Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. We conducted a genome-wide association study including 1,854 PACG cases and 9,608 controls across 5 sample collections in Asia. Replication experiments were conducted in 1,917 PACG cases and 8,943 controls collected from a further 6 sample collections. We report significant associations at three new loci: rs11024102 in PLEKHA7 (per-allele odds ratio (OR) = 1.22; P = 5.33 × 10−12), rs3753841 in COL11A1 (per-allele OR = 1.20; P = 9.22 × 10−10) and rs1015213 located between PCMTD1 and ST18 on chromosome 8q (per-allele OR = 1.50; P = 3.29 × 10−9). Our findings, accumulated across these independent worldwide collections, suggest possible mechanisms explaining the pathogenesis of PACG.
Congenital cataracts are an important cause of bilateral visual impairment in infants. Through genome-wide linkage analysis in a four-generation family of Irish descent, the disease-associated gene causing autosomal-dominant congenital nuclear cataract was mapped to chromosome 4p16.1. The maximum logarithm of odds (LOD) score was 2.62 at a recombination fraction θ=0, obtained for marker D4S432 physically close to the Wolfram gene (WFS1). By sequencing the coding regions and intron–exon boundaries of WFS1, we identified a DNA substitution (c.1385A-to-G) in exon 8, causing a missense mutation at codon 462 (E462G) of the Wolframin protein. This is the first report of a mutation in this gene causing an isolated nuclear congenital cataract. These findings suggest that the membrane trafficking protein Wolframin may be important for supporting the developing lens.
nuclear cataract; linkage; WFS1 gene; heterogeneity
Mutations in PRPF31 are responsible for autosomal dominant retinitis pigmentosa (adRP, RP11 form) and affected families show nonpenetrance. Differential expression of the wildtype PRPF31 allele is responsible for this phenomenon: coinheritance of a mutation and a higher expressing wildtype allele provide protection against development of disease.
It has been suggested that a major modulating factor lies in close proximity to the wildtype PRPF31 gene on Chromosome 19, implying that a cis-acting factor directly alters PRPF31 expression. Variable expression of CNOT3 is one determinant of PRPF31 expression. This study explored the relationship between CNOT3 (a trans-acting factor) and its paradoxical cis-acting nature in relation to RP11.
Linkage analysis on Chromosome 19 was performed in mutation-carrying families, and the inheritance of the wildtype PRPF31 allele in symptomatic–asymptomatic sibships was assessed—confirming that differential inheritance of wildtype chromosome 19q13 determines the clinical phenotype (P < 2.6 × 10−7).
A theoretical model was constructed that explains the apparent conflict between the linkage data and the recent demonstration that a trans-acting factor (CNOT3) is a major nonpenetrance factor: we propose that this apparently cis-acting effect arises due to the intimate linkage of CNOT3 and PRPF31 on Chromosome 19q13—a novel mechanism that we have termed “linked trans-acting epistasis.”
PRPF31; CNOT3; retinitis pigmentosa; epistasis
Several studies have demonstrated the important role of non-coding RNAs as regulators of posttranscriptional processes, including stem cells self-renewal and neural differentiation. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (ihPSCs) show enormous potential in regenerative medicine due to their capacity to differentiate to virtually any type of cells of human body. Deciphering the role of non-coding RNAs in pluripotency, self-renewal and neural differentiation will reveal new molecular mechanisms involved in induction and maintenances of pluripotent state as well as triggering these cells toward clinically relevant cells for transplantation. In this brief review we will summarize recently published studies which reveal the role of non-coding RNAs in pluripotency and neural differentiation of hESCs and ihPSC.
pluripotent stem cells; pluripotency; non-coding RNA; differentiation; human embryonic stem cells
Anterior chamber depth (ACD) is a key anatomical risk factor for primary angle closure glaucoma (PACG). We conducted a genome-wide association study (GWAS) on ACD to discover novel genes for PACG on a total of 5,308 population-based individuals of Asian descent. Genome-wide significant association was observed at a sequence variant within ABCC5 (rs1401999; per-allele effect size = −0.045 mm, P = 8.17×10−9). This locus was associated with an increase in risk of PACG in a separate case-control study of 4,276 PACG cases and 18,801 controls (per-allele OR = 1.13 [95% CI: 1.06–1.22], P = 0.00046). The association was strengthened when a sub-group of controls with open angles were included in the analysis (per-allele OR = 1.30, P = 7.45×10−9; 3,458 cases vs. 3,831 controls). Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants influencing anterior chamber dimensions.
