Identification of novel RPGR ORF15 mutations in X-linked progressive cone-rod dystrophy (XLCORD) families.
OBJECTIVE
To test the incidence of mutations in RPGR ORF15 in six families with X-linked progressive retinal degeneration (cone-rod dystrophy [XLCORD], macular or cone dystrophy) and to undertake a detailed phenotypic assessment of families in whom ORF15 mutations were identified.


METHODS
To amplify and sequence ORF15 in its entirety, a cloning strategy was developed. Families with mutations in ORF15 underwent electrophysiological testing, color vision assessment, color fundus photography, and fundus autofluorescence (AF) imaging.


RESULTS
Novel protein truncation mutations were identified in two families. In family A, a 2-bp mutation was identified in ORF15+A1094C G1095T, predicted to result in a truncated protein (E364D/E365X). In family B, a G-to-T transversion (ORF15+1176G>T) resulted in a nonsense mutation (G392X). Characteristics of phenotype in both families included progressive deterioration of central vision and subsequently night vision, mild photophobia, and moderate to high myopia. Ophthalmoscopic abnormalities were generally confined to the macula. A parafoveal ring of increased AF was observed, and electrophysiological evidence of a greater generalized abnormality in cone than rod responses were consistent with a cone-rod dystrophy phenotype.


CONCLUSIONS
The cloning strategy for ORF15 facilitated comprehensive sequence analysis in patients. Two families were identified with nonsense mutations, and clinical evaluation revealed them both to have a similar phenotype. The presence of a parafoveal ring of increased AF was an early indicator of affected status in these families. No disease-causing mutations in ORF15 were detected in four other families, suggesting that ORF15 mutations may not be the most common cause of XLCORD.
Ebenezer
Neil D
ND
Division of Molecular Genetics, University College London, UK.
Michaelides
Michel
M
Jenkins
Sharon A
SA
Audo
Isabelle
I
Webster
Andrew R
AR
Cheetham
Michael E
ME
Stockman
Andrew
A
Maher
Eamonn R
ER
Ainsworth
John R
JR
Yates
John R
JR
Bradshaw
Keith
K
Holder
Graham E
GE
Moore
Anthony T
AT
Hardcastle
Alison J
AJ
D000328:Adult; D000368:Aged; D018389:Codon, Nonsense; D003117:Color Vision Defects / Q000235:genetics; D004596:Electroretinography; D005136:Eye Proteins / Q000235:genetics*; D005260:Female; D040181:Genetic Diseases, X-Linked / Q000235:genetics* / Q000503:physiopathology; D005838:Genotype; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics; D006579:Heterozygote; D006801:Humans; D008297:Male; D008875:Middle Aged; D016366:Open Reading Frames / Q000235:genetics*; D010375:Pedigree; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology* / Q000502:physiology; D012162:Retinal Degeneration / Q000235:genetics* / Q000503:physiopathology
D018389:Codon, Nonsense; D005136:Eye Proteins; D020662:Guanine Nucleotide Exchange Factors; C099929:RPGR protein, human