title: Prevalence and functionality of paucimorphic and private MC4R mutations in a large, unselected European British population, scanned by meltMADGE.
abstract: Identification of unknown mutations has remained laborious, expensive, and only viable for studies of selected cases. Population-based "reference ranges" of rarer sequence diversity are not available. However, the research and diagnostic interpretation of sequence variants depends on such information. Additionally, this is the only way to determine prevalence of severe, moderate, and silent mutations and is also relevant to the development of screening programs. We previously described a system, meltMADGE, suitable for mutation scanning at the population level. Here we describe its application to a population-based study of MC4R (melanocortin 4 receptor) mutations, which are associated with obesity. We developed nine assays representing MC4R and examined a population sample of 1,100 subjects. Two "paucimorphisms" were identified (c.307G>A/p.Val103Ile in 27 subjects and c.-178A>C in 22 subjects). Neither exhibited any anthropometric effects, whereas there would have been >90% power to detect a body mass index (BMI) effect of 0.5 kg/m(2) at P=0.01. Two "private" variants were also identified. c.335C>T/p.Thr112Met has been previously described and appears to be silent. A novel variant, c.260C>A/p.Ala87Asp, was observed in a subject with a BMI of 31.5 kg/m(2) (i.e., clinically obese) but not on direct assay of a further 3,525 subjects. This mutation was predicted to be deleterious and analysis using a cyclic AMP (cAMP) responsive luciferase reporter assay showed substantial loss of function of the mutant receptor. This population-based mutation scan of MC4R suggests that there is no severe MC4R mutation with high prevalence in the United Kingdom, but that obesity-causing MC4R mutation at 1 in 1,100 might represent one of the commonest autosomal dominant disorders in man.
authors.affiliation: Human Genetics Division, School of Medicine, University of Southampton, Southampton General Hospital, Southampton, United Kingdom.
authors.forename: Khalid K
authors.initials: KK
authors.lastname: Alharbi
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Spanakis
authors.forename: Karen
authors.initials: K
authors.lastname: Tan
authors.forename: Matt J
authors.initials: MJ
authors.lastname: Smith
authors.forename: Mohammed A
authors.initials: MA
authors.lastname: Aldahmesh
authors.forename: Sandra D
authors.initials: SD
authors.lastname: O'Dell
authors.forename: Avan Aihie
authors.initials: AA
authors.lastname: Sayer
authors.forename: Debbie A
authors.initials: DA
authors.lastname: Lawlor
authors.forename: Shah
authors.initials: S
authors.lastname: Ebrahim
authors.forename: George
authors.initials: G
authors.lastname: Davey Smith
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Rahilly
authors.forename: Sadaf
authors.initials: S
authors.lastname: Farooqi
authors.forename: Cyrus
authors.initials: C
authors.lastname: Cooper
authors.forename: David I W
authors.initials: DI
authors.lastname: Phillips
authors.forename: Ian N M
authors.initials: IN
authors.lastname: Day
mesh_terms: D000368:Aged; D004252:DNA Mutational Analysis; D005260:Female; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009691:Nucleic Acid Denaturation; D018807:Polymorphism, Single-Stranded Conformational; D044105:Receptor, Melanocortin, Type 4 / Q000235:genetics*; D013696:Temperature; D006113:United Kingdom
chemical_list: C470072:MC4R protein, human; D044105:Receptor, Melanocortin, Type 4