Progressive RPE atrophy and photoreceptor death in KIZ-associated autosomal recessive retinitis pigmentosa

Background: To evaluate the long-term progression of autosomal recessive retinitis pigmentosa (RP) due to mutations in KIZ using multimodal imaging and a quantitative analytical approach. Methods: Whole exome sequencing (WES) and targeted capture sequencing were used to identify mutation. Fundus photography, short-wavelength autofluorescence (SW-AF), spectral-domain optical coherence tomography (SD-OCT) imaging, and electroretinography (ERG) were analyzed. Serial measurements of peripheral retinal pigment epithelium (RPE) atrophy area with SW-AF, as well as the ellipsoid zone (EZ) width using SD-OCT were performed. Results: Two homozygous variants in KIZ-a c.226C>T mutation as well as a previously unreported c.119_122delAACT mutation-were identified in four unrelated patients. Fundus examination and ERG revealed classic rod-cone dysfunction, and SD-OCT demonstrated outer retinal atrophy with centrally preserved EZ line. SW-AF imaging revealed hyperautofluorescent rings with surrounding parafoveal, mid-peripheral and widespread loss of autofluorescence. The RPE atrophy area increased annually by 4.9%. Mean annual exponential rates of decline for KIZ patients were 8.5% for visual acuity and 15.9% for 30 Hz Flicker amplitude. The average annual reduction distance of the EZ distance was 66.5 mu m per year. Conclusions: RPE atrophy progresses along with a loss of photoreceptors, and parafoveal RPE hypoautofluorescence is commonly seen in KIZ-associated RP patients. KIZ-associated RP is an early-onset severe rod-cone dystrophy.