Diagrammatic representation of the molecular basis for the B3  allele with the IVS3 + 5G → A splice site mutation.

The IVS3 + 5G → A mutation of the B3 allele changes the consensus sequence of the splice donor site and causes the removal of exon 3 during the mRNA splicing processes, making the exon a pseudoexon. The dashed lines represent the intron regions, and the solid lines illustrate the linkages of exons during mRNA processing.