Molecular Analysis of PAX6 Gene in Patients With Aniridia

Abstract

Purpose: : Aniridia is a rare genetic congenital eye condition characterized by the underdevelopment of the iris that usually occurs in both eyes and is inherited as an autosomal dominant trait with high penetrance. Associated ocular anomalies can include congenital cataract, lens subluxation, glaucoma, and coloboma of the retina and the optic nerve. Congenital aniridia is associated to changes in PAX6 gene (Paired Box Gene 6 - ENSEMBL - ENSG00000007372), located at chromosome 11p13. PAX6 is a phylogenetically conserved transcription factor, associated to eye development, regulating the tissue-specific expression of several molecules. The mutations are scattered throughout the gene. The vast majority of mutations reported so far are nonsense mutations, frameshift mutations or splicing errors that are predicted to cause premature truncation of the PAX6 protein, causing haploinsufficiency. The screening of mutations and polymorphisms in patients and their no affected relatives becomes important for the investigation of genotype-phenotype correlation and the definition of the haplotype. In this study we report the molecular analysis of the PAX6 gene in one Brazilian family with congenital aniridia (4 cases).

Methods: : Total genomic DNA was isolated from peripheral blood of a two generation family with congenital aniridia (father, mother, one son, two daughters / four affected members - mother and children). The coding exons of the human PAX6 gene were amplified by PCR and direct automated sequencing was performed.

Results: : The molecular analysis revealed a C>T mutation at genomic position 24483 in exon 10 of the mother's allele, segregating with the disease. This mutation causes the change of the amino-acid 254 (arginine) leading to a stop codon (R254X). Besides this mutation, the mother also presented in heterozygosity the g.7683A>G and g.14514C>A changes in exon 2 and intron 4, respectively, both not described and not detected in the children, which indicates that they inherited the same maternal allele.

Conclusions: : The molecular study of the PAX6 gene in affected individuals becomes essential for genetic counseling of patients and families, since the analysis of the disease in Brazil is restricted to clinical studies. A greater number of individuals is required to define the PAX6 mutational spectrum in Brazilian subjects with aniridia.

Keywords: iris • genetics • mutations