A truncated form of rod photoreceptor PDE6 β-subunit causes autosomal dominant congenital stationary night blindness by interfering with the inhibitory activity of the γ-subunit

A novel homozygous missense substitution p.Thr313Ile in the PDE6B gene underlies autosomal recessive retinitis pigmentosa in a consanguineous Pakistani family

BACKGROUND

Retinitis pigmentosa (RP) is one of the most frequent hereditary retinal diseases that often starts with night blindness and eventually leads to legal blindness. Our study aimed to identify the underlying genetic cause of autosomal recessive retinitis pigmentosa (arRP) in a consanguineous Pakistani family.

METHODS

Following a detailed ophthalmological examination of the patients by an ophthalmologist, whole-exome sequencing was performed on the proband's DNA to delineate the genetic cause of RP in the family. In-depth computational methods, in-silico analysis, and familial co-segregation study were performed for variant detection and validation.

RESULTS

We studied an inbred Pakistani family with two siblings affected by retinitis pigmentosa. The proband, a 32 years old female, was clinically diagnosed with RP at the age of 6 years. A classical night blindness symptom was reported in the proband since her early childhood. OCT report showed a major reduction in the outer nuclear layer and the ellipsoid zone width, leading to the progression of the disease. Exome sequencing revealed a novel homozygous missense mutation (c.938C > T;p.Thr313Ile) in exon 12 of the PDE6B gene. The mutation p.Thr313Ile co-segregated with RP phenotype in the family. The altered residue (p.Thr313) was super conserved evolutionarily across different vertebrate species, and all available in silico tools classified the mutation as highly pathogenic.

CONCLUSION

We present a novel homozygous pathogenic mutation in the PDE6B gene as the underlying cause of arRP in a consanguineous Pakistani family. Our findings highlight the importance of missense mutations in the PDE6B gene and expand the known mutational repertoire of PDE6B-related RP.

Genomic insight into the nocturnal adaptation of the black-crowned night heron (Nycticorax nycticorax)

BACKGROUND

The black-crowned night heron (Nycticorax nycticorax) is an ardeid bird successfully adapted to the nocturnal environment. Previous studies had indicated that the eyes of the night herons have evolved several specialized morphological traits favoring nocturnal vision. However, the molecular mechanisms of the nocturnal vision adaptation of night herons remained inattentions. In this study, the whole genome of N. nycticorax was sequenced and comparative analyses were performed on the vision-related and olfactory receptor (OR) genes to understand the molecular mechanisms of the visual and olfactory adaptation of night herons.

RESULTS

The results indicated that a number of vision genes were under positive or relaxed selection in N. nycticorax, whereas a number of other vision genes were under relaxed or intensified selection in the boat-billed heron (Cochlearius cochlearius), which suggested that the two species adapt to nocturnality with different genetic mechanisms. The different selections acting on vision genes are probably associated with the enlargement of eye size and the enhancement of visual sensitivity in night herons. The analyses on olfactory receptor (OR) genes indicated that the total number of OR genes in the genomes of N. nycticorax and C. cochlearius were about half those in the little egret (Egretta garzetta), whereas the diversity of their OR genes was not remarkably different. Additionally, the number of expressed OR genes in the transcriptomes of N. nycticorax was also fewer than that in E. garzetta. These results suggest a reduced olfactory capability in night herons compared with E. garzetta.

CONCLUSIONS

Our results provided evidence that several vision genes of the night herons were subjected to different natural selections, which can contribute to a better understanding of the genetic mechanisms of visual adaptions of the night heron. In addition, the finding of the reduced number of total and expressed OR genes in night herons may reflect a trade-off between olfaction and vision.

Clinical and Genetic Characteristics of Korean Congenital Stationary Night Blindness Patients

In this study, we investigated the clinical and genetic characteristics of 19 Korean patients with congenital stationary night blindness (CSNB) at two tertiary hospitals. Clinical evaluations, including fundus photography, spectral-domain optical coherence tomography, and electroretinography, were performed. Genetic analyses were conducted using targeted panel sequencing or whole exome sequencing. The median age was 5 (3–21) years at the initial examination, 2 (1–8) years at symptom onset, and 11 (5–28) years during the final visit. Genetic mutations were identified as CNGB1 and GNAT1 for the Riggs type (n = 2), TRPM1 and NYX for the complete type (n = 3), and CACNA1F (n = 14) for the incomplete type. Ten novel variants were identified, and best-corrected visual acuity (BCVA) and spherical equivalents (SE) were related to each type of CSNB. The Riggs and TRPM1 complete types presented mild myopia and good BCVA without strabismus and nystagmus, whereas the NYX complete and incomplete types showed mixed SE and poor BCVA with strabismus and nystagmus. This is the first case series of Korean patients with CSNB, and further studies with a larger number of subjects should be conducted to correlate the clinical and genetic aspects of CSNB.