The anterior chamber is the space within the eye which is bound by the cornea, and the anterior surfaces of the iris and lens. Anterior chamber depth (ACD) is the distance measured along the eye's optical axis, from the cornea to the lens surface. ACD is an important risk factor for primary angle closure glaucoma (PACG), a major cause of irreversible blindness worldwide, and in particular, individuals of Asian ethnicity. In order to identify the genes that underlie PACG susceptibility, we conducted a two-staged study. We first conducted a large scale genetic study on a total of 5,308 population-based individuals of Asian descent to identify the genetic variants that influence ACD. This was followed by testing for associations between the identified genetic variant and PACG in another independent collection of 4,276 PACG cases and 18,801 controls. We found that a genetic variant within ABCC5 was associated with an increased risk of having PACG. Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants that influence the anterior chamber dimensions of the eye.
Here we report recruitment of a three-generation Romani (Gypsy) family with autosomal dominant cone-rod dystrophy (adCORD). Involvement of known adCORD genes was excluded by microsatellite (STR) genotyping and linkage analysis. Subsequently, two independent total-genome scans using STR markers and single-nucleotide polymorphisms (SNPs) were performed. Haplotype analysis revealed a single 6.7-Mb novel locus between markers D10S1757 and D10S1782 linked to the disease phenotype on chromosome 10q26. Linkage analysis gave a maximum LOD score of 3.31 for five fully informative STR markers within the linked interval corresponding to the expected maximum in the family. Multipoint linkage analysis of SNP genotypes yielded a maximum parametric linkage score of 2.71 with markers located in the same chromosomal interval. There is no previously mapped CORD locus in this interval, and therefore the data reported here is novel and likely to identify a new gene that may eventually contribute to new knowledge on the pathogenesis of this condition. Sequencing of several candidate genes within the mapped interval led to negative findings in terms of the underlying molecular pathogenesis of the disease in the family. Analysis by comparative genomic hybridization excluded large chromosomal aberrations as causative of adCORD in the pedigree.
linkage analysis; cone-rod dystrophy; novel locus
Here, we report two novel GUCA1A (the gene for guanylate cyclase activating protein 1) mutations identified in unrelated Spanish families affected by autosomal dominant retinal degeneration (adRD) with cone and rod involvement. All patients from a three-generation adRD pedigree underwent detailed ophthalmic evaluation. Total genome scan using single-nucleotide polymorphisms and then the linkage analysis were undertaken on the pedigree. Haplotype analysis revealed a 55.37 Mb genomic interval cosegregating with the disease phenotype on chromosome 6p21.31-q15. Mutation screening of positional candidate genes found a heterozygous transition c.250C>T in exon 4 of GUCA1A, corresponding to a novel mutation p.L84F. A second missense mutation, c.320T>C (p.I107T), was detected by screening of the gene in a Spanish patients cohort. Using bioinformatics approach, we predicted that either haploinsufficiency or dominant-negative effect accompanied by creation of a novel function for the mutant protein is a possible mechanism of the disease due to c.250C>T and c.320T>C. Although additional functional studies are required, our data in relation to the c.250C>T mutation open the possibility that transacting factors binding to de novo created recognition site resulting in formation of aberrant splicing variant is a disease model which may be more widespread than previously recognized as a mechanism causing inherited RD.
Mutations in BEST1 gene, encoding the bestrophin-1 (Best1) protein are associated with macular dystrophies. Best1 is predominantly expressed in the retinal pigment epithelium (RPE), and is inserted in its basolateral membrane. We investigated the cellular localization in polarized MDCKII cells of disease-associated Best1 mutant proteins to study specific sorting motifs of Best1. Real-time PCR and western blots for endogenous expression of BEST1 in MDCK cells were performed. Best1 mutant constructs were generated using site-directed mutagenesis and transfected in MDCK cells. For protein sorting, confocal microscopy studies, biotinylation assays and statistical methods for quantification of mislocalization were used. Analysis of endogenous expression of BEST1 in MDCK cells revealed the presence of BEST1 transcript but no protein. Confocal microscopy and quantitative analyses indicate that transfected normal human Best1 displays a basolateral localization in MDCK cells, while cell sorting of several Best1 mutants (Y85H, Q96R, L100R, Y227N, Y227E) was altered. In contrast to constitutively active Y227E, constitutively inactive Y227F Best1 mutant localized basolaterally similar to the normal Best1 protein. Our data suggest that at least three basolateral sorting motifs might be implicated in proper Best1 basolateral localization. In addition, non-phosphorylated tyrosine 227 could play a role for basolateral delivery.
