A novel mutation of the RP1 gene (Lys778ter) associated with autosomal dominant retinitis pigmentosa

BACKGROUND

Besides the three known genes (RHO, RDS/Peripherin, NRL) involved in autosomal dominant retinitis pigmentosa (adRP), a fourth gene, RP1, has been recently identified. Initial reports suggest that mutations in the RP1 gene are the second most frequent cause of adRP. The clinical findings were described in a family with adRP and a novel mutation in the RP1 gene.

METHOD

Index patients from 15 independent families with adRP in which RHO mutations had been excluded in previous examinations were screened for mutations in the RP1 gene by means of direct DNA sequencing. Evaluation of the RP1 phenotype in patients included funduscopy, kinetic perimetry, dark adapted final threshold test, standard electroretinography and, in one case, multifocal electroretinography.

RESULTS

One novel nonsense mutation (Lys778ter) in one of these 15 patients was detected. Cosegregation of the mutation with the disease phenotype could be established in the index patient's family. The phenotype comprises variable expression of clinical disease probably including one case of incomplete penetrance, a onset of symptoms beginning in adulthood, and evidence of regionally varying retinal function loss.

CONCLUSION

The Lys778ter mutation localises inside the critical region harbouring all mutations described so far. The ophthalmic findings support previous observations that variation of disease expression appears as a typical feature of the RP1 phenotype.

Identification of Usher syndrome subtypes by ERG implicit time

PURPOSE

Usher syndrome (US) is a recessively inherited disorder combining retinitis pigmentosa (RP) and a sensorineural hearing loss. The classification in subtypes is based mainly on auditory tests. The purpose of this study was to analyze implicit time (IT) differences in the electroretinogram (ERG) between RP alone, US I, and US II.

METHODS

The data of 15 control subjects and of 15 patients with US I, 15 with US II, and 15 with RP with nonzero 33-Hz flicker ERG responses were analyzed. The ITs of three signal peaks (P1-P3) were evaluated. Sensitivity and specificity of a test to distinguish between US I and II based on timing differences were determined. Multifocal (mf)ERGs were used to assess differences in disease topography.

RESULTS

Despite the similar amplitude loss with retinal eccentricity in the mfERG in all three groups, the peak delay in US I was negligible compared with that in US II and RP. In the flicker ERG data, US I and control subjects had almost identical peak times, and the same was true for subjects with US II and RP. Because of the slight overlap between US I and II, the diagnostic test achieved a sensitivity of 100% and a specificity of 93.3%.

CONCLUSIONS

Substantial timing differences between US I and II and their usefulness for a diagnostic test were demonstrated. This finding may also be the basis for further investigations regarding the structural differences of retinal impairment between US I and II on a cellular level.

Slow and fast rod ERG pathways in patients with X-linked complete stationary night blindness carrying mutations in the NYX gene

PURPOSE

To study the slow and fast rod signals of the scotopic 15-Hz flicker ERG in patients carrying mutations in the NYX gene, which has been recently identified as the cause of the complete form of congenital stationary night blindness, CSNB1.

METHODS

Twenty eyes of 11 patients with CSNB1 who had nondetectable standard ERG rod b-waves were involved in the study. Scotopic ERG response amplitudes and phases to flicker intensities ranging from -3.37 to -0.57 log scotopic trolands. sec (scot td. sec) were measured at a flicker frequency of 15 Hz. ERG signals to flicker intensities between -3.37 and -1.97 and between -1.17 and -0.57 log scot td. sec were considered to represent primarily the slow and fast rod ERG pathway, respectively. Additionally, standard ERGs were performed. Twenty-two normal volunteers served as control subjects.

RESULTS

For the slow rod ERG pathway, all patients exhibited ERG signals that were indistinguishable from noise. Accordingly, there was no systematic phase behavior for the slow rod signals. For the fast rod ERG pathway, the signals were significantly above noise, but they were significantly reduced in amplitude and advanced in phase.

CONCLUSIONS

There is evidence that the slow and the fast rod ERG signals can be attributed to the rod bipolar-AII cell pathway and the rod-cone-coupling pathway, respectively. The current study provides evidence to suggest that a defective NYX gene product (nyctalopin) prevents detectable signal transmission through ON rod bipolar cells, but there is a residual transmission through rod-cone gap junctions in CSNB1, possibly through the OFF cone pathway.

CNGA3 mutations in hereditary cone photoreceptor disorders

We recently showed that mutations in the CNGA3 gene encoding the alpha-subunit of the cone photoreceptor cGMP-gated channel cause autosomal recessive complete achromatopsia linked to chromosome 2q11. We now report the results of a first comprehensive screening for CNGA3 mutations in a cohort of 258 additional independent families with hereditary cone photoreceptor disorders. CNGA3 mutations were detected not only in patients with the complete form of achromatopsia but also in incomplete achromats with residual cone photoreceptor function and (rarely) in patients with evidence for severe progressive cone dystrophy. In total, mutations were identified in 53 independent families comprising 38 new CNGA3 mutations, in addition to the 8 mutations reported elsewhere. Apparently, both mutant alleles were identified in 47 families, including 16 families with presumed homozygous mutations and 31 families with two heterozygous mutations. Single heterozygous mutations were identified in six additional families. The majority of all known CNGA3 mutations (39/46) are amino acid substitutions compared with only four stop-codon mutations, two 1-bp insertions and one 3-bp in-frame deletion. The missense mutations mostly affect amino acids conserved among the members of the cyclic nucleotide gated (CNG) channel family and cluster at the cytoplasmic face of transmembrane domains (TM) S1 and S2, in TM S4, and in the cGMP-binding domain. Several mutations were identified recurrently (e.g., R277C, R283W, R436W, and F547L). These four mutations account for 41.8% of all detected mutant CNGA3 alleles. Haplotype analysis suggests that the R436W and F547L mutant alleles have multiple origins, whereas we found evidence that the R283W alleles, which are particularly frequent among patients from Scandinavia and northern Italy, have a common origin.

