Retinitis Pigmentosa Families Research Articles

Next-Generation Sequencing–Based Molecular Diagnosis of a Chinese Patient Cohort With Autosomal Recessive Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a highly heterogeneous genetic disease; therefore, an accurate molecular diagnosis is essential for appropriate disease treatment and family planning. The prevalence of RP in China had been reported at 1 in 3800, resulting in an estimated total of 340,000 Chinese RP patients. However, genetic studies of Chinese RP patients have been very limited. To date, no comprehensive molecular diagnosis has been done for Chinese RP patients. With the emergence of next-generation sequencing (NGS), comprehensive molecular diagnosis of RP is now within reach. The purpose of this study was to perform the first NGS-based comprehensive molecular diagnosis for Chinese RP patients. Thirty-one well-characterized autosomal recessive RP (arRP) families were recruited. For each family, the DNA sample from one affected member was sequenced using our custom capture panel, which includes 163 retinal disease genes. Variants were called, filtered, and annotated by our in-house automatic pipeline. Twelve arRP families were successfully molecular diagnosed, achieving a diagnostic rate of approximately 40%. Interestingly, approximately 63% of the pathogenic mutations we identified are novel, which is higher than that observed in a similar study on European descent (45%). Moreover, the clinical diagnoses of two families were refined based on the pathogenic mutations identified in the patients. We conclude that comprehensive molecular diagnosis can be vital for an accurate clinical diagnosis of RP. Applying this tool on patients from different ethnic groups is essential for enhancing our knowledge of the global spectrum of RP disease-causing mutations.

Detection and analysis of the Rhodopsin gene in a consanguineous Chinese Han autosomal dominant retinitis pigmentosa family

Background Rhodopsin (RHO) gene is the most common disease gene for autosomal dominant retinitis pigmentosa (adRP),one of the main pathogenesis is that misfolded mutant RHO proteins accumulate in the endoplasmic reticulum and cause endoplasmic reticulum stress (ERS).Objective This study aimed to determine the genetic basis for a consanguineous Chinese Han adRP family.Methods This study procedure complied with Helsinki Declaration.All participants in the family were investigated under the informed consent.Regular ocular examination was performed on the patients in this family.Next-generation sequencing (NGS) was carried out to screen the mutations in 189 genes associated with hereditary retinal diseases (HRDs).After being analyzed and filtered,variations detected by NGS were validated by Sanger sequencing and evaluating of pathogenicity.The wild-type RHOWT and mutant RHOP53Rwere cloned into the vector pEGFP-N1.Then the two plasmids were transfected into adult retinal pigmentosa epithelium cell line(ARPE19) and human embryo kidney 293 line (HEK293) to observe the location of rhodopsin-GFP fusion protein in cells,and the expression of ERS related protein XBP1 in the cells was detected by quantitative-PCR and Western blot.Results This family included 5 generations with the typical adRP characteristics.Genetic analysis identified a heterozygous variation,p.P53R in RHO gene,which was fully cosegregated in the family.Wild-type RHOWT-GFP fusion proteins showed the green fluorescence on the endoplasmic reticulum and cytomembrane,but the misfolded mutant RHO-GFP fusion protein gathered only in endoplasmic reticulum.Compared to wild-type RHOWT,the XBP1 was activated and increased by (1.28 ±0.09) fold.The introns of 26 bases in XBP1 mRNA were removed in the HEK293 cells with mutant RHO-GFP fusion protein,and the expression of XBP1 was stronger in the HEK293 cells with mutant RHO-GFP than that in HEK293 cells with wild type RHO-GFP and cells with blank pEGFP-N1 plasmid.Conclusions Heterozygous variant RHO p.P53R is very likely the pathogenical mutation in the adRP family.The RHOP53R mutant rhodopsin protein can not be delivery effectively from the endoplasmic reticulum to the cell membrane,and these proteins accumulate in the endoplasmic reticulum,which causes ERS. Key words: Autosomal dominant retinitis pigmentosa; Rhodopsin; Next-generation sequencing; Endoplasmic reticulum stress

Rhodopsin p.N78I dominant mutation causing sectorial retinitis pigmentosa in a pedigree with intrafamilial clinical heterogeneity