BVMD; Best1 protein; cell polarity; MDCK cells
Leber congenital amaurosis (LCA) is an infantile-onset form of inherited retinal degeneration characterized by severe vision loss1, 2. Two-thirds of LCA cases are caused by mutations in 17 known disease genes3 (RetNet Retinal Information Network). Using exome sequencing, we identified a homozygous missense mutation (c.25G>A, p.Val9Met) in NMNAT1 as likely disease-causing in two siblings of a consanguineous Pakistani kindred affected by LCA. This mutation segregated with disease in their kindred, including in three other children with LCA. NMNAT1 resides in the previously identified LCA9 locus and encodes the nuclear isoform of nicotinamide mononucleotide adenylyltransferase, a rate-limiting enzyme in nicotinamide adenine dinucleotide (NAD+) biosynthesis4, 5. Functional studies showed the p.Val9Met mutation decreased NMNAT1 enzyme activity. Sequencing NMNAT1 in 284 unrelated LCA families identified 14 rare mutations in 13 additional affected individuals. These results are the first to link an NMNAT isoform to disease and indicate that NMNAT1 mutations cause LCA.
Mutations in the CRB1 gene are associated with variable phenotypes of severe retinal dystrophies, ranging from Leber Congenital Amaurosis (LCA) to rod-cone dystrophy (also called retinitis pigmentosa (RP)). Moreover, retinal dystrophies resulting from CRB1 mutations may be accompanied by specific fundus features: preservation of the para-arteriolar retinal pigment epithelium (PPRPE) and retinal telangiectasia with exudation (also referred to as Coats-like vasculopathy). In this publication we report seven novel mutations and classify over 150 reported CRB1 sequence variants that were found in more that 240 patients. The data from previous reports was used to analyse a potential correlation between CRB1 variants and the clinical features of respective patients. This meta-analysis suggests that the differential phenotype of patients with CRB1 mutations is due to additional modifying factors rather than particular mutant allele combination.
CRB1; LCA; Retinitis Pigmentosa; rod-cone dystrophy
Background Variation in the complement factor H gene (CFH) is associated with risk of late age-related macular degeneration (AMD). Previous studies have been case–control studies in populations of European ancestry with little differentiation in AMD subtype, and insufficient power to confirm or refute effect modification by smoking.
Methods To precisely quantify the association of the single nucleotide polymorphism (SNP rs1061170, ‘Y402H’) with risk of AMD among studies with differing study designs, participant ancestry and AMD grade and to investigate effect modification by smoking, we report two unpublished genetic association studies (n = 2759) combined with data from 24 published studies (26 studies, 26 494 individuals, including 14 174 cases of AMD) of European ancestry, 10 of which provided individual-level data used to test gene–smoking interaction; and 16 published studies from non-European ancestry.
Results In individuals of European ancestry, there was a significant association between Y402H and late-AMD with a per-allele odds ratio (OR) of 2.27 [95% confidence interval (CI) 2.10–2.45; P = 1.1 x 10−161]. There was no evidence of effect modification by smoking (P = 0.75). The frequency of Y402H varied by ancestral origin and the association with AMD in non-Europeans was less clear, limited by paucity of studies.
Conclusion The Y402H variant confers a 2-fold higher risk of late-AMD per copy in individuals of European descent. This was stable to stratification by study design and AMD classification and not modified by smoking. The lack of association in non-Europeans requires further verification. These findings are of direct relevance for disease prediction. New research is needed to ascertain if differences in circulating levels, expression or activity of factor H protein explain the genetic association.
Age-related macular degeneration (AMD); Complement factor H gene; meta-ananlysis
Cataracts are the commonest cause of blindness worldwide. Inherited cataract is a clinically and genetically heterogeneous disease that most often shows autosomal dominant inheritance. In this study, we report the identification of a novel locus for cerulean cataract type 5 (CCA5), also known as blue-dot cataract on chromosome 12q24. To date, four loci for autosomal dominant congenital cerulean cataract have been mapped on chromosomes, 17q24, 22q11.2–12.2, 2q33–35 and 16q23.1. To map this locus we performed genetic linkage analysis using microsatellite markers in a five-generation English family. After the exclusion of all known loci and several candidate genes we obtained significantly positive LOD score (Z) for marker D12S1611 (Zmax=3.60; at θ=0). Haplotype data indicated that CCA5 locus lies within a region of 14.3 Mb interval between the markers D12S1718 and D12S1723. Our data are strongly suggestive of a new locus for CCA5 on chromosome 12.
