Alu elements and post-transcriptional processing of transcripts.

The majority of human genes include transposable Alu repetitive elements in their introns. These elements are bounded by AAAA and TTTT sequences, which allow both transposition among inrons and formation of hairpin loops.  If these sequences accumulate mutations, they may wrongly signal transcriptional processing events, resulting in alternative splicing of exons, or altered polyadenylation, which may affect gene function.

Figure from Deininger Genome Biology 2011 12:236 ; text ©2013 by Steven M. Carr