PRPH2-Related Retinal Dystrophies: Mutational Spectrum in 103 Families from a Spanish Cohort

PRPH2, one of the most frequently inherited retinal dystrophy (IRD)-causing genes, implies a high phenotypic variability. This study aims to analyze the PRPH2 mutational spectrum in one of the largest cohorts worldwide, and to describe novel pathogenic variants and genotype-phenotype correlations. A study of 220 patients from 103 families recruited from a database of 5000 families. A molecular diagnosis was performed using classical molecular approaches and next-generation sequencing. Common haplotypes were ascertained by analyzing single-nucleotide polymorphisms. We identified 56 variants, including 11 novel variants. Most of them were missense variants (64%) and were located in the D2-loop protein domain (77%). The most frequently occurring variants were p.Gly167Ser, p.Gly208Asp and p.Pro221_Cys222del. Haplotype analysis revealed a shared region in families carrying p.Leu41Pro or p.Pro221_Cys222del. Patients with retinitis pigmentosa presented an earlier disease onset. We describe the largest cohort of IRD families associated with PRPH2 from a single center. Most variants were located in the D2-loop domain, highlighting its importance in interacting with other proteins. Our work suggests a likely founder effect for the variants p.Leu41Pro and p.Pro221_Cys222del in our Spanish cohort. Phenotypes with a primary rod alteration presented more severe affectation. Finally, the high phenotypic variability in PRPH2 hinders the possibility of drawing genotype-phenotype correlations.

Comprehensive Genotyping and Phenotyping Analysis of GUCY2D-Associated Rod- and Cone-Dominated Dystrophies

PURPOSE

To describe the genetic and clinical spectrum of GUCY2D-associated retinopathies and to accurately establish their prevalence in a large cohort of patients.

DESIGN

Retrospective case series.

METHODS

Institutional study of 47 patients from 27 unrelated families with retinal dystrophies carrying disease-causing GUCY2D variants from the Fundación Jiménez Díaz hospital dataset of 8000 patients. Patients underwent ophthalmological examination and molecular testing by Sanger or exome sequencing approaches. Statistical and principal component analyses were performed to determine genotype-phenotype correlations.

RESULTS

Four clinically different associated phenotypes were identified: 66.7% of families with cone/cone-rod dystrophy, 22.2% with Leber congenital amaurosis, 7.4% with early-onset retinitis pigmentosa, and 3.7% with congenital night blindness. Twenty-three disease-causing GUCY2D variants were identified, including 6 novel variants. Biallelic variants accounted for 28% of patients, whereas most carried dominant alleles associated with cone/cone-rod dystrophy. The disease onset had statistically significant differences according to the functional variant effect. Patients carrying GUCY2D variants were projected into 3 subgroups by allelic combination, disease onset, and presence of nystagmus or night blindness. In contrast to patients with the most severe phenotype of Leber congenital amaurosis, 7 patients with biallelic GUCY2D had a later and milder rod form with night blindness in infancy as the first symptom.

CONCLUSIONS

This study represents the largest GUCY2D cohort in which 4 distinctly different phenotypes were identified, including rare intermediate presentations of rod-dominated retinopathies. We established that GUCY2D is linked to about 1% of approximately 3000 molecularly characterized families of our cohort. All of these findings are critical for defining cohorts for inclusion in future clinical trials.

RPE65-related retinal dystrophy: Mutational and phenotypic spectrum in 45 affected patients

INTRODUCTION

Biallelic pathogenic RPE65 variants are related to a spectrum of clinically overlapping inherited retinal dystrophies (IRD). Most affected individuals progress to severe disease, with 50% of patients becoming legally blind by 20 years of age. Deeper knowledge of the mutational spectrum and the phenotype-genotype correlation in RPE65-related IRD is needed.

PATIENTS AND METHODS

Forty-five affected subjects from 27 unrelated families with a clinical diagnosis of RPE65-related IRD were included. Clinical evaluation consisted of self-reported ophthalmological history and objective ophthalmological examination. Patients' genotype was classified according to variant class (truncating or missense) or to variant location at different protein domains. The main phenotypic outcome measure was age at onset (AAO) of symptomatic disease and a Kaplan-Meier analysis of disease symptom event-free survival was performed.