cerulean cataract; linkage; heterogeneity
Heterozygous mutations in the PRPF31 gene cause autosomal dominant retinitis pigmentosa (adRP), a hereditary disorder leading to progressive blindness. In some cases, such mutations display incomplete penetrance, implying that certain carriers develop retinal degeneration while others have no symptoms at all. Asymptomatic carriers are protected from the disease by a higher than average expression of the PRPF31 allele that is not mutated, mainly through the action of an unknown modifier gene mapping to chromosome 19q13.4. We investigated a large family with adRP segregating an 11-bp deletion in PRPF31. The analysis of cell lines derived from asymptomatic and affected individuals revealed that the expression of only one gene among a number of candidates within the 19q13.4 interval significantly correlated with that of PRPF31, both at the mRNA and protein levels, and according to an inverse relationship. This gene was CNOT3, encoding a subunit of the Ccr4-not transcription complex. In cultured cells, siRNA–mediated silencing of CNOT3 provoked an increase in PRPF31 expression, confirming a repressive nature of CNOT3 on PRPF31. Furthermore, chromatin immunoprecipitation revealed that CNOT3 directly binds to a specific PRPF31 promoter sequence, while next-generation sequencing of the CNOT3 genomic region indicated that its variable expression is associated with a common intronic SNP. In conclusion, we identify CNOT3 as the main modifier gene determining penetrance of PRPF31 mutations, via a mechanism of transcriptional repression. In asymptomatic carriers CNOT3 is expressed at low levels, allowing higher amounts of wild-type PRPF31 transcripts to be produced and preventing manifestation of retinal degeneration.
Retinitis pigmentosa (RP) is an inherited disorder of the retina that is caused by mutations in more than 50 genes. Dominant mutations in one of these, PRPF31, can be non-penetrant. That is, some carriers of mutations suffer from the disease while others do not display any symptoms. In these particular individuals, functional PRPF31 transcripts are expressed at higher levels compared to affected persons, thus compensating for the deleterious effects of the mutated allele. Up to now, the nature of such a stochastic and protective effect was unknown. In this work, we identify CNOT3 as the modifier gene responsible for penetrance of PRPF31 mutations. We show that CNOT3 is a negative regulator of PRPF31 expression and modulates PRPF31 transcription by directly binding to its promoter. In asymptomatic carriers of mutations, CNOT3 expression is lower, allowing higher amounts of PRPF31 to be produced and therefore inhibiting the development of symptoms. Finally, we find that a polymorphism within a CNOT3 intronic region is associated with the clinical manifestation of the disease.
Posterior polymorphous corneal dystrophy (PPCD) is a rare autosomal dominant genetically heterogeneous disorder. Nineteen Czech PPCD pedigrees with 113 affected family members were identified, and 17 of these kindreds were genotyped for markers on chromosome 20p12.1- 20q12. Comparison of haplotypes in 81 affected members, 20 unaffected first degree relatives and 13 spouses, as well as 55 unrelated controls, supported the hypothesis of a shared ancestor in 12 families originating from one geographic location. In 38 affected individuals from nine of these pedigrees, a common haplotype was observed between D20S48 and D20S107 spanning approximately 23 Mb, demonstrating segregation of disease with the PPCD1 locus. This haplotype was not detected in 110 ethnically matched control chromosomes. Within the common founder haplotype, a core mini-haplotype was detected for D20S605, D20S182 and M189K2 in all 67 affected members from families 1–12, however alleles representing the core mini-haplotype were also detected in population matched controls. The most likely location of the responsible gene within the disease interval, and estimated mutational age, were inferred by linkage disequilibrium mapping (DMLE+2.3). The appearance of a disease-causing mutation was dated between 64–133 generations. The inferred ancestral locus carrying a PPCD1 disease-causing variant within the disease interval spans 60 Kb on 20p11.23, which contains a single known protein coding gene, ZNF133. However, direct sequence analysis of coding and untranslated exons did not reveal a potential pathogenic mutation. Microdeletion or duplication was also excluded by comparative genomic hybridization using a dense chromosome 20 specific array. Geographical origin, haplotype and statistical analysis suggest that in 14 unrelated families an as yet undiscovered mutation on 20p11.23 was inherited from a common ancestor. Prevalence of PPCD in the Czech Republic appears to be the highest worldwide and our data suggests that at least one other novel locus for PPCD also exists.
MicroRNAs (miRNAs) are key components of the gene regulatory network in many species. During the past few years, these regulatory elements have been shown to be involved in an increasing number and range of diseases. Consequently, the compilation of a comprehensive map of natural variability in a healthy population seems an obvious requirement for future research on miRNA-related pathologies.
