Persistent cone dysfunction in acute exudative polymorphous vitelliform maculopathy.
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Acute Disease↗
Biomedical subjects
David G Birch
Publications and source records attributed to David G Birch.
The very large G-protein-coupled receptor VLGR1: a component of the ankle link complex required for the normal development of auditory hair bundles.
Sensory hair bundles in the inner ear are composed of stereocilia that can be interconnected by a variety of different link types, including tip links, horizontal top connectors, shaft connectors, and ankle links. The ankle link antigen is an epitope specifically associated with ankle links and the calycal processes of photoreceptors in chicks. Mass spectrometry and immunoblotting were used to identify this antigen as the avian ortholog of the very large G-protein-coupled receptor VLGR1, the product of the Usher syndrome USH2C (Mass1) locus. Like ankle links, Vlgr1 is expressed transiently around the base of developing hair bundles in mice. Ankle links fail to form in the cochleae of mice carrying a targeted mutation in Vlgr1 (Vlgr1/del7TM), and the bundles become disorganized just after birth. FM1-43 [N-(3-triethylammonium)propyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide] dye loading and whole-cell recordings indicate mechanotransduction is impaired in cochlear, but not vestibular, hair cells of early postnatal Vlgr1/del7TM mutant mice. Auditory brainstem recordings and distortion product measurements indicate that these mice are severely deaf by the third week of life. Hair cells from the basal half of the cochlea are lost in 2-month-old Vlgr1/del7TM mice, and retinal function is mildly abnormal in aged mutants. Our results indicate that Vlgr1 is required for formation of the ankle link complex and the normal development of cochlear hair bundles.
Acoustic Stimulation↗
Spectrum and frequency of mutations in IMPDH1 associated with autosomal dominant retinitis pigmentosa and leber congenital amaurosis.
PURPOSE: The purpose of this study was to determine the frequency and spectrum of inosine monophosphate dehydrogenase type I (IMPDH1) mutations associated with autosomal dominant retinitis pigmentosa (RP), to determine whether mutations in IMPDH1 cause other forms of inherited retinal degeneration, and to analyze IMPDH1 mutations for alterations in enzyme activity and nucleic acid binding. METHODS: The coding sequence and flanking intron/exon junctions of IMPDH1 were analyzed in 203 patients with autosomal dominant RP (adRP), 55 patients with autosomal recessive RP (arRP), 7 patients with isolated RP, 17 patients with macular degeneration (MD), and 24 patients with Leber congenital amaurosis (LCA). DNA samples were tested for mutations by sequencing only or by a combination of single-stranded conformational analysis and by sequencing. Production of fluorescent reduced nicotinamide adenine dinucleotide (NADH) was used to measure enzymatic activity of mutant IMPDH1 proteins. The affinity and the specificity of mutant IMPDH1 proteins for single-stranded nucleic acids were determined by filter-binding assays. RESULTS: Five different IMPDH1 variants, Thr116Met, Asp226Asn, Val268Ile, Gly324Asp, and His 372Pro, were identified in eight autosomal dominant RP families. Two additional IMPDH1 variants, Arg105Trp and Asn198Lys, were found in two patients with isolated LCA. None of the novel IMPDH1 mutants identified in this study altered the enzymatic activity of the corresponding proteins. In contrast, the affinity and/or the specificity of single-stranded nucleic acid binding were altered for each IMPDH1 mutant except the Gly324Asp variant. CONCLUSIONS: Mutations in IMPDH1 account for approximately 2% of families with adRP, and de novo IMPDH1 mutations are also rare causes of isolated LCA. This analysis of the novel IMPDH1 mutants substantiates previous reports that IMPDH1 mutations do not alter enzyme activity and demonstrates that these mutants alter the recently identified single-stranded nucleic acid binding property of IMPDH. Studies are needed to further characterize the functional significance of IMPDH1 nucleic acid binding and its potential relationship to retinal degeneration.
Adolescent↗
Prevalence of disease-causing mutations in families with autosomal dominant retinitis pigmentosa: a screen of known genes in 200 families.
