title: Genetic analyses in a sample of individuals with high or low BMD shows association with multiple Wnt pathway genes.
abstract: Using a moderate-sized cohort selected with extreme BMD (n = 344; absolute value BMD, 1.5-4.0), significant association of several members of the Wnt signaling pathway with bone densitometry measures was shown. This confirms that extreme truncate selection is a powerful design for quantitative trait association studies of bone phenotypes.
  
  
  BACKGROUND
  Although the high heritability of BMD variation has long been established, few genes have been conclusively shown to affect the variation of BMD in the general population. Extreme truncate selection has been proposed as a more powerful alternative to unselected cohort designs in quantitative trait association studies. We sought to test these theoretical predictions in studies of the bone densitometry measures BMD, BMC, and femoral neck area, by investigating their association with members of the Wnt pathway, some of which have previously been shown to be associated with BMD in much larger cohorts, in a moderate-sized extreme truncate selected cohort (absolute value BMD Z-scores = 1.5-4.0; n = 344).
  
  
  METHODS
  Ninety-six tag-single nucleotide polymorphism (SNPs) lying in 13 Wnt signaling pathway genes were selected to tag common genetic variation (minor allele frequency [MAF] > 5% with an r(2) > 0.8) within 5 kb of all exons of 13 Wnt signaling pathway genes. The genes studied included LRP1, LRP5, LRP6, Wnt3a, Wnt7b, Wnt10b, SFRP1, SFRP2, DKK1, DKK2, FZD7, WISP3, and SOST. Three hundred forty-four cases with either high or low BMD were genotyped by Illumina Goldengate microarray SNP genotyping methods. Association was tested either by Cochrane-Armitage test for dichotomous variables or by linear regression for quantitative traits.
  
  
  RESULTS
  Strong association was shown with LRP5, polymorphisms of which have previously been shown to influence total hip BMD (minimum p = 0.0006). In addition, polymorphisms of the Wnt antagonist, SFRP1, were significantly associated with BMD and BMC (minimum p = 0.00042). Previously reported associations of LRP1, LRP6, and SOST with BMD were confirmed. Two other Wnt pathway genes, Wnt3a and DKK2, also showed nominal association with BMD.
  
  
  CONCLUSIONS
  This study shows that polymorphisms of multiple members of the Wnt pathway are associated with BMD variation. Furthermore, this study shows in a practical trial that study designs involving extreme truncate selection and moderate sample sizes can robustly identify genes of relevant effect sizes involved in BMD variation in the general population. This has implications for the design of future genome-wide studies of quantitative bone phenotypes relevant to osteoporosis.
authors.affiliation: Diamantina Institute for Cancer, Immunology and Metabolic Medicine, Brisbane, Australia.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Sims
authors.forename: Neil
authors.initials: N
authors.lastname: Shephard
authors.forename: Kim
authors.initials: K
authors.lastname: Carter
authors.forename: Tracy
authors.initials: T
authors.lastname: Doan
authors.forename: Alison
authors.initials: A
authors.lastname: Dowling
authors.forename: Emma L
authors.initials: EL
authors.lastname: Duncan
authors.forename: John
authors.initials: J
authors.lastname: Eisman
authors.forename: Graeme
authors.initials: G
authors.lastname: Jones
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Nicholson
authors.forename: Richard
authors.initials: R
authors.lastname: Prince
authors.forename: Ego
authors.initials: E
authors.lastname: Seeman
authors.forename: Gethin
authors.initials: G
authors.lastname: Thomas
authors.forename: John A
authors.initials: JA
authors.lastname: Wass
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Brown
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density / Q000235:genetics*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D051153:Wnt Proteins / Q000235:genetics*
chemical_list: D051153:Wnt Proteins