At last. A standard electroretinography protocol

Mutations within the cGMP-binding domain of CNGA1 causing autosomal recessive retinitis pigmentosa in human and animal model

Retinitis pigmentosa is a group of progressive inherited retinal dystrophies that may present clinically as part of a syndromic entity or as an isolated (nonsyndromic) manifestation. In an Indian family suffering from retinitis pigmentosa, we identified a missense variation in CNGA1 affecting the cyclic nucleotide binding domain (CNBD) and characterized a mouse model developed with mutated CNBD. A gene panel analysis comprising 105 known RP genes was used to analyze a family with autosomal-recessive retinitis pigmentosa (arRP) and revealed that CNGA1 was affected. From sperm samples of ENU mutagenesis derived F₁ mice, we re-derived a mutant with a Cnga1 mutation. Homozygous mutant mice, developing retinal degeneration, were examined for morphological and functional consequences of the mutation. In the family, we identified a rare CNGA1 variant (NM_001379270.1) c.1525 G > A; (p.Gly509Arg), which co-segregated among the affected family members. Homozygous Cnga1 mice harboring a (ENSMUST00000087213.12) c.1526 A > G (p.Tyr509Cys) mutation showed progressive degeneration in the retinal photoreceptors from 8 weeks on. This study supports a role for CNGA1 as a disease gene for arRP and provides new insights on the pathobiology of cGMP-binding domain mutations in CNGA1-RP.

In vivo potency testing of subretinal rAAV5.hCNGB1 gene therapy in the Cngb1 knockout mouse model of retinitis pigmentosa

Retinitis pigmentosa type 45 (RP45) is an autosomal-recessively inherited blinding disease caused by mutations in the cyclic nucleotide gated channel subunit beta 1 (CNGB1) gene. In this study, we developed and tested a novel gene supplementation therapy suitable for clinical translation. To this end, we designed a recombinant adeno-associated virus (rAAV) vector carrying a genome that features a novel human rhodopsin promoter (hRHO194) driving rod-specific expression of full-length human CNGB1 (rAAV5.hCNGB1). rAAV5.hCNGB1 was evaluated for efficacy in the Cngb1 knockout (Cngb1-/-) mouse model of RP45. In particular, increasing doses of rAAV5.hCNGB1 were delivered via single subretinal injection in 4-week-old Cngb1-/- mice and the treatment effect was assessed over a follow-up period of 9 months at the level of (i) retinal morphology, (ii) retinal function, (iii) vision-guided behavior, and (iv) transgene expression. We found that subretinal treatment with rAAV5.hCNGB1 resulted in efficient expression of the human CNGB1 protein in mouse rods and was able to normalize the expression of the endogenous mouse CNGA1 subunit, which together with CNGB1 forms the native heterotetrameric cGMP-gated cation channel in rod photoreceptors. The treatment led to a dose-dependent recovery of rod photoreceptor-driven function and preservation of retinal morphology in Cngb1-/- mice. In summary, these results demonstrate the efficacy of hCNGB1 gene supplementation therapy in the Cngb1-/- mouse model of RP45 and support the translation of this approach towards future clinical application.

An extended 15 Hz ERG protocol (1): the contributions of primary and secondary rod pathways and the cone pathway

The minimum in the amplitude versus flash strength curve of dark-adapted 15 Hz electroretinograms (ERGs) has been attributed to interactions between the primary and secondary rod pathways. The 15 Hz ERGs can be used to examine the two rod pathways in patients. However, previous studies suggested that the cone-driven pathway also contributes to the 15 Hz ERGs for flash strengths just above that of the minimum. We investigated cone pathway contributions to improve upon the interpretation of (abnormal) 15 Hz ERGs measured in patients. We recorded 15 Hz ERGs in five healthy volunteers, using a range of flash strengths that we extended to high values. The stimuli were varied in both colour (blue, green, amber, and red) and flash duration (short flash and square wave) in order to stimulate rods and cones in various ways. The differences in the responses to the four colours could be fully explained by the spectral sensitivity of rods for flash strengths up to approximately 12.5 log quanta·deg(-2). At higher flash strengths, higher-order harmonics appeared in the responses which could be attributed to cones being more sensitive than rods to higher frequencies. Furthermore, the amplitude curves of the blue and green responses showed a second minimum suggesting rod to cone interactions. We present a descriptive model of the contributions of the rod and cone pathways. In clinical application, we would advise using the short flash flicker instead of the square wave flicker, as the responses are of larger amplitude, and cone pathway contributions can be recognized from large higher-order harmonics.

