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1.  Inheritance of rare functional GCKR variants and their contribution to triglyceride levels in families 
Human Molecular Genetics  2014;23(20):5570-5578.
Significant resources have been invested in sequencing studies to investigate the role of rare variants in complex disease etiology. However, the diagnostic interpretation of individual rare variants remains a major challenge, and may require accurate variant functional classification and the collection of large numbers of variant carriers. Utilizing sequence data from 458 individuals with hypertriglyceridemia and 333 controls with normal plasma triglyceride levels, we investigated these issues using GCKR, encoding glucokinase regulatory protein. Eighteen rare non-synonymous GCKR variants identified in these 791 individuals were comprehensively characterized by a range of biochemical and cell biological assays, including a novel high-throughput-screening-based approach capable of measuring all variant proteins simultaneously. Functionally deleterious variants were collectively associated with hypertriglyceridemia, but a range of in silico prediction algorithms showed little consistency between algorithms and poor agreement with functional data. We extended our study by obtaining sequence data on family members; however, functional variants did not co-segregate with triglyceride levels. Therefore, despite evidence for their collective functional and clinical relevance, our results emphasize the low predictive value of rare GCKR variants in individuals and the complex heritability of lipid traits.
doi:10.1093/hmg/ddu269
PMCID: PMC4168830  PMID: 24879641
2.  A Panel of Diverse Assays to Interrogate the Interaction between Glucokinase and Glucokinase Regulatory Protein, Two Vital Proteins in Human Disease 
PLoS ONE  2014;9(2):e89335.
Recent genetic and clinical evidence has implicated glucokinase regulatory protein (GKRP) in the pathogenesis of type 2 diabetes and related traits. The primary role of GKRP is to bind and inhibit hepatic glucokinase (GCK), a critically important protein in human health and disease that exerts a significant degree of control over glucose metabolism. As activation of GCK has been associated with improved glucose tolerance, perturbation of the GCK-GKRP interaction represents a potential therapeutic target for pharmacological modulation. Recent structural and kinetic advances are beginning to provide insight into the interaction of these two proteins. However, tools to comprehensively assess the GCK-GKRP interaction, particularly in the context of small molecules, would be a valuable resource. We therefore developed three robust and miniaturized assays for assessing the interaction between recombinant human GCK and GKRP: an HTRF assay, a diaphorase-coupled assay, and a luciferase-coupled assay. The assays are complementary, featuring distinct mechanisms of detection (luminescence, fluorescence, FRET). Two assays rely on GCK enzyme activity modulation by GKRP while the FRET-based assay measures the GCK-GKRP protein-protein interaction independent of GCK enzymatic substrates and activity. All three assays are scalable to low volumes in 1536-well plate format, with robust Z’ factors (>0.7). Finally, as GKRP sequesters GCK in the hepatocyte nucleus at low glucose concentrations, we explored cellular models of GCK localization and translocation. Previous findings from freshly isolated rat hepatocytes were confirmed in cryopreserved rat hepatocytes, and we further extended this study to cryopreserved human hepatocytes. Consistent with previous reports, there were several key differences between the rat and human systems, with our results suggesting that human hepatocytes can be used to interrogate GCK translocation in response to small molecules. The assay panel developed here should help direct future investigation of the GCK-GKRP interaction in these or other physiologically relevant human systems.
doi:10.1371/journal.pone.0089335
PMCID: PMC3929664  PMID: 24586696
3.  Correlation of rare coding variants in the gene encoding human glucokinase regulatory protein with phenotypic, cellular, and kinetic outcomes 
Defining the genetic contribution of rare variants to common diseases is a major basic and clinical science challenge that could offer new insights into disease etiology and provide potential for directed gene- and pathway-based prevention and treatment. Common and rare nonsynonymous variants in the GCKR gene are associated with alterations in metabolic traits, most notably serum triglyceride levels. GCKR encodes glucokinase regulatory protein (GKRP), a predominantly nuclear protein that inhibits hepatic glucokinase (GCK) and plays a critical role in glucose homeostasis. The mode of action of rare GCKR variants remains unexplored. We identified 19 nonsynonymous GCKR variants among 800 individuals from the ClinSeq medical sequencing project. Excluding the previously described common missense variant p.Pro446Leu, all variants were rare in the cohort. Accordingly, we functionally characterized all variants to evaluate their potential phenotypic effects. Defects were observed for the majority of the rare variants after assessment of cellular localization, ability to interact with GCK, and kinetic activity of the encoded proteins. Comparing the individuals with functional rare variants to those without such variants showed associations with lipid phenotypes. Our findings suggest that, while nonsynonymous GCKR variants, excluding p.Pro446Leu, are rare in individuals of mixed European descent, the majority do affect protein function. In sum, this study utilizes computational, cell biological, and biochemical methods to present a model for interpreting the clinical significance of rare genetic variants in common disease.
