Clinical findings of end-stage retinitis pigmentosa with a homozygous PDE6A variant (p.R653X)

Novel variants in PDE6A and PDE6B genes and its phenotypes in patients with retinitis pigmentosa in Chinese families

BACKGROUND

Retinitis pigmentosa (RP) is a genetically heterogeneous disease with 89 causative genes identified to date. However, only approximately 60% of RP cases genetically solved to date, predicating that many novel disease-causing variants are yet to be identified. The purpose of this study is to identify novel variants in PDE6A and PDE6B genes and present its phenotypes in patients with retinitis pigmentosa in Chinese families.

METHODS

Five retinitis pigmentosa patients with PDE6A variants and three with PDE6B variants were identified through a hereditary eye disease enrichment panel (HEDEP), all patients' medical and ophthalmic histories were collected, and ophthalmological examinations were performed, followed by an analysis of the possible causative variants. Sanger sequencing was used to verify the variants.

RESULTS

We identified 20 variants in eight patients: 16 of them were identified in either PDE6A or PDE6B in a compound heterozygous state. Additional four heterozygous variants were identified in the genes ADGRA3, CA4, OPTN, RHO. Two novel genetic changes in PDE6A were identified (c.1246G > A and c.1747 T > A), three novel genetic changes in PDE6B were identified (c.401 T > C, c.2293G > C and c.1610-1612del), out of the novel identified variants one was most probably non-pathogenic (c.2293G > C), all other novel variants are pathogenic. Additional variant was identified in CA4 and RHO, which can cause ADRP (c.243G > A, c.688G > A). In addition, a novel variant in ADGRA3 was identified (c.921-1G > A).

CONCLUSIONS

This study reveals novel and known variants in PDE6A and PDE6B genes in Chinese families with autosomal recessive RP, and expands the clinical and genetic findings of photoreceptor-specific enzyme deficiencies.

PDE6C: Novel Mutations, Atypical Phenotype, and Differences Among Children and Adults

Purpose

Genetic variation in PDE6C is associated with achromatopsia and cone dystrophy, with only a few reports of cone-rod dystrophy in the literature. We describe two pediatric and two adult patients with PDE6C related cone and cone-rod dystrophy and the first longitudinal data of a pediatric patient with PDE6C-related cone dystrophy.

Methods

This cohort of four patients underwent comprehensive ophthalmologic evaluation at the National Eye Institute's Ophthalmic Genetics clinic, including visual field testing, retinal imaging and electroretinogram (ERG). Next-generation sequencing-based genetic testing was performed and subsequent analysis of the variants was done through three-dimensional protein models generated by Phyre2 and Chimera.

Results

All cases shared decreased best-corrected visual acuity and poor color discrimination. Three of the four patients had a cone-rod dystrophy, presenting with an ERG showing decreased amplitude on both photopic and scotopic waveforms and a mild to moderately constricted visual field. One of the children was diagnosed with cone dystrophy, having a preserved peripheral field. The children had none to minor structural retinal changes, whereas the adults had clear macular dystrophy.

Conclusions

PDE6C-related cone-rod dystrophy consists of a severe phenotype characterized by early-onset nystagmus, decreased best-corrected visual acuity, poor color discrimination, progressive constriction of the visual field, and night blindness. Our work contributes with valuable information toward understanding the visual prognosis and allelic heterogeneity of PDE6C-related cone and cone-rod dystrophy.

A new PDE6A missense variant p.Arg544Gln in rod-cone dystrophy

PURPOSE

Thus far, only one Japanese patient with autosomal recessive rod-cone dystrophy (AR-RCD) associated with the phosphodiesterase 6A gene (PDE6A) has been reported. The purpose of this study was to analyze the clinical features of a Japanese female patient with AR-RCD with a novel missense variant in PDE6A.

METHODS

We performed whole-exome sequencing (WES) to identify the disease-causing variant and a comprehensive ophthalmic examination including full-field electroretinography (ERG).

RESULTS

WES analysis revealed that the patient carried a novel homozygous missense variant (c.1631G > A; p.Arg544Gln) in PDE6A. Her unaffected parents carried the heterozygous variant. The patient reported night blindness in her early 20 s. At the age of 25 years, she underwent a comprehensive ophthalmic examination. Her corrected visual acuity was 20/13 in the right and 20/10 in the left eyes. Fundus images showed degenerative changes with bone spicule pigmentation in the mid-peripheral retina, and peripheral retinal vessels were not attenuated. Ultra-wide-field fundus autofluorescence images demonstrated large hypoautofluorescent regions corresponding to the degenerative changes, surrounded by hyperautofluorescence. Cross-sectional optical coherence tomography demonstrated a preserved ellipsoid zone and retinal thickness in the center of the macula, with perifoveal atrophy. ERG responses were subnormal, revealing that rod-mediated responses were more affected than cone-mediated responses, consistent with findings observed in RCD.

CONCLUSIONS

This is the second case of a patient with AR-RCD associated with PDE6A in the Japanese population. These findings will contribute to a better clinical understanding of PDE6A-associated RCD and valuable insights for gene therapy trials.

Endoplasmic reticulum stress: New insights into the pathogenesis and treatment of retinal degenerative diseases

Physiological equilibrium in the retina depends on coordinated work between rod and cone photoreceptors and can be compromised by the expression of mutant proteins leading to inherited retinal degeneration (IRD). IRD is a diverse group of retinal dystrophies with multifaceted molecular mechanisms that are not fully understood. In this review, we focus on the contribution of chronically activated unfolded protein response (UPR) to inherited retinal pathogenesis, placing special emphasis on studies employing genetically modified animal models. As constitutively active UPR in degenerating retinas may activate pro-apoptotic programs associated with oxidative stress, pro-inflammatory signaling, dysfunctional autophagy, free cytosolic Ca²⁺ overload, and altered protein synthesis rate in the retina, we focus on the regulatory mechanisms of translational attenuation and approaches to overcoming translational attenuation in degenerating retinas. We also discuss current research on the role of the UPR mediator PERK and its downstream targets in degenerating retinas and highlight the therapeutic benefits of reprogramming PERK signaling in preclinical animal models of IRD. Finally, we describe pharmacological approaches targeting UPR in ocular diseases and consider their potential applications to IRD.