title: Genetic variation within a metabolic motif in the chromogranin a promoter: pleiotropic influence on cardiometabolic risk traits in twins.
abstract: BACKGROUND
  The cardiometabolic syndrome comprised of multiple correlated traits, but its origin is incompletely understood. Chromogranin A (CHGA) is required for formation of the catecholamine secretory pathway in sympathochromaffin cells. In twin pair studies, we found that CHGA traits aggregated with body mass index (BMI), as well as its biochemical determinant leptin. METHODS Here we used the twin method to probe the role of heredity in generating such risk traits, and then investigated the role of risk-trait-associated CHGA promoter genetic variation in transfected chromaffin cells. Trait heritability (h(2)) and shared genetic determination among traits (pleiotropy, genetic covariance, ρ(G)) were estimated by variance components in twin pairs.
  
  
  RESULTS
  CHGA, BMI, and leptin each displayed substantial h(2), and the traits also aggregated with several features of the metabolic syndrome (e.g., insulin resistance, blood pressure (BP), hypertension, catecholamines, and C-reactive protein (CRP)). Twin studies demonstrated genetic covariance (pleiotropy, ρ(G)) for CHGA, BMI, and leptin with other metabolic traits (insulin resistance, BP, and CRP). We therefore investigated the CHGA locus for mechanisms of codetermination with such metabolic traits. A common functional variant in the human CHGA promoter (G-462A, rs9658634, minor allele frequency ~21%) was associated with leptin and CRP secretion, as well as BMI, especially in women; marker-on-trait effects on BMI were replicated across twin populations on two continents. In CHGA promoter/luciferase reporter plasmids transfected into chromaffin cells, G-462A alleles differed markedly in reporter expression. The G-462A variant disrupted predicted transcriptional control by a PPARγ/RXRα motif and costimulation by PPARγ/RXRα and their cognate ligands, differentially activated the two alleles. During chromatin immunoprecipitation, endogenous PPARγ bound the motif.
  
  
  CONCLUSIONS
  Multiple features of the metabolic syndrome are thus under joint (pleiotropic) genetic determination, with CHGA as one such contributory locus: a common polymorphism in the promoter (G-462A) of CHGA predicts such heritable metabolic traits as BMI and leptin. CHGA promoter variant G-462A was not only associated with such metabolic traits but also disrupted a PPARγ/RXRα motif and responded differentially to characteristic trans-activators of that motif. The results suggest novel links between the catecholaminergic system and risk for the metabolic syndrome as well as systemic hypertension.
authors.affiliation: Department of Medicine, University of California, San Diego, CA, USA.
authors.forename: Fangwen
authors.initials: F
authors.lastname: Rao
authors.forename: Stephane
authors.initials: S
authors.lastname: Chiron
authors.forename: Zhiyun
authors.initials: Z
authors.lastname: Wei
authors.forename: Maple M
authors.initials: MM
authors.lastname: Fung
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Chen
authors.forename: Gen
authors.initials: G
authors.lastname: Wen
authors.forename: Srikrishna
authors.initials: S
authors.lastname: Khandrika
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ziegler
authors.forename: Beben
authors.initials: B
authors.lastname: Benyamin
authors.forename: Grant
authors.initials: G
authors.lastname: Montgomery
authors.forename: John B
authors.initials: JB
authors.lastname: Whitfield
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Martin
authors.forename: Jill
authors.initials: J
authors.lastname: Waalen
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Hamilton
authors.forename: Sushil K
authors.initials: SK
authors.lastname: Mahata
authors.forename: Daniel T
authors.initials: DT
authors.lastname: O'Connor
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D002097:C-Reactive Protein / Q000235:genetics; D019439:Chromaffin Cells / Q000378:metabolism; D053379:Chromogranin A / Q000235:genetics*; D005260:Female; D058685:Genetic Pleiotropy; D006801:Humans; D020738:Leptin / Q000235:genetics; D008297:Male; D024821:Metabolic Syndrome / Q000235:genetics*; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012306:Risk; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: C506150:CHGA protein, human; D053379:Chromogranin A; D020738:Leptin; D002097:C-Reactive Protein