Clinical Phenotype of PDE6B-Associated Retinitis Pigmentosa

In this retrospective, longitudinal, observational cohort study, we investigated the phenotypic and genotypic features of retinitis pigmentosa associated with variants in the PDE6B gene. Patients underwent clinical examination and genetic testing at a single tertiary referral center, including best-corrected visual acuity (BCVA), kinetic visual field (VF), full-field electroretinography, full-field stimulus threshold, spectral domain optical coherence tomography, and fundus autofluorescence imaging. The genetic testing comprised candidate gene sequencing, inherited retinal disease gene panel sequencing, whole-genome sequencing, and testing for familial variants by Sanger sequencing. Twenty-four patients with mutations in PDE6B from 21 families were included in the study (mean age at the first visit: 32.1 ± 13.5 years). The majority of variants were putative splicing defects (8/23) and missense (7/23) mutations. Seventy-nine percent (38/48) of eyes had no visual acuity impairment at the first visit. Visual acuity impairment was mild in 4% (2/48), moderate in 13% (6/48), and severe in 4% (2/48). BCVA was symmetrical in the right and left eyes. The kinetic VF measurements were highly symmetrical in the right and left eyes, as was the horizontal ellipsoid zone (EZ) width. Regarding the genetic findings, 43% of the PDE6B variants found in our patients were novel. Thus, this study contributed substantially to the PDE6B mutation spectrum. The visual acuity impairment was mild in 83% of eyes, providing a window of opportunity for investigational new drugs. The EZ width was reduced in all patients and was highly symmetric between the eyes, making it a promising outcome measure. We expect these findings to have implications on the design of future PDE6B-related retinitis pigmentosa (RP) clinical trials.

Progress in treating inherited retinal diseases: Early subretinal gene therapy clinical trials and candidates for future initiatives

Due to improved phenotyping and genetic characterization, the field of 'incurable' and 'blinding' inherited retinal diseases (IRDs) has moved substantially forward. Decades of ascertainment of IRD patient data from Philadelphia and Toronto centers illustrate the progress from Mendelian genetic types to molecular diagnoses. Molecular genetics have been used not only to clarify diagnoses and to direct counseling but also to enable the first clinical trials of gene-based treatment in these diseases. An overview of the recent reports of gene augmentation clinical trials by subretinal injections is used to reflect on the reasons why there has been limited success in this early venture into therapy. These first-in human experiences have taught that there is a need for advancing the techniques of delivery of the gene products - not only for refining further subretinal trials, but also for evaluating intravitreal delivery. Candidate IRDs for intravitreal gene delivery are then suggested to illustrate some of the disorders that may be amenable to improvement of remaining central vision with the least photoreceptor trauma. A more detailed understanding of the human IRDs to be considered for therapy and the calculated potential for efficacy should be among the routine prerequisites for initiating a clinical trial.

Longitudinal Clinical Follow-up and Genetic Spectrum of Patients With Rod-Cone Dystrophy Associated With Mutations in PDE6A and PDE6B

Importance

A precise phenotypic characterization of retinal dystrophies is needed for disease modeling as a basis for future therapeutic interventions.

Objective

To compare genotype, phenotype, and structural changes in patients with rod-cone dystrophy (RCD) associated with mutations in PDE6A or PDE6B.

Design, Setting, and Participants

In a retrospective cohort study conducted in Paris, France, from January 2007 to September 2017, 54 patients from a cohort of 1095 index patients with RCD underwent clinical examination, including personal and familial history, best-corrected visual acuity (BCVA), color vision, slitlamp examination, full-field electroretinography, kinetic visual fields (VFs), retinophotography, optical coherence tomography, near-infrared fundus autofluorescence, and short-wavelength fundus autofluorescence imaging. Genotyping was performed using microarray analysis, targeted next-generation sequencing, and Sanger sequencing validation with familial segregation when possible. Data were analyzed from September 1, 2017, to February 1, 2018. Clinical variables were subsequently analyzed in 2018.