RESULTS

Twenty-nine different RPE65 variants were identified in our cohort, 7 of them novel. Patients carrying two missense alleles showed a later disease onset than those with 1 or 2 truncating variants (log-rank test p <0.05). While 60% of patients carrying a missense/missense genotype presented symptoms before or during the first year of life, almost all patients with at least 1 truncating allele (91%) had an AAO ≤1 year (p <0.05).

CONCLUSION

Our findings suggest an association between the type of RPE65 variant carried and AAO. These findings provide useful data on RPE65-associated IRD phenotypes and may help improve clinical and therapeutic management of these patients.

Unravelling the pathogenic role and genotype-phenotype correlation of the USH2A p.(Cys759Phe) variant among Spanish families

INTRODUCTION

Mutations in USH2A cause both isolated Retinitis Pigmentosa (RP) and Usher syndrome (that implies RP and hearing impairment). One of the most frequent variants identified in this gene and among these patients is the p.(Cys759Phe) change. However, the pathogenic role of this allele has been questioned since it was found in homozygosity in two healthy siblings of a Spanish family. To assess the causative role of USH2A p.(Cys759Phe) in autosomal recessive RP (ARRP) and Usher syndrome type II (USH2) and to establish possible genotype-phenotype correlations associated with p.(Cys759Phe), we performed a comprehensive genetic and clinical study in patients suffering from any of the two above-mentioned diseases and carrying at least one p.(Cys759Phe) allele.

MATERIALS AND METHODS

Diagnosis was set according to previously reported protocols. Genetic analyses were performed by using classical molecular and Next-Generation Sequencing approaches. Probands of 57 unrelated families were molecularly studied and 63 patients belonging to these families were phenotypically evaluated.

RESULTS

Molecular analysis characterized 100% of the cases, identifying: 11 homozygous patients for USH2A p.(Cys759Phe), 42 compound heterozygous patients (12 of them with another missense USH2A pathogenic variant and 30 with a truncating USH2A variant), and 4 patients carrying the p.(Cys759Phe) allele and a pathogenic variant in another RP gene (PROM1, CNGB1 or RP1). No additional causative variants were identified in symptomatic homozygous patients. Statistical analysis of clinical differences between zygosity states yielded differences (p≤0.05) in age at diagnosis of RP and hypoacusis, and progression of visual field loss. Homozygosity of p.(Cys759Phe) and compound heterozygosity with another USH2A missense variant is associated with ARRP or ARRP plus late onset hypoacusis (OR = 20.62, CI = 95%, p = 0.041).

CONCLUSIONS

The present study supports the role of USH2A p.(Cys759Phe) in ARRP and USH2 pathogenesis, and demonstrates the clinical differences between different zygosity states. Phenotype-genotype correlations may guide the genetic characterization based upon specific clinical signs and may advise on the clinical management and prognosis based upon a specific genotype.

Identification of the Photoreceptor Transcriptional Co-Repressor SAMD11 as Novel Cause of Autosomal Recessive Retinitis Pigmentosa

Retinitis pigmentosa (RP), the most frequent form of inherited retinal dystrophy is characterized by progressive photoreceptor degeneration. Many genes have been implicated in RP development, but several others remain to be identified. Using a combination of homozygosity mapping, whole-exome and targeted next-generation sequencing, we found a novel homozygous nonsense mutation in SAMD11 in five individuals diagnosed with adult-onset RP from two unrelated consanguineous Spanish families. SAMD11 is ortholog to the mouse major retinal SAM domain (mr-s) protein that is implicated in CRX-mediated transcriptional regulation in the retina. Accordingly, protein-protein network analysis revealed a significant interaction of SAMD11 with CRX. Immunoblotting analysis confirmed strong expression of SAMD11 in human retina. Immunolocalization studies revealed SAMD11 was detected in the three nuclear layers of the human retina and interestingly differential expression between cone and rod photoreceptors was observed. Our study strongly implicates SAMD11 as novel cause of RP playing an important role in the pathogenesis of human degeneration of photoreceptors.

