Ornithine Delta-Aminotransferase Deficiency

Rare genetic disorder affecting mitochondrial metabolism of ornithine. It is characterized by the presence of gyrate atrophy of the retina leading to night blindness that begins in late childhood, accompanied by sharply demarcated circular areas of chorioretinal atrophy. The areas of atrophy enlarge during the second and third decades. Posterior subcapsular cataracts have been associated by the end of the second decade. Computed tomography and magnetic resonance imaging (MRI) studies demonstrated the presence of type II muscle fiber changes in large muscle groups because of hyperornithinemia-induced deficiency of high-energy creatine phosphate. Brain MRI revealed degenerative lesions in the white matter in 50% of the gyrate atrophy patients, and 70% present premature atrophic changes. Early degenerative, atrophic brain changes and abnormal EEG are features of gyrate atrophy, in addition to the well-characterized eye and muscle manifestations.

OAT Deficiency; Hyperornithinemia Gyrate Atrophy of the Choroid and Retina.

Genetic disorder leading to visual disturbances caused by progressive chorioretinal atrophy.

Autosomal recessive transmission; high incidence in the Finnish population. The gene has been mapped on chromosome 10.

OAT is a mitochondrial enzyme requiring pyridoxal phosphate. In the neonatal period, the role of OAT reaction is to synthesize ornithine to produce arginine via citrulline; later, the role of OAT is to catabolize excess ornithine generated from dietary arginine. The cause of chorioretinal degeneration could be insufficient proline synthesis from ornithine in the retinal pigment epithelium.

Plasma ornithine levels more than 10 to 20 times normal. Diagnosis usually established by specialized ophthalmologic examination.

Night blindness and myopia in early childhood are the first symptoms. Retinopathy can be detected at electroretinography before visual disturbances are obvious. Chorioretinal atrophy can be detected at funduscopy. Considerable differences in severity of the disease. Subcapsular cataracts at the end of the second decade of life. Blindness caused by chorioretinal atrophy between 40 and 50 years of age in patients unresponsive to pyridoxine. Muscle pathology with type II fiber atrophy and tubular aggregates in some patients. Treatment consists of pharmacological doses of pyridoxine (vitamin B6) and/or a low-arginine diet.

No specific precautions before anesthesia except for the surgical procedure involved.

Individual affected might be visually impaired or blind. Bright operating room will provide reassurance. The presence of muscle atrophy or dysfunction should be considered when using neuromuscular blocking agents.

No known implication between anesthesia medication and administration of large doses of vitamin B6.

HHH Syndrome: Resembles ornithinemia with gyrate atrophy except there are no visual problems or fundus changes. The pathophysiology involves diminished ornithine transport into mitochondria, resulting in ornithine accumulation in the cytoplasm and reduced ability to clear carbamoyl phosphate and ammonia loads. Autosomal recessive inheritance has been suggested.