The genetic and clinical features of X linked recessive COD loci
| Locus | ||||
|---|---|---|---|---|
| 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) | |
| References | Bartley et al,7 Jacobson et al,1 Hong et al,6 Seymour et al,9 Brown et al4 | Bergen et al,8 Meire et al3 | Mäntyjärvi et al,2 this study | Pinckers and Timmerman,31 Bergen and Pinckers18 |
| General ophthalmological characteristics | Onset within the first three decades and usually before the age of 20, | Onset within the first three decades and usually in childhood | Onset in early childhood | |
| gradual progression of visual loss, | Gradual progression of visual loss, | Very slow progression of visual loss | Slight progression of visual loss | |
| photophobia, moderate to high myopia | high myopia | moderate to high myopia | moderate to high myopia | |
| Visual fields | Generalised depression in younger patients, central scotomas in older patients, peripheral dysfunction in few cases | Central scotomas | Central sensitivity reduction, central scotomas, concentric constriction | Central sensitivity decrease, central scotomas |
| Colour vision | Mixed deutan-tritan defect, type I red-green defect, errors with no specific axis, no colour perception in advanced cases | Red-green defects, no colour perception in advanced cases | Red or type I red-green defects | Type 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 groups | Severe cone dysfunction, reduced rod responses in later stages | Defective cone responses in all, diminished rod responses in some cases | Reduced cone ERG, reduced rod ERG in later stages |
| Fundus | Ranges 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 atrophy | Ranges from granular macula in young patients to geographical atrophy in older patients, no tapetal reflex, myopic degeneration with prominent choroidal pattern | Only myopic changes and irregular pigmentation in the macular area, no tapetal reflex, no bull’s eye apprearance | Little 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 impairment | Central cone disease progressing to diffuse cone-rod dysfunction | Central cone disease progressing to diffuse cone-rod dysfunction | Peripheral cone disease progressing to diffuse cone-rod dysfunction: colour vision becomes impaired later compared to visual acuity and ERG | |
| Molecular defect | Mutations in RPGR exon ORF15 | Not described yet | Not described yet | Not described yet |
| (References) | (Demirci et al,10 Yang et al11) | |||