title: A novel mutation (I143NT) in guanylate cyclase-activating protein 1 (GCAP1) associated with autosomal dominant cone degeneration.
abstract: OBJECTIVE
  To identify pathogenic mutations in the guanylate cyclase-activating protein 1 (GCAP1) and GCAP2 genes and to characterize the biochemical effect of mutation on guanylate cyclase (GC) stimulation.
  
  
  METHODS
  The GCAP1 and GCAP2 genes were screened by direct sequencing for mutations in 216 patients and 421 patients, respectively, with various hereditary retinal diseases. A mutation in GCAP1 segregating with autosomal dominant cone degeneration was further evaluated biochemically by employing recombinant proteins, immunoblotting, Ca2+-dependent stimulation of GC, fluorescence emission spectra, and limited proteolysis in the absence and presence of Ca2+.
  
  
  RESULTS
  A novel GCAP1 mutation, I143NT (substitution of Ile at codon 143 by Asn and Thr), affecting the EF4 Ca2+-binding loop, was identified in a heterozygote father and son with autosomal dominant cone degeneration. Both patients had much greater loss of cone function versus rod function; previous histopathologic evaluation of the father's eyes at autopsy (age 75 years) showed no foveal cones but a few, scattered cones remaining in the peripheral retina. Biochemical analysis showed that the GCAP1-I143NT mutant adopted a conformation susceptible to proteolysis, and the mutant inhibited GC only partially at high Ca2+ concentrations. Individual patients with atypical or recessive retinitis pigmentosa (RP) had additional heterozygous GCAP1-T114I and GCAP2 gene changes (V85M and F150C) of unknown pathogenicity.
  
  
  CONCLUSIONS
  A novel GCAP1 mutation, I143NT, caused a form of autosomal dominant cone degeneration that destroys foveal cones by mid-life but spares some cones in the peripheral retina up to 75 years. Properties of the GCAP1-I143NT mutant protein suggested that it is incompletely inactivated by high Ca2+ concentrations as should occur with dark adaptation. The continued activity of the mutant GCAP1 likely results in higher-than-normal scotopic cGMP levels which may, in turn, account for the progressive loss of cones.
authors.affiliation: Ocular Molecular Genetics Institute, Massachusetts Eye and Ear Infirmary, Boston, MA, USA.
authors.forename: Koji M
authors.initials: KM
authors.lastname: Nishiguchi
authors.forename: Izabela
authors.initials: I
authors.lastname: Sokal
authors.forename: Lili
authors.initials: L
authors.lastname: Yang
authors.forename: Nirmalya
authors.initials: N
authors.lastname: Roychowdhury
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
authors.forename: Eliot L
authors.initials: EL
authors.lastname: Berson
authors.forename: Thaddeus P
authors.initials: TP
authors.lastname: Dryja
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Baehr
mesh_terms: D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D004252:DNA Mutational Analysis; D004591:Electrophoresis, Polyacrylamide Gel; D004596:Electroretinography; D005260:Female; D005799:Genes, Dominant; D006162:Guanylate Cyclase / Q000235:genetics* / Q000378:metabolism; D051604:Guanylate Cyclase-Activating Proteins; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D010375:Pedigree; D017949:Retinal Cone Photoreceptor Cells / Q000187:drug effects / Q000201:enzymology / Q000473:pathology*; D012162:Retinal Degeneration / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D013050:Spectrometry, Fluorescence
chemical_list: D002135:Calcium-Binding Proteins; C496736:GUCA1A protein, human; C496739:GUCA1B protein, human; D051604:Guanylate Cyclase-Activating Proteins; D006162:Guanylate Cyclase; D002118:Calcium