Localizing multiple X chromosome-linked retinitis pigmentosa loci using multilocus homogeneity tests

Identification of circular RNAs hosted by the RPGR ORF15 genomic locus

Mutations in the retina-specific isoform of the gene encoding retinitis pigmentosa GTPase regulator (RPGRorf15) cause X-linked retinitis pigmentosa, a severe and early onset inherited retinal degeneration. The underlying pathogenic mechanisms and variability in disease severity remain to be fully elucidated. The present study examines structural features of the ORF15 exonic region to provide new insights into the disease pathogenesis. Using canine and human RNA samples, we identified several novel RPGR ORF15-like linear RNA transcripts containing cryptic introns (exitrons) within the annotated exon ORF15. Furthermore, using outward-facing primers designed inside exitrons in the ORF15 exonic region, we found many of previously unidentified circular RNAs (circRNAs) that formed via back fusion of linear parts of the RPGRorf15 pre-mRNAs. These circRNAs (resistant to RNAse R treatment) were found in all studied cells and tissues. Notably, some circRNAs were present in cytoplasmic and polysomal RNA fractions. Although certain RPGR circRNAs may be cell type specific, we found some of the same circRNAs expressed in different cell types, suggesting similarities in their biogenesis and functions. Sequence analysis of RPGR circRNAs revealed several remarkable features, including identification of N6-methyladenosine (m6A) consensus sequence motifs and high prevalence of predictive microRNA binding sites pointing to the functional roles of these circRNAs. Our findings also illustrate the presence of non-canonical RPGR circRNA biogenesis pathways independent of the known back splicing mechanism. The obtained data on novel RPGR circRNAs further underline structural complexity of the RPGR ORF15 region and provide a potential molecular basis for the disease phenotypic heterogeneity.

Retinitis Pigmentosa'nın Genetik ve Klinik Değerlendirilmesi

Background: The aim of this study was to evaluate the most common underlying genetic and clinical etiologies of retinitis pigmentosa (RP) disease in our geographical area. Material and Method: In our archive, there are about 3000 patients who applied to our clinic between the years 2015-2021. The files of approximately 700 patients with a definitive genetic diagnosis were retrospectively scanned. A definitive genetic diagnosis was made in 22 of these patients. During our research, we collected some clinical parameters including the prenatal, natal, and postnatal history of the patients, history of surgery and seizures, and family history. In family history, we did a detailed pedigree with at least 3 generational analyses, questioned parental kinship, looked for similar members in families, and identified inheritance patterns of their disorder. We draw 3 generations pedigree and we collected peripheral venous blood samples from patients and sent them to a commercial lab for gene panels or WES. After obtaining the definitive genetic diagnosis of all patients, we compiled a table with the other parameters we questioned. Results: As a result of our WES analysis in patients 1 and 2, homozygous c.1331_1332 dupAG/p. Thr445ArgfsTer10 Class 2 variant was detected in the POC1B gene of patient #2.In the RP panel 1 reports of patients 3 and 4, the genomic alteration of c.2254dupA (p.Ser752Lysfs*14) was detected in exon 15 of the ABCA4 (NM_000350) gene. Patient 5, EYS c.4964T>C heterozygous. Patient 6. SEMA4A C.1168A>G (heterozygous). Patient 7, SEMA4A C.1168A>G (heterozygous), RP1 c.5402C>T (heterozygous), CGNB1 c.1382C>T (heterozygous).Patient #8, . Heterozygous variation of p.Thr390Ala (c.1168A>G) in the SEMA4A gene is present.As a result of our WES analysis, a homozygous c.2021C>A/p.Pro674His Class 2 variant was detected in the RPGRIP1 gene of patient #9. Heterozygous c.119-2A>C Class 1 mutation was detected in the NR2E3 gene of patient 10. Homozygous c.271C>T/p.Gln91* Class 1 mutation was detected in the MFRP gene in patient 11. Patient #12 was diagnosed at the age of 7-8 years. When we look at the exome sequencing results, a homozygous mutation in the CNGB1 gene c.413-1G> of patient 13 was detected. Heterozygous p.Ser361Tyr (c.1082C>A) change detected in the ABCA4 gene of patient #14 was detected. The heterozygous p.Glu150Lys (c.448G>A) change detected in the RHO gene of patient #15 was pathogenic according to ClinVar database and in silico analysis. rated as. Prediagnosis was Bardet-Biedle Syndrome in patient 16. P.Gly244Asp change was detected in RPE65 gene of patients 17 and 18. Automated DNA sequencing of patient #19 and patient #20 results in a homozygous sequence variation in the coding sequence of the NR2E3 genes, a homozygous CGG>CAG nucleotide substitution, and an amino acid replacement of Arg311Gln. Heterozygous mutation was detected in the same gene region in patient 21 (fathers). Variation in NR2E3 is the most likely cause of these patients' eye condition, as it is a complete genotype and is strongly associated with RP in many published families. Genetic results on an allele of the BBS1 gene of patient 22 (chr11:66.278.121-66.291.364 (13.2kb)/ISCN: seq [GRCH37]11q13.2(66.278).121-66.291.364)x1). The other allele has a heterozygous point mutation (c.1424dupT p.Ser476fs-rs886039798). Conclusıons: As determined in our study, the disease can be encountered with many different genetic etiologies. In this regard, patients undergoing genetic testing should be carefully examined for both SNP (single nucleotide polymorphism) and CNV (copy number variation).In addition, before genetic tests are performed, it should be well determined whether there is an isolated RP or an accompanying RP. In this respect, patients should be evaluated by making a detailed anamnesis and physical examination and drawing a pedigree containing at least 3 generations. Therefore, it was concluded that accompanying abnormalities should also be examined in the evaluation of retinitis pigmentosa anomalies.

Candidate Genetic Modifiers for RPGR Retinal Degeneration

Purpose

To define genetic variants associated with variable severity of X-linked progressive retinal atrophy 1 (XLPRA1) caused by a five-nucleotide deletion in canine RPGR exon ORF15.

Methods

A genome-wide association study (GWAS) was performed in XLPRA1 phenotype informative pedigree. Whole genome sequencing (WGS) was used for mutational analysis of genes within the candidate genomic region. Retinas of normal and mutant dogs were used for gene expression, gene structure, and RNA duplex analyses.

