Hyperornithinemia. Gyrate atrophy of the choroid or Fuchs disease. Ornithine-5-aminotransferase deficiency.
Incidence
This is a familiar condition inherited as an autosomal recessive trait. Several mutations are known.
Clinical Characteristics
It is a slowly progressive disease whose initial manifestation is nyctalopia followed by concentric narrowing of visual fields and loss of vision. Fundoscopic evaluation shows the classical appearance of spider-web retina covered with chocolate dust. Hyperornithinemia is characteristic of the disease. It is due to deficiency of the enzyme ornithine aminotransferase. This is a pyridoxal dependent enzyme so a small proportion of cases respond to pharmacological doses of pyridoxine. The condition may be seen in childhood but usually is seen in adolescence and especially in adulthood. Blindness is seen in adulthood. Creatine in plasma may be normal or decreased. Creatinine in plasma and urine can be normal or decreased. Ornithine in plasma, urine and CSF is elevated from childhood to adolescence and adulthood. Arginine and lysine are also elevated in urine. 3-amino-2-piperidone is also elevated. Electroretinogram (ERG) is extinct in adolescence and adulthood. EEG may be abnormal as well as EMG. The EEG is abnormal in 30 % of the times. Muscle electron microscopy show tubular aggregates in type 2 fibres, with abnormal mitochondria. Liver electron microscopy may show abnormal mitochondria in adolescence and adulthood. Patients tend to have myopia, hemeralopia. May also have posterior subcapsular cataract and proximal muscle weakness. Some patients react favorably to vitamin B6 from 40 to 200 mg/day. In cases that are not vitamin B6 responsive, dietary protein restriction is indicated. Creatinine supplementation tend to improve somewhat muscle histology. This condition is also called ornithine-5-aminotransferase deficiency or hyperornithinemia.
Precipitants
no
Provocation Tests
no
Diagnostic Procedures
EB-W, F, L, M. Enzyme can be measured in lymphocytes, fibroblasts, liver, muscle and hair roots. Ornithine in plasma, urine and CSF is elevated from childhood to adolescence and adulthood. Arginine and lysine are also elevated in urine. 3-amino-2-piperidone is also elevated. Electroretinogram (ERG) is extinct in adolescence and adulthood.