ObjectiveThe purpose of this study was to determine the molecular basis of retinitis pigmentosa (RP) in a 4 affected sib-family segregating this retinal phenotype. MethodsAffected sibs underwent complete ophthalmologic examination including funduscopic inspection, electroretinogram, fluorescein angiography, visual field measurement, and optical coherence tomography. Both parents were deceased after their sixties and were reported with no visual handicap. Molecular analysis included direct nucleotide sequencing of the rhodopsin gene (RHO), at chromosome 3q21–q24, in DNA from a total of 4 affected sibs. A total of 200 ethnically matched alleles were included as mutation controls. ResultsSector RP was clinically documented in this family. Wide phenotypic variability was observed with visual acuities ranging from 20/20 to 20/200 and variable funduscopic appearance. Molecular analysis disclosed a c.233A>T mutation at RHO exon 1, predicting a missense p.N78I substitution. ConclusionsEven though RP can be caused by mutations in a variety of genes, the RHO gene was chosen to be investigated in this RP family since it has been previously associated to sector disease. This case exemplifies the value of guiding RP molecular analysis based on funduscopic features.

Analysis of clinical phenotype and mode of inheritance in retinitis pigmentosa patients with consanguineous marriage

To analyse the mode of inheritance and clinical characteristics of retinitis pigmentosa (RP) patients with consanguineous marriage. RP patients were recruited for this study in Ningxia Eye Hospital from September 2009 to July 2011. All patients received complete ophthalmic examination. The mode of inheritance were determined based on family history and marriage history. Clinical features were characterized by complete ophthalmic examinations including visual acuity, macular OCT, visual field and electroretinogram (ERG). A total of 143 individuals with RP (33 families) were recruited. Based on analysis of family history and marriage history, 20 RP families (23 patients) had consanguineous marriage history accounted for 60.6% RP families (16.1% RP patients). There were 4 patients (from 4 families) diagnosed as Usher syndrome. In 20 RP families with consanguineous marriage history, 7 families (35.0%) were Hui ethnicity and 13 families (65%) were Han ethnicity. The marriages of 15 families were between first cousins and 3 families were between second cousins, only 2 families were between half cousins matrimony. Of 23 RP patients, 12 were males and 11 were females. The average age of onset was 11.4 ± 6.8 years and the average age of recruitment was (32.0 ± 13.5) years. The best-corrected visual acuity was less than 0.6 in 78.2% patients. According to the features of the fundus, 13 patients were classical retinitis pigmentosa and 10 patients were retinitis pigmentosa sine pigmento. Visual field examination showed that all patients had varying degrees of peripheral visual field defect. Retinal neuroepithelial layer of macular and peripheral retina became thinner and retinal photoreceptors were disappeared. The average thickness of macular fovea was (186.1 ± 78.7) µm on right eyes and (187.4 ± 76.3) µm on left eyes. The incidence of RP with consanguineous marriages was high in Ningxia Region. The mode of inheritance of RP patients with consanguinity is autosomal recessive. The common marriage pattern of consanguinity is between first cousins. The age of onset is early and the ocular fundus changes of some patients are atypical, this should be paid attention clinically.

Mutations in C8orf37, Encoding a Ciliary Protein, are Associated with Autosomal-Recessive Retinal Dystrophies with Early Macular Involvement

Cone-rod dystrophy (CRD) and retinitis pigmentosa (RP) are clinically and genetically overlapping heterogeneous retinal dystrophies. By using homozygosity mapping in an individual with autosomal-recessive (ar) RP from a consanguineous family, we identified three sizeable homozygous regions, together encompassing 46 Mb. Next-generation sequencing of all exons, flanking intron sequences, microRNAs, and other highly conserved genomic elements in these three regions revealed a homozygous nonsense mutation (c.497T>A [p.Leu166(∗)]) in C8orf37, located on chromosome 8q22.1. This mutation was not present in 150 ethnically matched control individuals, single-nucleotide polymorphism databases, or the 1000 Genomes database. Immunohistochemical studies revealed C8orf37 localization at the base of the primary cilium of human retinal pigment epithelium cells and at the base of connecting cilia of mouse photoreceptors. C8orf37 sequence analysis of individuals who had retinal dystrophy and carried conspicuously large homozygous regions encompassing C8orf37 revealed a homozygous splice-site mutation (c.156-2A>G) in two siblings of a consanguineous family and homozygous missense mutations (c.529C>T [p.Arg177Trp]; c.545A>G [p.Gln182Arg]) in siblings of two other consanguineous families. The missense mutations affect highly conserved amino acids, and in silico analyses predicted that both variants are probably pathogenic. Clinical assessment revealed CRD in four individuals and RP with early macular involvement in two individuals. The two CRD siblings with the c.156-2A>G mutation also showed unilateral postaxial polydactyly. These results underline the importance of disrupted ciliary processes in the pathogenesis of retinal dystrophies.