Results

GWAS followed by haplotype phasing identified an approximately 4.6 Mb candidate genomic interval on CFA31 containing seven protein-coding genes expressed in retina (ROBO1, ROBO2, RBM11, NRIP1, HSPA13, SAMSN1, and USP25). Furthermore, we identified and characterized two novel lncRNAs, ROBO1-AS and ROBO2-AS, that display overlapping gene organization with axon guidance pathway genes ROBO1 and ROBO2, respectively, producing sense-antisense gene pairs. Notably, ROBO1-AS and ROBO2-AS act in cis to form lncRNA/mRNA duplexes with ROBO1 and ROBO2, respectively, suggesting important roles for these lncRNAs in the ROBO regulatory network. A subsequent WGS identified candidate genes within the genomic region on CFA31 that might be implicated in modifying severity of XLPRA1. This approach led to discovery of genetic variants in ROBO1, ROBO1-AS, ROBO2-AS, and USP25 that are strongly associated with the XLPRA1 moderate phenotype.

Conclusions

The study provides new insights into the genetic basis of phenotypic variation in severity of RPGR^orf15-associated retinal degeneration. Our findings suggest an important role for ROBO pathways in disease progression further expanding on our previously reported changes of ROBO1 expression in XLPRA1 retinas.

Critical Decrease in the Level of Axon Guidance Receptor ROBO1 in Rod Synaptic Terminals Is Followed by Axon Retraction

Purpose

To define remodeling of photoreceptor synaptic terminals and second-order retinal neurons in canine X-linked progressive retinal atrophy 1 caused by a five-nucleotide deletion in the RPGR exon ORF15.

Methods

Retinas of normal and mutant dogs were used for gene expression, Western blot, and immunohistochemistry. Cell-specific markers were used to examine disease-dependent retinal remodeling.

Results

In mutant retinas, a number of rod axon terminals retract into the outer nuclear layer. This neuritic atrophy preceded significant loss of rods and was evident early in disease. Rod bipolar and horizontal cell processes were found to extend into the outer nuclear layer, where they seemed to form contacts with the spherules of rod photoreceptors. No ectopic rewiring was observed. Because cytoskeletal reorganization was previously shown to underlie photoreceptor axon retraction, we examined normal and mutant retinas for expression of axon guidance receptors ROBO1 and ROBO2, which are known to regulate actin cytoskeleton dynamics. We found that the overall expression of both ROBO1 and ROBO2 is retained at the same level in premature and fully developed normal retinas. However, analysis of predisease and early disease retinas identified markedly decreased levels of ROBO1 in rod spherules compared with controls. In contrast, no differences in ROBO1 signals were noted in cone pedicles in normal and mutant retinas, where ROBO1 levels remained similarly low.

Conclusions

Depletion of ROBO1 in rod synaptic terminals correlates with the remodeling of axonal and dendritic processes in the outer retina of dogs with X-linked progressive retinal atrophy 1 and may play a role in the retraction of rod axons.

A heterozygous mutation in RPGR associated with X-linked retinitis pigmentosa in a patient with Turner syndrome mosaicism (45,X/46,XX)

Turner syndrome with retinitis pigmentosa (RP) is rare, with only three cases reported based on clinical examination alone. We summarized the 4-year follow-up and molecular findings in a 28-year-old patient with Turner syndrome and the typical features of short stature and neck webbing, who also had X-linked RP. Her main complaints were night blindness and progressive loss of vision since the age of 9 years. Ophthalmologic examination, optical coherent tomographic imaging, and visual electrophysiology tests showed classic manifestations of RP. The karyotype of peripheral blood showed mosaicism (45,X [72%]/46,XX[28%]). A novel heterozygous frameshift mutation (c.2403_2406delAGAG, p.T801fsX812) in the RP GTPase regulator (RPGR) gene was detected using next generation sequencing and validated by Sanger sequencing. We believe that this is the first report of X-linked RP in a patient with Turner syndrome associated with mosaicism, and an RPGR heterozygous mutation. We hypothesize that X-linked RP in this woman is not related to Turner syndrome, but may be a manifestation of the lack of a normal paternal X chromosome with intact but mutated RPGR.

Unravelling the genetics of inherited retinal dystrophies: Past, present and future

The identification of the genes underlying monogenic diseases has been of interest to clinicians and scientists for many years. Using inherited retinal dystrophies as an example of monogenic disease we describe the history of molecular genetic techniques that have been pivotal in the discovery of disease causing genes. The methods that were developed in the 1970's and 80's are still in use today but have been refined and improved. These techniques enabled the concept of the Human Genome Project to be envisaged and ultimately realised. When the successful conclusion of the project was announced in 2003 many new tools and, as importantly, many collaborations had been developed that facilitated a rapid identification of disease genes. In the post-human genome project era advances in computing power and the clever use of the properties of DNA replication has allowed the development of next-generation sequencing technologies. These methods have revolutionised the identification of disease genes because for the first time there is no need to define the position of the gene in the genome. The use of next generation sequencing in a diagnostic setting has allowed many more patients with an inherited retinal dystrophy to obtain a molecular diagnosis for their disease. The identification of novel genes that have a role in the development or maintenance of retinal function is opening up avenues of research which will lead to the development of new pharmacological and gene therapy approaches. Neither of which can be used unless the defective gene and protein is known. The continued development of sequencing technologies also holds great promise for the advent of truly personalised medicine.

Analysis of RP2 and RPGR Mutations in Five X-Linked Chinese Families with Retinitis Pigmentosa

Mutations in RP2 and RPGR genes are responsible for the X-linked retinitis pigmentosa (XLRP). In this study, we analyzed the RP2 and RPGR gene mutations in five Han Chinese families with XLRP. An approximately 17Kb large deletion including the exon 4 and exon 5 of RP2 gene was found in an XLRP family. In addition, four frameshift mutations including three novel mutations of c.1059 + 1 G > T, c.2002dupC and c.2236_2237del CT, as well as a previously reported mutation of c.2899delG were detected in the RPGR gene in the other four families. Our study further expands the mutation spectrum of RP2 and RPGR, and will be helpful for further study molecular pathogenesis of XLRP.