Clinical aspects of Usher syndrome and the USH2A gene in a cohort of 433 patients

IMPORTANCE

A new statistical approach is needed to describe the clinical differences between type I and type II Usher syndrome and between the 2 most frequent mutations in the USH2A gene.

OBJECTIVES

To describe the primary phenotypic characteristics and differences between type I and type II Usher syndrome and to establish a phenotype-genotype correlation for the 2 most frequent mutations in the USH2A gene.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional study at a genetics department, in which clinical evaluations were performed for 433 patients (297 unrelated families) who were classified as having type I, II, III, atypical, or unclassified Usher syndrome according to their clinical history, pedigree data, results from ophthalmological studies, and audiological, neurophysiological, and vestibular test results. Molecular studies were performed for 304 patients (256 unrelated families). The Mann-Whitney U test or the χ2 test was used for calculating the differences between mean values for the analyzed parameters.

MAIN OUTCOMES AND MEASURES

Age at diagnosis; age at onset of night blindness, visual field loss, visual acuity loss, and cataracts; and severity and age at diagnosis of hearing loss.

RESULTS

The comparison between patients with type I Usher syndrome and those with type II Usher syndrome revealed P < .001 for most items analyzed. The most frequent mutations in the USH2A gene were the p.Glu767Serfs*21 and p.Cys759Phe mutations, with an allelic frequency of 23.2% (63 of 272 alleles) and 8.1% (22 of 272 alleles), respectively. The phenotypic analysis for patients carrying p.Cys759Phe showed P < .001 for most items analyzed when compared with patients carrying p.Glu767Serfs*21 and when compared with patients carrying other mutations in the USH2A gene. None of the p.Cys759Phe patients exhibited a severe hearing loss phenotype, and more than 60% had only mild hearing loss. Most patients carrying the p.Glu767Serfs*21 mutation (72.1%) were moderately deaf.

CONCLUSIONS AND RELEVANCE

Our study presents the clinical differences between type I and type II Usher syndrome and between the 2 most frequent mutations in the USH2A gene. Detailed genotype-phenotype correlations, as presented in our study, allow for a better correlation of clinical signs with a known genotype and can improve the clinical management, genetic counseling, and risk assessment of patients with Usher syndrome because an estimated prognosis of their disease can be made.

Expanding the phenotype of PRPS1 syndromes in females: neuropathy, hearing loss and retinopathy

Background

Phosphoribosyl pyrophosphate synthetase (PRS) I deficiency is a rare medical condition caused by missense mutations in PRPS1 that lead to three different phenotypes: Arts Syndrome (MIM 301835), X-linked Charcot-Marie-Tooth (CMTX5, MIM 311070) or X-linked non-syndromic sensorineural deafness (DFN2, MIM 304500). All three are X-linked recessively inherited and males affected display variable degree of central and peripheral neuropathy. We applied whole exome sequencing to a three-generation family with optic atrophy followed by retinitis pigmentosa (RP) in all three cases, and ataxia, progressive peripheral neuropathy and hearing loss with variable presentation.

Methods

Whole exome sequencing was performed in two affecteds and one unaffected member of the family. Sanger sequencing was used to validate and segregate the 12 candidate mutations in the family and to confirm the absence of the novel variant in PRPS1 in 191 controls. The pathogenic role of the novel mutation in PRPS1 was assessed in silico and confirmed by enzymatic determination of PRS activity, mRNA expression and sequencing, and X-chromosome inactivation.

Results

A novel missense mutation was identified in PRPS1 in the affected females. Age of onset, presentation and severity of the phenotype are highly variable in the family: both the proband and her mother have neurological and ophthalmological symptoms, whereas the phenotype of the affected sister is milder and currently confined to the eye. Moreover, only the proband displayed a complete lack of expression of the wild type allele in leukocytes that seems to correlate with the degree of PRS deficiency and the severity of the phenotype. Interestingly, optic atrophy and RP are the only common manifestations to all three females and the only phenotype correlating with the degree of enzyme deficiency.

