Late-onset autosomal dominant macular dystrophy with choroidal neovascularization and nonexudative maculopathy associated with mutation in the RDS gene

PRPH2-associated Retinal Diseases: A Systematic Review of Phenotypic Findings

PURPOSE

PRPH2-associated retinal diseases (PARD) result from pathogenic PRPH2 variants, primarily affecting photoreceptor outer segments and retinal pigment epithelium. The focus of this article is to review and discuss the phenotyping of PARD subtypes.

DESIGN

A systematic review METHODS: The review followed PRISMA 2020 guidelines with searches on PubMed, Medline, Web of Science, Google Scholar, and Cochrane Library. Eligible studies were those which discussed molecularly confirmed PARD or described associated diseases such as butterfly pattern dystrophy.

INCLUSION

cross-sectional, cohort, case-control studies, book chapters.

EXCLUSION

non-English, conference papers, non-peer-reviewed, or non-full text articles.

RESULTS

PARD is responsible for 25% of pattern dystrophy and up to 5% of inherited retinal dystrophies. There is clear evidence of phenotypic variability between individuals carrying the same pathogenic variant. Fundus autofluorescence, fluorescein angiography, optical coherence tomography, while in research adaptive optics reveal detailed phenotypic characteristics, notably in retinal pigment epithelium changes and photoreceptor disruption. The phenotypic of PARD variability presents diagnostic challenges, with phenotypic features often overlapping with other retinal diseases including age-related macular degeneration, Stargardt disease and retinitis pigmentosa.

CONCLUSION

This review emphasizes revising diagnostic criteria by incorporating more recent imaging techniques and confirming diagnosis with the use of genetic testing. Understanding phenotypic diversity and intrafamilial variability in PARD is crucial for developing new treatments and for patient prognosis and future research should focus on larger cohorts studying genotype-phenotype correlations.

Retinal Dystrophies Associated With Peripherin-2: Genetic Spectrum and Novel Clinical Observations in 241 Patients

Purpose

To describe the clinical, electrophysiological and genetic spectrum of inherited retinal diseases associated with variants in the PRPH2 gene.

Methods

A total of 241 patients from 168 families across 15 sites in 9 countries with pathogenic or likely pathogenic variants in PRPH2 were included. Records were reviewed for age at symptom onset, visual acuity, full-field ERG, fundus colour photography, fundus autofluorescence (FAF), and SD-OCT. Images were graded into six phenotypes. Statistical analyses were performed to determine genotype-phenotype correlations.

Results

The median age at symptom onset was 40 years (range, 4-78 years). FAF phenotypes included normal (5%), butterfly pattern dystrophy, or vitelliform macular dystrophy (11%), central areolar choroidal dystrophy (28%), pseudo-Stargardt pattern dystrophy (41%), and retinitis pigmentosa (25%). Symptom onset was earlier in retinitis pigmentosa as compared with pseudo-Stargardt pattern dystrophy (34 vs 44 years; P = 0.004). The median visual acuity was 0.18 logMAR (interquartile range, 0-0.54 logMAR) and 0.18 logMAR (interquartile range 0-0.42 logMAR) in the right and left eyes, respectively. ERG showed a significantly reduced amplitude across all components (P < 0.001) and a peak time delay in the light-adapted 30-Hz flicker and single-flash b-wave (P < 0.001). Twenty-two variants were novel. The central areolar choroidal dystrophy phenotype was associated with 13 missense variants. The remaining variants showed marked phenotypic variability.

Conclusions

We described six distinct FAF phenotypes associated with variants in the PRPH2 gene. One FAF phenotype may have multiple ERG phenotypes, demonstrating a discordance between structure and function. Given the vast spectrum of PRPH2 disease our findings are useful for future clinical trials.