PURPOSE: To survey families with clinical evidence of autosomal dominant retinitis pigmentosa (adRP) for mutations in genes known to cause adRP. METHODS: Two hundred adRP families, drawn from a cohort of more than 400 potential families, were selected by analysis of pedigrees. Minimum criteria for inclusion in the adRP cohort included either evidence of at least three generations of affected individuals or two generations with evidence of male-to-male transmission. Probands from each family were screened for mutations in 13 genes known to cause adRP: CA4, CRX, FSCN2, IMPDH1, NRL, PRPF3 (RP18), PRPF8 (RP13), PRPF31 (RP11), RDS, RHO, ROM1, RP1, and RP9. Families without mutations in autosomal genes and in which an X-linked mode of inheritance could not be excluded were tested for mutations in ORF 15 of X-linked RPGR. Potentially pathogenic variants were evaluated based on a variety of genetic and computational criteria, to confirm or exclude pathogenicity. RESULTS: A total of 82 distinct, rare (nonpolymorphic) variants were detected among the genes tested. Of these, 57 are clearly pathogenic based on multiple criteria, 10 are probably pathogenic, and 15 are probably benign. In the cohort of 200 families, 94 (47%) have one of the clearly pathogenic variants and 10 (5%) have one of the probably pathogenic variants. One family (0.5%) has digenic RDS-ROM1 mutations. Two families (1%) have a pathogenic RPGR mutation, indicating that families with apparent autosomal transmission of RP may actually have X-linked genetic disease. Thus, 107 families (53.5%) have mutations in known genes, leaving 93 whose underlying cause is still unknown. CONCLUSIONS: Together, the known adRP genes account for retinal disease in approximately half of the families in this survey, mostly Americans of European origin. Among the adRP genes, IMPDH1, PRPF8, PRPF31, RDS, RHO, and RP1 each accounts for more than 2% of the total; CRX, PRPF3, and RPGR each accounts for roughly 1%. Disease-causing mutations were not found in CA4, FSCN2, NRL, or RP9. Because some mutations are frequent and some regions are more likely to harbor mutations than others, more than two thirds of the detected mutations can be found by screening less than 10% of the total gene sequences. Among the remaining families, mutations may lie in regions of known genes that were not tested, mutations may not be detectable by PCR-based sequencing, or other loci may be involved.
DNA Mutational Analysis↗
Genomic rearrangements of the PRPF31 gene account for 2.5% of autosomal dominant retinitis pigmentosa.
PURPOSE: To determine whether genomic rearrangements in the PRPF31 (RP11) gene are a frequent cause of autosomal dominant retinitis pigmentosa (adRP) in a cohort of patients with adRP. METHODS: In a cohort of 200 families with adRP, disease-causing mutations have previously been identified in 107 families. To determine the cause of disease in the remaining families, linkage testing was performed with markers for 13 known adRP loci. In a large American family, evidence was found of linkage to the PRPF31 gene, although DNA sequencing revealed no mutations. SNP testing throughout the genomic region was used to determine whether any part of the gene was deleted. Aberrant segregation of a SNP near exon 1 was observed, leading to the testing of additional SNPs in the region. After identifying an insertion-deletion mutation, the remaining 92 families were screened for genomic rearrangements in PRPF31 with multiplex ligation-dependent probe amplification (MLPA). RESULTS: Five unique rearrangements were identified in the 93 families tested. In the large family used for linkage exclusion testing, an insertion-deletion was found that disrupts exon 1. The other four mutations identified in the cohort were deletions, ranging from 5 kb to greater than 45 kb. Two of the large deletions encompass all PRPF31 as well as several adjacent genes. The two smaller deletions involve either 5 or 10 completely deleted exons. CONCLUSIONS: In an earlier long-term study of 200 families with adRP, disease-causing mutations were identified in 53% of the families. Mutation-testing by sequencing missed large-scale genomic rearrangements such as insertions or deletions. MLPA was used to identify genomic rearrangements in PRPF31 in five families, suggesting a frequency of approximately 2.5%. Mutations in PRPF31 now account for 8% of this adRP cohort.
Adolescent↗
Phenotypic characterization of a large family with RP10 autosomal-dominant retinitis pigmentosa: an Asp226Asn mutation in the IMPDH1 gene.