doi:10.1172/JCI46425
PMCID: PMC3248284  PMID: 22182842
4.  Six new loci associated with body mass index highlight a neuronal influence on body weight regulation 
Willer, Cristen J | Speliotes, Elizabeth K | Loos, Ruth J F | Li, Shengxu | Lindgren, Cecilia M | Heid, Iris M | Berndt, Sonja I | Elliott, Amanda L | Jackson, Anne U | Lamina, Claudia | Lettre, Guillaume | Lim, Noha | Lyon, Helen N | McCarroll, Steven A | Papadakis, Konstantinos | Qi, Lu | Randall, Joshua C | Roccasecca, Rosa Maria | Sanna, Serena | Scheet, Paul | Weedon, Michael N | Wheeler, Eleanor | Zhao, Jing Hua | Jacobs, Leonie C | Prokopenko, Inga | Soranzo, Nicole | Tanaka, Toshiko | Timpson, Nicholas J | Almgren, Peter | Bennett, Amanda | Bergman, Richard N | Bingham, Sheila A | Bonnycastle, Lori L | Brown, Morris | Burtt, Noël P | Chines, Peter | Coin, Lachlan | Collins, Francis S | Connell, John M | Cooper, Cyrus | Smith, George Davey | Dennison, Elaine M | Deodhar, Parimal | Elliott, Paul | Erdos, Michael R | Estrada, Karol | Evans, David M | Gianniny, Lauren | Gieger, Christian | Gillson, Christopher J | Guiducci, Candace | Hackett, Rachel | Hadley, David | Hall, Alistair S | Havulinna, Aki S | Hebebrand, Johannes | Hofman, Albert | Isomaa, Bo | Jacobs, Kevin B | Johnson, Toby | Jousilahti, Pekka | Jovanovic, Zorica | Khaw, Kay-Tee | Kraft, Peter | Kuokkanen, Mikko | Kuusisto, Johanna | Laitinen, Jaana | Lakatta, Edward G | Luan, Jian'an | Luben, Robert N | Mangino, Massimo | McArdle, Wendy L | Meitinger, Thomas | Mulas, Antonella | Munroe, Patricia B | Narisu, Narisu | Ness, Andrew R | Northstone, Kate | O'Rahilly, Stephen | Purmann, Carolin | Rees, Matthew G | Ridderstråle, Martin | Ring, Susan M | Rivadeneira, Fernando | Ruokonen, Aimo | Sandhu, Manjinder S | Saramies, Jouko | Scott, Laura J | Scuteri, Angelo | Silander, Kaisa | Sims, Matthew A | Song, Kijoung | Stephens, Jonathan | Stevens, Suzanne | Stringham, Heather M | Tung, Y C Loraine | Valle, Timo T | Van Duijn, Cornelia M | Vimaleswaran, Karani S | Vollenweider, Peter | Waeber, Gerard | Wallace, Chris | Watanabe, Richard M | Waterworth, Dawn M | Watkins, Nicholas | Witteman, Jacqueline C M | Zeggini, Eleftheria | Zhai, Guangju | Zillikens, M Carola | Altshuler, David | Caulfield, Mark J | Chanock, Stephen J | Farooqi, I Sadaf | Ferrucci, Luigi | Guralnik, Jack M | Hattersley, Andrew T | Hu, Frank B | Jarvelin, Marjo-Riitta | Laakso, Markku | Mooser, Vincent | Ong, Ken K | Ouwehand, Willem H | Salomaa, Veikko | Samani, Nilesh J | Spector, Timothy D | Tuomi, Tiinamaija | Tuomilehto, Jaakko | Uda, Manuela | Uitterlinden, André G | Wareham, Nicholas J | Deloukas, Panagiotis | Frayling, Timothy M | Groop, Leif C | Hayes, Richard B | Hunter, David J | Mohlke, Karen L | Peltonen, Leena | Schlessinger, David | Strachan, David P | Wichmann, H-Erich | McCarthy, Mark I | Boehnke, Michael | Barroso, Inês | Abecasis, Gonçalo R | Hirschhorn, Joel N
Nature genetics  2008;41(1):25-34.
Common variants at only two loci, FTO and MC4R, have been reproducibly associated with body mass index (BMI) in humans. To identify additional loci, we conducted meta-analysis of 15 genome-wide association studies for BMI (n > 32,000) and followed up top signals in 14 additional cohorts (n > 59,000). We strongly confirm FTO and MC4R and identify six additional loci (P < 5 × 10−8): TMEM18, KCTD15, GNPDA2, SH2B1, MTCH2 and NEGR1 (where a 45-kb deletion polymorphism is a candidate causal variant). Several of the likely causal genes are highly expressed or known to act in the central nervous system (CNS), emphasizing, as in rare monogenic forms of obesity, the role of the CNS in predisposition to obesity.
doi:10.1038/ng.287
PMCID: PMC2695662  PMID: 19079261

Results 1-4 (4)