Catalytic activities of mitochondrial ATP synthase in patients with mitochondrial DNA T8993G mutation in the ATPase 6 gene encoding subunit a

We investigated the biochemical phenotype of the mtDNA T8993G point mutation in the ATPase 6 gene, associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP), in three patients from two unrelated families. All three carried >80% mutant genome in platelets and were manifesting clinically various degrees of the NARP phenotype. Coupled submitochondrial particles prepared from platelets capable of succinate-sustained ATP synthesis were studied using very sensitive and rapid luminometric and fluorescence methods. A sharp decrease (>95%) in the succinate-sustained ATP synthesis rate of the particles was found, but both the ATP hydrolysis rate and ATP-driven proton translocation (when the protons flow from the matrix to the cytosol) were minimally affected. The T8993G mutation changes the highly conserved residue Leu(156) to Arg in the ATPase 6 subunit (subunit a). This subunit, together with subunit c, is thought to cooperatively catalyze proton translocation and rotate, one with respect to the other, during the catalytic cycle of the F(1)F(0) complex. Our results suggest that the T8993G mutation induces a structural defect in human F(1)F(0)-ATPase that causes a severe impairment of ATP synthesis. This is possibly due to a defect in either the vectorial proton transport from the cytosol to the mitochondrial matrix or the coupling of proton flow through F(0) to ATP synthesis in F(1). Whatever mechanism is involved, this leads to impaired ATP synthesis. On the other hand, ATP hydrolysis that involves proton flow from the matrix to the cytosol is essentially unaffected.

A new locus for autosomal dominant retinitis pigmentosa on the short arm of chromosome 17

Retinitis pigmentosa (RP) is a group of genetically and clinically heterogeneous retinopathies, some of which have been shown to result from mutations in two different known retinal genes, rhodopsin (3q) and peripherin-rds (6p). Three additional anonymous loci at 7p, 7q and pericentric 8 have been implicated by linkage studies. There are still, however, a few families in which all known loci have been excluded. In this report we present data indicating a location, on the short arm of chromosome 17, for the autosomal dominant RP (ADRP) locus in a large South African (SA) family of British ancestry. Positive two-point lod scores have been obtained for nine markers (D17S938, Z = 5.43; D17S796, Z = 4.82; D17S849, Z = 3.6; D17S786, Z = 3.55; TP53, Z = 3.55; D17S578, Z = 3.29; D17S960, Z = 3.16; D17S926, Z = 1.51; D17S804, Z = 0.47 all at theta = 0.10 except D17S804 and D17S926, theta = 0.20). These data provide definitive evidence for the localization of an ADRP gene on chromosome 17p. The human recoverin gene has been localized to 17p13.1 and was consequently a prime candidate for ADRP in the family studied. However, mutation screening of the three exons of this gene failed to produce any evidence of recoverin being the gene involved in the pathogenesis of ADRP in this SA family.

Genealogy, natural history, and phenotype of Alström syndrome in a large Acadian kindred and three additional families

We describe a large Acadian kindred including 8 Alstrom Syndrome (AS) patients, with an age range of 4 to 26 at the time of clinical assessment. The affected subjects come from 5 nuclear families within this kindred. The phenotype includes early childhood retinopathy, progressive sensorineural hearing loss, truncal obesity, and acanthosis nigricans. In addition, hyperinsulinemia and hypertriglyceridemia with normal cholesterol levels were observed in most affected individuals tested. Non-insulin dependent diabetes mellitus and growth retardation appear to be age-related manifestations that occur post-adolescence. Younger affected children are not overtly hyperglycemic and are normal or above average height for age. Although the AS patients in kindred 1 presumably carry the same mutation, many manifestations of the disease are variable. For example, of the 8 children in the Acadian kindred, 4 have scoliosis, 2 have had infantile cardiomyopathy, 2 are hypothyroid, 1 has had hepatic dysfunction and is hypertensive, and 4 have developed asthma. Seven subjects described in this kindred exhibit developmental delay. One additional manifestation not described widely in the literature, advanced bone age, was observed in all subjects tested. The clinical data from this large Acadian kindred, together with information obtained from 4 additional AS patients in 3 unrelated kindreds, confirm and extend clinical observations previously described. In addition, the Acadian kindred with multiple affected individuals, probably arising from a common founder, should allow for identification of the chromosomal localization of a gene causing AS.

