The best-studied example of the cis-regulatory ‘switch off’ phenomenon has been associated with aniridia (MIM 106210), a panocular developmental eye disorder in which most cases are due to het-LOF mutations in PAX6. A proportion of cases that are clinically indistinguishable from those with nonsense mutations result from deletions or translocation BPs located 3′ to the gene (32). This evidence concerns the gene PAX6 and isolated aniridia.