Macular neovascularization in inherited retinal diseases: A review

Inherited retinal diseases (IRDs) are the most common cause of blindness in working-age adults. Macular neovascularization (MNV) may be a presenting feature or occurs as a late-stage complication in several IRDs. We performed an extensive literature review on MNV associated with IRDs. MNV is a well-known complication of Sorsby fundus dystrophy and pseudoxanthoma elasticum. Those with late-onset Stargardt disease may masquerade as exudative age-related macular degeneration (AMD) when MNV is the presenting feature. Peripherinopathies may develop MNV that responds well to a short course of anti-vascular endothelial growth factor (anti-VEGF) therapy, while bestrophinopathies tend to develop MNV in the early stages of the disease without vision loss. Enhanced S-cone syndrome manifests type 3 MNV that typically regresses into a subfoveal fibrotic nodule. MNV is only a rare complication in choroideraemia and rod-cone dystrophies. Most IRD-related MNVs exhibit a favorable visual prognosis requiring less intensive regimens of anti-vascular endothelial growth factor therapy compared to age-related macular degeneration. We discuss the role of key imaging modalities in the diagnosis of MNV across a wide spectrum of IRDs and highlight the gaps in our knowledge with respect to the natural history and prognosis to pave the way for future directions of research.

Comparative study of PRPH2 D2 loop mutants reveals divergent disease mechanism in rods and cones

Mutations in the photoreceptor-specific tetraspanin gene peripherin-2 (PRPH2) lead to widely varying forms of retinal degeneration ranging from retinitis pigmentosa to macular dystrophy. Both inter- and intra-familial phenotypic heterogeneity has led to much interest in uncovering the complex pathogenic mechanisms of PRPH2-associated disease. Majority of disease-causing mutations in PRPH2 reside in the second intradiscal loop, wherein seven cysteines control protein folding and oligomerization. Here, we utilize knockin models to evaluate the role of three D2 loop cysteine mutants (Y141C, C213Y and C150S), alone or in combination. We elucidated how these mutations affect PRPH2 properties, including oligomerization and subcellular localization, and contribute to disease processes. Results from our structural, functional and molecular studies revealed that, in contrast to our understanding from prior investigations, rods are highly affected by PRPH2 mutations interfering with oligomerization and not merely by the haploinsufficiency associated with these mutations. On the other hand, cones are less affected by the toxicity of the mutant protein and significantly reduced protein levels, suggesting that knockdown therapeutic strategies may sustain cone functionality for a longer period. This observation provides useful data to guide and simplify the current development of effective therapeutic approaches for PRPH2-associated diseases that combine knockdown with high levels of gene supplementation needed to generate prolonged rod improvement.

Choroidal neovascularization associated with butterfly-shaped pattern dystrophy - a case report

The pattern dystrophies (PDs) are a group of primarily autosomal dominant inherited macular diseases that cause the deposition of lipofuscin in retinal pigment epithelium (RPE) and may lead to significant vision loss in later life. Patients can develop choroidal neovascularization (CNV) and/ or geographic atrophy (GA) and for this reason they are often misdiagnosed as age-related macular degeneration (AMD). We presented a case of a 66-year-old patient complaining of vision loss in the right eye (RE) for 8 months. At the initial examination, his best corrected visual acuity (BCVA) was 0.6 in the RE. Optical coherence tomography angiography (OCTA), fundus autofluorescence (FAF) and fundus fluorescein angiography (FFA) allowed to diagnose butterfly-shaped PD in both eyes with choroidal neovascularization (CNV) in the RE. The patient was treated with three intravitreal anti-vascular epithelial growth factor (anti-VEGF, ranibizumab) injections during six weeks intervals, which improved and stabilized the BCVA of the RE to 0.7 during the over two-year observation period. Our report contributes to the still limited data regarding CNV associated with butterfly-shaped PDs and the results of treatment with ranibizumab. Abbreviations: AMD = age-related macular degeneration, anti-VEGF = anti-vascular epithelial growth factor, AOFVD = adult-onset foveomacular vitelliform dystrophy, BCVA = best corrected visual acuity, CNV = choroidal neovascularization, FAF = fundus autofluorescence, FFA = fundus fluorescein angiography, GA = geographic atrophy, LE = left eye, MIDD = maternally inherited diabetes and deafness, OCT = optical coherence tomography, OCTA = optical coherence tomography angiography, OU = oculus uterque, both eyes, PD = pattern dystrophy, PDSFF = pattern dystrophy simulating fundus flavimaculatus, PDT = photodynamic therapy, PRPH2 = peripherine-2, RE = right eye, RPE = retinal pigment epithelium, VA = visual acuity.