Main Outcomes and Measures

Phenotype and genotype comparison of patients carrying mutations in PDE6A or PDE6B.

Results

Of the 54 patients included in the study, 19 patients of 17 families (11 women [58%]; mean [SD] age at diagnosis, 14.83 [10.63] years) carried pathogenic mutations in PDE6A, and 35 patients of 26 families (17 women [49%]; mean [SD] age at diagnosis, 21.10 [11.56] years) had mutations in PDE6B, accounting for prevalences of 1.6% and 2.4%, respectively. Among 49 identified genetic variants, 14 in PDE6A and 15 in PDE6B were novel. Overall, phenotypic analysis revealed no substantial differences between the 2 groups except for night blindness as a presenting symptom that was noted to be more prevalent in the PDE6A than PDE6B group (80% vs 37%, respectively; P = .005). The mean binocular BCVA and VF decrease over time (measured as mean individual slopes coefficients) was comparable between patients with PDE6A and PDE6B mutations: 0.04 (0.12) vs 0.02 (0.05) for BCVA (P = .89) and 14.33 (7.12) vs 13.27 (6.77) for VF (P = .48).

Conclusions and Relevance

Mutations in PDE6A and PDE6B accounted for 1.6% and 2.4%, respectively, in a cohort of French patients with RCD. The functional and structural findings reported may constitute the basis of disease modeling that might be used for better prognostic estimation and candidate selection for photoreceptor therapeutic rescue.

Coexistence of GNAT1 and ABCA4 variants associated with Nougaret-type congenital stationary night blindness and childhood-onset cone-rod dystrophy

PURPOSE

A single variant (p.G38D) in the GNAT1 gene, encoding the rod-specific transducin α-subunit in phototransduction, has been reported only in one French family with Nougaret-type autosomal dominant congenital stationary night blindness (CSNB). We identified a Japanese family with Nougaret-type CSNB and cone-rod dystrophy (CORD).

METHODS

Five patients with CSNB and two patients with childhood-onset CORD were recruited. We performed a comprehensive ophthalmic examination including electroretinography (ERG). Disease-causing variants were identified by whole exome sequencing, with candidates confirmed by Sanger sequencing in nine family members.

RESULTS

The GNAT1 variant (p.G38D) was identified in all four CSNB patients, whereas the two CORD patients carried biallelic truncated known ABCA4 variants as well as the GNAT1 variant. Clinically, no remarkable findings were observed in fuduscopy, fundus autofluorescence, or optical coherence tomography images from the CSNB patients. No response was detectable by rod ERG. The a-waves of standard and bright flash ERG were delayed and broadened rather than biphasic, and b/a-wave amplitude ratio was negative. Cone and 30-Hz flicker responses were normal, and overall, the ERG findings were compatible with previous descriptions of Nougaret-type CSNB. ERG of the CORD patients with macular atrophy showed non-recordable rod response and severely decreased standard flash, cone and 30-Hz flicker responses.

CONCLUSIONS

This is the second report of a Nougaret-type CSNB family with the GNAT1 variant. Our novel findings suggest that coexistence of the GNAT1 and biallelic ABCA4 variants is associated with an overlapping phenotype with both Nougaret-type CSNB and CORD.

A novel intronic mutation of PDE6B is a major cause of autosomal recessive retinitis pigmentosa among Caucasus Jews

PURPOSE

To identify the genetic basis for retinitis pigmentosa (RP) in a cohort of Jewish patients from Caucasia.

METHODS

Patients underwent a detailed ophthalmic evaluation, including funduscopic examination, visual field testing, optical coherence tomography (OCT), and electrophysiological tests, electroretinography (ERG) and visual evoked potentials (VEP). Genetic analysis was performed with a combination of whole exome sequencing (WES) and Sanger sequencing. Bioinformatic analysis of the WES results was performed via a customized pipeline. Pathogenicity of the identified intronic variant was evaluated in silico using the web tool Human Splicing Finder, and in vitro, using a minigene-based splicing assay. Linkage disequilibrium (LD) analysis was used to demonstrate a founder effect, and the decay of LD over generations around the mutation in Caucasus Jewish chromosomes was modeled to estimate the age of the most recent common ancestor.