PURPOSE: To evaluate the clinical features associated with the RP10 form of autosomal-dominant retinitis pigmentosa in 11 affected members of various ages from one family with a defined IMPDH1 mutation (Asp226Asn). DESIGN: Prospective, observational case series. METHODS: Visual function assessment included visual acuity, color vision, visual field, dark adaptometry, full-field electroretinography (ffERG), and multifocal electroretinography (mfERG). Ophthalmologic examinations, fundus photography, and optical coherence tomographic scans were also performed. Blood samples were obtained to screen for basic immune function. RESULTS: Visual acuity was slightly reduced in the teenage years and substantially reduced in association with cystoid macular edema (CME) at all ages. Color defects were observed in three patients (one teen, two adults). Dark-adapted thresholds were elevated. Visual fields were markedly constricted by age 40 (<or=20 degrees). Rod and cone a-wave and b-wave ffERG responses were small or nondetectable by age 20, with greater rod than cone loss at all ages. The normal to significantly delayed ffERG cone b-wave implicit times in different patients were explained by their mfERG implicit times from the central retina. The amplification factors (log S) and recovery kinetics derived from the full-field rod a-waves were normal. Optical coherence tomography revealed subretinal fluid accumulation in the majority of eyes. Cystoid macular edema was diagnosed in four patients. No unusual immunologic findings were noted. CONCLUSIONS: The Asp226Asn mutation is associated with a severe, early-onset form of retinal degeneration in members of this family.
Adolescent↗
The Iroquois homeobox gene, Irx5, is required for retinal cone bipolar cell development.
In the mouse retina, at least ten distinct types of bipolar interneurons are involved in the transmission of visual signals from photoreceptors to ganglion cells. How bipolar interneuron diversity is generated during retinal development is poorly understood. Here, we show that Irx5, a member of the Iroquois homeobox gene family, is expressed in developing bipolar cells starting at postnatal day 5 and is localized to a subset of cone bipolar cells in the mature mouse retina. In Irx5-deficient mice, defects were observed in the expression of some, but not all, immunohistological markers that define mature Type 2 and Type 3 OFF cone bipolar cells, indicating a role for Irx5 in bipolar cell differentiation. The differentiation of these two bipolar cell types has previously been shown to require the homeodomain-CVC transcription factor, Vsx1. However, the defects observed in Irx5-deficient retinas do not coincide with a reduction of Vsx1 expression, and conversely, the expression of Irx5 in cone bipolar cells does not require the presence of a functional Vsx1 allele. These results indicate that there are at least two distinct genetic pathways (Irx5-dependent and Vsx1-dependent) regulating the development of Type 2 and Type 3 cone bipolar cells.
Animals↗
Functional characterization of mouse RDH11 as a retinol dehydrogenase involved in dark adaptation in vivo.
We previously cloned mouse RDH11 (mRDH11) as a gene regulated by the transcription factor sterol regulatory element-binding proteins and showed that it is a retinol dehydrogenase expressed in non-ocular tissues such as the liver and testis and in the retina (Kasus-Jacobi, A., Ou, J., Bashmakov, Y. K., Shelton, J. M., Richardson, J. A., Goldstein, J. L., and Brown, M. S. (2003) J. Biol. Chem. 278, 32380-32389). It was proposed to function in the recycling of the visual chromophore 11-cis-retinal after photoisomerization by a bleaching light, a pathway referred to as the visual cycle. In this work, we describe our studies on the ocular function of mRDH11. We created a knockout mouse by replacing the mrdh11 coding sequence with the lacZ reporter gene for expression profiling. 5-Bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) staining demonstrated active transcription of this gene in photoreceptor cells. We show by immunoblot analysis that mRDH11 is associated with retinal membranes purified from a non-outer segment fraction of the retina. No obvious retinal defect was found during development and aging of RDH11-deficient mice. The functional consequences of mRDH11 disruption were investigated by electroretinography. Dark adaptation was delayed by a factor of 2.5-3 compared with wild-type mice. However, the kinetics of 11-cis-retinal recycling during dark adaptation was not affected, suggesting that mRDH11 is not involved in the visual cycle. We propose that mRDH11 disruption affects retinoid metabolism in photoreceptor inner segments and delays the kinetics of dark adaptation through modulation of calcium homeostasis.
Aging↗
Visual maturation of term infants fed long-chain polyunsaturated fatty acid-supplemented or control formula for 12 mo.
