Lotta Gränse

Mutations in a BTB-Kelch Protein, KLHL7, Cause Autosomal-Dominant Retinitis Pigmentosa

Retinitis pigmentosa (RP) refers to a genetically heterogeneous group of progressive neurodegenerative diseases that result in dysfunction and/or death of rod and cone photoreceptors in the retina. So far, 18 genes have been identified for autosomal-dominant (ad) RP. Here, we describe an adRP locus (RP42) at chromosome 7p15 through linkage analysis in a six-generation Scandinavian family and identify a disease-causing mutation, c.449G-->A (p.S150N), in exon 6 of the KLHL7 gene. Mutation screening of KLHL7 in 502 retinopathy probands has revealed three different missense mutations in six independent families. KLHL7 is widely expressed, including expression in rod photoreceptors, and encodes a 75 kDa protein of the BTB-Kelch subfamily within the BTB superfamily. BTB-Kelch proteins have been implicated in ubiquitination through Cullin E3 ligases. Notably, all three putative disease-causing KLHL7 mutations are within a conserved BACK domain; homology modeling suggests that mutant amino acid side chains can potentially fill the cleft between two helices, thereby affecting the ubiquitination complexes. Mutations in an identical region of another BTB-Kelch protein, gigaxonin, have previously been associated with giant axonal neuropathy. Our studies suggest an additional role of the ubiquitin-proteasome protein-degradation pathway in maintaining neuronal health and in disease.

Electrophysiologic findings in two young patients with Bothnia dystrophy and a mutation in the RLBP1 gene

Purpose: To characterize the clinical phenotype, with emphasis on electrophysiology, of two children with suspected Bothnia dystrophy. Methods: Two unrelated affected patients, 10 and 11 years old, were studied. Ophthalmological examination included testing of visual acuity, fundus inspection and fundus photography, kinetic perimetry, full-field electroretinogram (ERG), and multifocal ERG. The presence of a mutation in exon 7 of the RLBP1 gene was investigated by DNA sequencing. Results: Both patients were homozygous for the Arg234Trp-causing mutation in the RLBP1 gene, but the resulting disease phenotype appeared to vary somewhat between them. Visual acuity was moderately reduced in one patient and normal in the other. Fundus inspection at this age revealed no pathology in either patient and there were no signs of retinitis punctata albescens, which has been described previously as a frequent clinical feature of Bothnia dystrophy. The result of kinetic perimetry was normal. The final rod threshold was moderately elevated. Full-field ERG demonstrated the uncommon combination of absent rod response and normal cone response after 40 minutes of dark adaptation. However, after prolonged dark adaptation (20–24 h), both the rod response and the dark adaptation threshold became normal. Multifocal ERG was performed in one of the patients (the one with normal visual acuity and normal fundus appearance) and showed a reduced cone response in the central region of the tested area. There was no improvement of the multifocal ERG result after 20–24 h of dark adaptation. Conclusion: Patients with mutations in the RLBP1 gene (Arg234Trp) may have a normal fundus appearance early in the disease course. Multifocal ERG can be used for the objective documentation of the disturbed macular function, especially when the patients visual acuity and fundus appearance are normal. The rod response is absent in the electroretinogram; however, after prolonged dark adaptation (20–24 hours), the rods recover completely. The central cones do not seem to recover.

Alterations in electroretinograms and retinal morphology in rabbits treated with vigabatrin

Purpose: To determine whether long-term treatment with the anti-epileptic drug vigabatrin causes damage to rabbit retina. Methods: Five rabbits were treated continuously with a daily dose of vigabatrin solution per orally during a period of 1–8 months. Two rabbits receiving water were used as controls. Repeated full-field electroretinograms (every two weeks) were assessed during this period. Vigabatrin serum concentration was repeatedly measured for securing successful drug administration. After termination of treatment the rabbits were sacrificed and the morphology of the sectioned retina was studied. Results: In all rabbits treated with vigabatrin the serum analyses repeatedly demonstrated elevated drug concentration. Full-field electroretinograms demonstrated normal rod function in all treated rabbits, but reduced cone function in two of the five treated rabbits verified by 30 Hz flicker stimulation. Morphologic studies of the sectioned retina demonstrated GFAP immunoactivity of the glial cells localized in the retinal periphery in all five treated rabbits, one of which had staining also in the centrally localized glial cells. The treated rabbits also demonstrated a weaker GAD staining in the IPL and less positive amacrine cells, compared to the controls. Only two treated rabbits had normal GABA staining while three had an enhanced GABA immunoreactivity and undistinguishable fibers in the IPL. In three out of five treated rabbits the Müller cells were short, stubby and fragmented, with swollen endfeet. Conclusion: This study demonstrates changes in histopathology caused by vigabatrin in an animal model, which has not been reported previously. We have found that vigabatrin orally administrated to rabbits does not affect rod function but may reduce cone function in the full-field electroretinogram, which is similar to the previously reported vigabatrin effect on the human ERG. The results indicate that vigabatrin may damage or influence, at least one cell type in the rabbit retina.

