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Cultured fibroblasts from a patient with gyrate atrophy of the retina do not convert L-ornithine, uniformly labeled with carbon-14, to proline. This metabolic block is caused by deficient L-ornithine:2-oxoacid aminotransferase activity in the patient. Her heterozygote father has intermediate activity of this enzyme.
Two patients with hyperornithinemia and gyrate atrophy of the choroid and retina, the first report in Japan, were described. Serum ornithine was increased 10- to 15-fold and serum lysine was slightly decreased in the affected patients. Urinary excretion of ornithine was also markedly increased. There was no increase in serum proline after the oral loading of ornithine in the patients, whereas serum proline increased after the loading in normal controls. Ornithine-ketoacid transaminase (OKT) activity was markedly reduced in phytohemagglutinin transformed lymphocytes from the patients. In all of their parents and one of the siblings, OKT activity was found to be decreased to about half of the normal control values. These findings indicate that the pathway from ornithine to proline is a major route of ornithine catabolism in man. A possible pathogenesis of ocular disturbance in the patients with OKT deficiency was postulated.
There is now strong evidence that the chorioretinal degeneration associated with ornithine-delta-aminotransferase (OAT) deficiency is a consequence of hyperornithinemia. Therefore development of a metabolic system for clearing ornithine from the circulation is being pursued as a potential treatment. The skin is considered an attractive location for such a metabolic system because autologous cells can be safely and easily utilized. This study was undertaken to determine the ornithine metabolizing capacity of epidermal keratinocytes expressing normal and superphysiologic amounts of OAT. The data show that overexpression of OAT in keratinocytes cultured from a gyrate atrophy patient restores ornithine metabolism and results in a rate of ornithine disappearance from the medium that is significantly higher than the rate of disappearance from the medium bathing normal keratinocytes. In addition, OAT activity determined in soluble protein prepared from sonicates suggests that the capacity to maintain plasma ornithine within the normal range is contained within an accomplishable graft of keratinocytes overexpressing OAT. However, the actual rate of ornithine disappearance from the media was significantly less than predicted from enzyme activity assays. Following ornithine metabolite production by intact cells suggests that ornithine metabolism is limited primarily by clearance of downstream metabolites, as opposed to substrate delivery.
In a patient with gyrate atrophy of the choroid and retina, an arginine-deficient diet has reduced plasma ornithine concentration fivefold during the past 20 months. Subjective improvement in her visual function was noted approximately 15 months after institution of her diet. This has been documented by improvements in the electroretinogram, dark-adaptation, and color vision. The improvement involves rod and, to a lesser extent, cone function. The results, although preliminary and limited to a single patient, suggest that reduction of plasma ornithine with a low arginine diet is beneficial in this disease.
Studies on the metabolism of selected amino acids were carried out in five patients with gyrate atrophy of the choroid and retina and four obligate heterozygotes. Hyperornithinemia, hyperornithinuria, and hypolysinemia were found in all patients. In one of the patients, the condition was diagnosed as early as 4 years of age. Ornithine loadings in the affected individuals did not induce the expected elevation of plasma glutamic acid and proline. Oral lysine tolerance tests in patients resulted in (1) enhancement of the hyperornithinuria and hyperlysinuria and (2) elevation of plasma lysine levels, which were below values obtained from normal controls. Supplementation of the regular diet with lysine for a period of 1 month increased plasma lysine but had no effect on plasma ornithine concentration.
Fundus fluorescein angiograms of 21 gyrate atrophy patients were evaluated. In 16 of 21 patients between 2 to 13 angiograms were taken during the follow-up which extended from 1.6 to 13.4 years. In 5 of 21 patients the fluorescein angiography was done once. Optic disc drusen occurred in 3 patients. Optic disc atrophy was not observed. Some attenuation occurred in the retinal arteries in the far-advanced stages. Up to the midretinal venous phase 5 of 13 patients had a markedly increased visibility of the larger choroidal vessels in areas of ophthalmoscopically intact retina. Pigment epithelial window defects presented in 17 of 21 patients. In 4, they were seen to enlarge into patches of chorioretinal atrophy during this long-term follow-up. Contrary to the general notion, the macula was affected frequently, i.e. in 9 of 21 patients; In 6 the pigment epithelial window defects presented in the macula, one had bilateral cystoid macular oedema, and in 2 patients the patches of chorioretinal atrophy were central.