BACKGROUND: Several studies found a benefit of long-chain polyunsaturated fatty acid (LCP) supplementation for visual or mental development, but others found no benefit. Likely contributors to differences among studies are the amount of LCP supplementation, functional outcomes, and sample size. OBJECTIVE: We evaluated LCP supplementation in amounts typical for human milk (based on local and worldwide surveys) in a large cohort of infants by using sweep visual evoked potential (VEP) acuity as the functional outcome. DESIGN: The study was a double-masked, randomized, controlled clinical trial in 103 term infants. By age 5 d, infants were randomly assigned to receive either formula with no docosahexaenoic acid (DHA) or arachidonic acid (ARA) or formula supplemented with DHA and ARA as 0.36% and 0.72%, respectively, of total fatty acids. Sweep VEP acuity was the primary outcome. Random dot stereoacuity, blood lipid profile, growth, and tolerance were secondary outcomes. RESULTS: VEP acuity in the LCP-supplemented group was significantly better than that in the control group at ages 6, 17, 26, and 52 wk. Stereoacuity in the LCP-supplemented group was significantly better than that in the control group at age 17 wk but not at ages 39 and 52 wk. By ages 17 and 39 wk, the red blood cell DHA concentration in the LCP-supplemented group was more than double and more than triple, respectively, that in the control group. Growth of infants fed LCP-supplemented and control formulas did not differ significantly, and both diets were well tolerated. CONCLUSION: LCP supplementation of term infant formula during the first year of life yields clear differences in visual function and in total red blood cell lipid composition.
Arachidonic Acid↗
Outcome measures and their application in clinical trials for retinal degenerative diseases: outline, review, and perspective.
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Clinical Trials as Topic↗
A randomized placebo-controlled clinical trial of docosahexaenoic acid (DHA) supplementation for X-linked retinitis pigmentosa.
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Dietary Supplements↗
Retinal disease in mice lacking hypoxia-inducible transcription factor-2alpha.
PURPOSE: To characterize ocular disease in HIF-2alpha-null mice. METHODS: Histologic, electroretinographic (ERG), and molecular studies were performed on samples obtained from age- and gender-matched HIF-2alpha-null (HIF-2alpha-KO), HIF-2alpha-heterozygous (HIF-2alpha-HET), and wild-type (WT) littermate mice. RESULTS: HIF-2alpha-KO mice exhibited marked thinning of the retina and abnormal retinal vasculature. The pathologic changes in HIF-2alpha-KO mice were associated with a virtual absence of postreceptor function. The expression of a surrogate marker for HIF-2alpha mRNA localized to vascular endothelial, amacrine, and retinal pigment epithelial (RPE) cells. Several HIF-2alpha target genes involved in angiogenesis, retinal protection, and stress responses have altered expression patterns in HIF-2alpha-KO retinas. CONCLUSIONS: HIF-2alpha-KO mice exhibit marked retinopathy consistent with complete loss of vision by 1 month of age. Impaired HIF-2alpha signaling in HIF-2alpha-KO mice likely produces functional deficits in cell types in which HIF-2alpha normally is expressed, ultimately resulting in retinopathy. Future studies will address whether the molecular abnormalities described in this study are directly responsible for the retinal disease in HIF-2alpha-KO mice.
Animals↗
Control of late off-center cone bipolar cell differentiation and visual signaling by the homeobox gene Vsx1.
Retinal bipolar cells are interneurons that transmit visual signals from photoreceptors to ganglion cells. Although the visual pathways mediated by bipolar cells have been well characterized, the genes that regulate their development and function are largely unknown. To determine the role in bipolar cell development of the homeobox gene Vsx1, whose retinal expression is restricted to a major subset of differentiating and mature cone bipolar (CB) cells, we targeted the gene in mice. Bipolar cell fate was not altered in the absence of Vsx1 function, because the pan-bipolar markers Chx10 and Ret-B1 continued to be expressed in inner nuclear layer neurons labeled by the Vsx1-targeting reporter gene, tauLacZ. The specification, number, and gross morphology of the subset of on-center and off-center (OFF)-CB cells defined by tauLacZ expression from the Vsx1 locus were also normal in Vsx1(tauLacZ)/Vsx1(tauLacZ) mice. However, the terminal differentiation of OFF-CB cells in the retina of Vsx1(tauLacZ)/Vsx1(tauLacZ) mice was incomplete, as demonstrated by a substantial reduction in the expression of at least four markers (recoverin, NK3R, Neto1, and CaB5) for these interneurons. These molecular abnormalities were associated with defects in retinal function and documented by electroretinography and in vitro ganglion cell recordings specific to cone visual signaling. In particular, there was a general reduction in the light-mediated activity of OFF, but not on-center, ganglion cells. Thus, Vsx1 is required for the late differentiation and function of OFF-CB cells and is associated with a heritable OFF visual pathway-specific retinal defect.
Animals↗
The phenotype of Leber congenital amaurosis in patients with AIPL1 mutations.
