Genetic and Clinical Analyses of the KIZ-c.226C>T Variant Resulting in a Dual Mutational Mechanism.

Retinitis pigmentosa (RP) is a heterogeneous inherited retinal disorder. Mutations in KIZ cause autosomal recessive (AR) RP. We aimed to characterize the genotype, expression pattern, and phenotype in a large cohort of KIZ cases. Sanger and whole exome sequencing were used to identify the KIZ variants. Medical records were reviewed and analyzed. Thirty-one patients with biallelic KIZ mutations were identified: 28 homozygous for c.226C>T (p.R76*), 2 compound heterozygous for p.R76* and c.3G>A (p.M1?), and one homozygous for c.247C>T (p.R83*). c.226C>T is a founder mutation among patients of Jewish descent. The clinical parameters were less severe in KIZ compared to DHDDS and FAM161A cases. RT-PCR analysis in fibroblast cells revealed the presence of four different transcripts in both WT and mutant samples with a lower percentage of the WT transcript in patients. Sequence analysis identified an exonic sequence enhancer (ESE) that includes the c.226 position which is affected by the mutation. KIZ mutations are an uncommon cause of IRD worldwide but are not rare among Ashkenazi Jews. Our data indicate that p.R76* affect an ESE which in turn results in the pronounced skipping of exon 3. Therefore, RNA-based therapies might show low efficacy since the mutant transcripts are spliced.

Relatively mild blue cone monochromacy phenotype caused by various haplotypes in the L- and M-cone opsin genes.

Purpose: Blue cone monochromacy (BCM) is an X-linked retinopathy caused by mutations in the red and green cone opsin genes. The aim of this study was to establish the clinical, genetic, and electrophysiological characteristics of a specific form of BCM. Methods: Patients harboring mutations in the OPN1LW/OPN1MW genes underwent a full clinical examination, including ocular examination, color vision, full-field electroretinography, color fundus and autofluorescence photography, and optical coherence tomography. Genetic analysis was performed using whole-exome sequencing, duplex PCR, PCR/restriction fragment length polymorphism, and Sanger sequencing. IBM SPSS Statistics v. 21.0 was used for the data analysis. Results: Twenty-five patients harboring various haplotypes in exon 3 of the OPN1LW/OPN1MW genes were recruited. They showed a milder incomplete phenotype of BCM than the typical BCM control group. They presented significantly better visual acuity (logarithm of the minimum angle of resolution [logMAR] 0.48 ± 0.26 vs. 1.10 ± 0.54; p < 0.0001) and a highly myopic refraction (-7.81 ± 5.81 D vs. -4.78 ± 5.27 D; p = 0.0222) compared with the BCM control group. The study group had higher 30-Hz cone flicker responses (28.60 ± 15.02 µv; n = 24), whereas the BCM group had none (0.66 ± 2.12 µv; n = 21; p < 0.0001). The Lanthony 15-HUE desaturated test was variable for the exon 3 haplotype group, with a tendency toward the deutan-protan axis. Conclusions: The present study included genetic and clinical data from the largest cohort of patients with exon 3 haplotypes that were previously shown to cause missplicing of the OPN1LW and OPN1MW genes. Analysis of the clinical data revealed better best-corrected visual acuity, more severe myopia, and higher 30-Hz cone flicker responses in the patients with exon 3 haplotypes than in those with typical BCM.