Twenty-nine Finnish patients (8-80 years old during follow-up) with hyperornithinemia and gyrate atrophy (HOGA) were followed 2 to 31 years to determine when and how rapidly visual acuities and visual functions were affected by the disease. Considerable variability was observed both in the age at which visual acuities began to decrease and the age at which visual acuities reached 20/200. Acuities in phakic eyes tended to decrease from 20/30 to 20/200 in ten years or less, while aphakic eyes exhibited generally slower loss of vision. Without benefit of cataract surgery, the percentage of eyes with acuity 20/200 or worse would have been 37% at age 30 and 64% at age 40, but through surgery actually performed was 20% at age 40. Constriction of visual fields with age was marked and correlated well with diminution in dark adaptation.
Four patients with gyrate atrophy of the choroid and retina were studied, all of whom exhibited the hyperornithinemia characteristic of this disorder. Elevated plasma histidine and diminished plasma lysine and branched-chain amino acids were also noted. The renal clearances of these four amino acids were not sufficiently elevated to explain their low plasma levels. In one subject, an arginine-deficient diet led to progressive reduction in plasma ornithine from 13 times normal to the upper limits of normal, along with the disappearance of ornithinuria and lysinuria. Orally administered alpha-aminoisobutyric acid facilitated the fall in plasma ornithine by increasing renal losses of ornithine. It also increased the clearances of most other amino acids. When plasma ornithine approached normal (less than 200 microM), plasma lysine became normal, plasma arginine became subnormal, and renal clearances of basic amino acids decreased. Long-term (1.5 yr) maintenance with a diet containing 10-20 g of protein plus essential amino acids served to keep plasma ornithine at between 55-355 microM; chorioretinal degeneration did not progress and vision apparently improved.
Four patients with hyperomithinemia and gyrate atrophy of the choroid and retina age described. In vivo response to vitamin B6 is documented in three of the four patients by significant reduction of fasting serum ornithine and increase of lysine after oral B6 supplementation. Oral glucose tolerance testing in one patient resulted in marked changes in serum ornithine and lysine concentrations, in addition to mild glucose intolerance. Histochemical staining of punch muscle biopsies showed intracellular inclusions in type 2 muscle fibers. Tubular aggregates, approximately 60 nm in diameter and adjacent to the sarcoplasmic membrane, were seen on electron microscopy. Obligate heterozygotes had a mean serum ornithine slightly higher than normal, but there was considerable overlap with the normal range. Oral ornithine tolerance tests distinguished carriers from controls in only one of five cases. Deficient activity of ornithine ketoacid aminotransferase (OKT) in cultured skin fibroblasts was documented in all four patients. Approximately half-normal levels were found in obligate heterozygotes. In vitro response to B6 was manifest by increased OKT activity at increased concentrations of pyridoxal phosphate in fibroblasts from the patients.
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A 44-year-old woman had a fundus appearance similar to that of gyrate atrophy, a macular lesion, and excessive urinary excretion of proline, hydroxyproline, and glycine. The patient also had abnormal ciliary processes and patchy atrophy of the irides. To our knowledge, this is the first reported case of ocular manifestations associated with iminoglycinuria.
Examination of two sisters ages 2 years 10 months and 6 years four months with gyrate atrophy of the choroid and retina provided an opportunity for detailed clinical investigation. Although the chorioretinal lesions were confined to the peripheral retina in the older case and were quite minimal in the younger case, there was electroretinographic evidence of marked involvement of the cone and rod systems. These cases offer an opportunity to assess an arginine restricted diet in preventing the progress of the disease.