Case populations must match the respective disease model: Genotype diversity causes linkage disequilibrium mapping failure in monogenic disorders

Traditional linkage analysis in large families is the most promising approach for mapping disease genes of monogenic heritable disorders when the number of informative meioses is sufficient. With rare diseases, however, the low availability of informative pedigrees poses a significant limitation. As an adjunct to family linkage methods, association studies based on the investigation of individual haplotypes from a number of unrelated patients (i.e. linkage disequilibrium analysis) have recently been employed in mapping hereditary disease loci. However, such haplotype analysis is hampered by a number of effects that influence statistical evaluation, e.g. i) population history and size, ii) allele and haplotype frequencies in the respective population(s), iii) heterogeneous mutation and natural selection processes, and iv) small sample sizes of patient groups. The purpose of the present study was to determine the utility and limitations of haplotype-based genetic mapping in estimating the location of the NYX gene, which has recently been identified as the causative gene for a rare inherited retinal disorder known as the complete type of X-linked congenital stationary night blindness (CSNB1). For this purpose we recapitulated haplotypes and tested for linkage disequilibrium in 20 unrelated male CSNB1 patients from three European populations and 44 healthy individuals. All subjects were genotyped for 17 polymorphic microsatellite loci covering the Xp11.4 region with an average marker density of approximately 0.29 cM. We found that a precise model to describe mutations at loci that erroneously break up linkage is highly required, and that the case population must match the respective disease model.

Tamoxifen side effects, age-related macular degeneration (AMD) or cancer associated retinopathy (CAR)?

PURPOSE

Differential diagnosis of maculopathies can be difficult but is important if patients also suffer from other diseases such as breast cancer treated with antiestrogens. The main possible diagnoses, especially in the elderly, are age-related macular degeneration, tamoxifen and cancer-associated retinopathy (CAR).

METHODS

We describe an 84-year-old patient with breast and colon cancer, who complained of a decrease in visual acuity after treatment with low-dose antiestrogens. She underwent a general ophthalmological investigation, perimetry and electroretinographic examination with multifocal (m-ERG) and flash-electroretinogram (flash-ERG).

RESULTS

Visual acuity was reduced to 1/50 and 0.3. The ophthalmological examination was normal, except for extensive bilateral maculopathy with shining crystalline deposits, central and peripheral visual field defects, slightly affected scotopic and photopic potentials in the flash-ERG, and an abnormal m-ERG.

CONCLUSIONS

The findings are expected with age-related macular degeneration with crystalline drusen, but also with CAR. Even if the single and total dosage of antiestrogens given to the patient is sufficient to cause tamoxifen retinopathy, this diagnosis can be excluded because, in tamoxifen retinopathy unlike in the case presented here, the deposits are not distributed in all retinal layers.

Leber congenital amaurosis and retinitis pigmentosa with Coats-like exudative vasculopathy are associated with mutations in the crumbs homologue 1 (CRB1) gene

Mutations in the crumbs homologue 1 (CRB1) gene cause a specific form of retinitis pigmentosa (RP) that is designated "RP12" and is characterized by a preserved para-arteriolar retinal pigment epithelium (PPRPE) and by severe loss of vision at age <20 years. Because of the early onset of disease in patients who have RP with PPRPE, we considered CRB1 to be a good candidate gene for Leber congenital amaurosis (LCA). Mutations were detected in 7 (13%) of 52 patients with LCA from the Netherlands, Germany, and the United States. In addition, CRB1 mutations were detected in five of nine patients who had RP with Coats-like exudative vasculopathy, a relatively rare complication of RP that may progress to partial or total retinal detachment. Given that four of five patients had developed the complication in one eye and that not all siblings with RP have the complication, CRB1 mutations should be considered an important risk factor for the Coats-like reaction, although its development may require additional genetic or environmental factors. Although no clear-cut genotype-phenotype correlation could be established, patients with LCA, which is the most severe retinal dystrophy, carry null alleles more frequently than do patients with RP. Our findings suggest that CRB1 mutations are a frequent cause of LCA and are strongly associated with the development of Coats-like exudative vasculopathy in patients with RP.