Essential and synergistic roles of RP1 and RP1L1 in rod photoreceptor axoneme and retinitis pigmentosa

Retinitis pigmentosa 1 (RP1) is a common inherited retinopathy with variable onset and severity. The RP1 gene encodes a photoreceptor-specific, microtubule-associated ciliary protein containing the doublecortin (DCX) domain. Here we show that another photoreceptor-specific Rp1-like protein (Rp1L1) in mice is also localized to the axoneme of outer segments (OSs) and connecting cilia in rod photoreceptors, overlapping with Rp1. Rp1L1-/- mice display scattered OS disorganization, reduced electroretinogram amplitudes, and progressive photoreceptor degeneration, less severe and slower than in Rp1-/- mice. In single rods of Rp1L1-/-, photosensitivity is reduced, similar to that of Rp1-/-. While individual heterozygotes are normal, double heterozygotes of Rp1 and Rp1L1 exhibit abnormal OS morphology and reduced single rod photosensitivity and dark currents. The electroretinogram amplitudes of double heterozygotes are more reduced than those of individual heterozygotes combined. In support, Rp1L1 interacts with Rp1 in transfected cells and in retina pull-down experiments. Interestingly, phototransduction kinetics are normal in single rods and whole retinas of individual or double Rp1 and Rp1L1 mutant mice. Together, Rp1 and Rp1L1 play essential and synergistic roles in affecting photosensitivity and OS morphogenesis of rod photoreceptors. Our findings suggest that mutations in RP1L1 could underlie retinopathy or modify RP1 disease expression in humans.

Six Patients with Bradyopsia (Slow Vision)

OBJECTIVE

Recently, it was discovered that subjects who showed a prolonged response suppression on their electroretinogram (ERG) and had symptoms of photophobia, problems adjusting to bright light, and difficulties seeing moving objects shared a mutation in the RGS9 (regulator of G-protein signaling 9) gene that is involved in the deactivation of photoreceptor responses. The disorder was termed bradyopsia (slow vision). This paper reports the clinical presentation and long-term follow-up of 6 bradyopsia patients.

DESIGN

Retrospective observational case series with a follow-up ranging from 6 to 30 years.

PARTICIPANTS

Six patients with a homozygous mutation in the RGS9 gene.

METHODS

Clinical symptoms and signs were compared between the subjects and between their visits over time.

MAIN OUTCOME MEASURES

Symptoms, visual acuity (VA), ocular findings, visual fields, dark-adaptation tests, color tests, fluorescein angiography, and ERG findings.

RESULTS

Data showed a consistency in the individual symptoms and ERG recordings, but an extreme variation in VA between visits. Beside some irregularities in the macula in some patients, no other related eye abnormalities were seen. The low-to-subnormal VA varied with background luminance and typically increased by 2 to 3 lines when pinholes were used. Dark-adaptation tests, color tests, and fluorescein angiography were normal. Visual field tests showed a minor diffuse sensitivity loss. No progressive changes were seen over time.

CONCLUSIONS

No signs of progression were noted in the 6 bradyopsia patients. Photophobia, impaired movement perception, variable reduced VA that improved with the use of pinholes and ERG abnormalities were typical for the disease.

Evidence of a possible impact of the menstrual cycle on the reproducibility of scotopic ERGs in women

The purpose of this study was to investigate the impact of gender and menstrual cycle on the electroretinogram (ERG). Photopic and scotopic ERGs were obtained in 14 females during the luteal and follicular phases of their menstrual cycle and compared to those obtained on two separate (7 days or 14 days apart) sessions from seven age-matched control male subjects. Our results confirm that the amplitude of the photopic ERGs of females is significantly (P < 0.05) larger than males, and this, irrespective of the cycle phase. In comparison, scotopic ERGs revealed significant male-female differences only during the follicular phase. While in males, no significant (P > 0.05) intersession (7 day or 14 day intervals) variability could be demonstrated, significant (P < 0.001) intersession (luteal-follicular) variability was observed in the scotopic ERGs of our female participants, with 8 of the 14 women, demonstrating a marked increase of 20.17 +/- 4.8% in the follicular ERG compared to the luteal. Our data suggests there should be separate normal ERG values for men and women and that the phase of the menstrual cycle should be taken into consideration when interpreting the ERG results from women.