Homozygous Mutation in MERTK Causes Severe Autosomal Recessive Retinitis Pigmentosa

Gene identification in retinitis pigmentosa is a prerequisite to future therapies. Accordingly, autosomal recessive retinitis pigmentosa families were genotyped to search for causative mutations. Members of a consanguineous Moroccan family had standard ophthalmologic examination, optical coherence tomography-3 scan, autofluorescence testing, and electroretinogram. Their DNA was genotyped with the 250K SNP microchip (Affymetrix) and homozygosity mapping was done. MERTK exons were polymerase chain reaction amplified and sequenced. Two sisters and one brother out of 6 siblings had rod cone dystrophy type of retinitis pigmentosa. Salient features were night blindness starting in early infancy, dot-like whitish deposits in fovea and macula with corresponding autofluorescent dots in youngest patients, decreased visual acuity, and cone responses higher than rod responses at electroretinogram. The patients were homozygous in regions from chromosomes 2 and 8, but only that of chromosome 2 was inherited from a common ancestor. Sequencing of the MERTK gene belonging to the chromosome 2 region showed that the 3 affected patients carried a novel homozygous mutation in exon 17, c.2323C>T, leading to p.Arg775X, while their unaffected brothers and sister, parents, and paternal grandfather were heterozygous. MERTK mutations lead to severe retinitis pigmentosa with discrete dot-like autofluorescent deposits at early stages, which are a hallmark of this MERTK-specific dystrophy.

Autosomal Dominant Retinitis Pigmentosa with Intrafamilial Variability and Incomplete Penetrance in Two Families Carrying Mutations inPRPF8

The aim of this study was to report detailed genotype/phenotype correlation in two British autosomal dominant retinitis pigmentosa (adRP) families with recently described mutations in PRPF8. Ten affected members from the two families (excluded for PRPF31 mutations) were assessed clinically. Seven subjects had fundus photography; some had electrophysiology, autofluorescence imaging, and visual field testing. Linkage analysis was performed from genomic DNA in one family. RNA was extracted from lymphocytes of the proband from both families, reverse transcribed into cDNA and subsequently screened for mutations in PRPF8. Segregation of mutations in each family was tested by direct genomic sequencing of the specific exons carrying the mutation. All affected members complained of nyctalopia with variable age of onset. In the first family, there was marked variation in the clinical phenotype among affected individuals ranging from severe rod-cone dystrophy to a 67-year-old patient with a normal retinal appearance and mild rod dysfunction on scotopic electroretinography (ERG). The second family demonstrated similar variability and a history of a nonpenetrant individual. Linkage analysis in the first family showed strong evidence for linkage to markers on chromosome 17p implicating PRPF8 as a candidate gene. A c.6353 C>T change causing a nonconservative missense mutation p.S2118F was found in exon 38 of PRPF8 by direct sequencing of the cDNA. The mutation c.6930G>C (p.R2310S) was found in the second family. This is the first report of marked intrafamilial variability associated with mutations in the PRPF8 gene, including incomplete penetrance. PRPF8 mutations should be suspected in patients with adRP and variable expressivity.

