title: Insights into the pathogenicity of rare missense GCK variants from the identification and functional characterization of compound heterozygous and double mutations inherited in cis.
abstract: OBJECTIVE
  To demonstrate the importance of using a combined genetic and functional approach to correctly interpret a genetic test for monogenic diabetes.
  
  
  METHODS
  We identified three probands with a phenotype consistent with maturity-onset diabetes of the young (MODY) subtype GCK-MODY, in whom two potential pathogenic mutations were identified: [R43H/G68D], [E248 K/I225M], or [G261R/D217N]. Allele-specific PCR and cosegregation were used to determine phase. Single and double mutations were kinetically characterized.
  
  
  RESULTS
  The mutations occurred in cis (double mutants) in two probands and in trans in one proband. Functional studies of all double mutants revealed inactivating kinetics. The previously reported GCK-MODY mutations R43H and G68D were inherited from an affected father and unaffected mother, respectively. Both our functional and genetic studies support R43H as the cause of GCK-MODY and G68D as a neutral rare variant.
  
  
  CONCLUSIONS
  These data highlight the need for family/functional studies, even for previously reported pathogenic mutations.
authors.affiliation: Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, UK.
authors.forename: Nicola L
authors.initials: NL
authors.lastname: Beer
authors.forename: Kara K
authors.initials: KK
authors.lastname: Osbak
authors.forename: Martijn
authors.initials: M
authors.lastname: van de Bunt
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Tribble
authors.forename: Anna M
authors.initials: AM
authors.lastname: Steele
authors.forename: Kirsty J
authors.initials: KJ
authors.lastname: Wensley
authors.forename: Emma L
authors.initials: EL
authors.lastname: Edghill
authors.forename: Kevin
authors.initials: K
authors.lastname: Colcough
authors.forename: Amy
authors.initials: A
authors.lastname: Barrett
authors.forename: Lucia
authors.initials: L
authors.lastname: Valentínová
authors.forename: Jana K
authors.initials: JK
authors.lastname: Rundle
authors.forename: Anne
authors.initials: A
authors.lastname: Raimondo
authors.forename: Joseph
authors.initials: J
authors.lastname: Grimsby
authors.forename: Sian
authors.initials: S
authors.lastname: Ellard
authors.forename: Anna L
authors.initials: AL
authors.lastname: Gloyn
mesh_terms: D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D005260:Female; D005820:Genetic Testing; D005941:Glucokinase / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D010375:Pedigree
chemical_list: D005941:Glucokinase