Prph2 disease mutations lead to structural and functional defects in the RPE

Prph2 is a photoreceptor-specific tetraspanin with an essential role in the structure and function of photoreceptor outer segments. PRPH2 mutations cause a multitude of retinal diseases characterized by the degeneration of photoreceptors as well as defects in neighboring tissues such as the RPE. While extensive research has analyzed photoreceptors, less attention has been paid to these secondary defects. Here, we use different Prph2 disease models to evaluate the damage of the RPE arising from photoreceptor defects. In Prph2 disease models, the RPE exhibits structural abnormalities and cell loss. Furthermore, RPE functional defects are observed, including impaired clearance of phagocytosed outer segment material and increased microglia activation. The severity of RPE damage is different between models, suggesting that the different abnormal outer segment structures caused by Prph2 disease mutations lead to varying degrees of RPE stress and thus influence the clinical phenotype observed in patients.

Photoreceptor Disc Enclosure Is Tightly Controlled by Peripherin-2 Oligomerization

Mutations in the PRPH2 gene encoding the photoreceptor-specific protein PRPH2 (also known as peripherin-2 or rds) cause a broad range of autosomal dominant retinal diseases. Most of these mutations affect the structure of the light-sensitive photoreceptor outer segment, which is composed of a stack of flattened "disc" membranes surrounded by the plasma membrane. The outer segment is renewed on a daily basis in a process whereby new discs are added at the outer segment base and old discs are shed at the outer segment tip. New discs are formed as serial membrane evaginations, which eventually enclose through a complex process of membrane remodeling (completely in rods and partially in cones). As disc enclosure proceeds, PRPH2 localizes to the rims of enclosed discs where it forms oligomers which fortify the highly curved membrane structure of these rims. In this study, we analyzed the outer segment phenotypes of mice of both sexes bearing a single copy of either the C150S or the Y141C PRPH2 mutation known to prevent or increase the degree of PRPH2 oligomerization, respectively. Strikingly, both mutations increased the number of newly forming, not-yet-enclosed discs, indicating that the precision of disc enclosure is regulated by PRPH2 oligomerization. Without tightly controlled enclosure, discs occasionally over-elongate and form large membranous "whorls" instead of disc stacks. These data show that the defects in outer segment structure arising from abnormal PRPH2 oligomerization are manifested at the stage of disc enclosure.SIGNIFICANCE STATEMENT The light-sensitive photoreceptor outer segment contains a stack of flattened "disc" membranes that are surrounded, or "enclosed," by the outer segment membrane. Disc enclosure is an adaptation increasing photoreceptor light sensitivity by facilitating the diffusion of the second messenger along the outer segment axes. However, the molecular mechanisms by which photoreceptor discs enclose within the outer segment membrane remain poorly understood. We now demonstrate that oligomers of the photoreceptor-specific protein peripherin-2, or PRPH2, play an active role in this process. We further propose that defects in disc enclosure because of abnormal PRPH2 oligomerization result in major structural abnormalities of the outer segment, ultimately leading to loss of visual function and cell degeneration in PRPH2 mutant models and human patients.

Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration

The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)^P23H/+ and Prph2^Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in Rho^P23H/+/Rtbdn^−/− and Prph2^Y141C/+/Rtbdn^−/− retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.

Genotype-phenotype associations in a large PRPH2-related retinopathy cohort

Molecular variant interpretation lacks disease gene-specific cohorts for determining variant enrichment in disease versus healthy populations. To address the molecular etiology of retinal degeneration, specifically the PRPH2-related retinopathies, we reviewed genotype and phenotype information obtained from 187 eyeGENE® participants from 161 families. Clinical details were provided by referring clinicians participating in the eyeGENE® Network. The cohort was sequenced for variants in PRPH2. Variant complementary DNA clusters and cohort frequency were compared to variants in public databases to help us to determine pathogenicity by current American College of Medical Genetics and Genomics/Association for Molecular Pathology interpretation criteria. The most frequent variant was c.828+3A>T, which affected 28 families (17.4%), and 25 of 79 (31.64%) variants were novel. The majority of missense variants clustered in the D2 intracellular loop of the peripherin-2 protein, constituting a hotspot. Disease enrichment was noted for 23 (29.1%) of the variants. Hotspot and disease-enrichment evidence modified variant classification for 16.5% of variants. The missense allele p.Arg172Trp was associated with a younger age of onset. To the best of our knowledge, this is the largest patient cohort review of PRPH2-related retinopathy. Large disease gene-specific cohorts permit gene modeling for hotspot and disease-enrichment analysis, providing novel variant classification evidence, including for novel missense variants.