RESULTS

In eight patients with RP from six unrelated families, all of Caucasus Jewish ancestry, we identified a novel homozygous intronic variant, located at position -9 of PDE6B intron 15. The c.1921-9C>G variant was predicted to generate a novel acceptor splice site, nine bases upstream of the original splice site of intron 15. In vitro splicing assay demonstrated that this novel acceptor splice site is used instead of the wild-type site, leading to an 8-bp insertion into exon 16, which is predicted to cause a frameshift. The presence of a common ancestral haplotype in mutation-bearing chromosomes was compatible with a founder effect.

CONCLUSIONS

The PDE6B c.1921-9C>G intronic mutation is a founder mutation that accounts for at least 40% (6/15 families) of autosomal recessive RP among Caucasus Jews. This result is highly important for molecular diagnosis, carrier screening, and genetic counseling in this population.

Riggs-type dominant congenital stationary night blindness: ERG findings, a new GNAT1 mutation and a systemic association

PURPOSE

Complete congenital stationary night blindness (CSNB) is most often x-linked or recessive, and associated with a transmission defect from photoreceptors to bipolar cells. This produces a characteristic "negative" Schubert-Bornschein type of scotopic rod-cone electroretinogram (ERG) with a large a-wave and minimal b-wave. CSNB from abnormalities in phototransduction can be recessive or dominant and is much less common. This produces a Riggs type of ERG with loss of the rod a-wave as well as the b-wave. We report the clinical and ERG findings from a family with autosomal dominant CSNB that was shown previously to have a new GNAT1 mutation with a novel mechanism of action. They provide a classic demonstration of the Riggs-type ERG and have an unusual systemic association.

METHODS

Clinical case report of a father and daughter.

RESULTS

A Chinese father and daughter presented with good visual acuity, moderate myopia, and lifelong night blindness. Both show normal fundi except for mild myopia, and fundus autofluorescence and OCT images are normal. Their ERGs illustrate the typical Riggs-type ERG with no rod a-wave (they have only a small cone-dominated combined response). They also have postural orthostatic tachycardia syndrome (POST), which is an autonomic dysfunction disorder thought usually to be sporadic. The retinal gene analyses revealed no abnormalities that might account for POST.

CONCLUSIONS

Our family's ERG showed essentially no rod response, consistent with a Danish GNAT1 pedigree but different from the Nougaret GNAT1 pedigree that shows partial preservation of rod signal. A genetic connection between CSNB and POST would be intriguing, but we found no evidence for this.

Expanded Retinal Disease Spectrum Associated With Autosomal Recessive Mutations in GUCY2D

PURPOSE

GUCY2D has been associated with autosomal recessive Leber congenital amaurosis and autosomal dominant cone-rod dystrophy. This report expands the phenotype of autosomal recessive mutations to congenital night blindness, which may slowly progress to mild retinitis pigmentosa.

DESIGN

Retrospective case series.

METHODS

Multicenter study of 5 patients (3 male, 2 female).

RESULTS

All patients presented with night blindness since childhood. Age at referral was 9-45 years. Length of follow-up was 1-7 years. Best-corrected visual acuity at presentation ranged from 20/15 to 20/30 and at most recent visit averaged 20/25. No patient had nystagmus or high refractive error. ISCEV standard electroretinography revealed nondetectable dark-adapted dim flash responses and reduced amplitude but not electronegative dark-adapted bright flash responses with similar waveforms to the reduced-amplitude light-adapted single flash responses. The 30 Hz flicker responses were relatively preserved. Macular optical coherence tomography revealed normal lamination in 3 patients, with abnormalities in 2. Goldmann visual fields were normal at presentation in children but constricted in 1 adult. One child showed loss of midperipheral fields over time. Fundus appearance was normal in childhood; the adult had sparse bone spicule-like pigmentation. Full-field stimulus testing (FST) revealed markedly decreased retinal sensitivity to light. Dark adaptation demonstrated lack of rod-cone break. Two patients had tritanopia. All 5 had compound heterozygous mutations in GUCY2D. Three of the 5 patients harbor the Arg768Trp mutation reported in GUCY2D-associated Leber congenital amaurosis.