Clinical characterization, linkage analysis, and PRPC8 mutation analysis of a family with autosomal dominant retinitis pigmentosa type 13 (RP13)

A Dutch family with autosomal dominant retinitis pigmentosa (adRP) displayed a phenotype characterized by an early age of onset, a diffuse loss of rod and cone sensitivity, and constricted visual fields (type I). One male showed a mild progression of the disease. Linkage analysis showed cosegregation of the genetic defect with markers from chromosome 17p13.1-p13.3, a region overlapping the RP13 locus. The critical interval of the RP locus as defined in this family was flanked by D17S926 and D17S786, with a maximal lod score of 4.2 (theta = 0.00) for marker D17S1529. Soon after the mapping of the underlying defect to the 17p13 region, a missense mutation (6970G>A; R2310K) was identified in exon 42 of the splicing factor gene PRPC8 in one patient of this family. Diagnostic restriction enzyme digestion of exon 42 amplified from genomic DNA of all family members revealed that the R2310K mutation segregated fully with the disease. The type I phenotype observed in this family is similar to that described for three other RP13 families with mutations in PRPC8.

Electroretinography is necessary for spasmus nutans diagnosis

The purpose of the present study was to determine whether that which clinically appeared to be spasmus nutans could actually represent retinal sensory deficits diagnosable by electroretinography. Eight patients clinically thought to have spasmus nutans underwent electroretinography according to international standards. Five had normal electroretinograms and represented cases of true spasmus nutans. Three patients had abnormal electroretinograms, indicating that they did not have spasmus nutans. The clinical findings used to diagnose spasmus nutans can be simulated by retinal dystrophies. A normal electroretinogram is needed to confirm the diagnosis of spasmus nutans.

Visual disturbance: where do I look?

Visual disturbances often signal serious ophthalmic disease. Comprehensive general medical and ophthalmic histories are most helpful. Information about the animal's vision, based on its performance in familiar and unfamiliar environments, should be obtained from the owner. As bilateral involvement and visual disturbances are often associated with systemic diseases, a complete physical examination is indicated. The ophthalmic examination consists of a series of diagnostic procedures to isolate and define the ophthalmic disorder. Several clinical tests can be performed easily in the examination room, including the light-induced pupillary reflex, the dazzle or photic reflex, the menace reflex, the obstacle course test and, if indicated, the flash electroretinogram, the visual evoked response and, recently, the pattern electroretinogram. Ophthalmic diseases that produce visual disturbances in dogs often affect the cornea, aqueous pathways, lens and ocular fundus; in cats, they usually affect the uveal tract and are associated with serious systemic diseases. Orbital diseases are not usually associated with visual disturbance unless the optic nerve is involved. Corneal diseases and cataract formation that involve the visual axis and pupillary aperture often cause visual disturbance. Inflammations of the Iris and ciliary body can produce both acute and long-term visual disturbance and even blindness. Diseases of the retina and optic nerve usually present as visual disturbances in the absence of pain.

Cone and rod function in cone degenerations

Progressive cone dystrophy (CD) is usually marked in the initial stages by reduced visual acuity, color vision deficiency and alterations in the photopic electroretinogram, while morphological alterations can be very mild; in some forms rods are affected in a later stage as well. We examined 40 patients with progressive cone dystrophy to determine the extent of functional losses in the cone system with psychophysical tests. A great variety of visual acuity and fundus alterations was found. Myopia was present in 74% of the patients. An autosomal dominant pattern of inheritance predominated (32%). No prevalence of gender was found. The age of onset ranged between 10 and 30 yr. All patients had progression of their symptoms. The total error score in color arrangement tests, the saturated Farnsworth Panel D-15 and the Farnsworth-Munsell 100-hue test, was pathologic with a predominance of confusions along the tritan and scotopic axis. Especially if visual acuity was below 0.5, color vision defects increased, but color vision defects were also found in patients with normal visual acuity. A general decrease of sensitivity in all three cone mechanisms was observed in measurements of spectral sensitivity. Moreover, cone-cone interaction as tested by transient tritanopia measurements was usually disturbed. In the dark adaptation function the threshold of the cone branch was usually elevated. These tests provide a good means to ascertain the correct diagnosis in early stages of the disease and to monitor progression in patients suffering from cone dystrophy.

