The Gyrate Atrophy Ocular and Systemic Study characterizes the natural history of ornithine levels and retinal degeneration (RD) associated with disease-causing OAT variants in the presence of standard care dietary treatment regimens over 4 years. The research goal is to understand the impact of OAT mutations on plasma ornithine levels and retinal degeneration. Funding Source- FDA OOPD

Gyrate atrophy is a rare inherited chorioretinal degeneration that is associated with hyperornithinemia, an inborn error of metabolism caused by autosomal recessive mutations in the ornithine aminotransferase (OAT) gene. Gyrate atrophy is characterized by childhood-onset nyctalopia and sharply demarcated areas of chorioretinal atrophy that initially involve the midperipheral fundus. The atrophic areas typically coalesce and enlarge towards the posterior pole in the second and third decades of life, leading to severe visual field constriction and vision loss if left untreated. The current standard care treatment of gyrate atrophy is an arginine restricted diet that is implemented in practice using dietary protein restriction with essential amino acid supplementation. However, dietary treatment is highly burdensome on patients and negatively impacts quality of life such that only about ~20% of patients are able to comply. Strict adherence to dietary protein restriction (particularly through adolescence), essential amino acid supplementation, and nutritional management of body weight especially during intercurrent illness and pregnancy are among the challenges of treatment. Periods of suboptimal dietary control led to plasma ornithine elevation and progressive chorioretinal degeneration.

Investigators are developing gene therapy as a potential one-time treatment that could arrest disease progression while avoiding or reducing the need for dietary treatment. To facilitate a future interventional gene therapy clinical trial, there is a need to evaluate natural history of and the relationship between potential clinical trial outcome measures.

The objectives of the OAT gene natural history study are as follows:

1. Natural History

   1. Characterize the natural history of retinal degeneration associated with disease-causing OAT variants in the presence of standard care dietary treatment regimens over four (4) years, using functional, structural, and patient-reported outcome measures.
   2. Characterize the natural history of ornithine levels associated with disease-causing OAT variants in the presence of standard care dietary treatment regimens over four (4) years.
   3. Determine within-patient variability of ornithine levels associated with disease-causing OAT variants in the presence of standard care dietary treatment regimens over four (4) years.
   4. Evaluate inter-eye correlation on ocular measures.

2. Metabolic-Structure-Function Relationships

   1. Explore relationship of structural outcomes with functional outcomes in individuals with disease-causing OAT variants.
   2. Explore relationship of plasma ornithine levels with structural and functional outcomes in individuals with disease-causing OAT variants.

3. Identify Rapid Progressors

   1. Explore possible risk factors (genotype, phenotype, environmental, comorbidities, and dietary therapy/supplements) for progression of the functional, structural, and patient-reported outcome measures over four (4) years in individuals with disease-causing OAT variants.
   2. Explore possible risk factors (genotype, phenotype, environmental, comorbidities, and dietary therapy/supplements) for ornithine levels over four (4) years in individuals with disease-causing OAT variants.

The expected impact of the OAT gene natural history study is to inform a future interventional clinical trial design and implementation, including the following:

1. Determine within-patient variability of ornithine levels.
2. Develop quantitative measures of progression of the area of preserved retina and establish its reproducibility, sensitivity to change, and relationship with other measures.
3. Establish rates of progression of retinal degeneration on all functional, structural, and patient-reported outcome measures, and determine which measures are most sensitive to change.
4. Determine primary time points and duration for a planned future treatment trial.
5. Use variability and inter-eye correlation of outcomes for trial sample size calculations.
6. Identify candidates for the future trial, including eligibility criteria based on risk factors and cut points for severity of disease most likely to benefit from treatment.
7. Establish study procedures and workflows for practical implementation of the same testing procedures in a future trial.

Inclusion Criteria:

• Participants must meet all the following inclusion criteria at the Screening Visit in order to be eligible to enroll into the genetic screening phase.
• Willing to participate in the study and able to communicate consent during the consent process.
• Willing and able to complete all study visit assessments at each visit over the forty-eight (48) month study period. Age ≥ 12 years.