Conclusions

These results are in line with recent evidence of the existence of intermediate phenotypes in PRS-I deficiency syndromes and demonstrate that females can exhibit a disease phenotype as severe and complex as their male counterparts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-014-0190-9) contains supplementary material, which is available to authorized users.

Contribution of mutation load to the intrafamilial genetic heterogeneity in a large cohort of Spanish retinal dystrophies families

PURPOSE

The aim of this study was to deepen our knowledge on the basis of intrafamilial genetic heterogeneity of inherited retinal dystrophies (RD) to further discern the contribution of individual alleles to the pathology.

METHODS

Families with intrafamilial locus and/or allelic heterogeneity were selected from a cohort of 873 characterized of 2468 unrelated RD families. Clinical examination included visual field assessments, electrophysiology, fundus examination, and audiogram. Molecular characterization was performed using a combination of different methods: genotyping microarray, single strand conformational polymorphism (SSCP), denaturing high pressure liquid chromatography (dHPLC), high resolution melt (HRM), multiplex ligation-dependent probe amplification (MLPA), Sanger sequencing, whole-genome homozygosity mapping, and next-generation sequencing (NGS).

RESULTS

Overall, intrafamilial genetic heterogeneity was encountered in a total of 8 pedigrees. There were 5 of 873 families (~0.6%) with causative mutations in more than one gene (locus heterogeneity), involving the genes: (1) USH2A, RDH12, and TULP1; (2) PDE6B and a new candidate gene; (3) CERKL and CRB1; (4) BBS1 and C2orf71; and (5) ABCA4 and CRB1. Typically, in these cases, each mutated gene was associated with different phenotypes. In the 3 other families (~0.35%), different mutations in the same gene (allelic heterogeneity) were found, including the frequent RD genes ABCA4 and CRB1.

CONCLUSIONS

This systematic research estimates that the frequency of overall mutation load promoting RD intrafamilial heterogeneity in our cohort of Spanish families is almost 1%. The identification of the genetic mechanisms underlying RD locus and allelic heterogeneity is essential to discriminate the real contribution of the monoallelic mutations to the disease, especially in the NGS era. Moreover, it is decisive to provide an accurate genetic counseling and in disease treatment.

Benefits of omega-3 fatty acid dietary supplementation on health-related quality of life in patients with meibomian gland dysfunction

Background

We assessed the impact of a dietary supplement based on the combination of omega-3 essential fatty acids and antioxidants on health-related quality of life in patients with meibomian gland dysfunction (MGD).

Methods

Patients of either sex (aged 18–85 years) diagnosed with MGD according to criteria identified at a 2011 International Workshop on Meibomian Gland Dysfunction participated in this randomized, double-masked, placebo-controlled study. Group A patients (controls) received an oral placebo supplement and group B patients received the oral study supplement (Brudysec^® 1.5 g; Brudy Laboratories, Barcelona, Spain). At baseline and at 3-month follow-up, the patients completed the 36-Item Short Form Health Survey questionnaire using a Spanish validated version. The Physical (PCS) and Mental (MCS) Component Summary scores were the main outcome variables.

Results

A total of 61 patients completed the study (group A, n=31; group B, n=30). There were no significant differences in PCS and MCS scores at baseline between the two study groups, but after 3 months of treatment, significantly higher mean PCS and MSC scores were observed in patients treated with the active omega-3 dietary supplement as compared with controls (mean [standard deviation] PCS score 53.33±5.57 versus 47.46±7.31, P=0.008; mean MCS score 54.60±5.64 versus 47.80±8.45, P=0.0005). Moreover, mean differences between values at 3 months as compared with baseline were statistically significant for patients in group B (PCS score 7.14±5.81, 95% confidence interval 4.97–9.31, P=0.000; MCS score 5.96±7.64, 95% confidence interval 3.10–8.81, P=0.0002), whereas mean differences in patients assigned to group A were not statistically significant.

Conclusion

Dietary supplementation with a combination of omega-3 essential fatty acids and antioxidants had a significant beneficial effect on HRQoL (health-related quality of life) in patients with MGD.