Altered antioxidant-oxidant status in the aqueous humor and peripheral blood of patients with retinitis pigmentosa

Retinitis Pigmentosa is a common form of hereditary retinal degeneration constituting the largest Mendelian genetic cause of blindness in the developed world. It has been widely suggested that oxidative stress possibly contributes to its pathogenesis. We measured the levels of total antioxidant capacity, free nitrotyrosine, thiobarbituric acid reactive substances (TBARS) formation, extracellular superoxide dismutase (SOD3) activity, protein, metabolites of the nitric oxide/cyclic GMP pathway, heme oxygenase-I and inducible nitric oxide synthase expression in aqueous humor or/and peripheral blood from fifty-six patients with retinitis pigmentosa and sixty subjects without systemic or ocular oxidative stress-related disease. Multivariate analysis of covariance revealed that retinitis pigmentosa alters ocular antioxidant defence machinery and the redox status in blood. Patients with retinitis pigmentosa present low total antioxidant capacity including reduced SOD3 activity and protein concentration in aqueous humor. Patients also show reduced SOD3 activity, increased TBARS formation and upregulation of the nitric oxide/cyclic GMP pathway in peripheral blood. Together these findings confirmed the hypothesis that patients with retinitis pigmentosa present reduced ocular antioxidant status. Moreover, these patients show changes in some oxidative-nitrosative markers in the peripheral blood. Further studies are needed to clarify the relationship between these peripheral markers and retinitis pigmentosa.

Decreased content of docosahexaenoate and arachidonate in plasma phospholipids in Usher's syndrome

Docosahexaenoate and arachidonate were found to be significantly decreased in plasma phospholipids from Usher's syndrome patients. The fatty acid content of plasma triacylglycerols was not changed in these patients. Usher's syndrome, an autosomal recessive disorder, involves an inherited visual cell degeneration. Photoreceptor membranes are richly endowed with docosahexaenoate and arachidonate, and a metabolic defect affecting these polyunsaturated fatty acids may occur. Moreover, blindness may be due, at least partially, to an alteration in the unsaturated phospholipids of photoreceptor membranes.

A randomized, placebo-controlled clinical trial of docosahexaenoic acid supplementation for X-linked retinitis pigmentosa

PURPOSE

Low docosahexaenoic acid (DHA) in X-linked retinitis pigmentosa (XLRP) may influence retinal function. The goals of this study were to elevate blood DHA levels and determine the effect on the rate of disease progression.

DESIGN

In a 4-year prospective randomized clinical trial, male patients with XLRP (mean age = 16 years; range = 4-38 years) received DHA (400 mg/d; n = 23; +DHA group) or placebo (n = 21) capsules.

METHODS

Red blood cell (RBC)-DHA concentrations were assessed every 6 months. Full-field cone electroretinograms (ERGs; the primary outcome measure), visual acuity, dark-adaptation, visual fields, rod ERGs, and fundus photos were recorded annually.

RESULTS

In the +DHA group, RBC-DHA increased 2.5-fold over placebo levels (70 vs 28 mg DHA/l). Repeated measures analysis of variance for cone ERG showed a significant main effect of year (P <.0001) but not of group (P =.16). Preservation of cone ERG function correlated with RBC-DHA (P =.018), and there was less change in fundus appearance in the +DHA group (P =.04). Neither visual acuity nor visual fields were changed. In subset analysis, DHA supplementation was beneficial in reducing rod ERG functional loss in patients aged <12 years (P =.040) and preserving cone ERG function in patients > or =12 years (P =.038).

CONCLUSIONS

Although DHA-supplemented patients had significantly elevated mean RBC-DHA levels, the rate of cone ERG functional loss was not significantly different between groups. Supplemental analyses provided evidence for a DHA benefit and a direction for subsequent investigations.

