascular Diseases; Heart Diseases; Hypertension
MeSH terms: Cardiovascular Diseases; Heart Diseases
Study type: Observational

Summary: 
      To evaluate the effects of genetic variants in all of the nine adrenergic receptor subtype
      genes, alone or in combination, on cardiovascular reactivity and other quantitative
      cardiovascular traits in a population of 1048 healthy young twins.
    

Detailed description: 
      BACKGROUND:

      Several studies have shown that cardiovascular reactivity (CVR) to acute laboratory stress is
      a stable and heritable trait and predictive of future blood pressure (BP) levels and
      essential hypertension (EH). The sympathetic nervous system (SNS) has a major role in BP
      regulation and adrenergic receptor subtypes mediate BP responses to acute challenges. As
      such, our hypothesis is that individual differences in CVR are partly determined by variation
      in genes encoding for adrenergic receptors mediating the sympathoadrenal response to stress.
      There is increasing evidence that this cardiovascular response is regulated by multiple
      adrenoceptor subtypes with structural homology. To date, nine homologous adrenergic receptor
      subtypes have been described. Only one study has found a gene-gene interaction upon CV
      disease incorporating two adrenergic receptor subtypes. Genetic variants in all the nine
      adrenergic receptor subtypes have never before been investigated in a single study as this
      study will do.

      DESIGN NARRATIVE:

      The study will evaluate the effects of genetic variants in all of the nine adrenergic
      receptor subtype genes, alone or in combination, on CVR and other quantitative cardiovascular
      traits in a population of 1048 healthy youth. Subjects are black and white twins that have
      already been comprehensively phenotyped as part of the Georgia Cardiovascular Twin Study
      (HL56622). Racial differences in adrenoceptor gene effects will receive special attention,
      because such differences may offer a partial explanation for the higher prevalence of
      essential hypertension (EH) in blacks. Primary measures are systolic BP at rest and in
      response to two behavioral stressors. Secondary measures are diastolic BP, cardiac output and
      total peripheral resistance (TPR) at rest and in response to the stressors, left ventricular
      mass (LVM), endothelium dependent arterial dilation to reactive hyperemia (EDAD), arterial
      stiffness and 24-hour ambulatory BP. This data set will be expanded through collection of
      buccal cell DNA from the parents of the twins, enabling performance of TDTs (transmission
      disequilibrium tests) and haplotype reconstruction and analyses. This candidate gene study in
      a large group of black and white twins including TDT and haplotype analyses provides an
      innovative approach to help identify individuals at particular risk for the development of EH
      and improve options for primary prevention as well as individualized therapy of EH
      (pharmacogenetics).