OPA1 mutations in patients with autosomal dominant optic atrophy and evidence for semi-dominant inheritance

We and others have shown recently that mutations in the OPA1 gene encoding a dynamin-related mitochondrial protein cause autosomal dominant optic atrophy (ADOA) linked to chromosome 3q28-q29. Here we report screening of the OPA1 gene in a sample of 78 independent ADOA families. OPA1 mutations were identified in 25 patients (detection rate 32.1%) including 16 novel mutations. We successfully amplified OPA1 cDNA prepared from leukocyte RNA of three patients, and found the amount of transcripts harboring the Arg366Stop mutation was significantly reduced compared with transcripts derived from the normal chromosome. Analysis of the distribution of OPA1 mutations in ADOA revealed that most missense mutations cluster within the putative GTPase domain, and that there is a preponderance of mutations, which result in premature translation termination. These observations support the notion that haploinsufficiency may represent a major pathomechanism for ADOA. In addition, we identified an ADOA patient who is a compound heterozygote for two OPA1 missense mutations. The fact that this patient is by far more severely affected than her simple heterozygotic parents and siblings implies that at least these OPA1 alleles behave semi-dominantly rather than purely dominantly. Clinical examination revealed considerable variability in disease expression among patients carrying OPA1 mutations and no strict correlation with either the position or the type of mutation.

Mutations in the gene encoding lecithin retinol acyltransferase are associated with early-onset severe retinal dystrophy

The chromophore of the visual pigments, 11-cis retinal, is derived from vitamin A (all-trans retinol) through a series of reactions that take place in retinal pigment epithelium (RPE); (ref. 1). The first of these reactions is catalyzed by lecithin retinol acyltransferase (LRAT); (ref. 2). We screened 267 retinal dystrophy patients for mutations in LRAT and identified disease-associated mutations (S175R and 396delAA) in three individuals with severe, early-onset disease. We showed that the S175R mutant has no acyltransferase activity in transfected COS-7 cells. Our findings highlight the importance of genetic defects in vitamin A metabolism as causes of retinal dystrophies and extend prospects for retinoid replacement therapy in this group of diseases.

Identification of three novel mutations in the USH1C gene and detection of thirty-one polymorphisms used for haplotype analysis

Usher syndrome (USH) is a clinically and genetically heterogeneous autosomal recessive disorder in which sensorineural hearing loss is associated with retinitis pigmentosa. Usher syndrome type 1, the most severe form, is characterized by profound congenital deafness, vestibular dysfunction, and prepubertal onset of retinitis pigmentosa. Six different USH1 genes have so far been mapped, of which two have already been identified. MYO7A, encoding the unconventional myosin VIIA, underlies USH1B. Recently, the USH1C gene was shown to encode harmonin, a PDZ domain-containing protein. A previous screening of 18 unrelated USH1 patients, without a detected MYO7A mutation, for the three USH1C mutations described to date had demonstrated the presence of the 238-239insC mutation in the heterozygous state in four of them. A complete USH1C mutation screening in these four carriers of the 238-239insC mutation resulted in the detection of the second mutation in all the individuals, and the identification of three novel mutations, namely two splice site mutations (IVS1+1G>T and IVS5+1G>A) and a nonsense mutation (R31X). Thirty-one polymorphisms were detected in the USH1C gene. We observed that the E519D substitution is non-pathogenic, which is of particular interest for molecular diagnosis. Our analysis indicated that all the carriers of the 238-239insC mutation share a common haplotype. A different common haplotype was found in the two IVS1+1G>T carriers. Future studies of additional carriers and non-carriers should document the here proposed founder effect of these two mutations.

L- and M-cone driven ERGs are differently altered in Best's macular dystrophy

To study the L- and M-cone pathways and their interactions in patients with Best's macular dystrophy (BMD), ERG response thresholds were measured to stimuli which modulated exclusively the L- or the M-cones, or both in various combinations. The ERG threshold data could be described with a vector addition model. Compared with normals, BMD patients showed generally larger amplitudes of the L-cone driven ERGs. However, the M-cone driven ERGs were similar in amplitude but significantly phase advanced. The data confirm our previous observations that L- and M-cone pathways can be affected differently by retinal degeneration, despite their large physiological and biochemical similarities.

Complete form of X-linked congenital stationary night blindness: refined mapping and evidence of genetic homogeneity

A number of distinct, partly non-overlapping genetic loci have been reported for the complete type of X-linked congenital stationary night blindness (CSNB1), suggesting genetic heterogeneity. In order to refine the localization of the CSNB1 gene and to demonstrate genetic homogeneity, linkage analysis was performed in two large CSNB1 families. Clinical features consistent with the diagnosis of CSNB1 were documented in five patients from a German seven-generation kindred by full ophthalmological examination including psychophysical and electroretinographical testing. Haplotype analysis in 30 members of the large German family was performed with 38 polymorphic markers predominantly covering the critical region. Linkage analyses defined a locus for CSNB1 with flanking markers DXS8042 and DXS228, refining the interval to 2.5 cM in Xp11.4. In addition, two-point linkage analysis was carried out using the MLINK computer program. In agreement with meiotic breakpoints, lod scores of 3.0 and greater were obtained for markers located to the proximal site of the former 5 cM CSNB consensus interval. A large Dutch CSNB1 family was re-evaluated with markers from the Xp11.4 region, and supports the CSNB1 minimal interval found in the German family. Together with previous results from three unrelated families from Sweden, Sardinia and Great Britain, our results provide evidence of genetic homogeneity in the disorder. Subsequent mutation analyses in CSNB1 patients revealed no pathogenic sequence alterations in DFFRX and CASK genes, but retain candidates for other diseases mapping to that region.