Biological safety assessment of docosahexaenoic acid supplementation in a randomized clinical trial for X-linked retinitis pigmentosa

BACKGROUND

In a 4-year placebo-controlled trial to elevate blood docosahexaenoic acid levels in patients with X-linked retinitis pigmentosa (XLRP), the goal was to assess the potential benefit of docosahexaenoic acid supplementation in altering disease progression. However, docosahexaenoic acid (22:6omega3) is a highly unsaturated fatty acid and considered a target molecule for free-radical oxidative damage. Thus, nutritional provision of docosahexaenoic acid might lead to an increase in antioxidant stress. Additional concerns, such as decreased platelet aggregation, increased bleeding time, and alterations in lipoprotein cholesterol levels, have been reported in supplementation studies with long-chain polyunsaturates.

OBJECTIVE

To assess the biological safety of long-term docosahexaenoic acid supplementation.

DESIGN

Forty-four male patients (mean age, 16 years) enrolled in a randomized, double-masked, clinical trial and received docosahexaenoic acid, 400 mg/d, or placebo. Blood samples were collected every 6 months. Biological safety analysis included fatty acids, vitamin A and E concentrations, antioxidant capacity, platelet aggregation, alanine aminotransferase activity, and lipoprotein cholesterol and triglyceride profiles.

RESULTS

Mean plasma docosahexaenoic acid levels were elevated 2.5-fold by supplementation compared with baseline. Patients receiving placebo capsules exhibited no change (P =.35) in plasma docosahexaenoic acid content. All adverse events reported were minor and equivalently distributed between groups. Plasma vitamin A concentrations remained unchanged during the trial. Mean plasma vitamin E concentrations were correlated with age (P =.005), such that as patients with XLRP matured, plasma vitamin E concentrations increased to approach normal values. There was a trend (P =.10) toward lower mean vitamin E concentrations in the docosahexaenoic acid-supplemented group after 4 years. Docosahexaenoic acid supplementation did not compromise plasma antioxidant capacity, platelet aggregation, liver function enzyme activity, or plasma lipoprotein lipid content in patients with XLRP.

CONCLUSION

Long-term docosahexaenoic acid supplementation to patients with XLRP was associated with no identifiable safety risks in this 4-year clinical trial.

Red blood cell fatty acid levels in patients with autosomal dominant retinitis pigmentosa

Fatty acid profiles were determined in red blood cell (RBC), plasma lipids and lipid fractions from 50 patients with autosomal dominant retinitis pigmentosa (ADRP) and 20 normal-sighted controls. In plasma of affected patients, significant increases in omega 6 long-chain derivatives compared to controls resulted in elevated fatty acid unsaturation whereas, in RBCs, significant decreases in the levels of omega 6 and omega 3 long-chain polyunsaturates and a reduced unsaturation index were demonstrated (P < 0.01). The disproportionate levels of long-chain fatty acids in plasma vs. RBCs were consistent with abnormal function of acyl group transfer from plasma lipids to target tissues such as RBCs or, possibly, retina. Metabolic lipid anomalies were evaluated in two sub-groups of patients with ADRP; ten with the highest and ten with the lowest RBC lipid levels of the omega 3 fatty acid, docosahexaenoic acid (DHA). Fatty acid product/precursor relationships in the sub-groups revealed reduced chain elongation and omega 3 fatty acid desaturation associated with reduced ratios of rod-to-cone electroretinographic amplitudes. Based on these results, we suggest that the heterogenic ADRP population includes a sub-group of patients characterized by abnormal fatty acid metabolism that may effect membrane structure and visual function.

Plasma lipid abnormalities in the miniature poodle with progressive rod-cone degeneration

The miniature poodle with progressive rod-cone degeneration (prcd) is a model for human retinitis pigmentosa (RP). Since previous studies from several laboratories have shown abnormalities in plasma lipids in human RP, we examined the plasma lipids of prcd-affected animals. Fasting blood was drawn on three separate occasions from affected and control miniature poodles and on one occasion from normal Irish setters and those affected with a different inherited retinal degeneration (rod-cone dysplasia). Plasma phospholipids from prcd-affected animals had significantly lower levels of docosahexaenoic acid (22:6 omega 3) and cholesterol, compared to control miniature poodles. No differences were observed in plasma levels of phospholipids, vitamin E, or vitamin A, and no lipid differences were found between control and affected Irish setters. The ratios of 22:5 omega 3 to 22:6 omega 3 and of 22:4 omega 6 to 22:5 omega 6 were significantly elevated in prcd-affected poodles compared to controls. Since the conversion of 22:5 omega 3 to 22:6 omega 3 and of 22:4 omega 6 to 22:5 omega 6 is catalysed by a delta 4-desaturase, these results are consistent with a defect in desaturase activity in the prcd-affected poodle.