Photoreceptor Disc Enclosure Occurs in the Absence of Normal Peripherin-2/rds Oligomerization

Mutations in the peripherin-2 gene (PRPH2, also known as rds) cause a heterogeneous range of autosomal dominant retinal diseases. PRPH2 encodes a photoreceptor-specific tetraspanin protein, PRPH2, that is a main structural component of the photoreceptor outer segment. PRPH2 distributes to the rims of outer segment disc membranes as they undergo the process of disc membrane enclosure. Within these rims, PRPH2 exists in homo-oligomeric form or as a hetero-oligomer with another tetraspanin protein, ROM1. While complete loss of PRPH2 prevents photoreceptor outer segment formation, mutations affecting the state of its oligomerization, including C150S, C213Y and Y141C, produce outer segment structural defects. In this study, we addressed whether any of these mutations also affect disc enclosure. We employed recently developed methodology for ultrastructural analysis of the retina, involving tissue processing with tannic acid, to assess the status of disc enclosure in knockin mouse models bearing either one or two alleles of the C150S, C213Y and Y141C PRPH2 mutations. While varying degrees of outer segment structural abnormalities were observed in each of these mouse models, they contained both newly forming “open” discs and mature “enclosed” discs. These data demonstrate that normal PRPH2 oligomerization is not essential for photoreceptor disc enclosure.

The Interplay between Peripherin 2 Complex Formation and Degenerative Retinal Diseases

Peripherin 2 (Prph2) is a photoreceptor-specific tetraspanin protein present in the outer segment (OS) rims of rod and cone photoreceptors. It shares many common features with other tetraspanins, including a large intradiscal loop which contains several cysteines. This loop enables Prph2 to associate with itself to form homo-oligomers or with its homologue, rod outer segment membrane protein 1 (Rom1) to form hetero-tetramers and hetero-octamers. Mutations in PRPH2 cause a multitude of retinal diseases including autosomal dominant retinitis pigmentosa (RP) or cone dominant macular dystrophies. The importance of Prph2 for photoreceptor development, maintenance and function is underscored by the fact that its absence results in a failure to initialize OS formation in rods and formation of severely disorganized OS membranous structures in cones. Although the exact role of Rom1 has not been well studied, it has been concluded that it is not necessary for disc morphogenesis but is required for fine tuning OS disc size and structure. Pathogenic mutations in PRPH2 often result in complex and multifactorial phenotypes, involving not just photoreceptors, as has historically been reasoned, but also secondary effects on the retinal pigment epithelium (RPE) and retinal/choroidal vasculature. The ability of Prph2 to form complexes was identified as a key requirement for the development and maintenance of OS structure and function. Studies using mouse models of pathogenic Prph2 mutations established a connection between changes in complex formation and disease phenotypes. Although progress has been made in the development of therapeutic approaches for retinal diseases in general, the highly complex interplay of functions mediated by Prph2 and the precise regulation of these complexes made it difficult, thus far, to develop a suitable Prph2-specific therapy. Here we describe the latest results obtained in Prph2-associated research and how mouse models provided new insights into the pathogenesis of its related diseases. Furthermore, we give an overview on the current status of the development of therapeutic solutions.

A case-control collapsing analysis identifies retinal dystrophy genes associated with ophthalmic disease in patients with no pathogenic ABCA4 variants

PURPOSE

Variants in the ABCA4 gene are causal for a variety of retinal dystrophy phenotypes, including Stargardt disease (STGD1). However, 15% of patients who present with symptoms compatible with STGD1/ABCA4 disease do not have identifiable causal ABCA4 variants. We hypothesized that a case-control collapsing analysis in ABCA4-negative patients with compatible symptoms would provide an objective measure to identify additional disease genes.

METHODS

We performed a genome-wide enrichment analysis of "qualifying variants"-ultrarare variants predicted to impact protein function-in protein-coding genes in 79 unrelated cases and 9028 unrelated controls.

