Genotype/phenotype association in Indian congenital aniridia

Congenital aniridia beyond black eyes: From phenotype and novel genetic mechanisms to innovative therapeutic approaches

Congenital PAX6-aniridia, initially characterized by the absence of the iris, has progressively been shown to be associated with other developmental ocular abnormalities and systemic features making congenital aniridia a complex syndromic disorder rather than a simple isolated disease of the iris. Moreover, foveal hypoplasia is now recognized as a more frequent feature than complete iris hypoplasia and a major visual prognosis determinant, reversing the classical clinical picture of this disease. Conversely, iris malformation is also a feature of various anterior segment dysgenesis disorders caused by PAX6-related developmental genes, adding a level of genetic complexity for accurate molecular diagnosis of aniridia. Therefore, the clinical recognition and differential genetic diagnosis of PAX6-related aniridia has been revealed to be much more challenging than initially thought, and still remains under-investigated. Here, we update specific clinical features of aniridia, with emphasis on their genotype correlations, as well as provide new knowledge regarding the PAX6 gene and its mutational spectrum, and highlight the beneficial utility of clinically implementing targeted Next-Generation Sequencing combined with Whole-Genome Sequencing to increase the genetic diagnostic yield of aniridia. We also present new molecular mechanisms underlying aniridia and aniridia-like phenotypes. Finally, we discuss the appropriate medical and surgical management of aniridic eyes, as well as innovative therapeutic options. Altogether, these combined clinical-genetic approaches will help to accelerate time to diagnosis, provide better determination of the disease prognosis and management, and confirm eligibility for future clinical trials or genetic-specific therapies.

Rare eye diseases in India: A concise review of genes and genetics

Rare eye diseases (REDs) are mostly progressive and are the leading cause of irreversible blindness. The disease onset can vary from early childhood to late adulthood. A high rate of consanguinity contributes to India’s predisposition to RED. Most gene variations causing REDs are monogenic and, in some cases, digenic. All three types of Mendelian inheritance have been reported in REDs. Some of the REDs are related to systemic illness with variable phenotypes in affected family members. Approximately, 50% of the children affected by REDs show associated phenotypes at the early stages of the disease. A precise clinical diagnosis becomes challenging due to high clinical and genetic heterogeneity. Technological advances, such as next-generation sequencing (NGS), have improved genetic and genomic testing for REDs, thereby aiding in determining the underlying causative gene variants. It is noteworthy that genetic testing together with genetic counseling facilitates a more personalized approach in the accurate diagnosis and management of the disease. In this review, we discuss REDs identified in the Indian population and their underlying genetic etiology.

Clinical and molecular aspects of congenital aniridia - A review of current concepts

Congenital aniridia is a pan ocular disorder characterized by partial or total loss of iris tissue as the defining feature. Classic aniridia, however, has a spectrum of ocular findings, including foveal hypoplasia, optic nerve hypoplasia, nystagmus, late-onset cataract, glaucoma, and keratopathy. The latter three are reasons for further visual compromise in such patients. This entity is often due to mutations in the PAX6 (Paired box protein Pax-6) gene. Recently, aniridia-like phenotypes have been reported due to non-PAX6 mutations as in PITX2, FOXC1, FOXD3, TRIM44, and CYP1B1 as well wherein there is an overlap of aniridia, such as iris defects with congenital glaucoma or anterior segment dysgenesis. In this review, we describe the various clinical features of classic aniridia, the comorbidities and their management, the mutation spectrum of the genes involved, genotype-phenotype correlation of PAX6 and non-PAX6 mutations, and the genetic testing plan. The various systemic associations and their implications in screening and genetic testing have been discussed. Finally, the future course of aniridia treatment in the form of drugs (such as ataluren) and targeted gene therapy has been discussed.

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.

Novel variants in PAX6 gene caused congenital aniridia in two Chinese families

PurposeTo reveal the underlying genetic defect in two four-generation Chinese families with aniridia and explore the pathologic mechanism.MethodsFull ophthalmic examinations were performed in two families with aniridia. The PAX6 gene was directly sequenced in patients of two families, and the detected variants were screened in unaffected family members and two hundred unrelated healthy controls. Real-time quantitative PCR was used to explore pathologic mechanisms of the two variants.ResultsAniridia, cataract, and oscillatory nystagmus were observed in patients of the two families. In addition, we observed corneal opacity and microphthalmus in family 1, and strabismus, left ectopia lentis, microphthalmus, and microcornea in family 2. Sanger sequencing detected a novel 1-bp duplication (c.50dupA) in family 1 and a novel 2-bp splice site deletion (c.765+1_765+2delGT) in family 2. Sequencing of cDNA indicated skipping of exon 9 caused by the splice site deletion, being predicted to cause a premature stop codon, as well as the duplication. The PAX6 mRNA significantly lower in patients with aniridia than in unaffected family members in both families, suggesting that the duplication and splice site deletion caused nonsense-mediated mRNA decay.ConclusionsOur study identified two novel PAX6 variants in two families with aniridia and revealed the pathogenicity of the variants; this would expand the variant spectrum of PAX6 and help us better understand the molecular basis of aniridia, thus facilitating genetic counseling.