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.

Metabolism of omega-3 fatty acids in patients with autosomal dominant retinitis pigmentosa

Abnormalities in lipid metabolism have been reported in numerous patients with retinitis pigmentosa. As an initial step in evaluating these anomalies, two trials of fatty acid intervention were conducted with autosomal dominant retinitis pigmentosa (adRP) patients and controls. The first trial addressed absorption and incorporation of omega 3 long-chain fatty acids from a fish-oil concentrate into red blood cell (RBC) lipids. The utilization of omega 3 long-chain fatty acids by adRP patients was found to be equivalent to that of controls. The second trial addressed the conversion of precursor, eicosapentaenoic acid (EPA, 20:5 omega 3), to end-product, docosahexaenoic acid (DHA, 22:6 omega 3), following oral supplementation of EPA ethyl ester. Although the levels of EPA and the intermediate, docosapentaenoic acid (22:5 omega 3), were both elevated by EPA supplementation in RBCs of adRP patients with rhodopsin gene mutations and controls, DHA production was elevated only in controls. Based on these results, we suggest the presence of a metabolic defect in the final stages of DHA biosynthesis.

Acanthocytosis, retinitis pigmentosa, pallidal degeneration. Report of two cases without serum lipid abnormalities

We describe two unrelated patients with Hallervorden-Spatz, disease characterized by prominent facio-bucco-lingual dyskinesia. Acanthocytosis and retinitis pigmentosa were additional findings. Brain MRI showed the typical 'tiger's eye' image of the globus pallidus. This phenotype closely resembled the so-called HARP syndrome (hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa and pallidal degeneration), but extensive serum lipid study failed to demonstrate any lipoprotein abnormality. Our results raise the question whether HARP syndrome is an autonomous entity or a particular phenotype of Hallervorden-Spatz disease.

Plasma levels of endothelin-1 in retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited retinal disorder clinically characterized by a pale, waxy optic nerve head, attenuated retinal blood vessels and bone spicule pigment in the retina. Hemodynamic studies have demonstrated that RP is associated with a reduction in the retinal and choroidal blood flow. Retinal hemodynamic impairment is also present in the early stages of RP and various hypotheses have been advanced as to its cause. The authors studied 20 patients, 12 males and 8 females, aged between 26 and 42 years (mean 34.6 years) affected by simplex RP. The twenty patients were divided in two groups according to the degree of sight impairment: group A consisted of 10 patients with a visual acuity of 0.3 +/- 0.1, visual field mean defect 18.988 +/- 3.419 dB and b-wave electroretinogram amplitude of 13.14 +/- 0.308 microV. Group B consisted of 10 patients with a visual acuity of 0.8 +/- 0.2, visual field MD 10.523 +/- 3.582 dB and b-wave electroretinogram amplitude of 26.000 +/- 0.757 microV. An increase in plasma levels of endothelin-1 (ET-1) was found as compared with healthy controls: 1.910 +/- 0.617 pg/ml vs. 1.180 +/- 0.210 pg/ml (p < 0.021), but there was no statistical difference between group A and B (p < 0.163). It is thought that an increase in ET-1 and retinal oxygen levels in RP could lead to vasoconstriction and a decrease in the retinal blood flow worsening the abiotrophic process.