Data on 14 populations from the 1000 Genomes Project were analyzed, along with new data extracted from 60 exomes of healthy individuals from a population from southern Spain, sequenced in the context of the Medical Genome Project, to derive an accurate map of miRNA variability.
Despite the common belief that miRNAs are highly conserved elements, analysis of the sequences of the 1,152 individuals indicated that the observed level of variability is double what was expected. A total of 527 variants were found. Among these, 45 variants affected the recognition region of the corresponding miRNA and were found in 43 different miRNAs, 26 of which are known to be involved in 57 diseases. Different parts of the mature structure of the miRNA were affected to different degrees by variants, which suggests the existence of a selective pressure related to the relative functional impact of the change. Moreover, 41 variants showed a significant deviation from the Hardy-Weinberg equilibrium, which supports the existence of a selective process against some alleles. The average number of variants per individual in miRNAs was 28.
Despite an expectation that miRNAs would be highly conserved genomic elements, our study reports a level of variability comparable to that observed for coding genes.
Myopia is a complex genetic disorder and a common cause of visual impairment among working age adults. Genome-wide association studies have identified susceptibility loci on chromosomes 15q14 and 15q25 in Caucasian populations of European ancestry. Here, we present a confirmation and meta-analysis study in which we assessed whether these two loci are also associated with myopia in other populations. The study population comprised 31 cohorts from the Consortium of Refractive Error and Myopia (CREAM) representing 4 different continents with 55,177 individuals; 42,845 Caucasians and 12,332 Asians. We performed a meta-analysis of 14 single nucleotide polymorphisms (SNPs) on 15q14 and 5 SNPs on 15q25 using linear regression analysis with spherical equivalent as a quantitative outcome, adjusted for age and sex. We calculated the odds ratio (OR) of myopia versus hyperopia for carriers of the top-SNP alleles using a fixed effects meta-analysis. At locus 15q14, all SNPs were significantly replicated, with the lowest P value 3.87 × 10−12 for SNP rs634990 in Caucasians, and 9.65 × 10−4 for rs8032019 in Asians. The overall meta-analysis provided P value 9.20 × 10−23 for the top SNP rs634990. The risk of myopia versus hyperopia was OR 1.88 (95 % CI 1.64, 2.16, P < 0.001) for homozygous carriers of the risk allele at the top SNP rs634990, and OR 1.33 (95 % CI 1.19, 1.49, P < 0.001) for heterozygous carriers. SNPs at locus 15q25 did not replicate significantly (P value 5.81 × 10−2 for top SNP rs939661). We conclude that common variants at chromosome 15q14 influence susceptibility for myopia in Caucasian and Asian populations world-wide.
Electronic supplementary material
The online version of this article (doi:10.1007/s00439-012-1176-0) contains supplementary material, which is available to authorized users.
We recently reported that mutations in the widely expressed nuclear protein TOPORS (topoisomerase I-binding arginine/serine rich) are associated with autosomal dominant retinal degeneration. However, the precise localization and a functional role of TOPORS in the retina remain unknown. Here, we demonstrate that TOPORS is a novel component of the photoreceptor sensory cilium, which is a modified primary cilium involved with polarized trafficking of proteins. In photoreceptors, TOPORS localizes primarily to the basal bodies of connecting cilium and in the centrosomes of cultured cells. Morpholino-mediated silencing of topors in zebrafish embryos demonstrates in another species a comparable retinal problem as seen in humans, resulting in defective retinal development and failure to form outer segments. These defects can be rescued by mRNA encoding human TOPORS. Taken together, our data suggest that TOPORS may play a key role in regulating primary cilia-dependent photoreceptor development and function. Additionally, it is well known that mutations in other ciliary proteins cause retinal degeneration, which may explain why mutations in TOPORS result in the same phenotype.
Inherited retinal disorders are clinically and genetically heterogeneous with more than 150 gene defects accounting for the diversity of disease phenotypes. So far, mutation detection was mainly performed by APEX technology and direct Sanger sequencing of known genes. However, these methods are time consuming, expensive and unable to provide a result if the patient carries a new gene mutation. In addition, multiplicity of phenotypes associated with the same gene defect may be overlooked.
To overcome these challenges, we designed an exon sequencing array to target 254 known and candidate genes using Agilent capture. Subsequently, 20 DNA samples from 17 different families, including four patients with known mutations were sequenced using Illumina Genome Analyzer IIx next-generation-sequencing (NGS) platform. Different filtering approaches were applied to identify the genetic defect. The most likely disease causing variants were analyzed by Sanger sequencing. Co-segregation and sequencing analysis of control samples validated the pathogenicity of the observed variants.
