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  • Updated 08.13.2020
  • Released 04.24.2006
  • Expires For CME 08.13.2023

Hyperornithinemia

Introduction

This article includes discussion of hyperornithinemia, atrophia gyrata, and gyrate atrophy of the choroid and retina. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Slowly progressive ophthalmological changes beginning in childhood and leading to blindness in the fifth decade are the characteristics of gyrate atrophy of the choroid and retina. Gyrate atrophy is an inherited metabolic disease that is caused by deficiency of the enzyme ornithine aminotransferase. The biochemical hallmark of the disease is the distinctly increased amino acid ornithine in plasma. In this article, the author provides an in-depth review of the clinical presentation, pathophysiology, diagnosis, and treatment options for gyrate atrophy.

Key points

• Hyperornithinemia is a slowly progressive disease, primarily of the eyes, with visual deterioration starting in late childhood and blindness around the fifth decade of life.

• It is an autosomal-recessive inborn error of metabolism due to deficiency of the enzyme ornithine aminotransferase.

• Chorioretinal degeneration and hyperornithinemia are diagnostic for the disease.

• Except for a few cases that respond to vitamin B6, treatment is strict protein restriction and supplementation of arginine-free amino acid mixture.

• Successful reduction of ornithine halts the progression of the disease.

Historical note and terminology

The report of a case of "atypical retinitis pigmentosa" by Jacobsohn in 1888 represents probably the first description of a patient with gyrate atrophy of the choroid and retina, as defined by the characteristic appearance of the ocular fundus and a typical history of visual deterioration (30). Cutler in 1895 and Fuchs in 1896 were the first ophthalmologists to recognize this condition as a distinct entity (13; 19). Fuchs gave the disorder its euphonious appellation. Usher reviewed 26 cases in 1935, emphasizing the genetic aspects (90). Despite of the observation in 1960 of an abnormally large lysine-ornithine spot in the urine of a patient with gyrate atrophy, hyperornithinemia and ornithinuria were not recognized as the biochemical counterparts of this disorder (41) until the report of Simell and Takki in 1973 (85 years after the initial ophthalmologic description). They postulated that the hyperornithinemia was presumably due to deficiency of ornithine aminotransferase (OAT) in 9 patients with gyrate atrophy of the choroid and retina (80).

Ornithine aminotransferase was first described in animal tissues by Quastel and Witty and Meister (60; 47). The deficiency of the ornithine aminotransferase in a patient with gyrate atrophy was first demonstrated by Valle and colleagues (92). Mitchell and colleagues identified the first mutations in the ornithine aminotransferase gene of patients with gyrate atrophy (50). The quantitative importance of the ornithine aminotransferase transamination reaction in the regulation of ornithine homeostasis was first proven by Seiler and colleagues (76).

To elucidate the pathophysiology of the disease, animal models were implemented by initially using intravitreal injection of L-ornithine (42) and later application of 5FMOrn as selective ornithine aminotransferase inhibitor (14). Since 1995, the transgenic mouse model for ornithine aminotransferase deficiency has provided an opportunity to glean deeper insights (100). The retarded hair growth (rhg) mutant mouse may offer an ideal model for gyrate atrophy of the choroid and retina in humans. This mouse mutant is caused by the same missense mutation that is known in some families (07).

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