CONCLUSIONS

Autosomal recessive GUCY2D mutations may cause congenital night blindness with normal acuity and refraction, and unique electroretinography. Progression to mild retinitis pigmentosa may occur.

A Novel Heterozygous Missense Mutation in GNAT1 Leads to Autosomal Dominant Riggs Type of Congenital Stationary Night Blindness

Autosomal dominant congenital stationary night blindness (adCSNB) is rare and results from altered phototransduction giving a Riggs type of electroretinogram (ERG) with loss of the rod a-wave and small b-waves. These patients usually have normal vision in light. Only few mutations in genes coding for proteins of the phototransduction cascade lead to this condition; most of these gene defects cause progressive rod-cone dystrophy. Mutation analysis of an adCSNB family with a Riggs-type ERG revealed a novel variant (c.155T>A p.Ile52Asn) in GNAT1 coding for the α-subunit of transducin, cosegregating with the phenotype. Domain predictions and 3D-modelling suggest that the variant does not affect the GTP-binding site as other GNAT1 adCSNB mutations do. It affects a predicted nuclear localization signal and a part of the first α-helix, which is distant from the GTP-binding site. The subcellular protein localization of this and other mutant GNAT1 proteins implicated in CSNB are unaltered in mammalian GNAT1 overexpressing cells. Our findings add a third GNAT1 mutation causing adCSNB and suggest that different pathogenic mechanisms may cause this condition.

Novel mutation in the choroideremia gene and multi-Mendelian phenotypes in Spanish families

Aims

We aimed to accurately diagnose several retinitis pigmentosa (RP) patients with complex ocular phenotypes by combining massive sequencing genetic diagnosis and powerful clinical imaging techniques.

Methods

Whole-exome sequencing (WES) of selected patients from two RP families was undertaken. The variants identified were validated by Sanger sequencing and cosegregation analysis. Accurate clinical re-evaluation was performed using electrophysiological and visual field records as well as non-invasive imaging techniques, such as swept-source optical coherence tomography and fundus autofluorescence.

Results

The WES results highlighted one novel and one reported causative mutations in the X-linked choroideremia gene (CHM), which challenged the initial RP diagnosis. Subsequent clinical re-evaluation confirmed the choroideremia diagnosis. Carrier females showed different degrees of affectation, even between twin sisters, probably due to lyonization. A severe multi-Mendelian phenotype was associated with coincidental dominant pathogenic mutations in two additional genes: PAX6 and PDE6B.

Conclusions

Genetic diagnosis via massive sequencing is instrumental in identifying causative mutations in retinal dystrophies and additional genetic variants with an impact on the phenotype. Multi-Mendelian phenotypes previously ascribed to rare syndromes can thus be dissected and molecularly diagnosed. Overall, the combination of powerful genetic diagnosis and clinical non-invasive imaging techniques enables efficient management of patients and their prioritisation for gene-specific therapies.

Molecular Diagnosis of Inherited Retinal Diseases in Indigenous African Populations by Whole-Exome Sequencing

Purpose

A majority of genes associated with inherited retinal diseases (IRDs) have been identified in patients of European origin. Indigenous African populations exhibit rich genomic diversity, and evaluation of reported genetic mutations has yielded low returns so far. Our goal was to perform whole-exome sequencing (WES) to examine variants in known IRD genes in underrepresented African cohorts.

Methods

Whole-exome sequencing was performed on 56 samples from 16 families with diverse IRD phenotypes that had remained undiagnosed after screening for known mutations using genotyping-based microarrays (Asper Ophthalmics). Variants in reported IRD genes were identified using WES and validated by Sanger sequencing. Custom TaqMan assays were used to screen for identified mutations in 193 unrelated indigenous Africans with IRDs.

Results

A total of 3494 variants were identified in 217 known IRD genes, leading to the identification of seven different mutations (including six novel) in six genes (RHO, PRPF3, PRPF31, ABCA4, CERKL, and PDE6B) in six distinct families. TaqMan screening in additional probands revealed identical homozygous CERKL and PDE6B variants in four more patients.

Conclusions

This is the first report of WES of patients with IRDs in indigenous African populations. Our study identified genetic defects in almost 40% of the families analyzed, significantly enhancing the molecular diagnosis of IRD in South Africa. Thus, WES of understudied cohorts seems to present an effective strategy for determining novel mutations in heterogeneous retinal diseases.