The phenotype of the patients included retinitis pigmentosa, congenital stationary night blindness, Best disease, early-onset cone dystrophy and Stargardt disease. In three of four control samples with known genotypes NGS detected the expected mutations. Three known and five novel mutations were identified in NR2E3, PRPF3, EYS, PRPF8, CRB1, TRPM1 and CACNA1F. One of the control samples with a known genotype belongs to a family with two clinical phenotypes (Best and CSNB), where a novel mutation was identified for CSNB. In six families the disease associated mutations were not found, indicating that novel gene defects remain to be identified.
In summary, this unbiased and time-efficient NGS approach allowed mutation detection in 75% of control cases and in 57% of test cases. Furthermore, it has the possibility of associating known gene defects with novel phenotypes and mode of inheritance.
NGS; retinal disorders; diagnostic tool.
To identify and functionally characterize the mutation responsible for autosomal dominant retinitis pigmentosa (adRP) in a large, six-generation French family.
Twenty individuals from this family participated in the genetic investigation. Six affected and 14 unaffected individuals from three-generations were available for linkage analysis using microsatellite markers flanking the rhodopsin (RHO) gene. A two-point logarithm of odds (LOD) score calculation was undertaken using GENEMARKER and MLINK software. Sanger sequencing of RHO was performed. Cellular localization of the mutant protein was performed by transforming SK-N-SH cells with pEGFP-N1-Rho, pEGFP-N1-Rho(P23H), and pEGFP-N1-Rho(c.614–622del).
The proband had nyctalopia, visual field constriction, peripheral bone spicule pigmentation of the fundus, central acuity (6/24 RE; 6/12 LE) at 55 years of age. Linkage analysis of this family suggested RHO as a possible candidate since the flanking marker D3S1292 yielded a LOD score of 2.43 at θ=0. Cloning of an exon 3 PCR product and direct sequencing of single clones identified a novel deletion in the third exon of RHO, c.614–622del (p.Y206-F208del). The deleted mutant protein localized to the endoplasmic reticulum and formed inclusion bodies.
This novel deletion in exon 3 of the RHO gene, c.614–622del results in a classical form of adRP in a multi-generation French family. Protein expression analyses confirmed that the deletion led to protein misfolding and suggest this is a class II mutation, similar to P23H, the most common class II mutation seen in North America.
To investigate the pathogenesis of the RNA splicing factor forms of RP, the authors generated and characterized the retinal phenotypes of Prpf3-T494M, Prpf8-H2309P knockin mice, and evaluated the retinal ultrastructure of Prpf31-knockout mice. All three mouse models demonstrate degenerative changes in the RPE with age, suggesting that the RPE may be the primary cell type affected in the RNA splicing factor forms of RP.
Mutations in genes that produce proteins involved in mRNA splicing, including pre-mRNA processing factors 3, 8, and 31 (PRPF3, 8, and 31), RP9, and SNRNP200 are common causes of the late-onset inherited blinding disorder retinitis pigmentosa (RP). It is not known how mutations in these ubiquitously expressed genes lead to retina-specific disease. To investigate the pathogenesis of the RNA splicing factor forms of RP, the authors generated and characterized the retinal phenotypes of Prpf3-T494M, Prpf8-H2309P knockin mice. The retinal ultrastructure of Prpf31-knockout mice was also investigated.
The knockin mice have single codon alterations in their endogenous Prpf3 and Prpf8 genes that mimic the most common disease causing mutations in human PRPF3 and PRPF8. The Prpf31-knockout mice mimic the null alleles that result from the majority of mutations identified in PRPF31 patients. The retinal phenotypes of the gene targeted mice were evaluated by electroretinography (ERG), light, and electron microscopy.
The RPE cells of heterozygous Prpf3+/T494M and Prpf8+/H2309P knockin mice exhibited loss of the basal infoldings and vacuolization, with accumulation of amorphous deposits between the RPE and Bruch[b]'s membrane at age two years. These changes were more severe in the homozygous mice, and were associated with decreased rod function in the Prpf3-T494M mice. Similar degenerative changes in the RPE were detected in Prpf31± mice at one year of age.
The finding of similar degenerative changes in RPE cells of all three mouse models suggests that the RPE may be the primary cell type affected in the RNA splicing factor forms of RP. The relatively late-onset phenotype observed in these mice is consistent with the typical adult onset of disease in patients with RP.
To identify the prevalence of rhodopsin (RHO) mutations in French patients with autosomal dominant rod-cone dystrophies (adRP).
