Reversal of cystoid macular edema in gyrate atrophy patients

Gyrate atrophy of the choroid and retina: Update on diagnosis and treatment

Gyrate atrophy of the choroid and retina (GACR) is a rare autosomal recessive disease characterised by elevated plasma ornithine levels due to deficiency of the enzyme ornithine aminotransferase (OAT). The accumulation of this amino acid in plasma leads to the development of patches of chorioretinal atrophy in the peripheral retina extending into the macular area. Patients usually present with night blindness followed by constriction of the visual field and, finally, decreased central vision and blindness. The disease is diagnosed by the presence of the characteristic clinical picture, the presence of hyperornithinaemia in plasma and the detection of mutations in the OAT enzyme gene. There is currently no effective gene therapy and the most common therapeutic intervention mainly involves dietary modifications with arginine restriction. This article aims to summarise the pathogenesis, clinical and diagnostic findings and treatment options in patients with GACR.

Cystoid macular oedema without leakage in fluorescein angiography: a literature review

Cystoid macular oedema (CMO), which is defined as a macular thickening and cystic changes due to accumulation of fluid, could be asymptomatic and only diagnosed using paraclinical techniques. Fluorescein angiography (FA) and optical coherence tomography (OCT) are useful in detecting CMO in clinical practice. Non-leaking CMO, also known as angiographically silent CMO, is referred to as cases of CMO without leakage in fluorescein angiography. This type of CMO has been reported in some retinal dystrophies, in cases of maculopathy as a side effect of certain drugs, and also in some systemic disorders. The exact mechanism and treatment options for this type of CMO are still not clear. This literature review aims to discuss different causes of non-leaking CMO, proposed mechanisms, and management options. Three sections including drugs, retinal dystrophies, and systemic disorders are discussed in this review.

A possible ocular biomarker for response to hyperornithinemia in gyrate atrophy: the effect of pyridoxine, lysine, and arginine-restricted diet in a patient with advanced disease

BACKGROUND

Loss of function variants in the ornithine aminotransferase (OAT) gene cause accumulation of ornithine levels, leading to gyrate atrophy. The benefit of ornithine-lowering therapies has been documented in a mouse model and young patients, however, the effect in adults with advanced disease has not been well described.

MATERIALS AND METHODS

Case report of an adult patient with advanced gyrate atrophy, who underwent treatment with pyridoxine and an arginine-restricted diet for four years.

RESULTS

A 51-year-old female with advanced chorioretinal degeneration presented with hyperornithinemia (961 vs. normal 18-135 µmol/L) and compound heterozygous pathogenic variants in OAT (p.Tyr299* and p.Ala270Pro). Treatment with pyridoxine and arginine-diet restriction yielded a maximal reduction in ornithine levels by 71% (275 µmol/L). Optical coherence tomography (OCT) showed a reduction in ellipsoid zone (EZ) thickness that correlated with lower ornithine levels and reversed with higher ornithine levels. While her best-corrected visual acuity remained unchanged, the progressive decline in her visual fields appeared to stabilize during a one-year period when ornithine levels were below 500 µmol/L.

CONCLUSIONS

In this report, we demonstrate that chorioretinal degeneration appears to stabilize in an adult patient with gyrate atrophy in association with a partial reduction in ornithine levels. We also observed a correlation with reduced EZ thickness on OCT and propose this may be a novel biomarker for ornithine reduction therapies. Our case study characterizes the potential retinal structure-function benefits of ornithine-lowering treatments even in cases of advanced chorioretinal degeneration. Thus, we recommend a low threshold for treating all patients with gyrate atrophy.

A review of treatment modalities in gyrate atrophy of the choroid and retina (GACR)

Gyrate atrophy of the choroid and retina (GACR) is a rare inborn error of amino acid metabolism caused by bi-allelic variations in OAT. GACR is characterised by vision decline in early life eventually leading to complete blindness, and high plasma ornithine levels. There is no curative treatment for GACR, although several therapeutic modalities aim to slow progression of the disease by targeting different steps within the ornithine pathway. No international treatment protocol is available. We systematically collected all international literature on therapeutic interventions in GACR to provide an overview of published treatment effects.

METHODS

Following the PRISMA guidelines, we conducted a systematic review of the English literature until December 22nd 2020. PubMed and Embase databases were searched for studies related to therapeutic interventions in patients with GACR.

RESULTS

A total of 33 studies (n = 107 patients) met the inclusion criteria. Most studies were designed as case reports (n = 27) or case series (n = 4). No randomised controlled trials or large cohort studies were found. Treatments applied were protein-restricted diets, pyridoxine supplementation, creatine or creatine precursor supplementation, l-lysine supplementation, and proline supplementation. Protein-restricted diets lowered ornithine levels ranging from 16.0-91.2%. Pyridoxine responsiveness was reported in 30% of included mutations. Lysine supplementation decreased ornithine levels with 21-34%. Quality assessment showed low to moderate quality of the articles.