Involvement of LCA5 in Leber congenital amaurosis and retinitis pigmentosa in the Spanish population

OBJECTIVE

We aimed to identify novel genetic defects in the LCA5 gene underlying Leber congenital amaurosis (LCA) in the Spanish population and to describe the associated phenotype.

DESIGN

Case series.

PARTICIPANTS

A cohort of 217 unrelated Spanish families affected by autosomal recessive or isolated retinal dystrophy, that is, 79 families with LCA and 138 families with early-onset retinitis pigmentosa (EORP). A total of 100 healthy, unrelated Spanish individuals were screened as controls.

METHODS

High-resolution homozygosity mapping was performed in 44 patients with LCA using genome-wide single nucleotide polymorphism (SNP) microarrays. Direct sequencing of the LCA5 gene was performed in 5 patients who showed homozygous regions at chromosome 6 and in 173 unrelated individuals with LCA or EORP. The ophthalmic history of 8 patients carrying LCA5 mutations was reviewed and additional examinations were performed, including electroretinography (ERG), optical coherence tomography (OCT), and fundus photography.

MAIN OUTCOME MEASURES

Single nucleotide polymorphism genotyping, identity-by-descent (IBD) regions, LCA5 mutations, best-corrected visual acuity, visual field assessments, fundus appearance, ERG, and OCT findings.

RESULTS

Four novel and 2 previously reported LCA5 mutations have been identified in 6 unrelated families with LCA by homozygosity mapping or Sanger sequencing. Thus, LCA5 mutations have a frequency of 7.6% in the Spanish population. However, no LCA5 mutations were found in 138 patients with EORP. Although most of the identified LCA5 mutations led to a truncated protein, a likely pathogenic missense variant was identified for the first time as a cause of LCA, segregating in 2 families. We also have characterized a novel splicing site mutation at the RNA level, demonstrating that the mutant LCA5 transcript was absent in a patient. All patients carrying LCA5 mutations presented nystagmus, night blindness, and progressive loss of visual acuity and visual field leading to blindness toward the third decade of life. Fundoscopy showed fundus features of pigmentary retinopathy with atrophic macular lesions.

CONCLUSIONS

This work reveals a higher frequency of LCA5 mutations in a Spanish LCA cohort than in other populations. This study established gene-specific frequencies and the underlying phenotype of LCA5 mutations in the Spanish population.

High frequency of CRB1 mutations as cause of Early-Onset Retinal Dystrophies in the Spanish population

BACKGROUND

CRB1 mutations are reported as cause of severe congenital and early-onset retinal dystrophies (EORD) with different phenotypic manifestations, including Leber congenital amaurosis (LCA), retinitis pigmentosa (RP) and cone-rod dystrophies. Comprehensive mutational scanning of the whole gene has been only performed in few cohorts, mainly in LCA patients. Here, we aimed investigating the real prevalence of CRB1 mutations in the Spanish population by extensive screening of CRB1 mutations in a large cohort of LCA and EORP cases.

METHODS

This report integrates data from previous studies on CRB1 defects in our Spanish cohort of LCA and early-onset RP (EORP) with new findings from a comprehensive mutational screening of the whole gene. The molecular tools used include mutation genotyping arrays, whole-genome homozygosity mapping, an optimized high-resolution melting (HRM) analysis and Sanger sequencing.

RESULTS

A large clinically well-characterized cohort of 404 Spanish cases was studied, 114 of which suffered from LCA and 290 from EORP. This study reveals that 11% of Spanish patients carried mutations in CRB1, ranging from 9% of EORP to 14% of LCA cases. More than three quarters of the mutations identified herein have been first described in this Spanish cohort, 13 of them are unreported new variants and 13 had been previously reported in our previous studies.

CONCLUSIONS

This work provides a wide spectrum of CRB1 mutations in the Spanish EORD patients and evidences the major role of CRB1 as causal gene in the Spanish EORP patients. It is noteworthy that a high rate of private mutations only described in our cohort has been found so far. To our knowledge, this study represents the most complete mutational screening of CRB1 in a Spanish LCA and EORP cohort, allowing us to establish gene-specific frequencies and to provide a wide spectrum of CRB1 mutations in the Spanish population.