Combining gene mapping and phenotype assessment for fast mutation finding in non-consanguineous autosomal recessive retinitis pigmentosa families

Among inherited retinal dystrophies, autosomal recessive retinitis pigmentosa (arRP) is the most genetically heterogenous condition with 32 genes currently known that account for ~60 % of patients. Molecular diagnosis thus requires the tedious systematic sequencing of 506 exons. To rapidly identify the causative mutations, we devised a strategy that combines gene mapping and phenotype assessment in small non-consanguineous families. Two unrelated sibships with arRP had whole-genome scan using SNP microchips. Chromosomal regions were selected by calculating a score based on SNP coverage and genotype identity of affected patients. Candidate genes from the regions with the highest scores were then selected based on phenotype concordance of affected patients with previously described phenotype for each candidate gene. For families RP127 and RP1459, 33 and 40 chromosomal regions showed possible linkage, respectively. By comparing the scores with the phenotypes, we ended with one best candidate gene for each family, namely tubby-like protein 1 (TULP1) and C2ORF71 for RP127 and RP1459, respectively. We found that RP127 patients were compound heterozygous for two novel TULP1 mutations, p.Arg311Gln and p.Arg342Gln, and that RP1459 patients were compound heterozygous for two novel C2ORF71 mutations, p.Leu777PhefsX34 and p.Leu777AsnfsX28. Phenotype assessment showed that TULP1 patients had severe early onset arRP and that C2ORF71 patients had a cone rod dystrophy type of arRP. Only two affected individuals in each sibship were sufficient to lead to mutation identification by screening the best candidate gene selected by a combination of gene mapping and phenotype characterization.

Whole-Exome Sequencing Links a Variant in DHDDS to Retinitis Pigmentosa

Increasingly, mutations in genes causing Mendelian disease will be supported by individual and small families only; however, exome sequencing studies have thus far focused on syndromic phenotypes characterized by low locus heterogeneity. In contrast, retinitis pigmentosa (RP) is caused by >50 known genes, which still explain only half of the clinical cases. In a single, one-generation, nonsyndromic RP family, we have identified a gene, dehydrodolichol diphosphate synthase (DHDDS), demonstrating the power of combining whole-exome sequencing with rapid invivo studies. DHDDS is a highly conserved essential enzyme for dolichol synthesis, permitting global N-linked glycosylation. Zebrafish studies showed virtually identical photoreceptor defects as observed with N-linked glycosylation-interfering mutations in the light-sensing protein rhodopsin. The identified Lys42Glu variant likely arose from an ancestral founder, because eight of the nine identified alleles in 27,174 control chromosomes were of confirmed Ashkenazi Jewish ethnicity. These findings demonstrate the power of exome sequencing linked to functional studies when faced with challenging study designs and, importantly, link RP to the pathways of N-linked glycosylation, which promise new avenues for therapeutic interventions.

Evidence for a Novel Autosomal Dominant Retinitis Pigmentosa Linked to Chromosome 1p22.1-q12 in a Chinese Family

Purpose: To identify the causative genetic locus in a Chinese autosomal dominant retinitis pigmentosa (adRP) family that contained seven affected members in three generations.Methods: After clinical diagnosis and exclusion of all mapped genes and loci, the SLINK program was used to simulate the maximum logarithm of the likelihood ratio (LOD) score for a linkage study in this small family. A genome-wide scan was performed using microsatellite markers at 10 cM intervals. Two-point and multipoint LOD scores were calculated, and haplotypes were constructed.Results: The H11 family clinical presentation included an early onset of night blindness, a progressive loss of the peripheral visual field, typical retinitis pigmentosa (RP) fundus changes, and a cataract complication. A maximum two-point LOD score of 2.54 (θ = 0) was found at markers D1S2739, D1S457, D1S187, D1S189, and D1S305, and multipoint linkage analysis yielded a maximum LOD score of 2.54 for marker D1S187. These LOD scores were the closest to the maximum simulated LOD score. Haplotype analysis revealed that this form of adRP segregates with a 38.25 cM region that spanned 50 Mb on chromosome 1p22.1-q12.Conclusions: Although this locus overlaps the RP19 locus caused by mutations in ABCA4 and the RP32 locus, both are inherited in an autosomal recessive mode rather than the autosomal dominant mode of inheritance found in the H11 family. The identification of this potential new locus for adRP further confirms the high level of heterogeneity for RP.

Coarse-to-fine or fine-to-coarse?

