BIOCHEMICAL FINDINGS IN HUMAN RETINITIS PIGMENTOSA WITH PARTICULAR RELATION TO VITAMIN A DEFICIENCY

Correlation between the Serum Concentration of Vitamin A and Disease Severity in Patients Carrying p.G90D in RHO, the Most Frequent Gene Associated with Dominant Retinitis Pigmentosa: Implications for Therapy with Vitamin A

The pathogenic variant p.G90D in RHO is believed to be responsible for a spectrum of phenotypes, including congenital stationary blindness (for the purpose of this study termed night blindness without degeneration; NBWD), Sector RP, Pericentral RP, and Classic RP. We present a correlation between the serum concentration of vitamin A and disease severity in patients with this variant. This prospective study involved 30 patients from 7 families (17 male; median age 46 years, range 8−73). Full ophthalmological examination including visual acuity, Goldmann perimetry, slit-lamp exam, optical coherence tomography, fundus autofluorescence, and electrophysiology was performed to determine the presenting phenotype. The serum concentration of vitamin A was determined from a fasting blood sample taken on the day of the exam, where it was found that 23.3% (7/30) of patients had NBWD, 13.3% (4/30) had Sector RP, 3.3% (1/30) had Pericentral RP, and 60% (18/30) had Classic RP. Multiple logistic regression revealed a significantly higher probability of having a milder phenotype (NBWD or Sector RP) in association with younger age (p < 0.05) and a higher concentration of vitamin A (p < 0.05). We hypothesize that vitamin A in its 11-cis-retinal form plays a role in stabilizing the constitutively active p.G90D rhodopsin and its supplementation could be a potential treatment strategy for p.G90D RHO patients.

Erythrocyte and platelet fatty acids in retinitis pigmentosa

The fatty acid composition and the glutathione-peroxidase activity (GSH-Px) of erythrocytes and platelets, the production of malondialdehyde (MDA) by platelets and the activity of the main systems of transmembrane cation transport in erythrocyte have been studied in 12 patients (5 males and 7 females) affected by retinitis pigmentosa (RP). A remarkable increase of saturated fatty acids (SFA), particularly of stearic acid (C18:0), has been noted in these patients. The reduced unsaturated/saturated fatty acids ratio (PUFA/SFA) observed in both erythrocytes and platelets and the decrease of arachidonic acid in platelets may depend by an active peroxidation process as documented by the increase of MDA. Platelet glutathione-peroxidase (PTL-GSH-PX) and plasma retinol were in the normal range, whereas erythrocyte glutathione-peroxidase (E-GSH-PX), MDA and plasma alfa-toco-pherol were increased in patients with RP. The activities of Na(+)-K+ pump, cotransport and Na(+)-Li+ countertransport were normal in RP erythrocytes.

Clinical and serum lipid findings in a large family with autosomal dominant retinitis pigmentosa

Retinitis pigmentosa, of unknown cause, has recently been associated with decreased amounts of the polyunsaturated fatty acid, docosahexaenoic acid, in the plasma of affected as compared with unaffected relatives. It has been suggested that this finding may serve as a marker for the disease and might indicate alterations in photoreceptor cell metabolism. The authors studied 54 members of a family with dominantly inherited retinitis pigmentosa in five generations. In addition to the typical clinical findings of retinitis pigmentosa, eight persons also had a bull's eye maculopathy, and four persons had uni- or bilateral optic nerve drusen. When the authors determined the plasma fatty acid and lipid contents, they saw the expected age-related effect on cholesterol and triglycerides, but an unexpected, significant reduction in fatty acids in the unaffected controls as compared with persons with retinitis pigmentosa. The authors' results emphasize the heterogeneity of phenotypic expression of retinitis pigmentosa within a single family.

Darier's disease and retinitis pigmentosa; is there a pathogenetic relationship?

Two brothers with Darier's disease and concomitant retinitis pigmentosa are reported. To our knowledge, these are the first cases with this combination of symptoms described in the literature. The dermatological conditions occurring with retinitis pigmentosa are reviewed. A disturbance in retinoids or retinoid binding proteins as a possible cause of both diseases is discussed.

