Three novel PAX6 mutations in patients with aniridia

Genetic analysis using next-generation sequencing and multiplex ligation probe amplification in Chinese aniridia patients

BACKGROUND

Congenital aniridia is a rare pan-ocular disease characterized by complete irideremia, partial iridocoloboma. The progressive nature of aniridia is frequently accompanied by secondary ocular complications such as glaucoma and aniridia-associated keratopathy, which can lead to severely impaired vision or blindness. The genetic basis of aniridia has been the subject of numerous studies, leading to the development of innovative therapeutic options based on PAX6 nonsense mutations. Specific knowledge of the genetics of aniridia has become increasingly important. To report the clinical features, elucidate the genetic etiology, and reveal the mutational spectrum of congenital aniridia in the Chinese population, sixty patients with congenital aniridia from 51 families were recruited. Candidate genes associated with developmental eye diseases were identified and analyzed using panel-based next-generation sequencing (NGS), and mutations were confirmed through polymerase chain reaction and Sanger sequencing. Multiplex ligation probe amplification (MLPA) of PAX6 and FOXC1 was performed to detect copy number variations in the patients without intragenic mutations.

RESULTS

Clinical examination revealed complete iris hypoplasia in 58 patients and partial iris hypoplasia in two patients. Additionally, two patients were diagnosed with Wilms' tumor-aniridia-genital anomalies-retardation syndrome and nephroblastoma. By combining panel-based NGS and MLPA, 43 intragenic mutations or deletions of PAX6, FOXC1, and BCOR were identified in 59 patients, including 33 point mutations (76.7%) in 43 patients and 10 deletions (23.3%) in 16 patients. The total detection rate was 98.3%. Phenotypic variation was observed between and within families.

CONCLUSIONS

Variations in PAX6 and its adjacent regions were the predominant causes of aniridia in China. In addition to intragenic point mutations in PAX6, deletion of PAX6 or its adjacent genes is a common cause of congenital aniridia. Furthermore, FOXC1 is an important gene associated with congenital aniridia. The combination of panel-based NGS and MLPA significantly enhanced the detection rate of gene mutations in patients with congenital aniridia.

The Genetic and Endoplasmic Reticulum-Mediated Molecular Mechanisms of Primary Open-Angle Glaucoma

Glaucoma is a heterogenous, chronic, progressive group of eye diseases, which results in irreversible loss of vision. There are several types of glaucoma, whereas the primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma, accounting for three-quarters of all glaucoma cases. The pathological mechanisms leading to POAG pathogenesis are multifactorial and still poorly understood, but it is commonly known that significantly elevated intraocular pressure (IOP) plays a crucial role in POAG pathogenesis. Besides, genetic predisposition and aggregation of abrogated proteins within the endoplasmic reticulum (ER) lumen and subsequent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent unfolded protein response (UPR) signaling pathway may also constitute important factors for POAG pathogenesis at the molecular level. Glaucoma is commonly known as a ‘silent thief of sight’, as it remains asymptomatic until later stages, and thus its diagnosis is frequently delayed. Thereby, detailed knowledge about the glaucoma pathophysiology is necessary to develop both biochemical and genetic tests to improve its early diagnosis as well as develop a novel, ground-breaking treatment strategy, as currently used medical therapies against glaucoma are limited and may evoke numerous adverse side-effects in patients.

PAX6 allelic heterogeneity in Mexican congenital aniridia patients: expanding the mutational spectrum with seven novel pathogenic variants

IMPORTANCE

The importance of the study was to describe the clinical characteristics and mutational analysis of Mexican patients with aniridia.

BACKGROUND

Aniridia is a panocular hereditary eye disease caused by mutations in the PAX6 transcription factor. Mutation detection rate is highly variable ranging from 30% to 90% in different populations. Very few studies have been published about the PAX6 mutational analysis in aniridia patients from Mexico. In order to establish a more representative PAX6 mutational frequency in the country, a cohort of 22 Mexican unrelated aniridia probands were analysed in this study.

DESIGN

Case series.

PARTICIPANTS

A total of 22 Mexican probands with bilateral isolated aniridia and their available relatives were included.

METHODS

Sanger sequencing was used for the mutational analysis of all coding exons and flanking intronic regions of PAX6.

MAIN OUTCOME MEASURES

Clinical characteristics and results of PAX6 mutational analysis in probands with aniridia and available family members.