Novel p.M96T variant of NRL and shRNA-based suppression and replacement of NRL mutants associated with autosomal dominant retinitis pigmentosa

Mutations in the gene encoding the transcription factor neural retina leucine zipper (NRL) are known to cause autosomal dominant (adRP) or recessive (arRP) retinitis pigmentosa (RP). In an adRP Spanish family, we detected a novel sequence variation (c.287T>C) in the NRL gene that results in the p.M96T protein change. A functional test of the ability of NRL, in conjunction with cone-rod homeobox (CRX), to transactivate a human rhodopsin (RHO) promoter was used to evaluate the pathogenic mechanisms of NRL. We found upregulation of the RHO promoter by p.M96T protein similar to that shown by other missense NRL mutations that cause adRP. Affected RP patients of the family carry the nucleotide change, although two other family members that also carry the c.287T>C variation remain asymptomatic. This result complicates the genetic counselling of the family. The pathogenic mechanisms associated with adRP NRL mutations appear to be caused by a gain of function. To suppress the negative effect of an NRL mutant, the suppression and replacement strategy seems to be the most suitable therapeutic approach capable of overcoming the mutational heterogeneity associated with NRL-linked adRP. Thus, we evaluated this methodology in the NRL gene for the first time.

High prevalence of mutations in peripherin/RDS in autosomal dominant macular dystrophies in a Spanish population

PURPOSE

Mutations in the peripherin/retinal degeneration slow (RDS) gene are a known cause of various types of central retinal dystrophies. The purpose of this study was to determine the prevalence of mutations in the peripherin/RDS gene in Spanish patients with different types of autosomal dominant macular dystrophy.

METHODS

Ophthalmic and electrophysiological examination was performed in patients from 61 unrelated autosomal dominant macular dystrophy (adMD) Spanish families. Screening for mutations in the peripherin/RDS gene by denaturing gradient gel electrophoresis (DGGE) and direct genomic sequencing was performed in index patients and extended to the family when positive.

RESULTS

We report four novel mutations in peripherin/RDS and a relatively high frequency (23%) of mutations in this gene in families with adMD. Thirteen different mutations were found in fifteen adMD families. Three novel missense, four nonsense and a cis-acting splicing mutation IVS2+2T>C, were found in a Spanish population while five more missense mutations were also reported in other populations. The Arg142Trp and Arg172Trp mutations, present in several populations, were both detected in two independent Spanish families. All the missense mutations produce an amino acid substitution in the second intradiscal loop of the peripherin, while the nonsense mutations presumably generate a truncated protein.

CONCLUSIONS

A high frequency (23%) of mutations in the peripherin/RDS gene was found in a cohort of 61 unrelated patients with various types of autosomal dominant central retinal dystrophies as compared with a low prevalence (1.3%) of mutations in this gene causing retinitis pigmentosa in a Spanish population. Different macular dystrophy phenotypes according to the mutations in peripherin/RDS are shown. However, a limited phenotype variation was observed for these mutations within the family.

Three novel and the common Arg677Ter RP1 protein truncating mutations causing autosomal dominant retinitis pigmentosa in a Spanish population

BACKGROUND

Retinitis pigmentosa (RP), a clinically and genetically heterogeneous group of retinal degeneration disorders affecting the photoreceptor cells, is one of the leading causes of genetic blindness. Mutations in the photoreceptor-specific gene RP1 account for 3-10% of cases of autosomal dominant RP (adRP). Most of these mutations are clustered in a 500 bp region of exon 4 of RP1.

METHODS

Denaturing gradient gel electrophoresis (DGGE) analysis and direct genomic sequencing were used to evaluate the 5' coding region of exon 4 of the RP1 gene for mutations in 150 unrelated index adRP patients. Ophthalmic and electrophysiological examination of RP patients and relatives according to pre-existing protocols were carried out.

RESULTS

Three novel disease-causing mutations in RP1 were detected: Q686X, K705fsX712 and K722fsX737, predicting truncated proteins. One novel missense mutation, Thr752Met, was detected in one family but the mutation does not co-segregate in the family, thereby excluding this amino acid variation in the protein as a cause of the disease. We found the Arg677Ter mutation, previously reported in other populations, in two independent families, confirming that this mutation is also present in a Spanish population.