Clinical diagnosis of the Usher syndromes. Usher Syndrome Consortium

The Usher syndromes are genetically distinct disorders which share specific phenotypic characteristics. This paper describes a set of clinical criteria recommended for the diagnosis of Usher syndrome type I and Usher syndrome type II. These criteria have been adopted by the Usher Syndrome Consortium and are used in studies reported by members of this Consortium.

A leucine to arginine amino acid substitution at codon 46 of rhodopsin is responsible for a severe form of autosomal dominant retinitis pigmentosa

To evaluate the extent to which rhodopsin mutations are involved in autosomal dominant forms of retinitis pigmentosa (adRP) we collected DNAs from patients with adRP and screened the rhodopsin coding sequence with single-strand conformational polymorphism (SSCP) analysis and DNA sequencing. This screening revealed a thymidine to guanine transversion at nucleotide 431 (nucleotide sequence numbers as per Genebank) in affected members of one family (RFS04). The nucleotide substitution leads to a missense mutation at the 46th amino acid of rhodopsin. The mutation occurs at an amino acid conserved in mammals and changes the hydrophobic nature of the protein at a transmembrane-spanning region. The mutation causes the substitution of a non-polar hydrophobic amino acid, leucine, for the basic amino acid arginine (Leu46Arg). This nucleotide substitution is unique to the family studied and occurs in the affected individuals in the family. Full-field electroretinograms (ERGs) in four affected members of the family showed nondetectable rod responses at an early age, with markedly reduced cone responses, and a faster than average rate of progression of the phenotype as measured by yearly ERGs.

Oscillatory potentials, retinopathy, and long-term glucose control in insulin-dependent diabetes

The main objective of the study was to assess effects of long-term lowering of glucosylated hemoglobin (HbA1%) on neurosensory function in insulin-dependent diabetes. Individual (OP-1, OP-2, OP-3) and summed (OP-sum) amplitudes of oscillatory potentials (OPs) of electroretinography were recorded at study start and 7-years later in 45 patients (the Oslo study). As an overall 7-year change, amplitudes of OP-2, OP-3 and OP-sum were reduced (p < 0.0001-0.01), retinopathy worsened (p = 0.005), intraocular pressure decreased (p < 0.001), systolic blood pressure increased (p < 0.0002), and glycemic control improved from HbA1 of 11.2 +/- 2.2% at study start to a 7-year cumulative mean of 9.5 +/- 1.5% (p < 0.0001). Multiple regression analysis did not identify any independent relations between change in OP-1, OP-2, OP-3, OP-sum and change in glycemic control or background variables, including change in age and duration of diabetes. However, cross-sectional observations at 7 years showed negative correlations between all OPs and age (p < 0.0001-0.003), and between OP-3 and duration (p = 0.003) and counts of microaneurysms (p = 0.02). The data suggest that various clinical background variables may influence individual and summed amplitudes of OPs differently. Reduced neurosensory retinal function (OPs) seemed to appear after 7-years, independently of vascular defects of retinopathy and long-term improvement in glucose control.

Polymorphic variation within "conserved" sequences at the 3' end of the human RDS gene which results in amino acid substitutions

The human RDS gene, previously mapped to chromosome 6p, encodes a protein found in the outer disc membrane of the photoreceptor cells of the retina. The cDNA sequence of the human gene shows 85% identity with the bovine peripherin gene and the rds (retinal degeneration slow) genes from mouse and rat. Mutations in the RDS gene have recently been implicated in autosomal dominant retinitis pigmentosa (adRP) in some families. Here we present evidence that the third exon of this gene is subject to polymorphic variation in humans. The three sequence alterations described in this paper give rise to amino acid substitutions. However, as these missense mutations also occur in the normal population they are not implicated as causing adRP. Interestingly such sequence variation is not found within other species examined including mouse and bovine. These intragenic polymorphisms will be of future potential value in studies to locate further disease causing mutations in adRP patients in the RDS gene.