To identify the disease-causing gene in a four-generation Chinese family affected with retinitis pigmentosa (RP). Linkage analysis was performed with a panel of microsatellite markers flanking the candidate genetic loci of RP. These loci included 38 known RP genes. The complete coding region and exon-intron boundaries of Usher syndrome 2A (USH2A) were sequenced with the proband DNA to screen the disease-causing gene mutation. Restriction fragment length polymorphism (RFLP) analysis and direct DNA sequence analysis were done to demonstrate co-segregation of the USH2A mutations with the family disease. One hundred normal controls were used without the mutations. The disease-causing gene in this Chinese family was linked to the USH2A locus on chromosome 1q41. Direct DNA sequence analysis of USH2A identified two novel mutations in the patients: one missense mutation p.G1734R in exon 26 and a splice site mutation, IVS32+1G>A, which was found in the donor site of intron 32 of USH2A. Neither the p.G1734R nor the IVS32+1G>A mutation was found in the unaffected family members or the 100 normal controls. One patient with a homozygous mutation displayed only RP symptoms until now, while three patients with compound heterozygous mutations in the family of study showed both RP and hearing impairment. This study identified two novel mutations: p.G1734R and IVS32+1G>A of USH2A in a four-generation Chinese RP family. In this study, the heterozygous mutation and the homozygous mutation in USH2A may cause Usher syndrome Type II or RP, respectively. These two mutations expand the mutant spectrum of USH2A.

Novel PRPF31 and PRPH2 Mutations and Co-occurrence of PRPF31 and RHO Mutations in Chinese Patients With Retinitis Pigmentosa

To screen mutations in the PRPF31, RHO, and PRPH2 genes in Chinese patients with retinitis pigmentosa (RP). Patients with RP were recruited from Retina Hong Kong. All the exons of the PRPF31, RHO, and PRPH2 genes were amplified and screened for mutations using single-stranded conformation polymorphism analysis followed by DNA sequencing. Frequencies of sequence changes were determined in patients and controls. In 76 patients from 54 families, 3 pathogenic mutations and 32 nonpathogenic sequence changes were identified. One family with autosomal dominant RP was found to harbor a novel truncating PRPF31 mutation (p.Phe262SerfsX59) and a known missense RHO mutation (p.Pro347Leu), and 1 affected woman was heterozygous for both mutations. One simplex RP case was caused by a novel truncating PRPH2 mutation (p.Ala78LeufsX99). Thirteen of the 32 nonpathogenic sequence changes were novel and were found in low frequencies in patients with RP and controls. Mutations in PRPF31, RHO, and PRPH2 were found in low frequencies (1 of 9 autosomal dominant RP families) in Chinese patients, and the PRPF31 and PRPH2 truncating mutations were novel. A search for a common cause for RP in Chinese patients is needed. The co-occurrence of 2 different gene mutations may modify the phenotype severity.

Identification of novel mutations in X-linked retinitis pigmentosa families and implications for diagnostic testing.

The goal of this study was to identify mutations in X-chromosomal genes associated with retinitis pigmentosa (RP) in patients from Germany, The Netherlands, Denmark, and Switzerland. In addition to all coding exons of RP2, exons 1 through 15, 9a, ORF15, 15a and 15b of RPGR were screened for mutations. PCR products were amplified from genomic DNA extracted from blood samples and analyzed by direct sequencing. In one family with apparently dominant inheritance of RP, linkage analysis identified an interval on the X chromosome containing RPGR, and mutation screening revealed a pathogenic variant in this gene. Patients of this family were examined clinically and by X-inactivation studies. This study included 141 RP families with possible X-chromosomal inheritance. In total, we identified 46 families with pathogenic sequence alterations in RPGR and RP2, of which 17 mutations have not been described previously. Two of the novel mutations represent the most 3'-terminal pathogenic sequence variants in RPGR and RP2 reported to date. In exon ORF15 of RPGR, we found eight novel and 14 known mutations. All lead to a disruption of open reading frame. Of the families with suggested X-chromosomal inheritance, 35% showed mutations in ORF15. In addition, we found five novel mutations in other exons of RPGR and four in RP2. Deletions in ORF15 of RPGR were identified in three families in which female carriers showed variable manifestation of the phenotype. Furthermore, an ORF15 mutation was found in an RP patient who additionally carries a 6.4 kbp deletion downstream of the coding region of exon ORF15. We did not identify mutations in 39 sporadic male cases from Switzerland. RPGR mutations were confirmed to be the most frequent cause of RP in families with an X-chromosomal inheritance pattern. We propose a screening strategy to provide molecular diagnostics in these families.