A novel truncated apolipoprotein B (apo B55) in a patient with familial hypobetalipoproteinemia and atypical retinitis pigmentosa

We have identified an apolipoprotein (apo) B mutation in a patient with an atypical form of retinitis pigmentosa (RP). In the family the eye disease is characterised by late age of onset and autosomal dominant inheritance. In addition to RP, the proband has low total cholesterol (4.5 mmol/l) and LDL-cholesterol (2.0 mmol/l) levels characteristic of the autosomal codominant apolipoprotein (apo) B deficiency disease hypobetalipoproteinemia (HBL). Using a monoclonal antibody directly against apo B and immunoblots of SDS polyacrylamide gel separated plasma, a normal apo B100 and a truncated apo B species with an estimated size of apo B54 was identified in the proband and his RP-affected sister. The location of the mutation in the apo B gene was identified using chemical cleavage of mismatch and this was confirmed by direct sequencing of an amplified fragment of DNA spanning the estimated site of the mutation. The mutation is a C----T transition at nucleotide 7692 which changes the CGA arginine2495 codon to a STOP codon resulting in the premature termination of apo B100. The truncated apo B protein is 2494 amino acids long with a predicted size of apo B55. Using allele specific oligonucleotides and oligonucleotide melting techniques, the proband, his sister and two other relatives out of a total of 20 family members, screened for the presence of the apo B55 mutation, were heterozygous for the mutation. The segregation of the apo B55 allele was confirmed in the family using the 3' variable number of tandem repeats of the apo B gene.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

A syndrome of retinitis pigmentosa, congenital ichthyosis, hypergonadotropic hypogonadism, small stature, mental retardation, cranial dysmorphism, and abnormal electroencephalogram

BACKGROUND

Retinal dystrophy and ichthyosis occur together in patients with the well-characterized disorders of Refsum disease and Sjögren-Larsson syndrome. Rud syndrome formerly was considered a genetically heterogeneous but distinct clinical entity with the manifestations of icthyosis, hypogonadism, small stature, mental retardation, epilepsy, and, infrequently, retinitis pigmentosa. Although there are at least 55 case reports of Rud syndrome in the medical literature, the existence of such a syndrome has recently been dismissed based on a new understanding of the ichthyoses. Most case reports previously reported as Rud syndrome can now be reassigned under a contemporary ichthyosis classification that does not include Rud syndrome as a distinct entity.

METHODS

Two unrelated women with a disorder showing retinitis pigmentosa, congenital ichthyosis, hypergonadotropic hypogonadism, small stature, mental retardation, cranial dysmorphism, and abnormal electroencephalograms underwent a comprehensive workup. The ocular and systemic findings are compared with those previously described for retinal dystrophy and ichthyosis disorders.

RESULTS

These cases were found to be clearly distinct from Refsum disease, Sjögren-Larsson syndrome, and any of the other ichthyosis disorders that have been suggested as a replacement for Rud syndrome.

CONCLUSION

The association of retinitis pigmentosa, congenital ichthyosis, hypergonadotropic hypogonadism, small stature, mental retardation, cranial dysmorphism, and abnormal electroencephalogram may represent a distinct syndrome previously considered a subset of the now defunct Rud syndrome.

Serum zinc levels in retinitis pigmentosa

Serum zinc and copper levels were analyzed in 26 retinitis pigmentosa patients and compared with serum zinc levels of a control group. Serum zinc levels were documented to be decreased with a mean concentration of 0.735 +/- 0.167 micrograms/ml (p less than 0.001). Serum copper levels, on the other hand, were found to be increased in retinitis pigmentosa patients with a mean value of 1.261 +/- 0.348 micrograms/ml (p less than 0.001).

Evaluation of fatty acids in membrane phospholipids of erythrocytes in retinitis pigmentosa patients

Several investigators have observed abnormalities of plasma DHA in various common forms of retinitis pigmentosa. Erythrocyte membranes are an accessible tissue which may more closely reflect neural membrane fatty acid levels, but little data is yet available on their fatty acid composition in retinitis pigmentosa patients. We have evaluated the DHA levels in red blood cells membrane phospholipids in various genetic forms of retinitis pigmentosa and relative controls. The results obtained indicate significantly lower DHA levels in red blood cell membrane phospholipids in retinitis pigmentosa patients with respect to controls (p < 0.01). This data is significant for autosomal dominant forms only (p < 0.01). Fatty acid content alterations in membrane phospholipids of red blood cells may be considered as markers for abnormalities in the lipid metabolism which disturb the retina integrity.