Table 2

The genetic and clinical features of X linked recessive COD loci

Xp21.1-11.4 (COD1)Xp21.1-11.3, may be either COD1 (left column) or the newly described locus (right column)Xp11.4-q13.1 (new locus)Xq27.2-q28 (COD2)
ReferencesBartley et al,7 Jacobson et al,1 Hong et al,6 Seymour et al,9 Brown et al4Bergen et al,8 Meire et al3Mäntyjärvi et al,2 this studyPinckers and Timmerman,31 Bergen and Pinckers18
General ophthalmological characteristicsOnset within the first three decades and usually before the age of 20,Onset within the first three decades and usually in childhoodOnset in early childhood
gradual progression of visual loss,Gradual progression of visual loss,Very slow progression of visual lossSlight progression of visual loss
photophobia, moderate to high myopiahigh myopiamoderate to high myopiamoderate to high myopia
Visual fieldsGeneralised depression in younger patients, central scotomas in older patients, peripheral dysfunction in few casesCentral scotomasCentral sensitivity reduction, central scotomas, concentric constrictionCentral sensitivity decrease, central scotomas
Colour visionMixed deutan-tritan defect, type I red-green defect, errors with no specific axis, no colour perception in advanced casesRed-green defects, no colour perception in advanced casesRed or type I red-green defectsType I red-green defect, primarily red cones are affected, no colour perception in advanced cases
Electroretinogram (ERG)Severe cone dysfunction early in life, moderately reduced rod responses in all age groupsSevere cone dysfunction, reduced rod responses in later stagesDefective cone responses in all, diminished rod responses in some casesReduced cone ERG, reduced rod ERG in later stages
FundusRanges from granular macula in younger patients to bull’s eye and geographical atrophy of the RPE in older patients ± tapetal-like sheen, thin peripheral RPE, peripapillary atrophyRanges from granular macula in young patients to geographical atrophy in older patients, no tapetal reflex, myopic degeneration with prominent choroidal patternOnly myopic changes and irregular pigmentation in the macular area, no tapetal reflex, no bull’s eye apprearanceLittle pigment clumping, no tapetal reflex, myopic degeneration, choriocapillary atrophy
Central cone disease progressing to diffuse cone-rod dysfunction: early colour vision impairment with a severity parallel to the degree of visual acuity impairmentCentral cone disease progressing to diffuse cone-rod dysfunctionCentral cone disease progressing to diffuse cone-rod dysfunctionPeripheral cone disease progressing to diffuse cone-rod dysfunction: colour vision becomes impaired later compared to visual acuity and ERG
Molecular defectMutations in RPGR exon ORF15Not described yetNot described yetNot described yet
(References)(Demirci et al,10 Yang et al11)