Clinical electrophysiology of two rod pathways: normative values and clinical application

BACKGROUND

The scotopic 15-Hz flicker electroretinogram (ERG) has two limbs (slow and fast ERG rod signals), and these have been attributed to two retinal rod pathways (the ON rod bipolar and AII amacrine pathway and the rodcone gap-junction pathway). The aim of this study was to provide normative values of the scotopic 15-Hz flicker ERG, to estimate the inter-individual variability, and to apply this method to a clinical setting.

METHODS

Twenty-two normal subjects, one patient with retinitis pigmentosa (RP), and two patients with Stargardt's mascular dystrophy (SMD) participated in the study. The SMD patients were screened for mutations in the 50 exons of the ABCA4 (formerly ABCR) gene. We measured ERG response amplitudes and phases to flicker intensities ranging from -3.37 to -0.57 log scotopic trolands s at a flicker frequency of 15 Hz.

RESULTS

The normal scotopic 15-Hz flicker ERG showed a biphasic amplitude pattern with a minimum at about-1.57 log scotopic trolands s, where there was an abrupt phase shift of about 180 deg. The inter-individual variability in ERG amplitude ranged from 47% to 67% for the slow and from 41% to 64% for the fast rod signal. Both the RP patient and the SMD patients (who were compound heterozygotes for mutations in the ABCA4 gene) showed reduced amplitudes for the two rod ERG pathways.

CONCLUSION

The inter-individual variability might be explained by anatomical differences between individual retinae. In the RP patient, the amplitude reductions corresponded well with the standard rod ERG. In the SMD patients, however, the scotopic 15-Hz flicker ERG revealed rod dysfunction, whereas the standard rod ERG was within normal limits. The scotopic 15-Hz flicker method may be more sensitive than the standard rod ERG.

Genetics and phenotypes of RPE65 mutations in inherited retinal degeneration

PURPOSE

To characterize the spectrum of RPE65 mutations present in 453 patients with retinal dystrophy with an interest in understanding the range of functional deficits attributable to sequence variants in this gene.

METHODS

The 14 exons of RPE65 were amplified by polymerase chain reaction (PCR) from patients' DNA and analyzed for sequence changes by single-strand conformation polymorphism (SSCP) and direct sequencing. Haplotype analysis was performed using RPE65 intragenic polymorphisms. Patients were examined clinically and with visual function tests.

RESULTS

Twenty-one different disease-associated DNA sequence changes predicting missense or nonsense point mutations, insertions, deletions, and splice site defects in RPE65 were identified in 20 patients in homozygous or compound heterozygous form. In one patient, paternal uniparental isodisomy (UPD) of chromosome 1 resulted in homozygosity for a probable functional null allele. Eight of the disease-associated mutations (Y79H, E95Q, E102X, D167Y, 669delCA, IVS7+4a-->g, G436V, and G528V) and one mutation likely to be associated with disease (IVS6+5g-->a) have not been reported previously. The most commonly occurring sequence variant identified in the patients studied was the IVS1+5g-->a mutation, accounting for 9 of 40 (22.5%) total disease alleles. This splice site mutation, as well as R91W, the most common missense mutation, exists on at least two different genetic backgrounds. The phenotype resulting from RPE65 mutations appears to be relatively uniform and independent of mutation class, suggesting that most missense mutations (15 of 40 disease alleles [37.5%]) result in loss of function. At young ages, this group of patients has somewhat better subjective visual capacity than is typically associated with Leber congenital amaurosis (LCA) type I, with a number of patients retaining some useful visual function beyond the second decade of life.

CONCLUSIONS

RPE65 mutations account for a significant percentage (11.4%) of disease alleles in patients with early-onset retinal degeneration. The identification and characterization of patients with RPE65 mutations is likely to represent an important resource for future trials of rational therapies for retinal degeneration.

Mutations in MERTK, the human orthologue of the RCS rat retinal dystrophy gene, cause retinitis pigmentosa

Mutation of a receptor tyrosine kinase gene, Mertk, in the Royal College of Surgeons (RCS) rat results in defective phagocytosis of photoreceptor outer segments by the retinal pigment epithelium (RPE) and retinal degeneration. We screened the human orthologue, MERTK, located at 2q14.1 (ref. 10), in 328 DNA samples from individuals with various retinal dystrophies and found three mutations in three individuals with retinitis pigmentosa (RP). Our findings are the first conclusive evidence implicating the RPE phagocytosis pathway in human retinal disease.

The role of the peripherin/RDS gene in retinal dystrophies

Peripherin/RDS is a transmembrane glycoprotein expressed in vertebrate photoreceptors. It is located at the rim of the disc membranes of the photoreceptor outer segments, where it is thought to play an important role in folding and stacking of the discs. Initially, the identification of a mutation in the rds mouse model defined the role of this gene in hereditary retinal dystrophies. To date over 60 different mutations have been reported in human retinal diseases, with most being restricted to single families. A characteristic of mutations in the peripherin/RDS gene is the broad phenotypic spectrum in patients, and the variability in clinical expression, even within families. Thus, genotype-phenotype correlations are difficult and only reliable for a minority of mutations.