Molecular studies of phenotype variation in canine RPGR-XLPRA1

PURPOSE

Canine X-linked progressive retinal atrophy 1 (XLPRA1) caused by a mutation in retinitis pigmentosa (RP) GTPase regulator (RPGR) exon ORF15 showed significant variability in disease onset in a colony of dogs that all inherited the same mutant X chromosome. Defective protein trafficking has been detected in XLPRA1 before any discernible degeneration of the photoreceptors. We hypothesized that the severity of the photoreceptor degeneration in affected dogs may be associated with defects in genes involved in ciliary trafficking. To this end, we examined six genes as potential disease modifiers. We also examined the expression levels of 24 genes involved in ciliary trafficking (seven), visual pathway (five), neuronal maintenance genes (six), and cellular stress response (six) to evaluate their possible involvement in early stages of the disease.

METHODS

Samples from a pedigree derived from a single XLPRA1-affected male dog outcrossed to unrelated healthy mix-bred or purebred females were used for immunohistochemistry (IHC), western blot, mutational and haplotype analysis, and gene expression (GE). Cell-specific markers were used to examine retinal remodeling in the disease. Single nucleotide polymorphisms (SNPs) spanning the entire RPGR interacting and protein trafficking genes (RAB8A, RPGRIP1L, CEP290, CC2D2A, DFNB31, and RAB11B) were genotyped in the pedigree. Quantitative real-time PCR (qRT-PCR) was used to examine the expression of a total of 24 genes, including the six genes listed.

RESULTS

Examination of cryosections from XLPRA1-affected animals of similar age (3-4 years) with different disease severity phenotype revealed mislocalization of opsins and upregulation of the Müller cell gliosis marker GFAP. Four to ten haplotypes per gene were identified in RAB8A, RPGRIP1L, CEP290, CC2D2A, DFNB31, and RAB11B for further assessment as potential genetic modifiers of XLPRA1. No correlation was found between the haplotypes and disease severity. During mutational analysis, several new variants, including a single intronic mutation in RAB8A and three mutations in exon 3 of DFNB31 were described (c.970G>A (V324I), c.978T>C (G326=), and c.985G>A (A329T)). Expression analysis of stress response genes in 16-week-old predisease XLPRA1 retinas revealed upregulation of GFAP but not HSPA5, DDIT3, HSPA4, HSP90B1, or HIF1A. Western blot analysis confirmed GFAP upregulation. In the same predisease group, no significant differences were found in the expression of 18 selected genes (RHO, OPN1LW, OPN1MW, RLBP1, RPGRORF15, RAB8A, RPGRIP1L, CEP290, CC2D2A, DFNB31, RAB11B, CRX, RCVRN, PVALB, CALB1, FGFR1, NTRK2, and NTRK3) involved in neuronal function.

CONCLUSIONS

Lack of association between haplotypes of RAB8A, RPGRIP1L, CEP290, CC2D2A, DFNB31, and RAB11B and the disease phenotype suggests that these genes are not genetic modifiers of XLPRA1. Upregulation of GFAP, an established indicator of the Müller cell gliosis, manifests as an important early feature of the disease.

Genetic analysis of Chinese families reveals a novel truncation allele of the retinitis pigmentosa GTPase regulator gene

AIM

To make comprehensive molecular diagnosis for retinitis pigmentosa (RP) patients in a consanguineous Han Chinese family using next generation sequencing based Capture-NGS screen technology.

METHODS

A five-generation Han Chinese family diagnosed as non-syndromic X-linked recessive RP (XLRP) was recruited, including four affected males, four obligate female carriers and eleven unaffected family members. Capture-NGS was performed using a custom designed capture panel covers 163 known retinal disease genes including 47 RP genes, followed by the validation of detected mutation using Sanger sequencing in all recruited family members.

RESULTS

Capture-NGS in one affected 47-year-old male reveals a novel mutation, c.2417_2418insG:p.E806fs, in exon ORF15 of RP GTPase regulator (RPGR) gene results in a frameshift change that results in a premature stop codon and a truncated protein product. The mutation was further validated in three of four affected males and two of four female carriers but not in the other unaffected family members.

CONCLUSION

We have identified a novel mutation, c.2417_2418insG:p.E806fs, in a Han Chinese family with XLRP. Our findings expand the mutation spectrum of RPGR and the phenotypic spectrum of XLRP in Han Chinese families, and confirms Capture-NGS could be an effective and economic approach for the comprehensive molecular diagnosis of RP.

Early-Onset X-Linked Retinitis Pigmentosa in a Heterozygous Female Harboring an Intronic Donor Splice Site Mutation in the Retinitis Pigmentosa GTPase Regulator Gene

PURPOSE

To report a heterozygous female presenting with an early-onset and severe form of X-linked retinitis pigmentosa (XLRP).

PATIENTS AND METHODS

This is a case series presenting the clinical findings in a heterozygous female with XLRP and two of her family members. Fundus photography, fundus autofluorescence, ocular coherence tomography, and visual perimetry are presented.

RESULTS

The proband reported here is a heterozygous female who presented at the age of 8 years with an early onset and aggressive form of XLRP. The patient belongs to a four-generation family with a total of three affected females and four affected males. The patient was initially diagnosed with retinitis pigmentosa (RP) at the age of 4 years. Genetic testing identified a heterozygous donor splice site mutation in intron 1 (IVS1 + 1G > A) of the retinitis pigmentosa GTPase regulator gene. The father of the proband was diagnosed with RP when he was a young child. The sister of the proband, evaluated at the age of 6 years, showed macular pigmentary changes.

CONCLUSIONS

Although carriers of XLRP are usually asymptomatic or have a mild disease of late onset, the proband presented here exhibited an early-onset, aggressive form of the disease. It is not clear why some carrier females manifest a severe phenotype. A better understanding of the genetic processes involved in the penetrance and expressivity of XLRP in heterozygous females could assist in providing the appropriate counseling to affected families.

