Novel and De-novo TruncatingPAX6Mutations and Ocular Phenotypes in Thai Aniridia 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.

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.

PAX6Mutations May Be Associated with High Myopia

PAX6 is a key regulator of eye development and there are many well recognized ophthalmic sequelae of mutations at this locus. The 14 exon PAX6 gene is well conserved across species and phyla. Coding region mutations manifest in a variety of phenotypes. Predicted premature protein truncations are generally associated with classical aniridia. Missense mutations are often found in cases with variant phenotypes such as ectopia pupillae; isolated foveal hypoplasia; nystagmus and hyaloid vessel proliferation. The locus has also been implicated, through a genome-wide sib-pair scan, to be important in the normal variation of myopia. We investigated the association between identified PAX6 mutations and refractive error in Australian patients from four pedigrees. Two of eight subjects with a 1410delC PAX6 mutation had a mean spherical equivalence < -9D, whilst a mean spherical equivalence < or = -5D was recorded in two from four subjects with an Arg240Stop PAX6 mutation and one of two subjects with a Glu93Stop mutation. One individual identified with a Pro346Ala PAX6 mutation had a mean spherical equivalence of +2.8 D. Thus, our observations generally support other incidental findings, that PAX6 mutation, particularly predicted haploinsufficiency, may be associated with extreme refractive error, although the mechanism by which this occurs is not clear.

Identification of novel mutant PAX6 alleles in Indian cases of familial aniridia

Background

Haploinsufficiency at the PAX6 locus causes aniridia, a panocular eye condition characterized by iris hypoplasia and a variety of other anterior and posterior eye defects leading to poor vision. This study was performed to identify novel PAX6 mutations that lead to familial aniridia in Indian patients.

Methods

Genomic DNA was isolated from affected individuals (clinically diagnosed aniridia) from nine unrelated aniridic pedigrees, unaffected family members, and unrelated normal controls. The coding regions of PAX6 were amplified and subjected to single strand conformation polymorphism (SSCP) gel analysis, and direct cloning and sequencing.

Results

SSCP band shifts, indicative of DNA base pair mutations, were observed in five of these unrelated families. Four mutations were shown to be previously unreported insertion or deletions in PAX6, leading to frameshifts. These new mutations were c.1174delTG (in exon 10), c.710delC (exon 6), c.406delTT (exon 5) and c.393insTCAGC (exon 5). The other nonsense mutation, a transition (c.1080C>T) in exon 9, has been reported previously as a mutation hotspot for PAX6 in other ethnic pedigrees. All mutant alleles transmitted through aniridic individuals in each family.

Conclusion

These new deletions and an insertion create frameshifts, which are predicted to introduce premature termination codons into the PAX6 reading frame. The genetic alterations carried by affected individuals are predicted to lead to loss-of-function mutations that would segregate in an autosomal dominant manner to subsequent generations. This is the first report of the 'hotspot' c.1080C>T transition from Indian families.