Twelve novel myosin VIIA mutations in 34 patients with Usher syndrome type I: confirmation of genetic heterogeneity

Usher syndrome is a heterogeneous autosomal recessive trait and the most common cause of hereditary deaf-blindness. Usher syndrome type I (USH1) is characterised by profound congenital sensorineural hearing loss, vestibular dysfunction, and prepubertal onset of retinitis pigmentosa. Of the at least six different loci for USH1, USH1B maps on chromosome 11q13, and the MYO7A gene has been shown to be defective in USH1B. MYO7A encodes myosin VIIA, an unconventional myosin, and it consists of 48 coding exons. In this study, MYO7A was analysed in 34 unrelated Usher type I patients by single-strand conformation polymorphism analysis and direct sequencing. We identified a total of 12 novel and unique mutations, all single base changes. In addition, we found a previously reported nonsense mutation (C31X) on nine alleles of a total of six patients from Denmark.

Comparative study of visual, auditory, and olfactory function in Usher syndrome

BACKGROUND

Usher syndrome is a genotypically and phenotypically heterogeneous group of autosomal recessive diseases featuring retinitis pigmentosa (RP) and sensorineural hearing loss. A general ciliary dysfunction has been suspected following reports of a mutated cytoskeletal protein (myosin VIIA) in type IB, and preliminary data has suggested an olfactory deficit. The purpose of this study was to quantitatively assess olfactory function in Usher syndrome patients and to search for a correlation between the degree of impairment of the three sensory systems as indication of an underlying ciliary defect.

METHODS

39 patients with Usher syndrome (8 type I, 31 type II) were examined. The ophthalmologic protocol included patient history, visual acuity, eye morphology, Goldmann perimetry, and electroretinography. The ENT protocol included a thorough examination, speech-recognition test, pure-tone audiometry and an olfactory function test.

RESULTS

In both groups, visual acuity was typically 20/40, the remaining visual field area was small, and the ERG responses were low to non-detectable. Average hearing loss was 100% in type I and 40% in type II. Olfactory thresholds were normal [median 9.7 (I) and 8.5 (II) vs. 8.5 in the control group]. There were multiple significant correlations between parameters of the same organ, but no relationship between parameters of different sensory systems.

CONCLUSION

Almost all Usher syndrome patients in this study had an advanced form of RP. In contrast, auditory function differed considerably between type I and type II. An impairment of the olfactory system could not be detected, and there was no correlation between parameters representing visual function, hearing ability, and olfactory sense.

Human rod monochromacy: linkage analysis and mapping of a cone photoreceptor expressed candidate gene on chromosome 2q11

We have performed linkage analysis in eight families with rod monochromacy, an autosomal recessively inherited condition with complete color blindness. Significant linkage was found with markers located at the pericentromeric region of chromosome 2. A maximum lod score of 5.36 was obtained for marker D2S2333 at theta = 0.00. Mapping of meiotic breakpoints localized the disease gene between markers D2S2187 and D2S2229. Homozygosity for a number of subsequent markers indicating identity by descent was found in two families and provides evidence for a further refinement of the locus proximal to D2S373. This defines an interval of approximately 3 cM covering the ACHM2 locus for rod monochromacy. Radiation hybrid mapping of the CNGA3 gene encoding the alpha-subunit of the cGMP gated cation channel in human cone photoreceptors resulted in a maximum lod score of 16.1 with marker D2S2311 combined with a calculated physical distance of 6.19cR10,000. Screening of the CEPH YAC library and subsequent STS mapping indicated the physical order cen-D2S2222-D2S2175-(D2S2187/D2S2311)-qtel ofmarkers on 2q11 and showed that the CNGA3 gene maps most closely to D2S2187 and D2S2311. These data indicate that the CNGA3 gene maps within the critical interval of the ACHM2 locus for rod monochromacy and thus is a candidate gene for this disease.

Total colourblindness is caused by mutations in the gene encoding the alpha-subunit of the cone photoreceptor cGMP-gated cation channel

Total colourblindness (OMIM 216900), also referred to as rod monochromacy (RM) or complete achromatopsia, is a rare, autosomal recessive inherited and congenital disorder characterized by photophobia, reduced visual acuity, nystagmus and the complete inability to discriminate between colours. Electroretinographic recordings show that in RM, rod photoreceptor function is normal, whereas cone photoreceptor responses are absent. The locus for RM has been mapped to chromosome 2q11 (ref. 2), however the gene underlying RM has not yet been identified. Recently, a suitable candidate gene, CNGA3, encoding the alpha-subunit of the cone photoreceptor cGMP-gated cation channel, a key component of the phototransduction pathway, has been cloned and assigned to human chromosome 2q11 (refs 3,4). We report the identification of missense mutations in CNGA3 in five families with RM. Homozygous mutations are present in two families, whereas the remaining families show compound heterozygous mutations. In all cases, the segregation pattern of the mutations is consistent with the autosomal recessive inheritance of the disease and all mutations affect amino acids that are highly conserved among cyclic nucleotide gated channels (CNG) in various species. This is the first report of a colour vision disorder caused by defects other than mutations in the cone pigment genes, and implies at least in this instance a common genetic basis for phototransduction in the three different cone photoreceptors of the human retina.

An L-type calcium-channel gene mutated in incomplete X-linked congenital stationary night blindness

The locus for the incomplete form of X-linked congenital stationary night blindness (CSNB2) maps to a 1.1-Mb region in Xp11.23 between markers DXS722 and DXS255. We identified a retina-specific calcium channel alpha1-subunit gene (CACNA1F) in this region, consisting of 48 exons encoding 1966 amino acids and showing high homology to L-type calcium channel alpha1-subunits. Mutation analysis in 13 families with CSNB2 revealed nine different mutations in 10 families, including three nonsense and one frameshift mutation. These data indicate that aberrations in a voltage-gated calcium channel, presumably causing a decrease in neurotransmitter release from photoreceptor presynaptic terminals, are a frequent cause of CSNB2.