Prioritization of retinal disease genes: an integrative approach

The discovery of novel disease-associated variations in genes is often a daunting task in highly heterogeneous disease classes. We seek a generalizable algorithm that integrates multiple publicly available genomic data sources in a machine-learning model for the prioritization of candidates identified in patients with retinal disease. To approach this problem, we generate a set of feature vectors from publicly available microarray, RNA-seq, and ChIP-seq datasets of biological relevance to retinal disease, to observe patterns in gene expression specificity among tissues of the body and the eye, in addition to photoreceptor-specific signals by the CRX transcription factor. Using these features, we describe a novel algorithm, positive and unlabeled learning for prioritization (PULP). This article compares several popular supervised learning techniques as the regression function for PULP. The results demonstrate a highly significant enrichment for previously characterized disease genes using a logistic regression method. Finally, a comparison of PULP with the popular gene prioritization tool ENDEAVOUR shows superior prioritization of retinal disease genes from previous studies. The java source code, compiled binary, assembled feature vectors, and instructions are available online at https://github.com/ahwagner/PULP.

Mutations in RPGR and RP2 account for 15% of males with simplex retinal degenerative disease

PURPOSE

To determine the proportion of male patients presenting simplex retinal degenerative disease (RD: retinitis pigmentosa [RP] or cone/cone-rod dystrophy [COD/CORD]) with mutations in the X-linked retinal degeneration genes RPGR and RP2.

METHODS

Simplex males were defined as patients with no known affected family members. Patients were excluded if they had a family history of parental consanguinity. Blood samples from a total of 214 simplex males with a diagnosis of retinal degeneration were collected for genetic analysis. The patients were screened for mutations in RPGR and RP2 by direct sequencing of PCR-amplified genomic DNA.

RESULTS

We identified pathogenic mutations in 32 of the 214 patients screened (15%). Of the 29 patients with a diagnosis of COD/CORD, four mutations were identified in the ORF15 mutational hotspot of the RPGR gene. Of the 185 RP patients, three patients had mutations in RP2 and 25 had RPGR mutations (including 12 in the ORF15 region).

CONCLUSIONS

This study represents mutation screening of RPGR and RP2 in the largest cohort, to date, of simplex males affected with RP or COD/CORD. Our results demonstrate a substantial contribution of RPGR mutations to retinal degenerations, and in particular, to simplex RP. Based on our findings, we suggest that RPGR should be considered as a first tier gene for screening isolated males with retinal degeneration.

RP2 phenotype and pathogenetic correlations in X-linked retinitis pigmentosa

OBJECTIVES

To assess the phenotype of patients with X-linked retinitis pigmentosa (XLRP) with RP2 mutations and to correlate the findings with their genotype.

METHODS

Six hundred eleven patients with RP were screened for RP2 mutations. From this screen, 18 patients with RP2 mutations were evaluated clinically with standardized electroretinography, Goldmann visual fields, and ocular examinations. In addition, 7 well-documented cases from the literature were used to augment genotype-phenotype correlations.

RESULTS

Of 11 boys younger than 12 years, 10 (91%) had macular involvement and 9 (82%) had best-corrected visual acuity worse than 20/50. Two boys from different families (aged 8 and 12 years) displayed a choroideremia-like fundus, and 9 boys (82%) were myopic (mean error, -7.97 diopters [D]). Of 10 patients with electroretinography data, 9 demonstrated severe rod-cone dysfunction. All 3 female carriers had macular atrophy in 1 or both eyes and were myopic (mean, -6.23 D). All 9 nonsense and frameshift and 5 of 7 missense mutations (71%) resulted in severe clinical presentations.

CONCLUSIONS

Screening of the RP2 gene should be prioritized in patients younger than 16 years characterized by X-linked inheritance, decreased best-corrected visual acuity (eg, >20/40), high myopia, and early-onset macular atrophy. Patients exhibiting a choroideremia-like fundus without choroideremia gene mutations should also be screened for RP2 mutations.

CLINICAL RELEVANCE

An identifiable phenotype for RP2-XLRP aids in clinical diagnosis and targeted genetic screening.

Use of LINKAGE programs for linkage analysis

Genetic linkage analysis remains a powerful tool for identifying regions of the genome that may harbor suceptibility loci. This unit describes the traditional approach of calculating two-point and multipoint lod scores when the underlying genetic model is known. Components of the genetic model include whether a trait is dominant, recessive, or codominant, whether it is autosomal or sex linked, and whether there is mutation at the disease gene locus, as well as the disease and marker allele frequencies and the penetrance of the disease allele. The approach to genetic linkage analysis presented in this unit assumes that the markers are loosely spaced, so that there is no linkage disequilibrium between genetic markers. Practical examples and step-by-step guidelines are presented.

Progressive retinal atrophy in the Border Collie: a new XLPRA

BACKGROUND

Several forms of progressive retinal atrophy (PRA) segregate in more than 100 breeds of dog with each PRA segregating in one or a few breeds. This breed specificity may be accounted for by founder effects and genetic drift, which have reduced the genetic heterogeneity of each breed, thereby facilitating the identification of causal mutations. We report here a new form of PRA segregating in the Border Collie breed. The clinical signs, including the loss of night vision and a progressive loss of day vision, resulting in complete blindness, occur at the age of three to four years and may be detected earlier through systematic ocular fundus examination and electroretinography (ERG).

RESULTS

Ophthalmic examinations performed on 487 dogs showed that affected dogs present a classical form of PRA. Of those, 274 have been sampled for DNA extraction and 87 could be connected through a large pedigree. Segregation analysis suggested an X-linked mode of transmission; therefore both XLPRA1 and XLPRA2 mutations were excluded through the genetic tests.

CONCLUSION

Having excluded these mutations, we suggest that this PRA segregating in Border Collie is a new XLPRA (XLPRA3) and propose it as a potential model for the homologous human disease, X-Linked Retinitis Pigmentosa.

Inner retinal abnormalities in X-linked retinitis pigmentosa with RPGR mutations

PURPOSE

To investigate in vivo the retinal microstructure in X-linked retinitis pigmentosa (XLRP) caused by RPGR mutations as a prelude to treatment initiatives for this common form of RP.

