title: Functional consequence of a novel Y129C mutation in a patient with two contradictory melanocortin-2-receptor mutations.
abstract: BACKGROUND
  Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease, characterised by isolated glucocorticoid deficiency in the absence of mineralocorticoid deficiency. Inactivating mutations in the ACTH receptor (melanocortin-2-receptor, MC2R) are well described and account for approximately 25% of cases. By contrast, activating MC2R mutations are extremely rare.
  
  
  METHODS
  We report a child of Saudi Arabian origin who was diagnosed with FGD following hypoglycaemic episodes that resulted in spastic quadriplegia.
  
  
  RESULTS
  MC2R gene analysis revealed an unusual combination of two homozygous missense mutations, consisting of the novel mutation Y129C and the previously described F278C activating mutation. Parents were heterozygous at both of these sites. In vitro analysis of the Y129C mutation using a fluorescent cell surface assay showed that this mutant was unable to reach the cell surface in CHO cells stably transfected with MC2R accessory protein (MRAP), despite the demonstration of an interaction with MRAP by co-immunoprecipitation. The double mutant Y129C-F278C also failed to traffic to the cell surface.
  
  
  CONCLUSIONS
  The tyrosine residue at position 129 in the second intracellular loop is critical in MC2R folding and/or trafficking to the cell surface. Furthermore, the absence of cell surface expression of MC2R would account for the lack of activation of the receptor due to the F278C mutation located at the C-terminal tail. We provide a novel molecular explanation for a child with two opposing mutations causing severe FGD.
authors.affiliation: Queen Mary University of London, Centre for Endocrinology, Barts & the London School of Medicine & Dentistry, London, UK.
authors.forename: Li F
authors.initials: LF
authors.lastname: Chan
authors.forename: Teng-Teng
authors.initials: TT
authors.lastname: Chung
authors.forename: Ahmed F
authors.initials: AF
authors.lastname: Massoud
authors.forename: Louise A
authors.initials: LA
authors.lastname: Metherell
authors.forename: Adrian J L
authors.initials: AJ
authors.lastname: Clark
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000502:physiology; D000483:Alleles; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004252:DNA Mutational Analysis; D006801:Humans; D047468:Immunoprecipitation; D007231:Infant, Newborn; D018613:Microscopy, Confocal; D009154:Mutation / Q000235:genetics* / Q000502:physiology*; D017510:Protein Folding; D044103:Receptor, Melanocortin, Type 2 / Q000235:genetics*; D011956:Receptors, Cell Surface / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000172:deficiency*
chemical_list: D044103:Receptor, Melanocortin, Type 2; D011956:Receptors, Cell Surface; D011965:Receptors, Glucocorticoid; D000324:Adrenocorticotropic Hormone