Cloning of cryptic exon 11a. a. RT-nested PCR products. A fragment spanning exons 10 to 14 was amplified by RT-nested PCR. Two amplified products were obtained from peripheral lymphocytes of a DMD patient (P) but not a control (C). A schematic representation of the exon structure of the amplified fragments is shown on the right. b. Sequences at the exon junctions. Subcloning and sequencing of the amplified products revealed that the larger product contained a 157-bp insertion (exon 11a) between exons 11 and 12. c. Schematic description of the location of exon 11a. The 5' and 3' ends of exon 11a (hatched box) are 5.2 kb downstream of exon 11, and 24.3 kb upstream of exon 12, respectively. Both the AG and GT splicing consensus dinucleotides are present adjacent to exon 11a.