A novel duplication in the PAX6 gene in a North Indian family with aniridia

Mutations in paired box gene 6 (PAX6) are the major cause of aniridia that may be associated with several other developmental anomalies of the eye, including microcornea in rare cases. Therefore, the purpose of this study was to identify the underlying genetic cause in a two-generation North Indian family diagnosed with aniridia. All the participants enrolled in the study, including the aniridia family and 20 healthy individuals (controls), underwent a comprehensive ophthalmic examination. Mutation screening was performed for the PAX6 gene by direct sequencing of the polymerase chain reaction products. A novel PAX6 duplication in exon 5 at position c.474dupC was identified in all three affected individuals from the family but not in the unaffected family members or unrelated controls. We reported a novel duplication in the PAX6 gene capable of causing the classic aniridia phenotype. This is the first report on the duplication in a North Indian family with autosomal dominant aniridia.

Clinical manifestations of congenital aniridia

PURPOSE

To study the various clinical manifestations associated with congenital aniridia in an Indian population.

METHODS

In this retrospective, consecutive, observational case series, all patients with the diagnosis of congenital aniridia seen at the institute from January 2005 to December 2010 were reviewed. In all patients, the demographic profile, visual acuity, and associated systemic and ocular manifestations were studied.

RESULTS

The study included 262 eyes of 131 patients with congenital aniridia. Median patient age at the time of initial visit was 8 years (range: 1 day to 73 years). Most cases were sporadic and none of the patients had parents afflicted with aniridia. The most common anterior segment abnormality identified was lenticular changes. Cataract was the predominant lens finding, observed in 93 of 231 (40.3%) phakic eyes. Other lens abnormalities were subluxation, coloboma, posterior lenticonus, and microspherophakia. Corneal involvement of varying degrees was seen in 157 of 262 (59.9%) eyes, glaucoma was identified in 95 of 262 (36.3%) eyes, and foveal hypoplasia could be assessed in 230 of 262 (87.7%) eyes. Median age when glaucoma and cataract were noted was 7 and 14 years, respectively. None of the patients had Wilm's tumor.

CONCLUSIONS

Congenital aniridia was commonly associated with classically described ocular features. However, systemic associations were characteristically absent in this population. Notably, cataract and glaucoma were seen at an early age. This warrants a careful evaluation and periodic follow-up in these patients for timely identification and appropriate management.

Glaucoma and Frequency of Ocular and General Diseases in 30 Patients with Aniridia: A Clinical Study

Purpose

To evaluate the following in patients with aniridia: age at first examination at the University Eye Hospital and age at diagnosis of glaucoma; visual acuity; frequency of family history of aniridia; and frequency of ocular and general diseases associated with aniridia.

Methods

This was a consecutive examination of 30 unrelated patients with aniridia and retrospective evaluation of ophthalmologic, pediatric, and internal findings. The relative frequency of age at glaucoma diagnosis within decades was evaluated for the 20 patients with aniridia and glaucoma. Statistical analysis was performed using the Mann-Whitney test.

Results

Relative frequency of the age of patients with aniridia at time of glaucoma diagnosis within the following decades was as follows: from birth to 9 years: 15%, 10-19: 15%, 20-29: 15%, 30-39: 15%, 40-49: 35%, and 50-59: 5%. Visual acuity in the better eye of 20/100 or less was found in 60%. Family history of aniridia was found in 33.3% of patients, with 1-4 relatives with aniridia. A total of 76.7% of patients had congenital cataract, and 66.7% had glaucoma. Mean maximum intraocular pressure of the 20 patients with glaucoma was 35.9 mmHg in the right and 32.6 mmHg in the left eye. A total of 53.3% had nystagmus, 26.6% corneal opacifications, 16.7% bilateral lens dislocation upwards, 6.7% optic nerve hypoplasia, 3.3% poor foveal development, and 3.3% Wilms tumor.

Conclusions

Up to the age of 40 years, 15% of patients were diagnosed with glaucoma per age decade. Frequent bilateral glaucoma and similar bilateral height of intraocular pressure suggest a genetic glaucoma disposition with malformation at Schlemm canal, besides possible sequential anatomic changes in the chamber angle. Associated ocular abnormalities limit visual prognosis.

Mutation analysis of PAX6 in a Chinese family and a patient with a presumed sporadic case of congenital aniridia

AIMS

Mutations in the PAX6 are the major cause of congenital aniridia. The objective of this study was to analyze genetic mutations in PAX6 in Chinese patients with congenital aniridia.

METHODS

Total genomic DNA was isolated from the peripheral blood of the aniridia patients, all healthy family members and 100 healthy volunteers. The 14 exons (including alternatively spliced exon 5a) of the PAX6 gene were amplified by polymerase chain reaction, and the products were sequenced to identify the mutation.

RESULTS

Two mutations of PAX6 were detected in exon 11 in the congenital aniridia patients. One mutation was caused by the duplication of the 4 nucleic acids CTCC (c.1286insCTCC), which would lead to a frameshift. The other mutation was caused by a transition from C to T (c.1311C → T), which would generate a stop codon. Neither mutation was present in the healthy family members or 100 healthy volunteers.

CONCLUSION

We examined the exon sequence of the PAX6 gene in a Chinese family and an unrelated individual with aniridia. The predicted outcome of both mutations is premature termination. The mutation found in the unrelated individual has not previously been reported and represents a new addition to the spectrum of mutations in PAX6.