title: C-reactive protein, an 'intermediate phenotype' for inflammation: human twin studies reveal heritability, association with blood pressure and the metabolic syndrome, and the influence of common polymorphism at catecholaminergic/beta-adrenergic pathway loci.
abstract: BACKGROUND
  C-reactive protein (CRP) both reflects and participates in inflammation, and its circulating concentration marks cardiovascular risk. Here we sought to understand the role of heredity in determining CRP secretion.
  
  
  METHODS
  CRP, as well as multiple facets of the metabolic syndrome, were measured in a series of 229 twins, both monozygotic (MZ) and dizygotic (DZ), to estimate trait heritability (h2). Single nucleotide polymorphism (SNP) genotyping was done at adrenergic pathway loci. Haplotypes were inferred from genotypes by likelihood methods. Association of CRP with hypertension and the metabolic syndrome was studied in a larger series of 732 individuals, including 79 with hypertension.
  
  
  RESULTS
  MZ and DZ twin variance components indicated substantial h2 for CRP, at approximately 56 +/- 7% (P < 0.001). CRP was significantly associated (P < 0.05) with multiple features of the metabolic syndrome in twins, including body mass index (BMI), blood pressure (BP), leptin and lipids. In established hypertension, elevated CRP was associated with increased BP, BMI, insulin, HOMA (index of insulin resistance), leptin, triglycerides and norepinephrine. Twin correlations indicated pleiotropy (shared genetic determination) for CRP with BMI (P = 0.0002), leptin (P < 0.001), triglycerides (P = 0.002) and systolic blood pressure (SBP) (P = 0.042). Approximately 9800 genotypes (43 genetic variants at 17 loci) were scored within catecholaminergic pathways: biosynthetic, receptor and signal transduction. Plasma CRP concentration in twins was predicted by polymorphisms at three loci in physiological series within the catecholamine biosynthetic/beta-adrenergic pathway: TH (tyrosine hydroxylase), ADRB1 (beta1-adrenergic receptor) and ADRB2 (beta2-adrenergic receptor). In the TH promoter, common allelic variation accounted for up to approximately 6.6% of CRP inter-individual variance. At ADRB1, variation at Gly389Arg predicted approximately 2.8% of CRP, while ADRB2 promoter variants T-47C and T-20C also contributed. Particular haplotypes and diplotypes at TH and ADRB1 also predicted CRP, though typically no better than single SNPs alone. Epistasis (gene-by-gene interaction) was demonstrated for particular combinations of TH and ADRB2 alleles, consistent with their actions in a pathway in series. In an illustration of pleiotropy, not only CRP but also plasma triglycerides were predicted by polymorphisms at TH (P = 0.0053) and ADRB2 (P = 0.027).
  
  
  CONCLUSIONS
  CRP secretion is substantially heritable in humans, demonstrating pleiotropy (shared genetic determination) with other features of the metabolic syndrome, such as BMI, triglycerides or BP. Multiple, common genetic variants in the catecholaminergic/beta-adrenergic pathway contribute to CRP, and these variants (especially at TH and ADRB2) seem to interact (epistasis) to influence the trait. The results uncover novel pathophysiological links between the adrenergic system and inflammation, and suggest new strategies to probe the role and actions of inflammation within this setting.
authors.affiliation: Department of Medicine, University of California at San Diego, California 92093-0838, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wessel
authors.forename: Guillermo
authors.initials: G
authors.lastname: Moratorio
authors.forename: Fangwen
authors.initials: F
authors.lastname: Rao
authors.forename: Manjula
authors.initials: M
authors.lastname: Mahata
authors.forename: Lian
authors.initials: L
authors.lastname: Zhang
authors.forename: William
authors.initials: W
authors.lastname: Greene
authors.forename: Brinda K
authors.initials: BK
authors.lastname: Rana
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kennedy
authors.forename: Srikrishna
authors.initials: S
authors.lastname: Khandrika
authors.forename: Pauline
authors.initials: P
authors.lastname: Huang
authors.forename: Elizabeth O
authors.initials: EO
authors.lastname: Lillie
authors.forename: Pei-An Betty
authors.initials: PA
authors.lastname: Shih
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Smith
authors.forename: Gen
authors.initials: G
authors.lastname: Wen
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Hamilton
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ziegler
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Witztum
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Schork
authors.forename: Geert W
authors.initials: GW
authors.lastname: Schmid-Schönbein
authors.forename: Daniel T
authors.initials: DT
authors.lastname: O'Connor
mesh_terms: D000328:Adult; D015992:Body Mass Index; D002097:C-Reactive Protein / Q000032:analysis / Q000235:genetics* / Q000276:immunology; D002395:Catecholamines / Q000032:analysis / Q000378:metabolism; D003324:Coronary Artery Disease / Q000235:genetics* / Q000276:immunology; D004843:Epistasis, Genetic; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood* / Q000235:genetics; D007249:Inflammation / Q000235:genetics* / Q000503:physiopathology; D040582:Inheritance Patterns; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood / Q000235:genetics* / Q000276:immunology; D018895:Microsatellite Repeats; D020641:Polymorphism, Single Nucleotide; D011943:Receptors, Adrenergic, beta / Q000235:genetics; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics
chemical_list: D002395:Catecholamines; D011943:Receptors, Adrenergic, beta; D002097:C-Reactive Protein; D014446:Tyrosine 3-Monooxygenase