Evaluation of the common variants of the ABCA4 gene in families with Stargardt disease and autosomal recessive retinitis pigmentosa

Stargardt disease (STGD) is one of the most common autosomal recessive retinal dystrophies with an estimated incidence of one in 10,000. It affects the central retina (macula). Retinitis pigmentosa (RP) comprises a large and exceptionally heterogeneous group of hereditary disorders of the retina. It is caused by the loss of photoreceptors. The condition is a degenerative disorder characterized by retinal pigment deposits and has an estimated incidence of one in 4,000. Although, to date, 45 known loci have been identified, none of them independently account for a substantial portion of RP. Recently, the photoreceptor cell-specific ATP-binding cassette transporter (ABCA4) gene was found to be mutated in patients with STGD as well as autosomal recessive RP. In order to further understand the contribution of this gene to the susceptibility to STGD and RP, we analyzed three unrelated STGD families and one autosomal recessive RP family specifically for the more common variants (A1038V, G1961E, 2588G-->C, R943Q or 2828G-->A) in the ABCA4 gene. Our analyses employing standard techniques such as polymerase chain reaction, restriction fragment length polymorphism, and direct DNA sequencing of amplified products were able to identify one common variant (R943Q) in all three STGD families but not in the RP family. All three affected STGD individuals, however, were heterozygous for this variation, and this alteration did not segregate with the disease and was also present in the normal controls. Similar analysis of other common variants revealed no pathogenic mutations in the STGD and RP families. It is likely that the variant identified in this study represents a rare polymorphism (non-pathogenic). Although, at present we cannot eliminate the possibility of this gene as a candidate gene, future extensive studies on this as well as other candidate genes may uncover the susceptibility gene for these recessive forms of the disorders in these families.

Identifying pathogenic genetic background of simplex or multiplex retinitis pigmentosa patients: a large scale mutation screening study

Background and purpose:More than half of the retinitis pigmentosa (RP) cases are genetically simplex or multiplex. To date, 37 causative genes of RP have been identified; however, the elucidation of...

Spectrum and Frequency of Mutations in IMPDH1 Associated with Autosomal Dominant Retinitis Pigmentosa and Leber Congenital Amaurosis

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. 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. 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. 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.

Comprehensive survey of mutations in RP2 and RPGR in patients affected with distinct retinal dystrophies: genotype–phenotype correlations and impact on genetic counseling

X-linked forms of retinitis pigmentosa (RP) (XLRP) account for 10 to 20% of families with RP and are mainly accounted for by mutations in the RP2 or RP GTPase regulator (RPGR) genes. We report the screening of these genes in a cohort of 127 French family comprising: 1) 93 familial cases of RP suggesting X-linked inheritance, including 48 out of 93 families with expression in females but no male to male transmission; 2) seven male sibships of RP; 3) 25 sporadic male cases of RP; and 4) two cone dystrophies (COD). A total of 5 out of the 93 RP families excluded linkage to the RP2 and RP3 loci and were removed form the cohort. A total of 14 RP2 mutations, 12 of which are novel, were identified in 14 out of 88 familial cases of RP and 1 out of 25 sporadic male case (4%). In 13 out of 14 of the familial cases, no expression of the disease was noted in females, while in 1 out of 14 families one woman developed RP in the third decade. A total of 42 RPGR mutations, 26 of which were novel, were identified in 80 families, including: 69 out of 88 familial cases (78.4%); 2 out of 7 male sibship (28.6%); 8 out of 25 sporadic male cases (32.0%); and 1 out of 2 COD. No expression of the disease was noted in females in 41 out of 69 familial cases (59.4%), while at least one severely affected woman was recognized in 28 out of 69 families (40.6%). The frequency of RP2 and RPGR mutations in familial cases of RP suggestive of X-linked transmission are in accordance to that reported elsewhere (RP2: 15.9% vs. 6-20%; RPGR: 78.4% vs. 55-90%). Interestingly, about 30% of male sporadic cases and 30% of male sibships of RP carried RP2 or RPGR mutations, confirming the pertinence of the genetic screening of XLRP genes in male patients affected with RP commencing in the first decade and leading to profound visual impairment before the age of 30 years.