METHODS

Patients with RPGR-XLRP (n = 12; age range, 10-56 years) were studied by optical coherence tomography (OCT) in a wide region of central retina. Overall retinal thickness and outer nuclear layer (ONL) and inner retinal parameters across horizontal and vertical meridians were analyzed and compared.

RESULTS

Retinal architecture of all patients with RPGR mutations was abnormal. At the fovea in younger patients, the ONL could be normal; but, at increasing eccentricities, there was a loss of photoreceptor laminar structure, even at the youngest ages studied. At later ages and advanced disease stages, the ONL was thin and reduced in extent. Inner retinal thickness, in contrast, was normal or hyperthick. Inner retinal thickening was detectable at all ages studied and was strongly associated with ONL loss.

CONCLUSIONS

Inner retinal laminar abnormalities in RPGR-XLRP are likely to reflect a neuronal-glial retinal remodeling response to photoreceptor loss and are detectable relatively early in the disease course. These results should be factored into emerging therapeutic strategies for this form of RP.

RCC1-like domain and ORF15: essentials in RPGR gene

Clinical research into mutations of the RPGR gene showed that lack of either the RCC1-like domain of the ORF15 causes X-linked retinitis pigmentosa. Thus, the ORF15 and RCC1-like domain play a crucial role in the human retina. Further sudies on the role of the RCC1-like domain in the visual Cascade and additional findings of related proteins in the retina or even other organs, will give us a more precise understanding of this protein.

RPGRmutation analysis and disease: an update

Mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene are the most common single cause of retinitis pigmentosa, accounting for up to 15 to 20% of cases in Caucasians. A total of 240 different RPGR mutations have been reported, including 24 novel ones in this work, which are associated with X-linked retinitis pigmentosa (XLRP) (95%), cone, cone-rod dystrophy, or atrophic macular atrophy (3%), and syndromal retinal dystrophies with ciliary dyskinesia and hearing loss (2%). All disease-causing mutations occur in one or more RPGR isoforms containing the carboxyl-terminal exon open reading frame 15 (ORF15), which are widely expressed but show their highest expression in the connecting cilia of rod and cone photoreceptors. Of reported RPGR mutations, 55% occur in a glutamic acid-rich domain within exon ORF15, which accounts for only 31% of the protein. RPGR forms complexes with a variety of other proteins and appears to have a role in microtubular organization and transport between photoreceptor inner and outer segments.

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.

Population haplotypes of exon ORF15 of the retinitis pigmentosa GTPase regulator gene in Germany : implications for screening for inherited retinal disorders

BACKGROUND

Mutations in exon ORF15 of the retinitis pigmentosa GTPase regulator gene (RPGR) within chromosomal region Xp21.1 are a significant cause of a number of retinal disorders. The high mutation rate is ascribed to the highly repetitive, purine-rich tracts within the exon ORF15 sequence. Importantly, all exon ORF15 mutations observed to date represent protein-truncating mutations (nonsense and frameshift mutations). Because of its repetitive motifs, mutation screening of the hot-spot region by direct DNA sequencing is a technically challenging task.

METHODS

We devised a screening strategy for exon ORF15 mutations that reserves DNA sequencing for precise sizing and base-order assessment of detected mutations. The screening strategy is based on a PCR/restriction fragment length polymorphism (RFLP) analysis of exon ORF15 and comparison with population-specific RFLP haplotypes. The latter were constructed from PCR/RFLP analysis of DNA samples from 100 healthy German male individuals. Mutational alterations of normal RFLP haplotype patterns were predicted.

RESULTS

Six distinct RFLP haplotypes (founder alleles H1-H6) were observed with frequencies ranging from 2% to 63%. All natural variations of exon ORF15 were in-frame alterations ranging in size between 3bp and 36bp. Prediction of mutation-specific RFLP patterns indicated a high detection rate of mutations.

CONCLUSION

A new strategy has been developed using routine protocols for mutation screening of difficult-to-sequence, highly repetitive exon ORF15 of the RPGR gene in a German population.

Mapping a new genetic locus for X linked retinitis pigmentosa to Xq28

We have defined a new genetic locus for an X linked form of retinitis pigmentosa (RP) on chromosome Xq28. We examined 15 members of a family in which RP appeared to be transmitted in an X linked manner. Ocular examinations were performed, and fundus photographs and electroretinograms were obtained for selected patients. Blood samples were obtained from all patients and an additional seven family members who were not given examinations. Visual acuity in four affected individuals ranged from 20/40 to 20/80+. Patients described the onset of night blindness and colour vision defects in the second decade of life, with the earliest at 13 years of age. Examined affected individuals had constricted visual fields and retinal findings compatible with RP. Based on full field electroretinography, cone function was more severely reduced than rod function. Female carriers had no ocular signs or symptoms and slightly reduced cone electroretinographic responses. Affected and non-affected family members were genotyped for 20 polymorphic markers on the X-chromosome spaced at 10 cM intervals. Genotyping data were analysed using GeneMapper software. Genotyping and linkage analyses identified significant linkage to markers DXS8061, DXS1073, and DXS1108 with two point LOD scores of 2.06, 2.17, and 2.20, respectively. Haplotype analysis revealed segregation of the disease phenotype with markers at Xq28.

RPGR is mutated in patients with a complex X linked phenotype combining primary ciliary dyskinesia and retinitis pigmentosa

INTRODUCTION

Primary ciliary dyskinesia (PCD) is a rare disease classically transmitted as an autosomal recessive trait and characterised by recurrent airway infections due to abnormal ciliary structure and function. To date, only two autosomal genes, DNAI1 and DNAH5 encoding axonemal dynein chains, have been shown to cause PCD with defective outer dynein arms. Here, we investigated one non-consanguineous family in which a woman with retinitis pigmentosa (RP) gave birth to two boys with a complex phenotype combining PCD, discovered in early childhood and characterised by partial dynein arm defects, and RP that occurred secondarily. The family history prompted us to search for an X linked gene that could account for both conditions.

RESULTS

We found perfect segregation of the disease phenotype with RP3 associated markers (Xp21.1). Analysis of the retinitis pigmentosa GTPase regulator gene (RPGR) located at this locus revealed a mutation (631_IVS6+9del) in the two boys and their mother. As shown by study of RPGR transcripts expressed in nasal epithelial cells, this intragenic deletion, which leads to activation of a cryptic donor splice site, predicts a severely truncated protein.