Combined vitamin A and E therapy prevents retinal electrophysiological deterioration in abetalipoproteinaemia

Eight patients with abetalipoproteinaemia had the typical ocular, systemic, and laboratory findings of this disease. Combined therapy with vitamins A and E was administered, starting as early as the first day of life and as late as 26 years of age. The patients were followed up for 2-6 years. Electroretinography was undertaken in all cases and electrooculography in some. After initiation of vitamin A and E therapy no progression of disturbed visual function could be detected in any patient. These objective tests of retinal function demonstrated that the combined vitamin A and E therapy may be useful in arresting retinal deterioration in abetalipoproteinaemia.

Amino acids in retinitis pigmentosa

A survey of fasting whole blood amino acids in 65 patients with various subtypes of retinitis pigmentosa performed. Eight X-linked recessive patients showed decreased taurine and aspartate. Nineteen autosomal recessive patients, and to lesser extent 10 autosomal dominant patients, showed reduced levels of whole blood threonine and histidine. Branched-chain amino acids and arginine were present in increased amounts in 2 patients with Laurence-Moon-Bardet-Biedl syndrome. These findings in LMBB patients are probably related in part to their obesity and emphasise that appropriate controls are required, and other factors (including age) known to affect amino acid levels must be accounted for. The biochemical implications of our findings are not yet apparent.

Uptake of taurine by platelets in retinitis pigmentosa

Uptake of 3H-taurine by platelets from twelve patients with retinitis pigmentosa (R.P.) and from healthy controls was measured. Platelets were incubated in autologous plasma with 3H-taurine for different times and at different substrate concentrations. The uptake of taurine by R.P. platelets at each incubation time was about two-thirds of the control value, the difference being statistically significant. Km was about the same, but Vmax was lower in R.P. platelets. The results suggest that R.P. is a disease affecting not only the eye but also taurine transport and/or storage in general.

Serum IgM in retinitis pigmentosa: a genetic study

Because of a published report that serum immunoglobulin M (IgM) was elevated in some cases of retinitis pigmentosa (RP), a genetic study was undertaken to determine if a particular pattern of inheritance was associated with elevated IgM. Seventy-five RP patients in 37 families were ascertained and classified by pattern of inheritance into six groups. Serum IgM was quantitated by the radial immunodiffusion technique. Fifty-one controls were also studied. Methods of adjusting the IgM values for sex, age, and race were derived, but only a sex adjustment was used, since no effect of age on IgM was found in this sample, and there were few data on race. There was no signifcant difference in mean IgM levels between RP patients and controls. The variance of the RP group was slightly greater than that of the controls. One-way analysis of variance of the six genetic categories of RP and controls was performed on the raw data and on the data after log transformation. The F-ratio was not significant, indicating that there was no difference in serum IgM levels among the seven groups. Possible reasons for the discrepancy in results between this study and the previous report are presented.

A therapeutic trial of vitamin A in patients with pigmentary retinal degenerations: a negative study

A prospective therapeutic trial was designed to test the hypothesis that measurable improvement of retinal functions might occur in some patients with pigmentary retinal degeneration when placed on high doses of solubilized vitamin A (Aquasol A, 50,000 I.U. per day by mouth for 28 days). After a standard ophthalmic history and examination pre-trial examinations consisting of visual acuity, visual fields, color vision tests, dark adaptations and cone thresholds were obtained on two separate occasions. Electroretinography was usually performed only once. Forty-seven patients were entered into the study of which 27 had typical retinitis pigmentosa. The patients showed no significant change in visual function from pre-trial results when tested after taking the vitamin A for 28 days. Post-trial electroretinography performed on 10 patients with recordable pre-trial electroretinograms showed no change. The 10 patients retested at six and 12 months after the trial showed no significant change in visual function.

Retinitis pigmentosa

The authors review the symptomatic and genetic aspects of the various entities of isolated retinitis pigmentosa (R.P), both in its typical form and in the forms associated with the affection of other ocular tissues. Syndromes in which R. P. is associated with the affection of other organs and systemic disorders are also cconsidered. Origin, diagnosis and the course of the disease are discussed with regard to electrophysiology, histopathology, fluorescein angiography and biochemistry. Animal research has provided new realizations about the ultrastructure and physiological mechanisms of retinal photoreceptors, and better understanding of abnormal changes. The possible pathogenesis of the human disease, based on research findings, is onsidered. Although R.P. is generally thought to be to be an "untreatable" disease, therapy may be effective in several pathological entities. Methods and results of therapy with vitamins, light deprivation and vision aids are discussed.

A-BETA-LIPOPROTEINAEMIA

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