RESULTS

Molecular analysis of PAX6 in 22 index cases with aniridia allowed the identification of a total of 16 different mutations. Seven of these pathogenic variants are novel, including c.183C>G, p.(Y61*); c.718delC, p.(R240Efs*3); c.1149_1152delTCAG, p.(P385Wfs*139); c.257_266delAAATAGCCCA, p.(K86Sfs*35); c.836_843dupGCAACACA p.(P282Afs*86); c.1032+2_1032+3insT; and c.141+2T>A. Inter and intrafamilial phenotypic heterogeneity was found.

CONCLUSIONS AND RELEVANCE

The mutational diagnostic rate in this series was 77%, which is comparable with reports from other populations. Importantly, no founder mutations were identified in this case series. Our results add 7 novel PAX6 pathogenic variants to the aniridia-related mutational spectrum and reveal considerable PAX6 allelic heterogeneity in this population.

PAX6 Expression and Retinal Cell Death in a Transgenic Mouse Model for Acute Angle-Closure Glaucoma

PURPOSE

PAX6 is a highly conserved protein essential for the control of eye development both in invertebrates and vertebrates. PAX6 expression persists in the adult inner retina, but little is known about its functions after completion of retinal differentiation. Therefore, we investigated PAX6 expression in wild-type and calcitonin receptor-like receptor transgenic (CLR(SMαA)) mice with angle-closure glaucoma.

METHODS

Intraocular pressure was measured by indentation tonometry in anesthetized mice. Eyes of mice of both genotypes were enucleated at various ages and retinas were processed for morphological analysis and PAX6 immunostaining. The content of PAX6 in retinal extracts was estimated by Western blot analysis. Retinal expression of glaucoma-related genes was analyzed by reverse transcription-polymerase chain reaction.

RESULTS

Control mice showed normal retinal morphology between p22 and p428 with steady PAX6 expression in the ganglion cell layer (GCL) and the inner nuclear layer (INL). CLR(SMαA) mice examined between p22 and p82 exhibited increased intraocular pressure and a progressive decrease in cell number including PAX6-expressing cells in the GCL. The INL was not affected up to postnatal day 42. Later, a significant increase in PAX6-expressing cells concomitant with an overall loss of cells was observed in the INL of CLR(SMαA) as compared with control mice. Retinal up-regulation of glaucoma-related genes was furthermore observed.

CONCLUSIONS

Distinctive changes of PAX6 expression in the inner retina of CLR(SMαA) mice suggest a role in regulatory mechanisms involved in glaucoma-related retinal cell death. The selective increase of PAX6 expression in the degenerating INL of CLR(SMαA) mice may represent an attempt to preserve retinal cytoarchitecture.

Mutational analysis and genotype-phenotype correlations in southern Indian patients with sporadic and familial aniridia

PURPOSE

Aniridia is a rare panocular disorder characterized by iris hypoplasia and other associated eye anomalies. Heterozygous null mutations in paired box gene 6 (PAX6) are the major cause of the classic aniridia phenotype. This study aims to detect the mutational spectrum of PAX6 and associated phenotypes in southern Indian patients with sporadic and familial aniridia.

METHODS

Genomic DNA was isolated from peripheral blood from all participants. The coding regions and flanking intronic sequences of PAX6 were screened with Sanger sequencing in 30 probands with aniridia. The identified variations were further evaluated in available family members and 150 healthy controls. The pathogenic potential of the mutations were assessed using bioinformatics tools.

RESULTS

Thirteen different mutations were detected in eight sporadic and five familial cases. Eleven novel mutations, including five insertions (c.7_10dupAACA, c.567dupC, c.704dupC, c.868dupA and c.753_754insTA), two deletions (c.242delC and c.249delT), and four splicing variants (c.10+1G>A, c.141G>A, c.141+4A>G and c.764A>G) were identified in this study. Clinical findings of the patients revealed phenotypic heterogeneity with the same or different mutations.

CONCLUSIONS

This study reported 11 novel mutations and thus expanded the spectrum of PAX6 mutations. Interestingly, all mutations reported in this study were truncations, which confirms the hypothesis that haploinsufficiency of PAX6 causes the aniridia phenotype. Our observations revealed inter- and intrafamilial phenotypic variability with PAX6 mutations. The common ocular findings associated with PAX6 mutations were iris hypoplasia, nystagmus, and foveal hypoplasia reported in almost all cases, with cataract, glaucoma, and keratopathy reported in approximately 50% of the patients.

Mutation spectrum of PAX6 in Chinese patients with aniridia

PURPOSE

To identify mutations in the paired box 6 (PAX6) gene of 33 probands with aniridia and to reveal the mutational spectrum in the Chinese population.