Implicit time topography of multifocal electroretinograms

PURPOSE

To describe the implicit time topography of multifocal electroretinograms in normal subjects and to examine the change in this topography in patients affected by retinitis pigmentosa.

METHODS

Thirty normal subjects and 38 patients with retinitis pigmentosa were examined with the Visual Evoked Response Imaging System using 61 hexagonal elements within a visual field of 30 degrees radius. The peak implicit times of the 61 first-order kernels (which are analogues of the photopic electroretinogram [ERG]) were measured to determine their distribution across the retina.

RESULTS

Implicit times had a low interindividual variability in the normal group. High implicit times were found at the blind spot, the upper and lower borders of the stimulated field, and the macula. Low values were present in the area encircling the macula and were most prominent in the temporal retina. In the group with retinitis pigmentosa, implicit times were unchanged in the central region but were prolonged in the peripheral regions.

CONCLUSIONS

The spatial distribution of multifocal ERG implicit times in a normal population follows a specific topographical pattern across the retina. This pattern has to be taken into account when interpreting results in patients. Deviations in retinitis pigmentosa were found, and they show the potential for diagnostic use.

Multifocal electroretinography in patients with Stargardt's macular dystrophy

AIMS

To describe the topography of multifocal electroretinograms (ERGs) and to explore its diagnostic value in patients with Stargardt's macular dystrophy (SMD).

METHODS

51 patients with SMD were examined by means of the m-sequence technique to characterise the topography of electroretinographic responses in the central visual field. The results were compared with data from 30 normal volunteers.

RESULTS

In 49 of 51 patients with SMD, macular electroretinographic activity was markedly diminished or non-detectable. Towards more peripheral areas, ERG responses of the SMD patients approached those of normals. Implicit times were not markedly delayed at any eccentricity.

CONCLUSION

In contrast with Ganzfeld electroretinography, multifocal electroretinography is useful to detect foveal dysfunction in SMD. Areas of dysfunction were found to be usually larger than expected from psychophysical measurements and morphological alteration. In early stages of the disease it was possible to detect foveal dysfunction, even in patients lacking morphological fundus changes and with good visual acuity.

Multifocal electroretinography in retinitis pigmentosa

PURPOSE

To investigate the diagnostic potential of multifocal electroretinography for the evaluation of retinal affection by retinitis pigmentosa in a clinical setting.

METHODS

For this prospective study, multifocal electroretinograms were obtained from 38 patients who matched the inclusion criteria of either a detectable photopic Ganzfeld response or visual fields of 10 degrees or more, and from 30 normal volunteers. Recordings were performed with the visual evoked response imaging system, using a resolution of 61 hexagonal elements within a 30-degree visual field. The results of the left eye of each patient and control subject were used for statistical evaluation by the Mann-Whitney U test.

RESULTS

The 38 eligible patients included those with Usher syndrome types I and II (one patient and six patients, respectively) and those with autosomal-recessive (18), X-recessive (two), and autosomal-dominant (11) forms of retinitis pigmentosa. In 27 (71%) of these 38 patients, at least a central response of the multifocal electroretinogram was detectable. Loss of multifocal electroretinogram response density in patients with retinitis pigmentosa was significant (P < .00001) in all five eccentricity groups (concentric rings), with a progression from center to periphery. Implicit time was significantly elevated in the third eccentricity group (P < .0038) and increased further toward the periphery (P < .00001). The results did not differ notably between retinitis pigmentosa subgroups.

CONCLUSIONS

Because the multifocal electroretinogram differentiates between affected and nonaffected retinal areas, eccentricity-dependent changes in both amplitude and implicit time were found. It can therefore add to the diagnostic information of many patients with retinitis pigmentosa.

Ocular findings in patients with autosomal dominant retinitis pigmentosa and Cys110Phe, Arg135Gly, and Gln344stop mutations of rhodopsin

This report describes ocular findings obtained in four patients from three families with autosomal dominant retinitis pigmentosa (adRP) due to missense mutations in the rhodopsin gene. Phenotypes were characterized by standard ophthalmologic examinations, visual fields, electroretinography (ERG), dark adaptation, and two-color dark-adapted threshold perimetry. Two patients aged 38 and 45 years, respectively, from a family with the Cys110Phe mutation showed mild fundus changes without bone spicules as well as small arcuate scotomas in the inferior quadrants of their visual fields but displayed severe functional loss of rods and cones in the ERG. Two-color dark-adapted threshold perimetry revealed a regional type of degeneration. A 48-year-old patient with an Arg135Gly mutation had typical RP with concentrically narrowed visual fields and nondetectable ERG responses. Central visual functions were well preserved for a long time. Two-color dark-adapted threshold perimetry indicated a diffuse type of retinal degeneration. An 18-year-old patient with a Gln344stop mutation has been followed for 13 years. His ERG was clearly reduced at the age of 5 years; since that time, disease progression has been very slow. Currently, there are relatively mild alterations in visual acuity, rod sensitivity, and visual fields. Our findings confirm that there is a large phenotypic variety among patients with adRP and different rhodopsin mutations.