CONCLUSION

Most of the mutations reported in the RP1 gene associated with adRP are expected to encode mutant truncated proteins that are approximately one third or half of the size of wild type protein. Patients with mutations in RP1 showed mild RP with variability in phenotype severity. We also observed several cases of non-penetrant mutations.

Mutations in the pre-mRNA splicing-factor genes PRPF3, PRPF8, and PRPF31 in Spanish families with autosomal dominant retinitis pigmentosa

PURPOSE

Mutations in the systemically expressed pre-mRNA splicing-factor genes PRPF3, PRPF8, and PRPF31 have recently been associated with autosomal dominant retinitis pigmentosa (adRP). This study was intended to identify mutations in PRPF3, PRPF8, and PRPF31 in 150 Spanish families affected by adRP, to measure the contribution of mutations in these genes to adRP in that population, and to correlate RP phenotype expression with mutations in pre-mRNA splicing-factor genes.

METHODS

Denaturing gradient gel electrophoresis (DGGE) and direct genomic sequencing were used to evaluate the complete coding region and flanking intronic sequences of the PRPF31 gene, exon 42 of PRPF8, and exon 11 of PRPF3 for mutations in 150 unrelated index patients with adRP. Ophthalmic and electrophysiological examination of patients with RP and their relatives was performed according to preexisting protocols.

RESULTS

Three nonsense mutations caused by insertion and deletion sequences and two missense mutations (Arg2310Gly) and within the stop codon of the PRPF8 gene (TGA-->TTG), were detected in five unrelated heterozygous patients. Three patients were heterozygous carriers of different nonsense mutations in exon 8 of the PRPF31, gene and one Thr494Met mutation was found in exon 11 of the PRPF3 gene. Cosegregation of the mutation in PRPF8 and PRPF3 with adRP was observed. However, two nonsense mutations in PRPF31 causing adRP detected in two families showed asymptomatic carriers.

CONCLUSIONS

Nine mutations, six of which are novel, in the pre-mRNA splicing-factor genes PRPF3, PRPF8, and PRPF31, causing adRP have been identified in the Spanish population. Their contribution to adRP is approximately 5% after correction in relation to mutations found in other genes causing adRP. The patients carrying a mutation in the pre-mRNA splicing-factor PRPF8 gene showed a type 1 diffuse RP. The existence of asymptomatic carriers of the nonsense mutation in the PRPF31 gene suggests incomplete penetrance for these mutations in the families.

Prevalence of 2314delG mutation in Spanish patients with Usher syndrome type II (USH2)

The Usher syndrome (USH) is a group of autosomal recessive diseases characterized by congenital sensorineural hearing loss and retinitis pigmentosa. Three clinically distinct forms of Usher syndrome have so far been recognized and can be distinguished from one another by assessing auditory and vestibular function. Usher syndrome type II (USH2) patients have congenital moderate-to-severe nonprogressive hearing loss, retinitis pigmentosa, and normal vestibular function. Genetic linkage studies have revealed genetic heterogeneity among the three types of USH, with the majority of USH2 families showing linkage to the USH2A locus in 1q41. The USH2A gene (MIM 276901) has been identified: three mutations, 2314delG, 2913delG, and 4353-54delC, were initially reported in USH2A patients, the most frequent of which is the 2314delG mutation. It has been reported that this mutation can give rise to typical and atypical USH2 phenotypes. USH2 cases represent 62% of all USH cases in the Spanish population, and 95% of these cases have provided evidence of linkage to the USH2A locus. In the present study, the three reported mutations were analyzed in 59 Spanish families with a diagnosis of USH type II. The 2314delG was the only mutation identified in our population: it was detected in 25% of families and 16% of USH2 chromosomes analyzed. This study attempts to estimate the prevalence of this common mutation in a homogeneous Spanish population.

Novel mutations in the TULP1 gene causing autosomal recessive retinitis pigmentosa

PURPOSE

To assess the contribution of TULP1 to autosomal recessive retinitis pigmentosa (arRP).