METHODS

Unrelated probands with aniridia from 27 newly selected families and six previously analyzed families participated in this study. The coding regions of PAX6 in the 27 new families were analyzed using cycle sequencing. Families that lacked detectable variations based on sequencing (14 new and six previously analyzed) were further analyzed using multiplex ligation-dependent probe amplification (MLPA).

RESULTS

Fifteen mutations were identified in 16 of the 33 families: c.[65_94del30; 99_105dup7], c.101_102insA, c.177delG, c.238_239insGCGA, c.1033-42_1033-26del17insG, c.1A>G, c.120C>A, c.718C>T, c.949C>T, c.1062C>A, c.1183G>A, c.1268A>T, and three gross deletions involving exons 1-14, exons 8-14, and exons 9-14. The first five mutations were novel and the c.1268A>T mutation was present in two families. Phenotypic variations were observed between families and between different affected patients within the families.

CONCLUSIONS

The PAX6 mutation spectrum in Chinese aniridia patients is comparable to that reported in other ethnic groups. Further studies of the 17 families with no detected mutations may provide additional information to improve the understanding of the molecular genetics of aniridia.

Current prospects for adult stem cell-based therapies in ocular repair and regeneration

Recent advances in stem cell biology have led to the exploration of stem cell-based therapies to treat a wide range of human diseases. In the ophthalmic field, much hope has been placed on the potential use of these cells to restore sight, particularly in those conditions in which other established treatments have failed and in which visual function has been irreversibly damaged by disease or injury. At present, there are many limitations for the immediate use of embryonic stem cells to treat ocular disease, and as more evidence emerges that adult stem cells are present in the adult human eye, it is clear that these cells may have advantages to develop into feasible therapeutic treatments without the problems associated with embryonic research and immune rejection. Here we discuss the current prospects for the application of various adult ocular stem cells to human therapies for restoration of vision.

[Congenital glaucoma and trabeculodysgenesis. Clinical and genetic aspects]

Congenital glaucoma is generally related to an iridocorneal angle malformation, with an obstacle to aqueous humor outflow. This spectrum of diseases can involve the angle, the iris and the cornea. The diagnosis relies on characteristic signs and is confirmed by an examination under general anaesthesia and paraclinical examinations (especially echography). An early diagnosis is essential for beginning surgical treatment. Several filtering surgery techniques with equivalent intraocular pressure results are available, but visual function must be protected in all cases. In many cases, genetic counseling relies on a careful clinical analysis and sometimes on a molecular analysis. A number of ocular and/or general abnormalities can be accompanied by glaucoma in infants and children. They must be screened in case of associated signs, but the existence of these abnormalities leads to suspicion of associated glaucoma.

Continuous expression of the homeobox gene Pax6 in the ageing human retina

PURPOSE

In the past few years, the essential role of the homeobox gene Pax6 for eye development has been demonstrated unambiguously in a variety of species including humans. In humans, Pax6 mutations lead to a variety of ocular malformations of the anterior and posterior segment. However, little is known about PAX6 expression in the adult human retina. We have therefore investigated PAX6 levels and localization in the human retina at various ages.

METHODS

Adult human eyes of various ages (17-79 years) were obtained from the Zurich Eye Bank. PAX6 expression levels and patterns were analysed by Western blot analysis of total retinal protein and by immunohistochemistry on paraffin sections, respectively.

RESULTS

PAX6 expression in the retina was detected up to 79 years of donor age and was predominantly localized to the ganglion cell layer and the inner part of the inner nuclear layer.

CONCLUSIONS

PAX6 remains distinctly expressed throughout the lifespan of the human retina suggesting a role for PAX6 in the retina after completion of eye morphogenesis.

Genetic analysis of the Caenorhabditis elegans pax-6 locus: roles of paired domain-containing and nonpaired domain-containing isoforms

PAX-6 proteins are involved in eye and brain development in many animals. In the nematode Caenorhabditis elegans the pax-6 locus encodes multiple PAX-6 isoforms both with and without a paired domain. Mutations in the C. elegans pax-6 locus can be grouped into three classes. Mutations that affect paired domain-containing isoforms cause defects in epidermal morphogenesis, epidermal cell fates, and gonad cell migration and define the class I (vab-3) complementation group. The class II mutation mab-18(bx23) affects nonpaired domain-containing isoforms and transforms the fate of a sensory organ in the male tail. Class III mutations affect both paired domain and nonpaired domain isoforms; the most severe class III mutations are candidate null mutations in pax-6. Class III mutant phenotypes do not resemble a simple sum of class I and class II phenotypes. A comparison of class I and class III phenotypes indicates that PAX-6 isoforms can interact additively, synergistically, or antagonistically, depending on the cellular context.