Renal-coloboma syndrome: A single nucleotide deletion in the PAX2 gene at Exon 8 is associated with a highly variable phenotype

Background: Renal-coloboma syndrome (RCS) is an autosomal dominant disorder characterized by renal abnormalities and optic nerve defects, caused by heterozygous mutations of the PAX2 gene. This gene encodes for the PAX2 developmental nuclear transcription factor, which is primarily expressed during embryogenesis in kidneys, eyes, ears and in the central nervous system. The aim of the present study was to characterize PAX2 mutations in a renal coloboma syndrome family with a highly variable phenotype. Methods: DNA screening was performed by direct sequencing. Results: Five subjects over three generations presented with renal hypodysplasia or horseshoe kidneys in association with bilateral optic nerve colobomas in four cases. one patient with early-onset renal failure had no detectable eye defects. All five subjects carried a novel PAX2 mutation consisting in a frameshift mutation located in Exon 8 (G911del), which causes premature termination of translation and loss of the PAX2 transactivation domain. Conclusion: This is the first report of a PAX2 mutation located in Exon 8. The variability of clinical symptoms may be explained by the limited disruption of the protein sequence at the transactivation domain.