RESULTS

Despite modest sample size, two known retinal dystrophy genes, PRPH2 and CRX, achieved study-wide significance (p < 1.33 × 10^-6) under a dominant disease model, and eight additional known retinal dystrophy genes achieved nominal significance (p < 0.05). Across these ten genes, the excess of qualifying variants explained up to 36.8% of affected individuals. Furthermore, under a recessive model, the cone-rod dystrophy gene CERKL approached study-wide significance.

CONCLUSION

Our results indicate that case-control collapsing analyses can efficiently identify pathogenic variants in genes in non-ABCA4 retinal dystrophies. The genome-wide collapsing analysis framework is an objective discovery method particularly suitable in settings with overlapping disease phenotypes.

Genetic testing for central areolar choroidal dystrophy

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for central areolar choroidal dystrophy (CACD). CACD is mostly inherited in an autosomal dominant manner. Transmission is rarely autosomal recessive. Overall prevalence is currently 1-9 per 100 000. CACD is caused by mutations in the PRPH2 and GUCY2D genes. Clinical diagnosis is based on clinical findings, ophthalmological examination, fluorescein angiography, electroretinography (showing cone dystrophy) and stereo fundus photography. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Evaluation of the association of single nucleotide polymorphisms in the PRPH2 gene with adult-onset foveomacular vitelliform dystrophy

OBJECTIVE

A minority of patients with adult-onset foveomacular vitelliform dystrophy (AFVD) carry mutations in the PRPH2 gene. This gene is highly polymorphic and it was suggested that single-nucleotide polymorphisms (SNPs) in PRPH2 may also be associated with AFVD. We aimed to evaluate for such an association.

METHODS

A single center cohort from a tertiary referral center including 52 consecutive patients with a clinical diagnosis of AFVD and 91 unaffected individuals was assessed. Sanger sequencing was performed for the PRPH2, BEST1, and IMPG1/2 genes. Investigation as to the frequency of minor alleles for SNPs in PRPH2 was performed and compared to HapMap and Exome Variant Server (EVS) data.

RESULTS

None of the patients carry a mutation in PRPH2, BEST1, or IMPG1/2. Five of 14 known SNPs (rs835, rs361524, rs434102, rs425876, rs390659) in exon 3 of PRPH2 were identified in AFVD patients. A high frequency and percentage of minor alleles of these five SNPs was found in the Israeli AFVD patients and controls compared with European, Chinese, Japanese and African populations identified via HapMap and EVS (p < 0.05). Power calculation suggested that the sample size was sufficient (80%) to rule out an association with an odds ratio above 2.5.

CONCLUSIONS

These results suggest that genetic variants in PRPH2 do not compose a major genetic risk factor for AFVD. The Israeli population shows a higher percentage of minor allele frequencies in SNPs in the PRPH2 gene, as compared with other populations. This emphasizes the need for appropriate genetic background when performing SNP association testing.

Peripherin mutations cause a distinct form of recessive Leber congenital amaurosis and dominant phenotypes in asymptomatic parents heterozygous for the mutation

BACKGROUND

Dominant mutations in peripherin (PRPH2) are associated with a spectrum of retinal dystrophy phenotypes, many of which are adult onset and involve the macula. Recessive PRPH2 mutations cause retinal dystrophy associated with prominent maculopathy in adulthood; however, the presenting childhood phenotype has not been defined. We characterise this phenotype.

METHODS

Retrospective case series of families harbouring bi-allelic PRPH2 mutations (2010-2014).

RESULTS

Three children (two families; assessed at 2 years old) and two adults (one family; assessed at 24 and 35 years old) with homozygous PRPH2 mutations (c.497G>A (p.Cys166Tyr) or c.136C>T (p.Arg46*)) all had infantile nystagmus and decreased vision noted soon after birth and a history of staring at lights during infancy (photophilia). The three children had high hyperopia, a normal or near normal fundus, and non-recordable electroretinographies (ERGs). The two adults had slight myopia, macular and peripheral retinal changes, and non-recordable ERGs. All five available carrier parents had macular±peripheral retinal findings, although they considered themselves asymptomatic except for one mother who had developed visual loss in one eye at 48 years old and had an associated subfoveal lesion.

