Metabolic follow-up of a Croatian patient with gyrate atrophy and a new mutation in the OAT gene: a case report

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.

Variable phenotypes of gyrate atrophy in siblings with a nonsense mutation in OAT gene

Background: Gyrate Atrophy (GA) is a rare autosomal recessive disorder characterized by progressive chorioretinal degeneration. It is caused due to mutations in OAT gene that encodes a defective ornithine-δ-aminotransferase enzyme. We aim to identify the molecular cause of the disease and correlate it with the phenotype.Materials and Methods: Clinical, biochemical and genetic analyses were performed in siblings with GA.Case Description: A 10-year-old girl presented with impaired vision was clinically diagnosed to have peripheral chorioretinal degeneration in both eyes due to GA with vitreous hemorrhage in the right eye. Similar chorioretinal degeneration was observed in the patient's sibling, while parents were normal. Biochemical analysis of plasma by LC-MS/MS showed an elevated ornithine level of 892.8 µmol/L in the patient and 572.3 µmol/L in the sibling. Familial genetic screening by Sanger sequencing revealed a nonsense mutation in exon 11 of the OAT gene (c.1192C>T; p.Arg398Ter) in all the family members with a homozygous mutation in the patient and sibling, and heterozygous mutation in the parents. The patient was under follow-up with an arginine-restricted diet. At the last follow-up, the vitreous hemorrhage of right eye had resolved with an improvement in visual acuity and left eye remained stable with 6/12.Conclusion: Our patient is a rare case of gyrate atrophy presented with vitreous hemorrhage and nonsense OAT gene mutation, inherited in the autosomal recessive pattern. This report highlights the phenotypic variability among the siblings with the same mutation in OAT gene for the first time.