CONCLUSION

These data provide the first clear demonstration of X linked transmission of PCD. This unusual mode of inheritance of PCD in patients with particular phenotypic features (that is, partial dynein arm defects and association with RP), which should modify the current management of families affected by PCD or RP, unveils the importance of RPGR in the proper development of both respiratory ciliary structures and connecting cilia of photoreceptors.

Clinical studies of X-linked retinitis pigmentosa in three Swedish families with newly identified mutations in the RP2 and RPGR-ORF15 genes

PURPOSE

To describe new disease-causing RP2 and RPGR-ORF15 mutations and their corresponding clinical phenotypes in Swedish families with X-linked retinitis pigmentosa (XLRP) and to establish genotype-phenotype correlations by studying the clinical spectrum of disease in families with a known molecular defect.

METHODS

Seventeen unrelated families with RP and an apparent X-linked pattern of disease inheritance were identified from the Swedish RP registry and screened for mutations in the RP2 and RPGR (for the RP3 disease) genes. These families had been previously screened for the RPGR exons 1-19, and disease-causing mutations were identified in four of them. In the remaining 13 families, we sequenced the RP2 gene and the newly discovered RPGR-ORF exon. Detailed clinical evaluations were then obtained from individuals in the three families with identified mutations.

RESULTS

Mutations in RP2 and RPGR-ORF15 were identified in three of the 13 families. Clinical evaluations of affected males and carrier females demonstrated varying degrees of retinal dysfunction and visual handicap, with early onset and severe disease in the families with mutations in the ORF15 exon of the RPGR gene.

CONCLUSIONS

A total of seven mutations in the RP2 and RPGR genes have been discovered so far in Swedish XLRP families. All affected individuals express a severe form of retinal degeneration with visual handicap early in life, although the degree of retinal dysfunction varies both in hemizygous male patients and in heterozygous carrier females. Retinal disease phenotypes in patients with mutations in the RPGR-ORF15 were more severe than in patients with mutations in RP2 or other regions of the RPGR.

RP2 and RPGR mutations and clinical correlations in patients with X-linked retinitis pigmentosa

We determined the mutation spectrum of the RP2 and RPGR genes in patients with X-linked retinitis pigmentosa (XLRP) and searched for correlations between categories of mutation and severity of disease. We screened 187 unrelated male patients for mutations, including 135 with a prior clinical diagnosis of XLRP, 11 with probable XLRP, 30 isolate cases suspected of having XLRP, and 11 with cone-rod degeneration. Mutation screening was performed by single-strand conformation analysis and by sequencing of all RP2 exons and RPGR exons 1-14, ORF15, and 15a. The refractive error, visual acuity, final dark-adapted threshold, visual field area, and 30-Hz cone electroretinogram (ERG) amplitude were measured in each patient. Among the 187 patients, we found 10 mutations in RP2, 2 of which are novel, and 80 mutations in RPGR, 41 of which are novel; 66% of the RPGR mutations were within ORF15. Among the 135 with a prior clinical diagnosis of XLRP, mutations in the RP2 and RPGR genes were found in 9 of 135 (6.7%) and 98 of 135 (72.6%), respectively, for a total of 79% of patients. Patients with RP2 mutations had, on average, lower visual acuity but similar visual field area, final dark-adapted threshold, and 30-Hz ERG amplitude compared with those with RPGR mutations. Among patients with RPGR mutations, those with ORF15 mutations had, on average, a significantly larger visual field area and a borderline larger ERG amplitude than did patients with RPGR mutations in exons 1-14. Among patients with ORF15 mutations, regression analyses showed that the final dark-adapted threshold became lower (i.e., closer to normal) and that the 30-Hz ERG amplitude increased as the length of the wild-type ORF15 amino acid sequence increased. Furthermore, as the length of the abnormal amino acid sequence following ORF15 frameshift mutations increased, the severity of disease increased.

Analysis of RPGR in a South African family with X-linked retinitis pigmentosa: research and diagnostic implications

Analysis of exon ORF15 of the RPGR gene has revealed a novel mutation in a South African family with X-linked retinitis pigmentosa (XLRP), which has implications for the rest of the family in terms of pre-symptomatic testing. The ability to test for this mutation will be beneficial for the accurate determination of carrier status in female relatives who may have been unaware of their risk before this study was performed. This work also highlights the need to be aware of the ramifications of mutation testing in what may appear to be small families. This is the first report of an RPGR ORF15 mutation in a South African family of mixed ancestry.

MHC susceptibility genes to IgA deficiency are located in different regions on different HLA haplotypes

Familial predisposition to IgA deficiency (IgAD) suggests that genetic factors influence susceptibility. Most studies support a polygenic inheritance with a susceptibility locus (designated IGAD1) in the MHC, but its exact location is still controversial. This study aimed to map the predisposing IGAD1 locus (or loci) within the MHC by investigating the pattern of association of the disease with several markers in the region. DNA-based techniques were used to type individual alleles of four polymorphic HLA genes (HLA-DR, -DQA1, -DQB1, and HLA-B), six microsatellites (all located between HLA-DR and HLA-B), and three single nucleotide polymorphisms on the TNF gene. The frequencies of these alleles were compared among ethnically matched populations comprising 182 patients and 343 controls. Additionally, we investigated parents and siblings of 100 of these patients. All four parental haplotypes were established in each family (n = 400), and transmission disequilibrium tests were performed. Surprisingly, our results did not support the hypothesis of a unique susceptibility gene being shared by all MHC susceptibility haplotypes. On HLA-DR1 and -DR7-positive haplotypes IGAD1 mapped to the class II region, whereas on haplotypes carrying HLA-DR3 the susceptibility locus mapped to the telomeric end of the class III region, as reported previously. Our results show how, in complex diseases, individuals may be affected for different genetic reasons and a single linkage signal to a region of a chromosome may actually be the result of disease-predisposing alleles in different linked genes in different pedigrees.

