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A recurrent PAX6 mutation is associated with aniridia and congenital progressive cataract in a Chinese family.

ABSTRACT: Aniridia is phenotyically and genetically heterogeneous. This study is to summarize the phenotypes and identify the genetic defect responsible for aniridia and congenital progressive cataract in a three generation Chinese family.A detailed family history and clinical data from patients were collected by ophthalmologic examination, including visual acuity, slit-lamp examination, tonometer, keratometry, corneal topography, optical coherence tomography, and ultrasonic A/B scan. All exons and flanking intronic sequences of the paired box 6 (PAX6) gene were amplified by polymerase chain reaction (PCR) and screened for mutation by direct DNA sequencing. Structure and function of the mutant PAX6 were analyzed by bioinformatics analysis.All the six patients shared common manifestations of complete aniridia, congenital cataract and thickened cornea, and broad phenotypic variability was observed in nystagmus, ptosis, strabismus, glaucoma, corneal pannus, corneal curvature, corneal vascularization, cataract subtype, ectopia lentis, axial length, and optic disc anomalies. Sequencing of the candidate gene detected a heterozygous c.307C>T transition in the coding region of PAX6, resulting in the substitution of a highly conserved arginine codon for a termination codon (p.R103X). The p.P103X mutation co-segregated with the affected individuals in the family. The change was supposed to cause structural and functional changes based on computational analysis.We identified a recurrent PAX6 c.307C>T mutation in an aniridia and congenital progressive cataract family, and summarized the variable phenotypes among the patients, which expanded the phenotypic spectrum of aniridia in a different ethnic background.

SUBMITTER: Jin C

PROVIDER: S-EPMC3291521 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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A recurrent PAX6 mutation is associated with aniridia and congenital progressive cataract in a Chinese family.

Jin Chongfei C Wang Qiwei Q Li Jinyu J Zhu Yanan Y Shentu Xingchao X Yao Ke K

Molecular vision 20120216

<h4>Purpose</h4>Aniridia is phenotyically and genetically heterogeneous. This study is to summarize the phenotypes and identify the genetic defect responsible for aniridia and congenital progressive cataract in a three generation Chinese family.<h4>Methods</h4>A detailed family history and clinical data from patients were collected by ophthalmologic examination, including visual acuity, slit-lamp examination, tonometer, keratometry, corneal topography, optical coherence tomography, and ultrasoni ...[more]

PMID: 22393272

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Project description:Aniridia and congenital cataract represent rare but severe developmental ocular conditions. We examined 33 probands from France for mutations in several transcription factors associated with these phenotypes, the forkhead box E3 (FOXE3), paired box gene 6 (PAX6), paired-like homeodomain transcription factor 2 (PITX2), and paired-like homeodomain transcription factor 3 (PITX3) genes.Out of 33 probands, 27 were affected with congenital cataract while the remaining six were affected with aniridia (with or without cataract). The coding regions of FOXE3, PAX6, PITX2, and PITX3 were examined by direct DNA sequencing of gene-specific PCR products.A novel dominant mutation at the stop codon of FOXE3, c.959G>C (p.X320SerextX72), was identified in a patient with congenital cataract. Another novel FOXE3 sequence change, c.571-579dup (p.Tyr191_Pro193dup), was identified in a patient with aniridia, mild lens opacities, and some additional ocular defects; this patient was also found to carry a nonsense mutation in PAX6. PAX6 mutations were identified in two additional probands with aniridia and cataracts. None of the observed sequence alterations were found in normal controls. No mutations were identified in PITX2 or PITX3.The p.X320SerextX72 mutation is only the fourth FOXE3 allele associated with a dominant phenotype since the majority of FOXE3 mutations appear to be recessive with no phenotype observed in heterozygous carriers. The encoded protein is predicted to contain a complete normal sequence followed by seventy-two erroneous amino acids; the position and effect of this mutation are similar to two of the previously reported dominant changes, suggesting a common mechanism for dominant alleles. The p.Tyr191_Pro193dup is predicted to result in an in-frame duplication of three amino acids; however, the contribution of this mutation to the phenotype is unclear since the affected patient also carries a nonsense mutation in PAX6 which acts upstream of FOXE3 in the molecular pathway. The identified PAX6 mutations correspond to the two most commonly observed mutant alleles and demonstrate phenotypes that are consistent with the previously reported spectrum.

Project description:BACKGROUND:Congenital aniridia is a severe autosomal dominant binocular developmental disorder, the primary feature of which is congenital absence or hypoplasia of the iris. PAX6 is the main disease-causing gene of congenital aniridia; inheritance is autosomal dominant. But the current mutations do not fully explain this disorder. METHODS:We investigated the mutation profile of genes related in three Chinese families with congenital aniridia through targeted sequencing technology. And we validated the candidate variants by PCR-based Sanger sequencing. Different degree impairments of islet function were observed in the patients with aniridia by carbohydrate tolerance butter and insulin release tests in our study. RESULTS:We identified four novel mutations of PAX6 from three Chinese families with congenital aniridia, which included heterozygous double mutation c.879_880delCA (p.S294Cfs*46) and c.1124C>G (p.P375R) in Family 1 with three patients, heterozygous frameshift mutation c.308delG (p.P103Qfs*21) in Family 2 with one patient, and c.1192delT (p.S398Pfs*126) in Family 3 with two patients. The three frameshift mutations of PAX6 are co-segregated with the aniridia from controls in the families, but the novel missense mutation is not co-segregated with the phenotype. The frameshift mutations in Family 1 and Family 2 have effects to truncate the protein, but the frameshift mutation in Family 3 will prolong it. We confirmed the phenomenon of male gonadal mosaicism of PAX6 by the sequencing of two linked novel mutations in Family 1. Most of the patients with isolated aniridia have different degrees of islet damage through related clinical tests. CONCLUSION:It is therefore noteworthy that we found different types of pathogenic mutation, which have effects of truncating or prolonging protein leaded by frameshift mutation. Our results of this study extended the pathogenic mutation spectrum of PAX6 for congenital aniridia and demonstrated the male germline chimerism by molecular experiments.

Dataset Information

A recurrent PAX6 mutation is associated with aniridia and congenital progressive cataract in a Chinese family.

Publications

A recurrent PAX6 mutation is associated with aniridia and congenital progressive cataract in a Chinese family.

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