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Prevalence and functionality of paucimorphic and private MC4R mutations in a large, unselected European British population, scanned by meltMADGE.
Alharbi KK, Spanakis E, Tan K, Smith MJ, Aldahmesh MA, O'dell SD, Sayer AA, Lawlor DA, Ebrahim S, Smith GD, O'rahilly S, Farooqi S, Cooper C, Phillips DI, Day IN.
Human Genetics Division, School of Medicine, University of Southampton, Southampton General Hospital, Southampton, United Kingdom.
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. Hum Mutat 0, 1-9, 2006.(c) 2006 Wiley-Liss, Inc.
PMID: 17072869 [PubMed - as supplied by publisher]
Mutation scanning by meltMADGE: validations using BRCA1 and LDLR, and demonstration of the potential to identify severe, moderate, silent, rare, and paucimorphic mutations in the general population.
Alharbi KK, Aldahmesh MA, Spanakis E, Haddad L, Whittall RA, Chen XH, Rassoulian H, Smith MJ, Sillibourne J, Ball NJ, Graham NJ, Briggs PJ, Simpson IA, Phillips DI, Lawlor DA, Ye S, Humphries SE, Cooper C, Smith GD, Ebrahim S, Eccles DM, Day IN.
Human Genetics Division, School of Medicine, University of Southampton, Southampton University Hospitals NHS Trust, Southampton SO16 6YD, United Kingdom.
We have developed a mutation-scanning approach suitable for whole population screening for unknown mutations. The method, meltMADGE, combines thermal ramp electrophoresis with MADGE to achieve suitable cost efficiency and throughput. The sensitivity was tested in blind trials using 54 amplicons representing the BRCA1 coding region and a panel of 94 unrelated family breast cancer risk consultands previously screened in a clinical diagnostic laboratory. All 10 common polymorphisms, 15/15 previously identified disease-causing mutations, and three previously untested single base changes were identified. Assays of LDLR exons 3 and 8 were validated in 460 familial hypercholesteremics and detected 8/9 known variants. We then applied the exon 3 assay in several DNA banks representing approximately 8000 subjects with known cholesterol values and applied both assays in one DNA bank (n = 3600). In exon 3 we identified one previously reported moderate mutation, P84S (n = 1), also associated with moderate hypercholesteremia in this subject; an unreported silent variant, N76N (n = 1); and known severe hypercholesteremia splice mutation 313+1G-->A (n = 2). Around exon 8 we identified a paucimorphism (n = 35) at the splice site 1061-8T-->C (known to be in complete linkage disequilibrium with T705I) and unreported sequence variants 1186+11G-->A (n = 1) and D335N G-->A (n = 1). The cholesterol value for D335N was on the 96.2 percentile and for T705I, 2/35 carriers were above the 99th percentile. Thus, variants with predicted severe, moderate, and no effect were identified at the population level. In contrast with case collections, CpG mutations predominated. MeltMADGE will enable definition of the full population spectrum of rare, paucimorphic, severe, moderate (forme fruste), and silent mutations and effects.
PMID: 15998910 [PubMed - indexed for MEDLINE]
Combination of His-tagged T4 endonuclease VII with microplate array diagonal gel electrophoresis for high-throughput mutation scanning.
Smith MJ, Pante-de-Sousa G, Alharbi KK, Chen XH, Day IN, Fox KR.
Human Genetics Division, School of Medicine, Southampton University Hospital, Southampton, UK.
PMID: 15914792 [PubMed - indexed for MEDLINE]
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