A Two-stage Approach Identifies a Q344X Mutation in the Rhodopsin Gene of a Chinese Singaporean Family with Autosomal Dominant Retinitis Pigmentosa

Introduction: Retinitis pigmentosa (RP) is a group of hereditary retinal diseases in which photoreceptor cells degenerate. It is both clinically and genetically heterogenous. Using a two stage approach by combining linkage analysis with mutation detection, we have rapidly identified the gene locus and the mutation site of a Chinese Singaporean family with autosomal dominant RP. Materials and Methods: Three Chinese Singaporean families were tested. One family showed autosomal dominant inheritance pattern, while the other two could be recessive or sporadic. Twelve di-nucleotide markers tightly linked to 6 genes known to be responsible for either autosomal dominant or recessive RP were selected for linkage analysis. Cosegregation of marker and disease inheritance pattern permits identification of the target candidate gene. RFLP (restriction fragment length polymorphism) markers were added to confirm the linkage result prior to the detailed mutation detection study. Results: With this two-stage strategy, the autosomal dominant RP family showed the rhodopsin locus segregating concordantly with the disease. Mutation screening later identified a nonsense mutation 5261C>T in the last exon of rhodopsin gene. It predicted a Q344X changes at the C-terminus of the gene product, truncating it by 5 amino acids. Conclusion: This systematic approach facilitates molecular diagnosis of a genetically heterogenous disease like RP. This is the first report of an RP mutation in Singapore. This 5261C>T mutation has been reported in the Caucasian, but not the Chinese population. The relatively milder phenotype in this family showed similarity to the reported US family, indicating the correlation of mutation site to severity of disease regardless of ethnicity.

Novel RPGR mutations with distinct retinitis pigmentosa phenotypes in French-Canadian families

Purpose To characterize the molecular defects in two x-linked retinitis pigmentosa (RP) families. We hypothesized that different RPGR mutations result in distinct RP phenotypes. Design Observational case series. Methods Fifteen members in family I and three members in family II were evaluated. Full ophthalmic evaluations were done. Linkage analyses were performed and likelihood of odds scores (LOD score) were calculated. For mutation analyses, we used dHPLC and automated sequencing. Results Two novel RPGR mutations were identified in the two families; a Glu 414 (2-bp del) frameshift mutation in family I and an IVS 2–1 (g to a) splice site mutation in family II. All male family members in family I were severely affected by RP but maintained central visual acuities until their 50s and did not develop a bull’s eye maculopathy. The female phenotype was highly variable. Some of the carriers exhibited a severe phenotype, one female displayed an asymmetric phenotype, and other carriers were asymptomatic. All members with the RPGR frameshift mutation exhibited rod-cone electroretinograms abnormalities, whereas five members had hearing loss. Male members of family II were severely affected, with early visual acuity loss, central scotomas, and bull’s eye maculopathy. The female family members were asymptomatic but displayed cone-rod electroretinograms changes. There was no hearing loss. Conclusions Different RPGR mutations lead to distinct RP phenotypes, with a highly variable inter- and intrafamilial phenotypic spectrum of disease that is associated with the type of mutation in RPGR and nonrandom X chromosome inactivation, respectively.

Identification of novel RP2 mutations in a subset of X-linked retinitis pigmentosa families and prediction of new domains.

X-linked Retinitis Pigmentosa (XLRP) shows a huge genetic heterogeneity with almost five distinct loci on the X chromosome. So far, only two XLRP genes have been identified, RPGR (or RP3) and RP2, being mutated in approximately 70% and 10% of the XLRP patients. Clinically there is no clearly significative difference between RP3 and RP2 phenotypes. In the attempt to assess the degree of involvement of the RP2 gene, we performed a complete mutation analysis in a cohort of patients and we identified five novel mutations in five different XLRP families. These mutations include three missense mutations, a splice site mutation, and a single base insertion, which, because of frameshift, anticipates a stop codon. Four mutations fall in RP2 exon 2 and one in exon 3. Evidence that such mutations are different from the 21 RP2 mutations described thus far suggests that a high mutation rate occurs at the RP2 locus, and that most mutations arise independently, without a founder effect. Our mutation analysis confirms the percentage of RP2 mutations detected so far in populations of different ethnic origin. In addition to novel mutations, we report here that a deeper sequence analysis of the RP2 product predicts, in addition to cofactor C homology domain, further putative functional domains, and that some novel mutations identify RP2 amino acid residues which are evolutionary conserved, hence possibly crucial to the RP2 function.