Detailed phenotypic characterization was performed including precise family history, best corrected visual acuity using the ETDRS chart, slit lamp examination, kinetic and static perimetry, full field and multifocal electroretinography (ERG), fundus autofluorescence imaging (FAF) and optical coherence tomography (OCT). For genetic diagnosis, genomic DNA of seventy-nine families was isolated by standard methods. The coding exons and flanking intronic regions of RHO were PCR amplified, purified and sequenced in the index patient.
Among this French adRP cohort, 16.5% revealed a RHO mutation. While three unrelated families showed each a novel missense mutation (p.Leu88Pro, p.Met207Lys and p.Gln344Pro), ten unrelated families showed recurrent previously published mutations (p.Asn15Ser, p.Leu131Pro, p.Arg135Trp, p.Ser334GlyfsX20 and p.Pro347Leu). All mutations co-segregated with the phenotype within a family and the novel mutations were not identified in a control population.
Our studies revealed that the prevalence of RHO mutations in French adRP patients is in accordance with other studies from Europe. Most of the changes identified herein reflect recurrent mutations within which p.Pro347Leu substitution is the most prevalent. Nevertheless, almost a quarter of the changes are novel indicating that, although RHO is the first gene implicated and probably the most studied gene in RP, it is still relevant to perform mutation analysis in the coding exons of RHO to detect novel changes. Our detailed phenotype-genotype analyses in all family members available deliver the basis for therapeutic approaches in those families.
Adolescent; Adult; Child; DNA Mutational Analysis; Electroretinography; European Continental Ancestry Group; genetics; Female; Fluorescein Angiography; France; epidemiology; Genes, Dominant; Genotype; Humans; Male; Middle Aged; Mutation; Pedigree; Phenotype; Photoreceptor Cells, Vertebrate; pathology; Polymerase Chain Reaction; Prevalence; Retinitis Pigmentosa; diagnosis; genetics; Rhodopsin; genetics; Tomography, Optical Coherence; Visual Acuity; Young Adult
The authors identified a new genetic factor, SLC16A12, which encodes a monocarboxylate transporter, as involved in age-related cataract. Sequence alterations in its 5′untranslated region affect translational efficiency, a potential mechanism to challenge homeostasis within the lens.
Knowledge of genetic factors predisposing to age-related cataract is very limited. The aim of this study was to identify DNA sequences that either lead to or predispose for this disease.
The candidate gene SLC16A12, which encodes a solute carrier of the monocarboxylate transporter family, was sequenced in 484 patients with cataract (134 with juvenile cataract, 350 with age-related cataract) and 190 control subjects. Expression studies included luciferase reporter assay and RT-PCR experiments.
One patient with age-related cataract showed a novel heterozygous mutation (c.-17A>G) in the 5′untranslated region (5′UTR). This mutation is in cis with the minor G-allele of the single nucleotide polymorphism (SNP) rs3740030 (c.-42T/G), also within the 5′UTR. Using a luciferase reporter assay system, a construct with the patient's haplotype caused a significant upregulation of luciferase activity. In comparison, the SNP G-allele alone promoted less activity, but that amount was still significantly higher than the amount of the common T-allele. Analysis of SLC16A12 transcripts in surrogate tissue demonstrated striking allele-specific differences causing 5′UTR heterogeneity with respect to sequence and quantity. These differences in gene expression were mirrored in an allele-specific predisposition to age-related cataract, as determined in a Swiss population (odds ratio approximately 2.2; confidence intervals, 1.23–4.3).
The monocarboxylate transporter SLC16A12 may contribute to age-related cataract. Sequences within the 5′UTR modulate translational efficiency with pathogenic consequences.
Cataracts are the most common cause of blindness worldwide. Inherited cataract is a clinically and genetically heterogeneous disease. Here we report a novel mutation in the paired-like homeodomain 3 (PITX3) gene segregating in a four generation English family with an isolated autosomal dominant posterior polar cataract.
A genome-wide linkage was performed by means of single nucleotide polymorphism (SNP) and microsatellite markers. Linkage analyses were performed with the GeneHunter and MLINK programs. Direct sequencing of PCR products was performed to detect mutation in the gene, using the BigDye version 3.1 and analyzed using Sequence analysis version 5.2.
Genome-wide linkage analysis with SNP markers, identified a disease-haplotype interval on chromosome 10q. Two point positive logarithm of odds (LOD) scores was obtained with markers D10S205 (Z=3.10 at θ=0.00), flanked by markers D10S1709 and D10S543, which harbors the homeobox gene PITX3. Sequence analysis of PITX3 revealed a 1-bp deletion that cosegregated with all the affected members of this family which resulted in a frameshift in codon 181 and likely to produce an aberrant protein consisting of 127 additional residues.