Must meet one (1) of the Genetic Screening Criteria below:

• At least 2 disease-causing variants in the OAT gene which are homozygous or heterozygous in trans, based on a report from a clinically certified lab, or a report from a research lab that has been pre-approved by the study Genetics Committee.
• At least 2 disease-causing variants in the OAT gene with unknown phase, based on a report from a clinically certified lab, or a report from a research lab that has been pre-approved by the study Genetics Committee, AND must meet both of the following phenotype criteria: .Classic fundus appearance of gyrate atrophy (based on investigator discretion) AND Elevated ornithine levels >300 μmol/L (documented on any prior lab report).

Note: if a participant has a variant(s) of unknown significance, they will still qualify if they meet the Genetic Screening Criteria above. Ocular Inclusion Criteria Participant must meet the following criteria at the Screening Visit to enroll into the genetic screening phase.

Both eyes must have a clinical diagnosis of retinal dystrophy. Both eyes must permit good quality photographic imaging (e.g., but not limited to, clear ocular media, adequate pupil dilation, stable fixation).

Exclusion Criteria:

• Participants must not meet any of the following exclusion criteria at the Screening Visit in order to be eligible to enroll into the genetic screening phase.
• Single pathogenic or likely pathogenic genetic variants known to be associated with autosomal dominant retinitis pigmentosa/retinal dystrophy (AD, heterozygous), X-374 linked retinitis pigmentosa/retinal dystrophy (XL, hemizygous), or mitochondrial inheritance.
• Expected to enter experimental treatment trial at any time during this study. History of more than 1 year of cumulative treatment, at any time, with an agent associated with pigmentary retinopathy, including hydroxychloroquine, chloroquine, thioridazine, and deferoxamine. Note: Since this is a Natural History Study collecting data on the progression of Gyrate Atrophy, pregnant women will not be specifically excluded from participation.

Ocular Exclusion Criteria:

• If either eye has any of the following ocular exclusion criteria at the Screening Visit, then the participant is not eligible to enroll into the genetic screening phase.
• Current vitreous hemorrhage.
• Current or any history of tractional or rhegmatogenous retinal detachment.
• Current or any history of (for example, but not limited to prior to cataract or refractive surgery) spherical equivalent of the refractive error worse than -8 Diopters of myopia. • • • History of intraocular surgery (for example, but not limited to cataract surgery, vitrectomy, penetrating keratoplasty, or LASIK) within the last 3 months.
• Current or any history of confirmed diagnosis of glaucoma (for example, but not limited to glaucomatous VF changes or nerve changes, or history of glaucoma filtering surgery). e. Current or any history of retinal vascular occlusion or proliferative diabetic retinopathy.
• History or current evidence of ocular disease that, in the opinion of the investigator, may confound assessment of visual function.
• The following medications and treatments are prohibited as they can affect progression of retinal pigmentosa. The participant must not have received or planning to receive the following treatments.
• Any use of ocular stem cell or gene therapy.
• Any treatment with ocriplasmin.
• Treatment with Ozurdex (dexamethasone), Iluvien or Yutiq (fluocinolone 404 acetonide) intravitreal implant.

The following medications and treatments are excluded within the specified timeframe:

• Treatment with an ophthalmic oligonucleotide within the last 9 months (last treatment date is less than 9 months prior to Screening Visit date).
• Treatment with any other product within five times the expected half-life of the product (time from last treatment date to Screening Visit date is at least 4115 times the half-life of the given product).
• Treatment that can alter visual acuity between Screening and Baseline (e.g., periorbital injections.)

The target population for GYROS will be patients with gyrate atrophy associated with disease-causing variants in the OAT gene.

After the study is completed, the de-identified, archived data will be transmitted to and stored at the FFB Consortium Coordinating Center, under the supervision of Allison Ayala, for use by other researchers including those outside of the study.

After manuscript is published

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