RDS/peripherin gene mutations are frequent causes of central retinal dystrophies

Patients from 76 independent families with various forms of mostly central retinal dystrophies were screened for mutations in the RDS/peripherin gene by means of SSCP analysis and direct DNA sequencing. Two nonsense mutations (Gln239ter, Tyr285ter), five missense mutations (Arg172Trp, Lys197Glu, Gly208Asp, Trp246Arg, Ser289Leu), and one single base insertion (Gly208insG), heterozygous in all cases, were detected. Only one of these mutations, Arg172Trp, has been reported previously. Cosegregation of the mutation with the disease phenotype could be established in selected families. Other missense mutations were excluded from a panel of 55-75 control subjects. The patients showed remarkable variation in phenotype and disease expression not only between cases with different mutations but also between affected members of the same family. This study indicates that RDS/peripherin mutations are a frequent cause of various types of central retinal dystrophies and that the RDS/peripherin gene exhibits a broad spectrum of allelic mutations. Comparative analysis of known mutations allowed us to hypothesise that the deleterious effect of RDS/peripherin gene mutations is the result of different molecular mechanisms.

[Juvenile neuronal ceroid lipofuscinosis (Batten-Mayou) disease. Ophthalmologic diagnosis and findings]

BACKGROUND

Juvenile neuronal ceroid lipofuscinosis (JNCL) is important to the ophthalmologist, since eye symptoms are usually the first evidence of the disease and permit establishment of an early diagnosis. The disorder usually begins with a dramatic loss of vision between age 4 and 10 due to bulls-eye maculopathy followed by rapid degeneration of the retina and pigment epithelium. Blindness results within 1 to 3 years after onset of symptoms. The further course of the disease is mainly determined by degradation of the CNS with motor and intellectual deficits. Most patients die before the age of 30.

METHODS

A case of two sisters is presented to demonstrate eye findings and diagnostic procedures, emphasizing electrophysiologic and morphologic tests (peripheral blood smear, histology).

RESULTS

Both sisters reported the first decrease in vision at the ages of 8 and 6 respectively; visual acuity at time of visit was light projection (20/400). Both had tapetoretinal degeneration with optic disc atrophy, narrowed vessels, pigment epitheliopathy and bullseye maculopathy. The ERG was almost extinguished in the older sister and greatly reduced in the younger one (scotopic more than photopic). Histologically, vacuolated lymphocytes were found in the peripheral blood smear, as were intracellular inclusions of the fingerprint and curvilinear type in the conjunctival biopsy.

CONCLUSION

During the course of JNCL, it is very common for the vision to be affected at the age of 6-7. The correct diagnosis, however, is often made years later when massive neurologic symptoms such as seizures appear. When there is sudden loss of vision in a child of this age combined with a tapetoretinal degeneration, a biopsy or at least a peripheral blood smear should be performed.

A second independent Tyr168Cys mutation in the tissue inhibitor of metalloproteinases-3 (TIMP3) in Sorsby's fundus dystrophy

Sorsby's fundus dystrophy (SFD) is a rare autosomal dominant macular disorder with age of onset usually in the fourth decade. It is characterised by loss of central vision owing to subretinal neovascularisation and disciform macular degeneration. In an effort to identify the SFD gene, the disease locus was first mapped to chromosome 22q13-qter by genetic linkage analysis, the same chromosomal region as the gene encoding the tissue inhibitor of metalloproteinases-3 (TIMP3). Subsequently, two separate mutations in TIMP3 were found in affected members of two unrelated SFD pedigrees (Tyr168Cys and Ser181Cys). More recently, two additional SFD related mutations, Ser156Cys and Gly167Cys, have provided further confirmation that heterozygous mutations in TIMP3 are causally responsible for the SFD phenotype. We now report the occurrence of the Tyr168Cys mutation in an SFD patient of Austrian descent and show that this mutation found earlier in an American SFD family arose independently. The new findings add to an emerging pattern of SFD mutations which all seem to affect the C-terminal region of the mature TIMP3 protein. In addition, all known mutations cause a change of an amino acid to a cysteine residue. This suggests a critical role for the additional C-terminal free thiol group in SFD pathogenesis.

A gene (SRPX) encoding a sushi-repeat-containing protein is deleted in patients with X-linked retinitis pigmentosa

X-linked retinitis pigmentosa (XLRP) is characterized by retinal degeneration with night blindness and progressive reduction of the visual fields. By linkage and deletion analysis a gene locus (RP3) has been mapped to the short arm of the X chromosome between the genes CYBB and OTC. Analysis of transcript in this region has revealed a gene which is abundantly expressed in human retina and encodes a putative membrane protein with significant homologies to short consensus repeat (SCR/sushi) domains known from selections and complement proteins. The gene termed SRPX (sushi-repeat-containing protein, x chromosome) is deleted in an RP patient who also suffers from chronic granulomatous disease and McLeod syndrome. A 75 kb deletion removing exon 1 of the gene was also found in two brothers of a second XLRP family. However, no further functionally significant mutations were detected by SSCP screening of all 10 exons in 34 unrelated XLRP patients nor by full length RT-PCR sequencing in two RP3 families. The role of this highly conserved retinal gene in the pathogenesis of RP therefore remains to be determined.

