Genetic Analyses in a Sample of Individuals With High or Low BMD Shows Association With Multiple Wnt Pathway Genes

Authors


  • Dr Eisman claims a consultancy with Amgen, deCODE, Eli Lilly, GE-Lunar, Merck Sharp & Dohme, Novartis, Organon, Roche-GSK, Sanofi-Aventis, and Servier; is a member of the Scientific Advisory Board for Amgen, Eli Lilly, Merck Sharp & Dohme (Chair), Novartis, Roche-GSK, Sanofi-Aventis, and Servier; is a member of the Oversight of Clinical Research committees for Amgen, Eli Lilly, Novartis, Organon, and Roche-GSK; an investigator in studies funded by Amgen, Eli Lilly, Novartis, Organon, and Roche-GSK; is on the following committees for the Department of Health and Ageing, Australian Government, Arthritis and Osteoporosis Expert Advisory Committee (Co-chair), Expert Advisory Subcommittee of the Australian Population Health Developmental Principle Committee (Member), National Health Priority Action Council's Nation Arthritis and Musculoskeletal Conditions Advisory Group (Chair); and is on the following committee for the Royal Australian College of General Practitioners, Osteoporosis Working Group, Musculoskeletal Guidelines Project (Chair). All other authors state that they have no conflicts of interest.

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.

Introduction: 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).

Materials and 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 r2 > 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.

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