Small Copy Number Neutral Intrachromosomal Translocation of PAX6 and Aniridia.

Abstract

Approximately 5% to 10% of individuals with classic aniridia do not receive a molecular diagnosis after clinical testing for variants in PAX6 and its downstream regulatory region. To apply optical genome mapping (OGM) and long-read whole-genome sequencing (lrWGS) to diagnose an individual with unexplained classic aniridia. High-quality DNA was extracted from the blood of a 16-year-old male patient with classic aniridia and prior negative clinical test results that included sequencing and copy number analysis of PAX6 exons and downstream regulatory region as well as genomic analysis via short-read whole-genome sequencing (srWGS) and analyzed using OGM and lrWGS. All analyses were performed in a research laboratory in Wisconsin from January 2019 to September 2025. OGM and lrWGS. Identification of a structural variant disrupting PAX6 expression in an individual with classic aniridia, following negative prior testing including srWGS. OGM identified a 55-kb deletion on 11p13 encompassing all PAX6 exons and exon 12 of ELP4, with insertion of this segment into 11q21. lrWGS delineated the exact breakpoints, confirming that the downstream regulatory region, required for normal PAX6 expression, remained at the 11p13 locus. Consequently, the translocated copy of PAX6 at 11q21 is expected to lack expression due to the loss of its essential regulatory elements. These findings in an individual with classic aniridia harboring an intrachromosomal rearrangement at the PAX6 locus identified by OGM and lrWGS may represent the smallest reported structural variant to separate the PAX6 coding sequence from its downstream regulatory region. This structural variant may have fallen below the detection threshold of srWGS due to its balanced nature and small size, suggesting OGM and lrWGS would be needed for definitive identification.