OBJECTIVES: To describe the phenotype of Leber congenital amaurosis (LCA) in 26 probands with mutations in aryl hydrocarbon receptor interacting protein-like 1 protein (AIPL1) and compare it with phenotypes of other LCA-related genes. To describe the electroretinogram (ERG) in heterozygote carriers. METHODS: Patients with AIPL1-related LCA were identified in a cohort of 303 patients with LCA by polymerase chain reaction single-strand confirmational polymorphism mutation screening and/or direct sequencing. Phenotypic characterization included clinical and ERG evaluation. Seven heterozygous carrier parents also underwent ERG testing. RESULTS: Seventeen homozygotes and 9 compound heterozygotes were identified. The W278X mutation was most frequent (48% of alleles). Visual acuities ranged from light perception to 20/400. Variable retinal appearances, ranging from near normal to varying degrees of chorioretinal atrophy and intraretinal pigment migration, were noted. Atrophic and/or pigmentary macular changes were present in 16 (80%) of 20 probands. Keratoconus and cataracts were identified in 5 (26%) of 19 patients, all of whom were homozygotes. The ERG of a parent heterozygote carrier revealed significantly reduced rod function, while ERGs for 6 other carrier parents were normal. CONCLUSIONS: The phenotype of LCA in patients with AIPL1 mutations is relatively severe, with a maculopathy in most patients and keratoconus and cataract in a large subset. Rod ERG abnormalities may be present in heterozygous carriers of AIPL1 mutations. CLINICAL RELEVANCE: Understanding and recognizing the phenotype of LCA may help in defining the course and severity of the disease. Identifying the gene defect is the first step in preparation for therapy since molecular diagnosis in LCA will mandate the choice of treatment.
Adaptor Proteins, Signal Transducing↗
A randomized, placebo-controlled clinical trial of docosahexaenoic acid supplementation for X-linked retinitis pigmentosa.
PURPOSE: Low docosahexaenoic acid (DHA) in X-linked retinitis pigmentosa (XLRP) may influence retinal function. The goals of this study were to elevate blood DHA levels and determine the effect on the rate of disease progression. DESIGN: In a 4-year prospective randomized clinical trial, male patients with XLRP (mean age = 16 years; range = 4-38 years) received DHA (400 mg/d; n = 23; +DHA group) or placebo (n = 21) capsules. METHODS: Red blood cell (RBC)-DHA concentrations were assessed every 6 months. Full-field cone electroretinograms (ERGs; the primary outcome measure), visual acuity, dark-adaptation, visual fields, rod ERGs, and fundus photos were recorded annually. RESULTS: In the +DHA group, RBC-DHA increased 2.5-fold over placebo levels (70 vs 28 mg DHA/l). Repeated measures analysis of variance for cone ERG showed a significant main effect of year (P <.0001) but not of group (P =.16). Preservation of cone ERG function correlated with RBC-DHA (P =.018), and there was less change in fundus appearance in the +DHA group (P =.04). Neither visual acuity nor visual fields were changed. In subset analysis, DHA supplementation was beneficial in reducing rod ERG functional loss in patients aged <12 years (P =.040) and preserving cone ERG function in patients > or =12 years (P =.038). CONCLUSIONS: Although DHA-supplemented patients had significantly elevated mean RBC-DHA levels, the rate of cone ERG functional loss was not significantly different between groups. Supplemental analyses provided evidence for a DHA benefit and a direction for subsequent investigations.
Adolescent↗
Dark adaptation of rod photoreceptors in normal subjects, and in patients with Stargardt disease and an ABCA4 mutation.
