Punctiform and Polychromatophilic Dominant Pre-Descemet Corneal Dystrophy

Confirmation of PRDX3 c.568G>C as the Genetic Basis of Punctiform and Polychromatic Pre-Descemet Corneal Dystrophy

PURPOSE

The aim of this study was to report the results of screening peroxiredoxin 3 (PRDX3) and PDZ domain-containing protein 8 (PDZD8) in a previously unreported pedigree with punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD) to confirm that the PRDX3 mutation c.568G>C is the genetic basis of PPPCD.

METHODS

Ophthalmologic examination of the proband and her affected father was performed with slit lamp biomicroscopy. Saliva was collected from the proband as a source of DNA, after which screening for PRDX3 and PDZD8 was performed.

RESULTS

Slit lamp examination of the proband revealed polychromatic deposits diffusely distributed at the pre-Descemet level in both corneas and anterior subcapsular in the crystalline lens of both eyes. The proband's father also demonstrated diffuse pre-Descemetic polychromatic deposits in both eyes but no lenticular deposits. Screening of PRDX3 in the proband demonstrated the c.568G>C (p.Asp190His) variant previously associated with PPPCD and failed to identify any variants in PDZD8.

CONCLUSIONS

We report the initial confirmation of PRDX3 as the genetic basis of PPPCD in a previously unreported pedigree and expand the phenotype of PPPCD to include polychromatic lenticular deposits.

Corneal dystrophies

Corneal dystrophies are broadly defined as inherited disorders that affect any layer of the cornea and are usually progressive, bilateral conditions that do not have systemic effects. The 2015 International Classification of Corneal Dystrophies classifies corneal dystrophies into four classes: epithelial and subepithelial dystrophies, epithelial-stromal TGFBI dystrophies, stromal dystrophies and endothelial dystrophies. Whereas some corneal dystrophies may result in few or mild symptoms and morbidity throughout a patient's lifetime, others may progress and eventually result in substantial visual and ocular disturbances that require medical or surgical intervention. Corneal transplantation, either with full-thickness or partial-thickness donor tissue, may be indicated for patients with advanced corneal dystrophies. Although corneal transplantation techniques have improved considerably over the past two decades, these surgeries are still associated with postoperative risks of disease recurrence, graft failure and other complications that may result in blindness. In addition, a global shortage of cadaveric corneal graft tissue critically limits accessibility to corneal transplantation in some parts of the world. Ongoing advances in gene therapy, regenerative therapy and cell augmentation therapy may eventually result in the development of alternative, novel treatments for corneal dystrophies, which may substantially improve the quality of life of patients with these disorders.

Punctiform and Polychromatic Pre-Descemet Corneal Dystrophy: Clinical Evaluation and Identification of the Genetic Basis

PURPOSE

This study reports the clinical features and genetic bases of 3 previously unreported families with punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD).

DESIGN

Observational case series.

METHODS

Full ophthalmic assessment was performed for members of 3 unreported families with PPPCD. Structural and biomechanical alterations of the cornea were screened. Whole exome sequencing (WES) was performed in the first family. Novel or rare variants that segregated with the affected status were screened in the other 2 families using Sanger sequencing. Identified variants that segregated with the affected status in all families were characterized by using in silico prediction tools and/or in vitro splice assays. Additionally, 2 previously reported PPPCD families were screened for variants identified in the 3 unreported PPPCD families.

RESULTS

PPPCD was diagnosed in 12 of the 21 examined members of the 3 unreported families. The only refractive, topographic, or biomechanical abnormality associated with PPPCD was a significantly increased corneal stiffness. WES and Sanger sequencing identified 2 variants that segregated with the affected status in all 3 families: a rare intronic PDZD8 c.872+10A>T variant and a novel missense PRDX3 c.568G>C (p.Asp190His) variant. The same PRDX3 variant was identified in the previously reported PPPCD family expressing the common PPPCD phenotype and was predicted by in silico prediction tools to be damaging to protein function.

CONCLUSIONS

PPPCD is associated with an alteration of corneal biomechanics and a novel missense variant in PRDX3. Screening of additional families will determine whether all families demonstrate a PRDX3 variant or whether locus heterogeneity may exist for PPPCD.

Multimodal imaging of pre-Descemet corneal dystrophy

PURPOSE

The aim of this study was to assess structural and histological changes associated with pre-Descemet corneal dystrophy with multimodal in vivo imaging.

