Ornithine Delta-Aminotransferase Deficiency

At a glance

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. Early degenerative, atrophic brain changes and abnormal EEG are features of gyrate atrophy, in addition to the well-characterized eye and muscle manifestations.

Synonyms

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

Incidence

More than 200 cases have been reported with an incidence of 1:50,000 reported in Finland.

Genetic inheritance

Autosomal recessive transmission; high incidence in the Finnish population.

Pathophysiology

The OAT gene is located on chromosome 10q26.13. In the neonatal period, the role of ornithine aminotransferase is to synthesize ornithine to produce arginine via citrulline. Later, the role of ornithine aminotransferase is to catabolize excess ornithine generated from dietary arginine. The mitochondrial enzyme ornithine aminotransferase requires pyridoxal phosphate. The cause of chorioretinal degeneration could be insufficient proline synthesis from ornithine in the retinal pigment epithelium.

Diagnosis

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

Clinical aspects

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. Computed tomography and 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. Also, brain MRI revealed degenerative lesions in the white matter in 50% of the gyrate atrophy patients, and 70% present premature atrophic changes. Treatment consists of pharmacological doses of pyridoxine (vitamin B₆) and/or a low-arginine diet.

Precautions before anesthesia

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

Anesthetic considerations

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.

Pharmacological implications

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

Other condition to be considered

• ☞HHH Syndrome: Genetically transmitted inborn error of metabolism resulting from a defect in the transport of ornithine into the mitochondrial matrix, clinically characterized by early growth retardation, ...