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Sidath E Liyanage, Robert F Cooper, Rola Ba-Abbad, Yusufu N B Sulai, Alfredo Dubra, Adam M Dubis, Joseph Carroll, Michel Michaelides; Imaging Photoreceptor Structure in Subjects with R9AP- and RGS9-associated Retinal Dysfunction (Bradyopsia). Invest. Ophthalmol. Vis. Sci. 2014;55(13):259.
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Mutations in the genes RGS9 and R9AP cause an autosomal recessive cone dysfunction syndrome characterized by reduced central vision, mild photophobia, normal color vision, lack of nystagmus, and normal fundi. It has many similarities to the cone dysfunction syndrome Oligocone Trichromacy. Here we examined three subjects using a multi-modal imaging approach to characterize the degree of residual cone structure.
Two sisters (23 years and 16 years old) from one family harboring a homozygous in-frame deletion (p.D32_Q34del) in R9AP, and a simplex male (62 years old) with a compound heterozygous mutation in RGS9 (p.R128X/p.W299R), underwent high-resolution quantitative retinal imaging. Spectral domain optical coherence tomography (SDOCT) was used to assess retinal lamination. Adaptive optics scanning light ophthalmoscopy (AOSLO) was performed to assess integrity of the photoreceptor mosaic and determine qualitative changes in reflectance.
SDOCT images from the two sisters showed normal macular lamination. The simplex observer had a focal area of foveal hyper-reflectivity in the right eye, with a normal appearance in the left eye. AOSLO imaging identified a small, focal hypo-reflective lesion (non-waveguiding cones) in the simplex subject’s right eye; the photoreceptor mosaic in his left eye and in both eyes of the two sisters was normal. No other abnormal reflectance differences were observed in the subjects’ photoreceptor mosaics. It is plausible that given the unilateral findings in the simplex case that the focal foveal abnormality may not be related to Bradyopsia but may possibly be due to previous injury.
Patients with either RGS9/R9AP-retinopathy (Bradyopsia) or Oligocone Trichromacy (OT) have very similar clinical phenotypes, characterized by stationary cone dysfunction, mild photophobia, normal color vision, and normal fundi. However, cellular imaging has shown very different cellular structures. Previous AOSLO imaging of OT revealed a sparse mosaic of cones remaining at the fovea, with no structure visible outside the central fovea; in direct contrast, the patients imaged in this study had a normal cone photoreceptor mosaic.
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