Epidemiology of retinitis pigmentosa in Denmark

A nation-wide registration of Danish cases of retinitis pigmentosa (RP) provided 1890 persons diagnosed during the period 1850-1989. Prevalent at 1 January 1988 were 1301 persons (1:3943) comprising a multitude of different RP-types. Age specific prevalence rates demonstrated increasing rates of RP during the first four decades of life and a rather stable prevalence over the next 20-30 years. Corrected for incompleteness, a late decrease was found, reflecting an incomplete ascertainment of the oldest patients. A moving average method indicated an even later steady state value for the age-specific prevalence. The Danish prevalence figures were standardized according to the WHO World Standardized Prevalence Rates and compared with large studies from the USA and UK. No statistically significant difference was found. Usher syndrome was present in 12% of all RP-cases and Bardet-Biedl syndrome comprised 5%. Mental retardation was found in 144 cases (11%), mostly characterized by atypical RP. Nineteen per cent of patients affected by nonsystemic RP had an onset later than 30 years of age, whereas only a few per cent of persons with systemic RP had an RP onset after age 30 years. The Mendelian inheritance type of all cases was evaluated according to an unambiguous genetic classification, finding a larger amount of X-linked RP compared with other studies. Among nonsystemic RP-cases, 14.3% were found to be inherited as an X-linked trait whereas only 8.4% were autosomal dominantly inherited. The largest fraction was, as in previous materials, the simplex group (isolated cases) comprising 42.9% of the nonsystemic RP patients. Some factors influencing the results are discussed, with special emphasis on the problems associated with precise definitions of the Mendelian inheritance groups. A diagram according to the author's definition was constructed as a guideline ready for clinical application.

A comprehensive mutation analysis of RP2 and RPGR in a North American cohort of families with X-linked retinitis pigmentosa

X-linked retinitis pigmentosa (XLRP) is a clinically and genetically heterogeneous degenerative disease of the retina. At least five loci have been mapped for XLRP; of these, RP2 and RP3 account for 10%-20% and 70%-90% of genetically identifiable disease, respectively. However, mutations in the respective genes, RP2 and RPGR, were detected in only 10% and 20% of families with XLRP. Mutations in an alternatively spliced RPGR exon, ORF15, have recently been shown to account for 60% of XLRP in a European cohort of 47 families. We have performed, in a North American cohort of 234 families with RP, a comprehensive screen of the RP2 and RPGR (including ORF15) genes and their 5' upstream regions. Of these families, 91 (39%) show definitive X-linked inheritance, an additional 88 (38%) reveal a pattern consistent with X-linked disease, and the remaining 55 (23%) are simplex male patients with RP who had an early onset and/or severe disease. In agreement with the previous studies, we show that mutations in the RP2 gene and in the original 19 RPGR exons are detected in <10% and approximately 20% of XLRP probands, respectively. Our studies have revealed RPGR-ORF15 mutations in an additional 30% of 91 well-documented families with X-linked recessive inheritance and in 22% of the total 234 probands analyzed. We suggest that mutations in an as-yet-uncharacterized RPGR exon(s), intronic changes, or another gene in the region might be responsible for the disease in the remainder of this North American cohort. We also discuss the implications of our studies for genetic diagnosis, genotype-phenotype correlations, and gene-based therapy.

Mutations of RPGR in X-linked retinitis pigmentosa (RP3)

Mutations in RPGR, retinitis pigmentosa GTPase regulator, are associated with RP3 type of X-linked retinitis pigmentosa, a severe, non-syndromic form of retinal degeneration. In the majority of subjects RPGR mutations are associated with a typical rod-cone degeneration, but in a small number, cone-rod dystrophy, deafness, and abnormalities in respiratory cilia have been noted. Alternative splicing of RPGR is complex in all species examined. In RP3 patients, mutations have been found in exons 1-14 and ORF15, thus delineating a transcript necessary for normal retinal function in humans. The great majority of mutations are predicted to result in premature termination of translation. These mutations are scattered over exons 1-14 and ORF15, while most missense mutations occur in a domain with homology to the protein RCC1, encoded by exons 1-10. Exon ORF15 is a "hot spot" for mutation, at least in the British population, in which it harbors 80% of the mutations found within a sample of 47 X-linked retinitis pigmentosa patients. Most RPGR mutations are unique to single families, which makes it difficult to demonstrate phenotype-genotype correlations.

X-linked cone-rod dystrophy (locus COD1): identification of mutations in RPGR exon ORF15

X-linked cone-rod dystrophy (COD1) is a retinal disease that primarily affects the cone photoreceptors; the disease was originally mapped to a limited region of Xp11.4. We evaluated the three families from our original study with new markers and clinically reassessed all key recombinants; we determined that the critical intervals in families 2 and 3 overlapped the RP3 locus and that a status change (from affected to probably unaffected) of a key recombinant individual in family 1 also reassigned the disease locus to include RP3 as well. Mutation analysis of the entire RPGR coding region identified two different 2-nucleotide (nt) deletions in ORF15, in family 2 (delAG) and in families 1 and 3 (delGG), both of which result in a frameshift leading to altered amino acid structure and early termination. In addition, an independent individual with X-linked cone-rod dystrophy demonstrated a 1-nt insertion (insA) in ORF15. The presence of three distinct mutations associated with the same disease phenotype provides strong evidence that mutations in RPGR exon ORF15 are responsible for COD1. Genetic heterogeneity was observed in three other families, including the identification of an in-frame 12-nt deletion polymorphism in ORF15 that did not segregate with the disease in one of these families.

Novel deletion of the RPGR gene in a Chinese family with X-linked retinitis pigmentosa

PURPOSE

To characterize a Chinese family with inherited retinitis pigmentosa (RP).

METHODS

Linkage studies and haplotype analysis were used for gene mapping, and single-strand conformation polymorphism (SSCP) analysis and direct DNA sequence analysis were used for identifying the responsible mutation.