PURPOSE: Psychophysical and electroretinographic (ERG) studies indicate that patients with Stargardt disease exhibit abnormally slow rod dark adaptation after illumination that bleaches a substantial fraction of rhodopsin. However, relatively little information is available concerning rod recovery in this disease after weaker adapting (i.e., conditioning) light. With the use of a paired-flash ERG method, properties of the derived rod response to a low-bleach (<1%) but rod-saturating conditioning flash were investigated in seven normal subjects and in five Stargardt patients with identified sequence variations in the ABCA4 gene. METHODS: In the first of two experiments, the interval between a fixed conditioning flash (67 or 670 scotopic cd s m(-2)) and a bright probe flash of fixed strength was varied to determine the falling-phase kinetics of the derived rod response to the conditioning flash. In the second, the instantaneous amplitude-intensity function for the rod response at an intermediate stage of recovery from the conditioning flash was determined by presenting a test flash of various strengths at a fixed time after the conditioning flash, and a probe flash at 200 ms after the test flash. RESULTS: The maximum peak amplitude of the dark-adapted, rod-mediated a-wave determined in Stargardt patients (211 +/- 87 microV) was on average lower than that determined in normal subjects (325 +/- 91 microV; P = 0.06). The derived rod response to the 670 scotopic cd s m(-2) conditioning flash determined in normal subjects and Stargardt patients exhibited a biphasic recovery, and the kinetics of the early stage of this recovery were similar in the two subject groups. For both normal subjects and patients, normalized amplitude-intensity functions describing the dark-adapted derived rod response exhibited half-saturation at approximately 1.5 log scotopic troland second. In both groups, the normalized amplitude-intensity function determined at approximately 2 seconds after the 67 scotopic cd s m(-2) conditioning flash and at approximately 9 seconds after the 670 scotopic cd s m(-2) conditioning flash exhibited an average desensitization (i.e., an increase of test flash strength at half-saturation) of approximately 0.5 to 0.6 log unit relative to that determined under dark-adapted conditions. CONCLUSIONS: The results indicate that, despite a reduction in the average dark-adapted maximum a-wave amplitude in the Stargardt/ABCA4 patients, the early-stage recovery kinetics of the derived rod response to a low-bleaching conditioning flash as well as the lingering rod desensitization produced by such a flash are similar to those determined in normal subjects.
ATP-Binding Cassette Transporters↗
Surrogate electroretinographic markers for assessing therapeutic efficacy in the retina.
Visual acuity remains the primary surrogate marker for clinical trials in ophthalmology (and the primary outcome for most US Food and Drug Administration applications) due to its long history, ease of measurement and clear relationship to clinically meaningful characteristics of daily life. However, treatment trials are being planned for diseases that are currently untreatable where visual acuity may not be the most appropriate outcome measure. Specialized electroretinographic tests can be powerful surrogate markers in such trials. The selection of outcome measures and surrogate markers depends in part on whether the goal is to preserve remaining vision in a progressive retinal degeneration or to improve vision in an eye that has already undergone extensive degeneration. Among the electroretinographic tests available are those involving the whole retina (full-field electroretinographic), the posterior pole (pattern electroretinographic) or focal areas within the macula (multifocal electroretinographic). The advantages and disadvantages of each will be discussed along with selected applications of each test to a specific category of disease.
Adult↗
Characterization of RP1L1, a highly polymorphic paralog of the retinitis pigmentosa 1 (RP1) gene.
PURPOSE: To determine the full-length sequence of a gene with similarity to RP1 and to screen for mutations in this newly characterized gene, named retinitis pigmentosa 1-like 1(RP1L1). Since mutations in the RP1 gene cause autosomal dominant retinitis pigmentosa, it is possible that mutations in RP1's most sequence similar relative, RP1L1, may also be a cause of inherited retinal degeneration. METHODS: A combination of cDNA clone sequencing, RACE, and database analysis were used to determine the RP1L1 mRNA sequence and its genomic organization. PCR analysis, semi-quantitative RT PCR, and in situ hybridization were used to determine the expression pattern of RP1L1. Single-strand conformational analysis and automated sequencing were used to screen probands from 60 adRP families for potential disease-causing mutations in RP1L1. RESULTS: The human RP1L1 gene is encoded in 4 exons, which span 50 kb on chromosome 8p. The length of the RP1L1 mRNA is large, over 7 kb, but its exact length is variable between individuals due to the presence of several length polymorphisms, including a 48 bp repeat. RP1L1 encodes a protein with a minimal length of 2,400 amino acids and a predicted weight of 252 kDa. Expression of RP1L1 is limited to the retina and appears to be specific to photoreceptors. Mutational analysis of 60 autosomal dominant retinitis pigmentosa probands revealed the presence of 38 sequence substitutions in RP1L1. Over half of these substitutions result in alteration of the RP1L1 protein, but none of these substitutions appear to be pathogenic. CONCLUSIONS: The RP1L1 gene encodes a large, highly polymorphic, retinal-specific protein. No RP1L1 disease-causing mutations were identified in any of the samples tested, making it unlikely that mutations in RP1L1 are a frequent cause of autosomal dominant retinitis pigmentosa. Additional experiments will be needed to determine if mutations in RP1L1 cause other forms of inherited retinal degeneration.
Amino Acid Sequence↗