title: Genetic association study of adiposity and melanocortin-4 receptor (MC4R) common variants: replication and functional characterization of non-coding regions.
abstract: Common genetic variants 3' of MC4R within two large linkage disequilibrium (LD) blocks spanning 288 kb have been associated with common and rare forms of obesity. This large association region has not been refined and the relevant DNA segments within the association region have not been identified. In this study, we investigated whether common variants in the MC4R gene region were associated with adiposity-related traits in a biracial population-based study. Single nucleotide polymorphisms (SNPs) in the MC4R region were genotyped with a custom array and a genome-wide array and associations between SNPs and five adiposity-related traits were determined using race-stratified linear regression. Previously reported associations between lower BMI and the minor alleles of rs2229616/Val103Ile and rs52820871/Ile251Leu were replicated in white female participants. Among white participants, rs11152221 in a proximal 3' LD block (closer to MC4R) was significantly associated with multiple adiposity traits, but SNPs in a distal 3' LD block (farther from MC4R) were not. In a case-control study of severe obesity, rs11152221 was significantly associated. The association results directed our follow-up studies to the proximal LD block downstream of MC4R. By considering nucleotide conservation, the significance of association, and proximity to the MC4R gene, we identified a candidate MC4R regulatory region. This candidate region was sequenced in 20 individuals from a study of severe obesity in an attempt to identify additional variants, and the candidate region was tested for enhancer activity using in vivo enhancer assays in zebrafish and mice. Novel variants were not identified by sequencing and the candidate region did not drive reporter gene expression in zebrafish or mice. The identification of a putative insulator in this region could help to explain the challenges faced in this study and others to link SNPs associated with adiposity to altered MC4R expression.
authors.affiliation: California Pacific Medical Center Research Institute, San Francisco, California, United States of America.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Evans
authors.affiliation: Diabetes Center and Department of Medicine, University of California, San Francisco, California, United States of America.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Calton
authors.affiliation: Department of Bioengineering and Therapeutic Sciences and Institute for Human Genetics, University of California, San Francisco, California, United States of America.
authors.forename: Mee J
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Cardiovascular Research Institute, Institute for Human Genetics, and Department of Dermatology, University of California, San Francisco, California, United States of America.
authors.forename: Pui-Yan
authors.initials: PY
authors.lastname: Kwok
authors.affiliation: Department of Epidemiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Iva
authors.initials: I
authors.lastname: Miljkovic
authors.affiliation: National Institute on Aging, Bethesda, Maryland, United States of America.
authors.forename: Tamara
authors.initials: T
authors.lastname: Harris
authors.affiliation: National Institute on Aging, Bethesda, Maryland, United States of America.
authors.forename: Annemarie
authors.initials: A
authors.lastname: Koster
authors.affiliation: Department of Epidemiology and Prevention, Division of Public Health Sciences, Wake Forest University, Winston-Salem, North Carolina, United States of America.
authors.forename: Yongmei
authors.initials: Y
authors.lastname: Liu
authors.affiliation: California Pacific Medical Center Research Institute, San Francisco, California, United States of America.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Tranah
authors.affiliation: Department of Bioengineering and Therapeutic Sciences and Institute for Human Genetics, University of California, San Francisco, California, United States of America.
authors.forename: Nadav
authors.initials: N
authors.lastname: Ahituv
authors.affiliation: Diabetes Center and Department of Medicine, University of California, San Francisco, California, United States of America.
authors.forename: Wen-Chi
authors.initials: WC
authors.lastname: Hsueh
authors.affiliation: Diabetes Center and Department of Medicine, University of California, San Francisco, California, United States of America.
authors.forename: Christian
authors.initials: C
authors.lastname: Vaisse
mesh_terms: D050154:Adiposity / Q000235:genetics* / Q000502:physiology; D000368:Aged; D000818:Animals; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics; D006801:Humans; D015810:Linkage Disequilibrium / Q000235:genetics; D008297:Male; D051379:Mice; D009765:Obesity / Q000235:genetics; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D044105:Receptor, Melanocortin, Type 4 / Q000235:genetics*; D015027:Zebrafish
chemical_list: D044105:Receptor, Melanocortin, Type 4