Cone–rod dystrophy (CRD) is a rare group of inherited retinal disorders presenting primary loss of cone photoreceptors and subsequent or simultaneous loss of rod photoreceptors. RAB28, which encodes a member of the Rab subfamily of the RAS-related small GTPases, is a recently identified gene in AR-CRDs. 1–3 Roosing et al. reported homozygous nonsense mutation in RAB28 as a cause of AR-CRD in a German family and a Moroccan Jewish family. 3 Recently, Riveiro-Álvarez et al. reported homozygous mutations in RAB28 in two Spanish families: a splice site variant and a missense mutation. 2 Herein, we report a new and likely-deleterious homozygous missense RAB28 variant in a Korean patient resulting in the CRD phenotype. The affected 11-year-old female presented with decreased visual acuity which was initially detected when she was 4 years. BCVA in both eyes were 20/40, 20/50, and 20/100 when she was 4, 10, and 11 years, respectively. Cycloplegic refraction showed–0.5 D spherical error with astigmatism of–3.0 D cylindrical error in the right eye, and–1.0 D spherical error with astigmatism of–3.5 D cylindrical error in the left eye. The fundus examination showed slightly atrophic fovea (Figure 1A). Fundus autofluorescence showed hyperfluorescent fovea in both eyes, which may be an artifact (Figure 1A). SD-OCT showed an ellipsoid zone defect in both macular areas with an intact periphery (Figure 1A). Lightadapted 3 ERG and 30 Hz flicker ERG showed almost extinguished wave, while dark-adapted 0.01 ERG and 3 ERG also showed reduced amplitude (Figure 1B). A color vision test showed severe color vision deficiency (only one of the 14 Ishihara plates). Automated visual field test (Humphrey 30-2) showed central scotoma in both eyes. Based on these findings, she was clinically diagnosed as having CRD. Her parents, who are not related, and a male sibling showed normal vision and fundus findings. For the genetic analyses, targeted sequencing of candidate genes comprising of 98 genes known to be associated with inherited retinal degenerations (including cone–rod dystrophy) was performed with 101-bp paired-end reads on an Illumina HiSeq 2500 platform (Illumina, San Diego, CA).

Sanger sequencing was done to confirm the presence of detected variation in all four family members. Targeted exome sequencing data were generated with 2 million sequencing reads, covering 97.42% of 98 targeted genes with a sequencing coverage of 100X as well as 99.09% of 50X. Targeted regions of RAB28 were fully covered, with a mean depth ranging from 195X to 342X. A homozygous missense variant (NM_004249. 3: c. 68C> T (p. Ser23Phe)) was detected in the proband with a high read depth from targeted exome sequencing. No pathogenic variants were identified in the other 97 genes including 8 genes known to be associated with AR-CRD (ABCA4, ADAM9,