Gel image to illustrate the deletion of exons 4 and 5 at the DNA level. The top band (1694 bp) represents the wild-type PCR product, which amplifies across exons 4 and 5; bottom band (1084 bp), the PCR product designed to amplify across the deletion breakpoint. Lane 1 indicates a patient heterozygous for the deletion; lane 2, a patient homozygous for the deletion; lane 3, a wild-type control; and lane 4, a negative control.