We studied the human ornithine aminotransferase (OAT) gene, mRNA, and enzyme activity in fibroblasts from a family with gyrate atrophy (G.A.) of the choroid and retina, using a normal human OAT cDNA as a probe. The family consists of an affected patient, who is heterozygous for a partial deletion of the functional OAT gene and whose cells produce no mRNA, and of his father, mother, two sons, and a daughter. Southern blot analysis of the OAT gene showed the partial deletion in the patient and in his father and daughter and in one son. Northern blot analysis revealed no OAT mRNA in the patient and approximately 50% of the normal level of OAT mRNA in the father, mother, two sons, and daughter. Assay showed that the OAT activity in these individuals mirrored the OAT mRNA levels. The results indicate that an active allele of the OAT gene expresses 50% of the total normal OAT mRNA and activity and that both alleles of the gene are inactive in the patient in this pedigree, a situation resulting in a complete absence of the OAT mRNA, in accordance with the autosomal recessive mechanism of this disease; they also indicate a 50% decrease of OAT mRNA and enzyme activity in obligate heterozygous carriers carrying one defective allele and that these defects are stably inherited.
The first case in Italy and the youngest case in the world of gyrate atrophy of the choroid associated with hyperornithinaemia is reported. A therapeutical attempt has been made and the possibility of following the evolution of the ocular lesion is very interesting.
The authors report two familial cases of algerian children with a hyperornithinaemia and a gyrate atrophy. Blood ornithine was 10 to 20 above the normal, lysine and glutamic acid were slightly decreased. Urinary ornithine levels were very high. The enzymatic activity of the ornithine keto-acid transaminase was not detectable in the patients skin fibroblasts. It was more than half the normal value in the children's mother. Owing to a better knowledge of the biochemical abnormalities a poor protein, poor arginine and more recently proline added diet has been recommended in order to alter the development of ocular lesions. Unfortunately the authors did not have the opportunity of following the children long enough to assess the result of this treatment.
A 15-year-old patient with hyperornithinaemia (0.6--1.2 mmol/l) and gyrate atrophy of the retina was given a low-arginine diet to reduce plasma ornithine to a concentration (0.15--0.25 mmol/l) near the normal range. After five weeks of treatment, there was improvement in the visual function of one eye which had been severely impaired without improvement for 3 years. This improved visual function was maintained until compliance with the diet deteriorated at eight months, after which visual function regressed towards pretreatment status. Overrestriction of dietary arginine produced hyperammonaemia, indicating that arginine is an essential aminoacid in ornithine transaminase deficiency. These results suggest that reduction of plasma ornithine may reverse a metabolic neuroretinopathy in this disease, and offer hope that progression of the retinal atrophy can be arrested as well.
Hyperornithinemia disappeared in three children with Gyrate atrophy of the choroid and retina during a low-arginine diet for 3 to 4 1/2 years. Because of the young age of the patients, we had an exceptional opportunity to follow the progression of the disease during this period. Despite the excellent biochemical control, electroretinographic changes progressed in two patients, and the chorioretinal atrophy progressed steadily in all the patients throughout the diet. Dark adaptation and color vision remained stable. In these patients, the normo-ornithinemia has not been able to halt the progression of the chorioretinal degeneration.
Deficient activity of L-ornithine:2-oxoacid aminotransferase is associated with gyrate atrophy of the choroid and retina with hyperornithinemia, an autosomal recessive disease leading to blindness. Liver tissue from two patients contained trace activity of the enzyme. The Michaelis (Km) value of the mutant enzyme for ornithine was 200 mM, 50-fold higher than normal, but increasing the concentrations of alpha-oxoglutarate and pyridoxal 5'-phosphate to 10 times those giving maximal activity of the normal enzyme had no effect on the mutant enzyme. Substrate inhibition of the mutant could not be demonstrated at 1,000 mM ornithine concentration, whereas ornithine concentrations above 70 mM inhibited the normal enzyme. The data suggest that the abnormal L-ornithine:2-oxoacid aminotransferase in the two patients studied has an altered binding site for ornithine.