RESULTS

Pedigree analysis suggests that RP in the Chinese family RP002 is inherited either as an autosomal recessive trait or as an X-linked trait. Linkage analysis of RP002 excluded all known autosomal recessive RP loci. Further analysis with 17 polymorphic markers covering the entire X chromosome localized the RP gene in RP002 between markers GATA175D03 and GATA144D04 on Xp11.4, a region where the RP3 gene (RPGR ) is found. Mutation analysis of the RPGR gene in RP002 revealed a novel 28-bp deletion in exon 7. This deletion resulted in an in-frame stop codon that eliminates the C-terminal two-thirds of the RPGR protein. The 28-bp deletion co-segregated with the disease in the family and was not present in 100 normal Chinese individuals. Female carriers of the deletion were affected with myopia and had ERG abnormalities and mild constriction of visual field.

CONCLUSIONS

A novel 28-bp deletion in the RPGR gene identified in an X-linked Chinese RP family causes severe RP in male patients as well as myopia and ERG abnormalities in female carriers. The deletion represents the largest microdeletion identified in RPGR to date, and expands the spectrum of RPGR mutations causing XLRP.

Update on the molecular genetics of retinitis pigmentosa

Retinitis pigmentosa (RP) is a heterogeneous group of retinal dystrophies characterized by photoreceptor cell degeneration. RP causes night blindness, a gradual loss of peripheral visual fields, and eventual loss of central vision. Advances in molecular genetics have provided new insights into the genes responsible and the pathogenic mechanisms of RP. The genetics of RP is complex, and the disease can be inherited in autosomal dominant, recessive, X-linked, or digenic modes. Twenty-six causative genes have been identified or cloned for RP, and an additional fourteen genes have been mapped, but not yet identified. Eight autosomal dominant forms are due to mutations in RHO on chromosome 3q21-24, RDS on 6p21.1-cen, RP1 on 8p11-21, RGR on 10q23, ROM1 on 11q13, NRL on 14q11.1-11.2, CRX on 19q13.3, and PRKCG on 19q13.4. Autosomal recessive genes include RPE65 on chromosome 1p31, ABCA4 on 1p21-13, CRB1 on 1q31-32.1, USH2A on 1q41, MERTK on 2q14.1, SAG on 2q37.1, RHO on 3q21-24, PDE6B on 4p16.3, CNGA1 on 4p14-q13, PDE6A on 5q31.2-34, TULP1 on 6p21.3, RGR on 10q, NR2E3 on 15q23, and RLBP1 on 15q26. For X-linked RP, two genes, RP2 and RP3 (RPGR), have been cloned. Moreover, heterozygous mutations in ROM1 on 11q13, in combination with heterozygous mutations in RDS on 6p21.1-cen, cause digenic RP (the two-locus mechanism). These exciting molecular discoveries have defined the genetic pathways underlying the pathogenesis of retinitis pigmentosa, and have raised the hope of genetic testing for RP and the development of new avenues for therapy.

Molecular cloning and characterization of dystrophin and Dp71, two products of the Duchenne Muscular Dystrophy gene, in zebrafish

Dystrophin, the protein responsible for Duchenne Muscular Dystrophy (DMD), plays a critical role in the maintenance of the muscle membrane integrity. There are several forms of dystrophin derived from the DMD gene by alternative promoter usage. In addition to full-length dystrophin (Dp427), four shorter transcripts have been identified: Dp260, Dp140, Dp116 and Dp71. The functional role played by the different products of the DMD gene is not yet determined. To get insight into the function of dystrophin and related products, we have investigated the presence of dystrophin in zebrafish. This choice takes advantage of large-scale mutagenesis screens in zebrafish, which have led to the identification of several mutants with motility defects. The identification and characterization of the genes affected by these mutations is likely to provide relevant information for the understanding of the molecular mechanisms of muscle development and function. Two cDNA clones encoding the homologues of dystrophin and Dp71 in zebrafish were identified and characterized. Both transcripts exhibit a high degree of sequence homology with the dystrophin and Dp71 proteins described in higher vertebrates. In addition, three alternative spliced transcripts that occur at the C-terminal end of the zebrafish DMD gene have been identified. These transcripts exhibit different patterns of tissue expression. We have also determined the chromosomal localization of dystrophin on the radiation hybrid map of the zebrafish genome. Our results indicate that the dystrophin gene is localized to linkage group one. Altogether, these results give new insights on the physiological role played by dystrophin and related proteins, and provide new tools for the identification of mutated genes associated with muscle defects in zebrafish.

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.

Three novel mutations causing a truncated protein within the RP2 gene in Italian families with X-linked retinitis pigmentosa

X-linked retinitis pigmentosa (XLRP) results from mutations in a number of loci, including RP2 at Xp11.3, and RP3 at Xp21.1. RP2 and RP3 genes have been identified by positional cloning. RP2 mutations are found in about 10% of XLRP patients. We performed a mutational screening of RP2 gene inpatients belonging to seven unrelated families in linkage with the RP2 locus. SSCP analysis detected three conformation variants, within exon 2 and 3. Direct sequencing of exon 2, disclosed a G-->A transition at nucleotide 449 (W150X), and a G-->T transversion in position 547 (E183X). Sequence analysis of exon 3 variant revealed an insertion (853/854insG), leading to a frameshift. In this patient, we detected an additional sequence alteration (A-->G at nucleotide 848, E283G). Each mutation was co-segregating with the disease in the affected family members available for the study. These mutations are expected to introduce a stop codon within the RP2 coding sequence probably resulting in a truncated or unstable protein.

Remapping of the RP15 locus for X-linked cone-rod degeneration to Xp11.4-p21.1, and identification of a de novo insertion in the RPGR exon ORF15

X-linked forms of retinitis pigmentosa (XLRP) are among the most severe, because of their early onset, often leading to significant vision loss before the 4th decade. Previously, the RP15 locus was assigned to Xp22, by linkage analysis of a single pedigree with "X-linked dominant cone-rod degeneration." After clinical reevaluation of a female in this pedigree identified her as affected, we remapped the disease to a 19.5-cM interval (DXS1219-DXS993) at Xp11.4-p21.1. This new interval overlapped both RP3 (RPGR) and COD1. Sequencing of the previously published exons of RPGR revealed no mutations, but a de novo insertion was detected in the new RPGR exon, ORF15. The identification of an RPGR mutation in a family with a severe form of cone and rod degeneration suggests that RPGR mutations may encompass a broader phenotypic spectrum than has previously been recognized in "typical" retinitis pigmentosa.