In a small part of Duchenne patients (7%) one or more exons are duplicated (Figure 1). A normal dystrophin gene contains 79 exons interrupted by introns. For some patients part of the gene is duplicated: a duplication. As with deletions, the duplication also involves the introns, but generally only the exons are mentioned: in the example in Figure 1 it is a duplication of exon 48-50.
Figure 1. A duplication in the dystrophin gene.
The consequences of duplications are similar to those of deletions: the genetic code is broken (Figure 2). Thinking back to the comparison that was written in Mutations: the recipe contains 2 steps of adding milk. In total twice the amount of milk is added and as a result the cake will fail.
Figure 6. Disruption of the genetic code by a duplication.
At the top drawing in Figure 2 the original RNA and protein are shown. At the bottom the genetic code is disrupted through the duplication of two yellow RNA subunits. The consequences are similar to those of the deletion : new protein subunit codes appear instead of the original ones and starting with the mutation, aberrant protein subunits are used to generate the protein. The aberrant subunits differ from those used in the deletion, but they are not the blue and yellow subunits needed for protein function.