CONCLUSIONS

Based primarily on case reports ornithine levels can be reduced by using a protein restricted diet, pyridoxine supplementation (variation-dependent) and/or lysine supplementation. The lack of pre-defined clinical outcome measures and structural follow-up in all included studies impeded conclusions on clinical effectiveness. Future research should be aimed at 1) Unravelling the OAT biochemical pathway to identify other possible pathologic metabolites besides ornithine, 2) Pre-defining GACR specific clinical outcome measures, and 3) Establishing an international historical cohort.

Molecular and Cellular Studies Reveal Folding Defects of Human Ornithine Aminotransferase Variants Associated With Gyrate Atrophy of the Choroid and Retina

The deficit of human ornithine aminotransferase (hOAT) is responsible for gyrate atrophy (GA), a rare recessive inherited disorder. Although more than 60 disease-associated mutations have been identified to date, the molecular mechanisms explaining how each mutation leads to the deficit of OAT are mostly unknown. To fill this gap, we considered six representative missense mutations present in homozygous patients concerning residues spread over the hOAT structure. E. coli expression, spectroscopic, kinetic and bioinformatic analyses, reveal that the R154L and G237D mutations induce a catalytic more than a folding defect, the Q90E and R271K mutations mainly impact folding efficiency, while the E318K and C394Y mutations give rise to both folding and catalytic defects. In a human cellular model of disease folding-defective variants, although at a different extent, display reduced protein levels and/or specific activity, due to increased aggregation and/or degradation propensity. The supplementation with Vitamin B6, to mimic a treatment strategy available for GA patients, does not significantly improve the expression/activity of folding-defective variants, in contrast with the clinical responsiveness of patients bearing the E318K mutation. Thus, we speculate that the action of vitamin B6 could be also independent of hOAT. Overall, these data represent a further effort toward a comprehensive analysis of GA pathogenesis at molecular and cellular level, with important relapses for the improvement of genotype/phenotype correlations and the development of novel treatments.

Partial regression of foveoschisis following vitamin B6 supplementary therapy for gyrate atrophy in a Chinese girl

BACKGROUND

To report a case of genetically confirmed gyrate atrophy (GA) of choroid and retina, who showed partial regression of foveoschisis following vitamin B6 supplementary therapy.

CASE PRESENTATION

A 6-year-old Chinese girl complained about night blindness and progressive decreased vision in both eyes. Her best corrected visual acuity (BCVA) was 20/63 OD and 20/100 OS. Fundus examination showed bilateral multiple, sharply demarcated, scallop-shaped chorioretinal atrophy areas in the midperipheral and peripheral of the fundus. Spectral domain optical coherence tomography (SD-OCT) showed increased central macular thickness (CMT) with multiple intraretinal cystic spaces in the both eyes. There was no leakage or staining in the macular area in late phase of fluorescein angiography (FA). Blood tests confirmed hyperornithinemia and genetic analysis revealed two heterozygous mutations on ornithine aminotransferase (OAT) gene. Based on clinical presentation and genetic test, the patient was diagnosed as GA of the choroid and retina and further treated with vitamin B6 supplementary for three weeks. Her serum ornithine levels did not change but CMT on SD-OCT declined with partial regression of intraretinal cystic spaces. Then, the patient discontinued the drug because of severe muscle pain, and foveoschisis increased to initial level a month later.

CONCLUSIONS

Foveoschisis is a rare complication of GA. Vitamin B6 supplementation may alleviate foveoschisis, but its effort for reducing serum ornithine level might be limited. Potential drug adverse effects should be noted in pediatric patients.

Analysis of optical coherence angiography in cystoid macular oedema associated with gyrate atrophy

BACKGROUND

To evaluate the relationship between superficial, deep foveal avascular zone (FAZ) and foveal cyst areas in eyes with cystoid macular oedema (CMO) associated with gyrate atrophy of the choroid and retina (GA).

METHODS

This is a retrospective collaborative multicenter study of optical coherence tomography-angiography (OCTA) images in GA. Superficial and deep FAZ and foveal cyst were measured using Image J by two independent experts. Values were corrected for myopia magnification. These values were compared with age-matched controls from normative data.

RESULTS

Twenty-three eyes from 12 patients with GA and CMO were included in the study. The mean ± standard deviation age was 22 ± 19.7 years, mean Snellen spectacle-corrected visual acuity of 20/70 with mean myopia of 5.7 ± 4.1 dioptres. Qualitatively, no focal occlusion of superficial and deep capillary plexus was noted. Mean superficial FAZ area (0.484 ± 0.317 mm²), deep FAZ area (0.626 ± 0.452 mm²), and foveal cyst area (0.630 ± 0.503 mm²) were significantly larger than superficial and deep FAZ areas in controls of same age range (p < 0.001). Macular cyst area correlated with superficial FAZ area (R = 0.59; p = 0.0057) and more strongly with deep FAZ area (R = 0.69; p < 0.001).

