Gyrate Atrophy of the Choroid and Retina Diagnosed by Ornithine-δ-aminotransferase Gene Analysis: A Case Report
A pair of 19-year-old female identical twins presented with complaints of gradual visual loss and progressive night vision deterioration occurring over the past several years. The older twin's best-corrected visual acuity (BCVA) was 20 / 32 in both eyes. The refractive error was -17.75 diopter (D) in the right eye and -17.25 D in the left eye. She had bilateral posterior subcapsular cataracts. On examination, her fundus exhibited bilateral severe chorioretinal atrophy involving the midperiphery (). Fundus fluorescein angiography revealed leakage at the margin of chorioretinal atrophy and dye accumulation in the maculae of both eyes (). Disclosed cystoid macular edema was evident in both eyes on optical coherence tomography (). Dynamic Goldmann perimetry demonstrated visual field constriction in both eyes, and a full-field electroretinogram showed markedly impaired photopic and scotopic responses. On plasma amino acid analysis, she had markedly elevated plasma levels of ornithine (783 µmol/L; normal range, 48 to 195 µmol/L). Screening for inherited metabolic disorder by tandem mass spectrometry (MS/MS) revealed plasma ornithine levels of 380 µmol/L (cutoff, 290 µmol/L).\nThe younger twin's BCVA was 20 / 25 in the right eye and 20 / 32 in the left eye. The refractive error was -17.0 D in the right eye and -16.0 D in the left eye. Her fundoscopy, fluorescein angiography, optical coherence tomography, Goldmann perimetry and full-field electroretinogram findings were similar to those of her older twin. Accordingly, her plasma levels of ornithine on amino acids analysis and MS/MS were 831 µmol/L and 424 µmol/L, respectively.\nThe clinical diagnosis of both patients was consistent with OAT deficiency and GA of the choroid and retina. OAT gene analysis resulted in the detection of two mutations in both patients: c.425G>A, a known mutation, and c.199+11_199+16dupAATTAA, a previously unclassified mutation. Both patients were treated with vitamin B6 (pyridoxine) 300 mg daily and an arginine-restricted diet. After three months of treatment, plasma ornithine levels as measured by MS/MS were 254 µmol/L in the older twin and 365 µmol/L in the younger twin. Their visual acuities in each eye were preserved with no progression of chorioretinal atrophy on fundoscopy after 15 months, and the plasma ornithine levels were controlled at 386 µmol/L and 408 µmol/L, respectively.