[Social ophthalmologic aspects of retinitis pigmentosa]

Inherited retinal degenerations cause severe visual handicaps or blindness later in life. In typical rod cone dystrophy (retinitis pigmentosa) there is relevant visual loss in the third decade with implications for the patients' professional life, their mobility and their private life. For this reason, the disease is relevant for the individual patient as well as for society in general. We investigated social issues in 233 retinitis pigmentosa patients: 9.9% are not able to read any more; 40.9% have never had a driver's license and 27.8% quit driving because of a visual handicap. The mean reduction in the capacity for work is 86%; 12.7% are unable to work and therefore receive public financial support; 22.6% are unable to work in their profession; 20.9% are receiving public support because of legal blindness. Against this background it seems to be important that ophthalmologists inform their patients thoroughly about the implications of the disease for their professional and private lives. Doing this, he/she should ask for support from social service professionals.

Extensive intrafamilial and interfamilial phenotypic variation among patients with autosomal dominant retinal dystrophy and mutations in the human RDS/peripherin gene

Clinical phenotypes of patients with mutations in the human RDS/peripherin gene are described. A 67-year-old woman, who carried a 1 base pair deletion in codon 307, presented with typical late onset autosomal dominant retinitis pigmentosa (RP). In another autosomal dominant pedigree, a nonsense mutation at codon 46 caused 'inverse' retinitis pigmentosa-like fundus changes associated with progressive cone-rod degeneration in a 58-year-old man, whereas his 40-year-old son presented with yellow deposits in the retinal pigment epithelial layer resembling a pattern dystrophy, and with moderately reduced rod and cone function, as determined by two colour dark adapted threshold perimetry and electroretinography. It is suggested that both clinical pictures within this latter family may represent manifestations of fundus flavimaculatus. The clinical data of the three patients provide further evidence for the remarkable variety of disease expression within and between families with mutations in the RDS/peripherin gene. Currently, the most comprehensive statement could be that RDS/peripherin mutations are associated either with typical RP or with various forms of flecked retinal disease.

Clinical findings in patients with congenital stationary night blindness of the Schubert-Bornschein type

We examined 23 patients (18 families) with congenital stationary night blindness (CSNB) who showed a "negative" electroretinogram of the Schubert-Bornschein type. The goal of the study was to find evidence for the classification proposed by Miyake (complete and incomplete type) based on electroretinograms (ERGs) and dark-adaptation function and to look for additional classification parameters that argue for or against heterogeneity. In all, 13 patients revealed the complete type and 10 the incomplete type. The mean age of our patients was 24.7 years (median, 21 years; SD, 14.5 years). In both groups, almost all patients were myopic (mean, -6.05 D; SD, 3.77 D; median, -6.12 D), and there was a reduction in visual acuity (mean, 0.34; SD, 0.14; median, 0.35) without significant differences between the subgroups. In all, 56.5% of the patients suffered from nystagmus and 52.2% squinted. These results confirm the Miyake classification and suggest that only ERG and dark-adaptation data allow a discrimination between the two subtypes. The ongoing molecular analysis will show whether there are correlates on the molecular level.

Ocular findings in a family with autosomal dominant retinitis pigmentosa and a frameshift mutation altering the carboxyl terminal sequence of rhodopsin

A family is described in which an 8 base pair deletion (nucleotides 5252-5259, codons 341-343) of the rhodopsin gene cosegregates with autosomal dominant retinitis pigmentosa (adRP). The deletion results in a shift in the reading frame, causing a rhodopsin molecule extended by one residue and substantially altered at the carboxyl terminus. Phenotypic expression is relatively mild. In affected members, night blindness did not occur before the age of 16, and late onset of visual field loss was consistently reported. Even older individuals (59 and 76 years) had preserved central islands in the visual field; a younger female patient had normal visual fields until the age of 34. ERG and psychophysical tests showed well preserved cone function at stages of virtually abolished rod function. Phenotypic differences and similarities between this form of adRP and others associated with mutations at the carboxyl terminus of the rhodopsin molecule are discussed. The cause of RP by mutations in this region remains to be clarified.

Deletions in exon 5 of the human rhodopsin gene causing a shift in the reading frame and autosomal dominant retinitis pigmentosa

By screening patients with autosomal dominant retinitis pigmentosa for mutations in the rhodopsin gene, two deletions (8 bp and 1 bp) have been identified in exon 5; these deletions cause a shift in the reading frame. The predicted proteins should be radically altered with translation continuing past the normal stop signal and resulting in a rhodopsin molecule that is, respectively, 1 and 10 amino acids longer. The clinical phenotype of the patients is described and is compared with that associated with other mutations in the same region of the gene.

[Retinitis pigmentosa. Clinical findings, results of molecular genetic techniques and research perspectives]

In recent years, research efforts in the basic and clinical sciences have yielded numerous new findings. The review given here outlines clinical findings, research results, and perspectives on the origin of hereditary retinal degeneration as far as molecular genetics, biochemistry, morphology, and clinical research are concerned: genotype-phenotype correlation, electroretinography, color perimetry, blue cone function, exogenous factors, refraction problems, fat metabolism, immunological aspects, retinal transplantation, and phenocopies of retinitis pigmentosa and related syndromes. The consequences for ophthalmological practice are pointed out and comprehensive, improved diagnostic procedures are recommended, using a checklist proposed here (see appendix).