CONCLUSIONS

Bi-allelic PRPH2 mutations cause a distinct Leber congenital amaurosis phenotype in infancy; affected adults have prominent maculopathy. Heterozygous parents can be asymptomatic but have clinically obvious macular phenotypes with or without peripheral retinal findings, which can be helpful in making the genetic diagnosis in affected children. The difference between the heterozygous and homozygous phenotypes is likely related to gene product dosage effect.

The Y141C knockin mutation in RDS leads to complex phenotypes in the mouse

Mutations in the photoreceptor-specific gene peripherin-2 (PRPH-2, also known as retinal degeneration slow/RDS) cause incurable retinal degeneration with a high degree of phenotypic variability. Patient phenotypes range from retinitis pigmentosa to various forms of macular and pattern dystrophy. Macular and pattern dystrophy in particular are associated with complex, poorly understood disease mechanisms, as severe vision loss is often associated both with defects in the photoreceptors, as well as the choroid and retinal pigment epithelium (RPE). Since there is currently no satisfactory model to study pattern dystrophy disease mechanisms, we generated a knockin mouse model expressing an RDS pattern dystrophy mutation, Y141C. Y141C mice exhibited clinical signs similar to those in patients including late-onset fundus abnormalities characteristic of RPE and choroidal defects and electroretinogram defects. Ultrastructural examination indicated that disc formation was initiated by the Y141C protein, but proper sizing and alignment of discs required wild-type RDS. The biochemical mechanism underlying these abnormalities was tied to defects in the normal process of RDS oligomerization which is required for proper RDS function. Y141C-RDS formed strikingly abnormal disulfide-linked complexes which were localized to the outer segment (OS) where they impaired the formation of proper OS structure. These data support a model of pattern dystrophy wherein a primary molecular defect occurring in all photoreceptors leads to secondary sequellae in adjacent tissues, an outcome which leads to macular vision loss. An understanding of the role of RDS in the interplay between these tissues significantly enhances our understanding of RDS-associated pathobiology and our ability to design rational treatment strategies.

A novel PRPF31 mutation in a large Chinese family with autosomal dominant retinitis pigmentosa and macular degeneration

Purpose

This study was intended to identify the disease causing genes in a large Chinese family with autosomal dominant retinitis pigmentosa and macular degeneration.

Methods

A genome scan analysis was conducted in this family for disease gene preliminary mapping. Snapshot analysis of selected SNPs for two-point LOD score analysis for candidate gene filter. Candidate gene PRPF31 whole exons' sequencing was executed to identify mutations.

Results

A novel nonsense mutation caused by an insertion was found in PRPF31 gene. All the 19 RP patients in 1085 family are carrying this heterozygous nonsense mutation. The nonsense mutation is in PRPF31 gene exon9 at chr19:54629961-54629961, inserting nucleotide “A” that generates the coding protein frame shift from p.307 and early termination at p.322 in the snoRNA binding domain (NOP domain).

Conclusion

This report is the first to associate PRPF31 gene's nonsense mutation and adRP and JMD. Our findings revealed that PRPF31 can lead to different clinical phenotypes in the same family, resulting either in adRP or syndrome of adRP and JMD. We believe our identification of the novel “A” insertion mutation in exon9 at chr19:54629961-54629961 in PRPF31 can provide further genetic evidence for clinical test for adRP and JMD.

Late-Onset Central Areolar Choroidal Dystrophy Caused by a Heterozygous Frame-Shift Mutation Affecting Codon 307 of the Peripherin/RDS Gene

Mutations in the peripherin/RDS gene have been identified in families with various retinopathies including those affecting primarily the macula and those restricted to the retinal periphery. Here, we describe the clinical findings of two sisters with late-onset central areolar choroidal dystrophy (CACD). The two siblings underwent genetic testing and were found to be carriers of a heterozygous frame-shift mutation 920delT affecting codon 307 of the peripherin/RDS gene and resulting in a truncated, likely functionless, protein with an altered C-terminus (Leu307fsX83). The identical mutation has previously been reported to cause slowly progressive autosomal dominant retinitis pigmentosa. In our two patients, the Leu307fsX83 mutation accounts for an unusually mild form of retinal degeneration.