CONCLUSIONS

The superficial and deep FAZ area in GA-associated CMO were noted to be significantly larger than in controls. It seems that RPE dysfunction leads to foveal cyst enlargement displacing the capillary plexus with resultant enlarged superficial and deep FAZ area.

Diagnostic value of a combination of next-generation sequencing, chorioretinal imaging and metabolic analysis: lessons from a consanguineous Chinese family with gyrate atrophy of the choroid and retina stemming from a novel OAT variant

BACKGROUND/AIM

Gyrate atrophy of the choroid and retina (GACR) is an extremely rare autosomal recessive inherited disorder characterised by progressive vision loss. To identify the disease-causing gene in a consanguineous Chinese pedigree with GACR, we aimed to accurately diagnose patients with GACR through a combination of next-generation sequencing (NGS) genetic diagnosis, clinical imaging and amino acid metabolic analysis.

METHODS

A consanguineous Chinese pedigree with GACR, including two patients, was recruited and a comprehensive ophthalmological evaluation was performed. DNA was extracted from a proband and her family members, and the sample from the proband was analysed using targeted NGS. Variants ‎detected by NGS were confirmed by Sanger sequencing and subjected to segregation analysis. Tandem mass spectrometry (MS/MS) was subsequently performed for metabolic assessment.

RESULTS

We identified a ‎novel, deleterious, homologous ornithine aminotransferase (OAT) variant, c.G248A: p.S83N, which contributes to ‎the progression of GACR in patients. Our results showed that the p.S83N autosomal recessive ‎variant of OAT is most likely ‎pathogenic, with changes in protein stability drastically decreasing functionality. MS/MS verified that ornithine levels in patients were significantly elevated.

CONCLUSIONS

Recruitment of a third-degree first cousin consanguineous marriage family with GACR allowed us to identify a novel pathogenic OAT variant in the Chinese population, broadening the mutation spectrum. Our findings reported the diagnostic value of a combination of NGS, retinal imaging and metabolic analysis of consanguineous marriage pedigrees in low-income/middle-income and low-incidence countries, including China, and may help to guide accurate diagnosis and ‎treatment of this disease.

Multimodal imaging of foveoschisis and macular pseudohole associated with gyrate atrophy: a family report

BACKGROUND

To report the results of multimodal imaging of a biochemically confirmed case of a family with gyrate atrophy (GA) associated with foveoschisis and macular pseudohole.

CASE PRESENTATION

Two sisters presented to us with progressive bilateral decreased vision. The 26-year old sister had a best corrected visual acuity (BCVA) of 20/32 in the right eye (RE) and 20/100 in the left eye (LE). Dilated fundus examination revealed multiple bilateral chorioretinal atrophy areas in the midperipheral and peripheral retina. Fluorescein angiography did not show any leak in the macular area. Swept-source optical coherence tomography (SS-OCT) showed increased central macular thickness in both eyes with foveoschisis. Optical coherence tomography angiography (OCTA) showed petaloid non-reflective areas and some perifoveal microvascular alterations similar to telangiectasias in the deep capillary complex. The 30-year-old sister had a BCVA of 20/20 in the RE and 20/32 in the LE. SS-OCT was normal in the RE and demonstrated a macular pseudohole with a fine epiretinal membrane in the LE. The persistent retinal tissue at the base of the pseudohole was disorganised. Blood tests showed hyperornithinemia in the 2 cases. Based on these observations, the patients were diagnosed with gyrate atrophy of the choroid and retina and were treated with a pyridoxine supplement and an arginine-restricted diet.

CONCLUSIONS

Foveoschisis and macular pseudohole may be associated in GA, increasing the risk of rapid vision loss. OCTA is an interesting imaging tool that can help to better understand the pathophysiological mechanism of these macular involvements in GA.

Target 5000: Target Capture Sequencing for Inherited Retinal Degenerations

There are an estimated 5000 people in Ireland who currently have an inherited retinal degeneration (IRD). It is the goal of this study, through genetic diagnosis, to better enable these 5000 individuals to obtain a clearer understanding of their condition and improved access to potentially applicable therapies. Here we show the current findings of a target capture next-generation sequencing study of over 750 patients from over 520 pedigrees currently situated in Ireland. We also demonstrate how processes can be implemented to retrospectively analyse patient datasets for the detection of structural variants in previously obtained sequencing reads. Pathogenic or likely pathogenic mutations were detected in 68% of pedigrees tested. We report nearly 30 novel mutations including three large structural variants. The population statistics related to our findings are presented by condition and credited to their respective candidate gene mutations. Rediagnosis rates of clinical phenotypes after genotyping are discussed. Possible causes of failure to detect a candidate mutation are evaluated. Future elements of this project, with a specific emphasis on structural variants and non-coding pathogenic variants, are expected to increase detection rates further and thereby produce an even more comprehensive representation of the genetic landscape of IRDs in Ireland.