A novel GCAP1 missense mutation (L151F) in a large family with autosomal dominant cone-rod dystrophy (adCORD).
OBJECTIVE
To elucidate the phenotypic and biochemical characteristics of a novel mutation associated with autosomal dominant cone-rod dystrophy (adCORD).


METHODS
Twenty-three family members of a CORD pedigree underwent clinical examinations, including visual acuity tests, standardized full-field ERG, and fundus photography. Genomic DNA was screened for mutations in GCAP1 exons using DNA sequencing and single-strand conformational polymorphism (SSCP) analysis. Function and stability of recombinant GCAP1-L151F were tested as a function of [Ca(2+)], and its structure was probed by molecular dynamics.


RESULTS
Affected family members experienced dyschromatopsia, hemeralopia, and reduced visual acuity by the second to third decade of life. Electrophysiology revealed a nonrecordable photopic response with later attenuation of the scotopic response. Affected family members harbored a C-->T transition in exon 4 of the GCAP1 gene, resulting in an L151F missense mutation affecting the EF hand motif 4 (EF4). This change was absent in 11 unaffected family members and in 100 unrelated normal subjects. GCAP1-L151F stimulation of photoreceptor guanylate cyclase was not completely inhibited at high physiological [Ca(2+)], consistent with a lowered affinity for Ca(2+)-binding to EF4.


CONCLUSIONS
A novel L151F mutation in the EF4 hand domain of GCAP1 is associated with adCORD. The clinical phenotype is characterized by early cone dysfunction and a progressive loss of rod function. The biochemical phenotype is best described as persistent stimulation of photoreceptor guanylate cyclase, representing a gain of function of mutant GCAP1. Although a conservative substitution, molecular dynamics suggests a significant change in Ca(2+)-binding to EF4 and EF2 and changes in the shape of L151F-GCAP1.
Sokal
Izabela
I
Department of Ophthalmology, University of Washington, Seattle, Washington, USA.
Dupps
William J
WJ
Grassi
Michael A
MA
Brown
Jeremiah
J
Affatigato
Louisa M
LM
Roychowdhury
Nirmalya
N
Yang
Lili
L
Filipek
Slawomir
S
Palczewski
Krzysztof
K
Stone
Edwin M
EM
Baehr
Wolfgang
W
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000595:Amino Acid Sequence; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002648:Child; D002896:Chromosomes, Human, Pair 6 / Q000235:genetics; D004252:DNA Mutational Analysis; D004591:Electrophoresis, Polyacrylamide Gel; D004596:Electroretinography; D005260:Female; D005799:Genes, Dominant; D005838:Genotype; D051604:Guanylate Cyclase-Activating Proteins; D006801:Humans; D015151:Immunoblotting; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010375:Pedigree; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism / Q000473:pathology*; D018807:Polymorphism, Single-Stranded Conformational; D012162:Retinal Degeneration / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014792:Visual Acuity
D002135:Calcium-Binding Proteins; C496736:GUCA1A protein, human; D051604:Guanylate Cyclase-Activating Proteins