The spectrum of retinal dystrophies caused by mutations in the peripherin/RDS gene

Peripherin/rds is an integral membrane glycoprotein, mainly located in the rod and cone outer segments. The relevance of this protein to photoreceptor outer segment morphology was first demonstrated in retinal degeneration slow (rds) mice. Thus far, over 90 human peripherin/RDS gene mutations have been identified. These mutations have been associated with a variety of retinal dystrophies, in which there is a remarkable inter- and intrafamilial variation of the retinal phenotype. In this paper, we discuss the characteristics of the peripherin/RDS gene and its protein product. An overview is presented of the broad spectrum of clinical phenotypes caused by human peripherin/RDS gene mutations, ranging from various macular dystrophies to widespread forms of retinal dystrophy such as retinitis pigmentosa. Finally, we review the proposed genotype-phenotype correlation and the pathophysiologic mechanisms underlying this group of retinal dystrophies.

Intrafamilial phenotypic variability in families with RDS mutations: exclusion of ROM1 as a genetic modifier for those with retinitis pigmentosa

OBJECTIVES

To identify suspected RDS mutations in families in which different people have been identified with either generalised retinal dystrophy or macular dystrophy.

METHODS

Two families with a retinal dystrophy were extensively phenotyped and blood was taken for mutation analysis of the RDS (all) and ROM1 (retinitis pigmentosa patients only) genes.

RESULTS

A novel p.Trp94X mutation in RDS was found in all three affected members of a two-generation family that was associated with retinitis pigmentosa in the son, pattern dystrophy in the daughter and fundus flavimaculatus in the mother. In the second family, the proband with retinitis pigmentosa carried a p.Arg220Trp mutation. The mother, who was unavailable for mutation screening, had adult vitelliform macular dystrophy. No ROM1 mutations were found in those with retinitis pigmentosa in either family.

CONCLUSION

Mutations in RDS can be associated with an intrafamilial variation in retinal disease. The phenotypes range from Stargardt-like macular dystrophy to classic retinitis pigmentosa.

CLINICAL RELEVANCE

Intrafamilial phenotypic variation may be due to the presence of environmental or genetic modifying factors. The presence of a modifying-sequence change in the coding region of ROM1 for two people with retinitis pigmentosa from two families with intrafamilial variation in RDS mutation phenotype has been excluded in this study.

Genetic and phenotypic heterogeneity in pattern dystrophy

BACKGROUND

The pattern dystrophies (PD) represent a clinically heterogeneous family of inherited macular diseases frequently caused by mutations in the peripherin/RDS gene. Most previous studies have detailed the clinical findings in single families, making it difficult to derive data from which progression and visual outcome can be generalised.

METHODS

Families were ascertained and clinically evaluated including angiography and electrophysiology where appropriate.

RESULTS

In each of the six families with autosomal dominant PD, a mutation in the peripherin/RDS gene was identified, including a novel Cys250Phe variant. These data suggest that the condition is characterised by the accumulation of yellow to grey subretinal flecks, followed by pigmentary change accompanied by patches of chorioretinal atrophy. Subsequently, 50% (16/32) of individuals with PD developed poor central vision because of chorioretinal geographic atrophy or subretinal neovascularisation. The risk of these complications appears to increase with age.

CONCLUSION

PD should not necessarily be considered a benign condition. Instead, patients should be counselled that there is a significant chance of losing central vision in their later years. Some elderly patients with probands showing PD may be misdiagnosed with age related macular degeneration owing to the phenotypic similarities between these conditions in the advanced state.

Genetic factors of age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness in the United States and developed countries. Although the etiology and pathogenesis of AMD remain unknown, a complex interaction of genetic and environmental factors is thought to exist. The incidence and progression of all of the features of AMD are known to increase significantly with age. The tendency for familial aggregation and the findings of gene variation association studies implicate a significant genetic component in the development of AMD. This review summarizes in detail the AMD-related genes identified by studies on genetically engineered and spontaneously gene-mutated (naturally mutated) animals, AMD chromosomal loci identified by linkage studies, AMD-related genes identified through studies of monogenic degenerative retinal diseases, and AMD-related gene variation identified by association studies.