The 542delC is a novel mutation in PITX3 causing an isolated posterior polar cataract.
To identify the genetic defect of a consanguineous Portuguese family with rod-cone dystrophy and varying degrees of decreased audition.
A detailed ophthalmic and auditory examination was performed on a Portuguese patient with severe autosomal recessive rod-cone dystrophy. Known genetic defects were excluded by performing autosomal recessive retinitis pigmentosa (arRP) genotyping microarray analysis and by Sanger sequencing of the coding exons and flanking intronic regions of eyes shut homolog–drosophila (EYS) and chromosome 2 open reading frame 71 (C2orf71). Subsequently, genome-wide homozygosity mapping was performed in DNA samples from available family members using a 700K single nucleotide polymorphism (SNP) microarray. Candidate genes present in the significantly large homozygous regions were screened for mutations using Sanger sequencing.
The largest homozygous region (~11 Mb) in the affected family members was mapped to chromosome 9, which harbors deafness, autosomal recessive 31 (DFNB31; a gene previously associated with Usher syndrome). Mutation analysis of DFNB31 in the index patient identified a novel one-base-pair deletion (c.737delC), which is predicted to lead to a truncated protein (p.Pro246HisfsX13) and co-segregated with the disease in the family. Ophthalmic examination of the index patient and the affected siblings showed severe rod-cone dystrophy. Pure tone audiometry revealed a moderate hearing loss in the index patient, whereas the affected siblings were reported with more profound and early onset hearing impairment.
We report a novel truncating mutation in DFNB31 associated with severe rod-cone dystrophy and varying degrees of hearing impairment in a consanguineous family of Portuguese origin. This is the second report of DFNB31 implication in Usher type 2.
To describe the clinical and molecular characteristics of two families with autosomal dominant Best disease and atypical electrooculography (EOG).
Four affected individuals from two families were ascertained. Detailed ophthalmic examinations, refraction, and biometry (anterior chamber depth [ACD] and axial length [AL]), gonioscopy, optical coherence tomography of the anterior segment and retina, retinal imaging, and electrophysiological assessment were performed. Arden ratios from EOG testing were calculated by direct measurement of the light peak to dark trough amplitudes. Mutations in bestrophin 1 (BEST1) were identified by bidirectional Sanger sequencing. In family 1, segregation of BEST1 alleles was performed by assaying four microsatellite markers (D11S935, D11S4102, D11S987, and D11S4162) that flank BEST1.
The proband from family 1 (three of four siblings affected with Best disease) was 42 years old with bilateral macular vitelliform lesions, advanced angle closure glaucoma (ACG), a normal electroretinogram, and no EOG light rise. Her 44-year-old brother had similar fundus appearances and an EOG light rise of 170%. Their 48-year-old sister had a normal left fundus, whereas the right fundus showed a vitelliform lesion and subretinal thickening. There was no EOG light rise detectable from either eye. Mutation analysis of BEST1 showed all affected siblings to be heterozygous for a missense mutation, c.914T>C, p.Phe305Ser. Their unaffected sister had an EOG light rise of 200%, a normal fundus appearance, and did not harbor the BEST1 mutation. Haplotype analysis of family 1 showed that the affected brother with the 170% EOG light rise had inherited the same nondiseased parental BEST1 allele as his unaffected sister. The other two affected sisters with undetectable EOG light rises shared a different nondiseased parental BEST1 allele. An unrelated 53-year-old female carrying the same c.914T>C, p.Phe305Ser mutation showed typical features of Best disease and an EOG light rise of 180%. All four siblings from family 1 had shorter axial biometry (ACD range 2.06–2.74 mm; AL range 20.46–22.60 mm) than the normal population, contributing to their risk of ACG development. Proband 2 had deeper ACDs (2.83 mm OD and 2.85 mm OS), but similar ALs (21.52 mm OD and 21.42 mm OS) compared to family 1. She had no gonioscopic evidence of angle closure.
A near normal EOG light rise is uncommon in molecularly confirmed Best disease, and in the present report is associated with the same mutation in two families, suggesting a specific role for this amino acid in the retinal pigment epithelium dysfunction associated with this disorder. Haplotype analysis in family 1 was consistent with an effect of the nondisease allele in mediating the presence of an EOG light rise. Clinical assessment of ACG risk is recommended for BEST1 mutation carriers and their first degree relatives.