Progressive cone dystrophy associated with mutation in CNGB3.
OBJECTIVE
To determine the molecular basis for phenotypic variability in a three-generation consanguineous family containing a single individual with complete achromatopsia and three individuals with progressive cone dystrophy.


METHODS
Four affected individuals underwent ophthalmic examination, electrophysiological assessment, color fundus photography, and psychophysical testing. Blood samples were obtained for DNA extraction and mutation screening of the cone-specific cGMP-gated (CNG) channel protein gene CNGB3 was undertaken.


RESULTS
The clinical findings in one family member were consistent with a diagnosis of complete achromatopsia, with nystagmus, photophobia, and poor visual acuity from early infancy and complete color-blindness, normal fundi, and absent cone responses with normal rod responses on electroretinography (ERG). Mutation analysis revealed her to be homozygous for the common CNGB3 achromatopsia mutation, 1148delC (Thr383fs). In contrast, the three other symptomatic individuals in the family had findings consistent with progressive cone dystrophy. Their visual problems began later in childhood (ranging from 3 to 14 years of age) and there was evidence of progressive deterioration in cone function. All three had a marked tritanopic color vision defect and fundoscopy revealed bilateral macular atrophy. Electrophysiological testing of these three subjects demonstrated clear evidence of progressive deterioration of cone responses over time; rod responses were normal. All three individuals with this progressive phenotype were found to be compound heterozygotes for the 1148delC (Thr383fs) frameshift mutation and a novel Arg403Gln missense mutation in CNGB3.


CONCLUSIONS
Mutations in CNGB3, which have been shown to cause achromatopsia, are now shown to be associated with autosomal recessive progressive cone dystrophy. In this study, a novel Arg403Gln mutation was identified, located in the middle of the pore domain of the cone CNG cation channel beta-subunit, which when associated with the nonsense mutation Thr383fs, resulted in progressive cone dystrophy.
Michaelides
Michel
M
Institute of Ophthalmology, University College London, London, United Kingdom.
Aligianis
Irene A
IA
Ainsworth
John R
JR
Good
Peter
P
Mollon
John D
JD
Maher
Eamonn R
ER
Moore
Anthony T
AT
Hunt
David M
DM
D000328:Adult; D002648:Child; D003119:Color Perception Tests; D003117:Color Vision Defects / Q000235:genetics* / Q000503:physiopathology; D003241:Consanguinity; D054815:Cyclic Nucleotide-Gated Cation Channels; D004252:DNA Mutational Analysis; D018450:Disease Progression; D004596:Electroretinography; D005260:Female; D016368:Frameshift Mutation; D005808:Genes, Recessive; D006801:Humans; D007473:Ion Channels / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D020125:Mutation, Missense; D010375:Pedigree; D017949:Retinal Cone Photoreceptor Cells / Q000503:physiopathology*; D012162:Retinal Degeneration / Q000235:genetics* / Q000503:physiopathology; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology
C415904:CNGB3 protein, human; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels