Research Article: Improving molecular diagnosis of aniridia and WAGR syndrome using customized targeted array-based CGH

Date Published: February 23, 2017

Publisher: Public Library of Science

Author(s): Fiona Blanco-Kelly, María Palomares, Elena Vallespín, Cristina Villaverde, Rubén Martín-Arenas, Camilo Vélez-Monsalve, Isabel Lorda-Sánchez, Julián Nevado, María José Trujillo-Tiebas, Pablo Lapunzina, Carmen Ayuso, Marta Corton, Anthony W.I. Lo.


Chromosomal deletions at 11p13 are a frequent cause of congenital Aniridia, a rare pan-ocular genetic disease, and of WAGR syndrome, accounting up to 30% of cases. First-tier genetic testing for newborn with aniridia, to detect 11p13 rearrangements, includes Multiplex Ligation-dependent Probe Amplification (MLPA) and karyotyping. However, neither of these approaches allow obtaining a complete picture of the high complexity of chromosomal deletions and breakpoints in aniridia. Here, we report the development and validation of a customized targeted array-based comparative genomic hybridization, so called WAGR-array, for comprehensive high-resolution analysis of CNV in the WAGR locus. Our approach increased the detection rate in a Spanish cohort of 38 patients with aniridia, WAGR syndrome and other related ocular malformations, allowing to characterize four undiagnosed aniridia cases, and to confirm MLPA findings in four additional patients. For all patients, breakpoints were accurately established and a contiguous deletion syndrome, involving a large number of genes, was identified in three patients. Moreover, we identified novel microdeletions affecting 3′ PAX6 regulatory regions in three families with isolated aniridia. This tool represents a good strategy for the genetic diagnosis of aniridia and associated syndromes, allowing for a more accurate CNVs detection, as well as a better delineation of breakpoints. Our results underline the clinical importance of performing exhaustive and accurate analysis of chromosomal rearrangements for patients with aniridia, especially newborns and those without defects in PAX6 after diagnostic screening.

Partial Text

Congenital aniridia [MIM#106210] is a rare genetic pan-ocular disease characterized by the complete or partial absence of the iris. It can appear uni- or bilaterally, isolated or in association to other ocular and/or systemic anomalies. Affected individuals can present additional congenital or progressive ocular anomalies [1, 2]. Among syndromic cases with aniridia, the most frequent form is the WAGR syndrome [MIM#194072, Wilms Tumor, Aniridia, Genitourinary anomalies and mental Retardation] [3]. In most of case, aniridia and related-syndromic conditions are caused by heterozygous loss-of-function defects in PAX6, located on chromosome 11p13. Missense mutations in PAX6 have been also associated with other isolated ocular anomalies [1, 2, 4]. Up to 30% of patients with aniridia carry chromosomal rearrangements at 11p13, with a high degree of breakpoint complexity [5, 6], including whole-gene deletions, microdeletions affecting only 3´ regulatory enhancers [5, 7–12] or contiguous gene deletions of PAX6 and other neighboring genes, mainly WT1 which is associated to WAGR syndrome [1, 13].

Nowadays, it is important to exhaustively explore the non-coding regions of PAX6 by mean of more robust and sensitive methods for CNVs detection that the routinely used in the study of aniridia. In this way, the percentage of patients with aniridia that appear not to carry PAX6 defects after routine genetic analysis could be probably reduced.[4].