METHODS

Retrospective case series including eight corneas from four unrelated male patients with pre-Descemet corneal dystrophy characterized by the presence of punctiform gray opacities located just anterior to the Descemet membrane at slit-lamp examination of both eyes. In vivo confocal microscopy images were obtained in the central, paracentral, and peripheral corneal zones from the superficial epithelial cell layer down to the corneal endothelium in both eyes. Spectral domain optical coherence tomography scans (central and limbal zones) and mapping of both corneas were acquired.

RESULTS

Diffuse small extracellular stromal deposits, presence of enlarged hyperreflective keratocytes in the posterior stroma with either hyperreflective or hyporeflective intracellular dots, and presence of activated keratocytes in the very anterior stroma were observed in all corneas with in vivo confocal microscopy. Spectral domain optical coherence tomography scans showed a hyperreflective line anterior to Descemet's membrane running from limbus to limbus and associated with a second thinner hyperreflective line just beneath Bowman's layer. Fine hyperreflective particles were observed in the posterior, mid, and anterior stroma on optical coherence tomography scans.

CONCLUSION

The clinical presentation and structural anomalies found in isolated sporadic pre-Descemet corneal dystrophy are in favor of a degenerative process affecting corneal keratocytes with no epithelial or endothelial involvement. The maximum damage is found just anterior to the Descemet membrane resulting in pre-Descemet membrane location of stromal opacities. Multimodal imaging of cornea reveals that the disorder affects the whole stroma and it permits better understanding of pre-Descemet corneal dystrophy pathophysiology together with ascertained diagnosis.

Confocal biomicroscopy in four patients with polychromatic corneal dystrophy

INTRODUCTION

Polychromatic corneal dystrophy is an unusual pre-descemet dystrophy, about which there are very few publications. The findings are presented in a case series of four patients with polychromatic corneal dystrophy, using a slit lamp, specular biomicroscopy, and confocal microcospy.

CLINICAL CASES

Four women, between 36 and 72 year-old, with the diagnosis of polychromatic corneal dystrophy in routine reviews. None reported visual symptoms or ocular history of interest. Anterior biomicroscopy showed multiple and small multicoloured brilliant opacities in the posterior area of the corneal stroma, with normal epithelium and anterior stroma. The opacities were bilateral and distributed throughout the entire cornea. Direct family members were examined, but none of them showed opacities. In the specular biomicroscopy, a normal endothelium, with pre-descemet hypereflective particles, was observed. With confocal microscopy, there were no abnormalities in epithelium, Bowman layer, or sub-basal nervous plexus. In two cases, the anterior stroma showed hyper-reflective keratocytes and with small hypereflective particles among them. In the middle stroma, hyper-reflective keratocytes were seen in the four cases, two of them showed tiny hypereflective particles, and in the other two there were abnormal keratocytes with prominent cytoplasmic processes. Posterior stroma in the four cases showed a lot of hypereflective keratocytes and hypereflective particles of different sizes. These particles prevented examining the endothelium.

CONCLUSIONS

Polychromatic corneal dystrophy has typical signs that allow it to be diagnosed and characterised. Although the biomicroscopy image only seems to show alterations in the posterior stroma, confocal microscopy shows that the dystrophy affects the entire corneal stroma.

Heredity and in vivo confocal microscopy of punctiform and polychromatic pre-Descemet dystrophy

PURPOSE

To describe and analyze the biomicroscopic features and in vivo confocal microscopy of the crystalline form of pre-Descemet corneal dystrophy (PDCD).

METHODS

We examined two non-related families using biomicroscopy, in vivo confocal microscopy, and a genetic study using a gene panel test, looking for mutations in the PIKFYVE gene.

RESULTS

A slit-lamp examination of the first family revealed polychromatic crystalline punctiform opacities distributed all over the stroma in 8 of 11 family members in three generations with an autosomal dominant inheritance. The second family showed in three of four members in two generations the same opacities located in the pre-Descemet region. It was also a hint for autosomal dominant inheritance. The in vivo confocal microscopy identified numerous rounded and hyperreflective stromal particles measuring 10-15 μm in diameter, with the highest density in the posterior stroma and with normal keratocytes. No systemic disease was diagnosed. No variants or mutations were identified in PIKFYVE gene.

CONCLUSIONS

Polychromatic deposits in patients with Punctiform and Polychromatic Pre-Descemet corneal dystrophy can be located not only in the deep stroma but also in the anterior and middle stroma. Our presentation reveals the possibility of considering this characteristic corneal disorder as a corneal dystrophy of its own and not as a subtype of pre-Descemet corneal dystrophy.