Novel Candidate Genes and a Wide Spectrum of Structural and Point Mutations Responsible for Inherited Retinal Dystrophies Revealed by Exome Sequencing

BACKGROUND

NGS-based genetic diagnosis has completely revolutionized the human genetics field. In this study, we have aimed to identify new genes and mutations by Whole Exome Sequencing (WES) responsible for inherited retinal dystrophies (IRD).

METHODS

A cohort of 33 pedigrees affected with a variety of retinal disorders was analysed by WES. Initial prioritization analysis included around 300 IRD-associated genes. In non-diagnosed families a search for pathogenic mutations in novel genes was undertaken.

RESULTS

Genetic diagnosis was attained in 18 families. Moreover, a plausible candidate is proposed for 10 more cases. Two thirds of the mutations were novel, including 4 chromosomal rearrangements, which expand the IRD allelic heterogeneity and highlight the contribution of private mutations. Our results prompted clinical re-evaluation of some patients resulting in assignment to a syndromic instead of non-syndromic IRD. Notably, WES unveiled four new candidates for non-syndromic IRD: SEMA6B, CEP78, CEP250, SCLT1, the two latter previously associated to syndromic disorders. We provide functional data supporting that missense mutations in CEP250 alter cilia formation.

CONCLUSION

The diagnostic efficiency of WES, and strictly following the ACMG/AMP criteria is 55% in reported causative genes or functionally supported new candidates, plus 30% families in which likely pathogenic or VGUS/VUS variants were identified in plausible candidates. Our results highlight the clinical utility of WES for molecular diagnosis of IRD, provide a wider spectrum of mutations and concomitant genetic variants, and challenge our view on syndromic vs non-syndromic, and causative vs modifier genes.

Next-generation sequencing confirms the implication of SLC24A1 in autosomal-recessive congenital stationary night blindness

Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous retinal disorder which represents rod photoreceptor dysfunction or signal transmission defect from photoreceptors to adjacent bipolar cells. Patients displaying photoreceptor dysfunction show a Riggs-electroretinogram (ERG) while patients with a signal transmission defect show a Schubert-Bornschein ERG. The latter group is subdivided into complete or incomplete (ic) CSNB. Only few CSNB cases with Riggs-ERG and only one family with a disease-causing variant in SLC24A1 have been reported. Whole-exome sequencing (WES) in a previously diagnosed icCSNB patient identified a homozygous nonsense variant in SLC24A1. Indeed, re-investigation of the clinical data corrected the diagnosis to Riggs-form of CSNB. Targeted next-generation sequencing (NGS) identified compound heterozygous deletions and a homozygous missense variant in SLC24A1 in two other patients, respectively. ERG abnormalities varied in these three cases but all patients had normal visual acuity, no myopia or nystagmus, unlike in Schubert-Bornschein-type of CSNB. This confirms that SLC24A1 defects lead to CSNB and outlines phenotype/genotype correlations in CSNB subtypes. In case of unclear clinical characteristics, NGS techniques are helpful to clarify the diagnosis.

Reduced rod electroretinograms in carrier parents of two Japanese siblings with autosomal recessive retinitis pigmentosa associated with PDE6B gene mutations

PURPOSE

To present the clinical and genetic findings in two siblings with autosomal recessive retinitis pigmentosa (RP) and their non-symptomatic parents.

METHODS

We studied two siblings, a 48-year-old woman and her 44-year-old brother, and their parents. They had general ophthalmic examinations including ophthalmoscopy, perimetry, and electroretinography (ERG). Their whole exomes were analyzed by the next-generation sequence technique.

RESULTS

The two siblings had night blindness for a long time, and clinical examinations revealed diffuse retinal degeneration with bone spicule pigmentation, constriction of the visual field, and non-recordable ERGs. Their parents were non-symptomatic and had normal fundi; however, their rod ERGs were reduced. Genetic examination revealed compound heterozygous mutations of I535N and H557Y in the PDE6B gene in the siblings, and the parents were heterozygous carriers of the mutations.

CONCLUSIONS

Heterozygous mutation in the PDE6B gene can cause a reduction in the rod function to different degrees. The retinal function of non-symptomatic carriers of autosomal recessive RP should be evaluated with care.