Electrophysiology and ocular blood flow in a family with dominant optic nerve atrophy and a mutation in the OPA1 gene

Objective: To characterize the clinical phenotype, with emphasis on electrophysiology and blood flow measurements, of a family with dominant optic nerve atrophy and an identified mutation in the OPA1 gene. Methods: Seven family members were examined. Ophthalmological evaluation included testing of visual acuity, ophthalmolscopy, kinetic perimetry, color vision testing, full-field electroretinography (ERG), multifocal electroretinography (MERG), and multifocal visual evoked potential (MVEP). Retrobulbar arterial blood flow and retinal capillary perfusion was measured in three patients using scanning laser Doppler flowmetry (SLDF) and color Doppler imaging techniques. PCR-SSCP and DNA sequencing determined the presence of a mutation in exon 18 of the OPA1 gene. Results: The clinical characteristics varied considerably in the family. The ERG and the MERG demonstrated normal retinal function, while the MVEP was abnormal in all examined patients. Retinal and optic nerve head capillary perfusion was significantly decreased in the three patients examined with SLDF. Retrobulbar blood flow velocities were significantly decreased in the central retinal and ophthalmic arteries. In all seven examined subjects, a microdeletion (1756–1767del(12 bp)) in the OPA1 gene was identified. Conclusion: Patients with a mutation in the OPA1 gene have a very variable phenotype. MVEP and blood flow measurements are two new objective methods for an easier detection of this specific genetic optic nerve atrophy.

Macular Dysfunction and Morphology in Spinocerebellar Ataxia Type 7 (SCA 7)

Purpose: To characterize the clinical phenotype regarding retinal function and macular appearance in patients with spinocerebellar ataxia type 7 (SCA 7), with an emphasis on electrophysiological findings. Methods: Three patients from two Swedish families were given an ophthalmological examination including visual acuity, fundus inspection, Farnsworths color vision test, Goldmann perimetry, full-field electroretinography (full-field ERG), multifocal electroretinography (mfERG) and optical coherence tomography (OCT). DNA was analyzed with polymerase chain reaction for CAG trinucleotide expansion repeats in the SCA 7 gene. Results: Molecular analysis demonstrated abnormally expanded CAG repeats in the gene for SCA 7, which encodes the protein ataxin-7, thus confirming the diagnosis SCA 7. In the oldest patient very discreet pigmentary changes in the maculae were found, but with that exception the patients had a normal ophthalmoscopic fundus appearance and OCT demonstrated only minor changes. MfERG indicated predominantly central involvement, especially in the early disease stages, which in pace with disease progression extended from the center to the more peripheral areas. Full-field ERG in the oldest patient demonstrated bilaterally distinctly prolonged 30-Hz flicker implicit time, verifying widespread cone photoreceptor degeneration. Conclusions: The patients with genetically confirmed SCA 7 presented an early macular dysfunction, preceding any signs of abnormalities in fundus appearance. According to the electrophysiological findings the primary dysfunction involves the cone photoreceptors in the foveal region, however in an older patient involvement of cone photoreceptors throughout the retina was verified. This is in accordance with the theory that ataxin-7 interacts with CRX transcription, since it is known that mutations in the CRX gene cause cone-rod dystrophy.

Multifocal Visual Evoked Potentials (mfVEP) in Diabetic Patients with and without Polyneuropathy

Previously not shown this study support that mfVEP is an indicator of optic nerve neuropathy in diabetic patients and there could be a correlation between the optic nerve dysfunction and diabetic poly neuropathy. The early optic nerve involvement might explain some of the visual complain in this group of diabetic patients. Purpose: To investigate the function of the visual pathway measured by mfVEP (multifocal Visual Evoked Potentials) in patients with diabetic retinopathy and neurophysiologically verified polyneuropathy Subjects and Methods: Thirty-two diabetic patients with the same degree of diabetic retinopathy were classified with neurography regarding polyneuropathy and further examined with mfVEP. The mfVEPs of eighteen patients with polyneuropathy were compared to those of fourteen diabetic patients without polyneuropathy and to those of ten nondiabetic subjects. Results: Diabetic duration, and the number of patients who had undergone panretinal photocoagulation for proliferative diabetic retinopathy were similar in the two patient groups, 29±13 vs 25±7 years, p=0.3. Both groups of patients with diabetic retinopathy had significantly lower amplitudes in the mfVEP than the healthy subjects. In addition the mfVEP amplitudes, which reflect selected areas of the visual function, were significantly reduced in the lower nasal quadrant in patients with neuropathy compared to patients without neuropathy. Conclusion: The results indicate that mfVEP could be an indicator of optic nerve neuropathy in patients with diabetic retinopathy. The early optic nerve involvement might explain some of the visual complaints in this group of diabetic patients.