METHODS

Fifteen exons of the gene were screened by single-strand conformation polymorphism analysis of 7 (of 49) arRP pedigrees showing cosegregation with TULP1 locus markers.

RESULTS

In one of the seven families two allelic mutations, IVS4-2delAGA and c.937delC, were found in exons 5 and 10, respectively.

CONCLUSIONS

Two novel mutations in TULP1 were found to be associated with arRP. That they both compromise the gene product supports their pathogenicity. This gene was present in no more than 2% of a panel of 49 Spanish families affected by arRP.

Identification of two rare variants (G-->A at nucleotide 721; C-->T at nucleotide 5200) in the rhodopsin gene. Mutations in brief no. 187. Online

The authors report two new rare DNA sequence variants in the Rhodopsin gene. This gene is involved in the pathogenesis of some retinal hereditary disorders as Retinitis Pigmentosa. These rare variants are G-->A at nucleotide 721 of the non-coding region and C-->T at nucleotide 5200 within codon 323 which does not alter the aminoacid cysteine. Therefore, they are not implicated in the development of the Retinitis Pigmentosa disease.

First mutation (S340X) in choroideremia gene in a Spanish family. Mutations in brief no. 173. Online

A study of choroideremia gene was performed in Spanish families affected with this disorder. One abnormal pattern was detected in exon eight corresponding to a new mutation not described before. The mutation was identified as a nonsense mutation S340X.

Detection of a novel Cys628STOP mutation of the myosin VIIA gene in Usher syndrome type Ib

A Spanish family with three Usher I syndrome-affected members was linked to markers located on chromosome 11q. A search for mutations on the myosin VIIA gene revealed a novel mutation (Cys628STOP) on exon 16 segregating with the disorder in a homozygous state. This nonsense mutation could be responsible for the disease since it leads to a truncated protein that presumably has no function.

A new locus for autosomal recessive retinitis pigmentosa (RP19) maps to 1p13-1p21

Autosomal recessive retinitis pigmentosa (arRP) is characterized by considerable allelic and nonallelic heterogeneity. Mutations have been described in the rhodopsin gene (RHO), the genes encoding the alpha and beta subunits of rod phosphodiesterase (PDEA and PDEB), and the gene encoding the alpha subunit of the cGMP-gated channel (CNCG). In addition, linkage studies in single extended pedigrees have defined two new arRP loci, at 1q and 6p. To identify the disease gene in a Spanish consanguineous arRP family, a linkage analysis was undertaken. After testing 102 polymorphic markers, a significant positive lod score (Zmax = 3.64 at theta = 0) was obtained with marker D1S188 at 1p13-p21, the same region where the Stargardt and fundus flavimaculatus (FFM) loci were previously defined. Exhaustive ophthalmologic examination of the patients clearly distinguished the disease from the Stargardt and FFM phenotypes and revealed an atypical form of arRP with choroidal atrophy as a distinctive feature.

Novel rhodopsin mutation in an autosomal dominant retinitis pigmentosa family: phenotypic variation in both heterozygote and homozygote Val137Met mutant patients

A family affected with autosomal dominant retinitis pigmentosa (RP) is presented. Two clinically affected patients (mother and daughter) were heterozygous for the same novel missense mutation (Val137Met) of the rhodopsin gene (RHO). Both heterozygous and homozygous cases were observed among their few symptomatic relatives. Wide clinical variation was exhibited among the individuals with mutations in this family. None of the controls showed this change in RHO, nor has it been previously reported in other RP families. No other RHO mutation was observed. Additional genetic or environmental factors could play a role in modulating the penetrance and clinical expression of this RHO mutation.

Ischemic optic neuropathy after intraocular lens implantation to correct high myopia in a phakic patient

A 33-year-old patient had uncomplicated anterior chamber intraocular lens implantation (Worst-Fechner biconcave myopia lens) to correct high myopia. Immediately after surgery, she developed anterior ischemic optic neuropathy likely associated with increased intraocular pressure and systemic hypotension. To our knowledge, this is the first documented case of anterior ischemic optic neuropathy after anterior chamber intraocular lens implantation to correct high myopia in a phakic eye.