Processed pseudogene insertions in somatic cells

Processed pseudogenes are copies of messenger RNAs that have been reverse transcribed into DNA and inserted into the genome using the enzymatic activities of active L1 elements. Processed pseudogenes generally lack introns, end in a 3' poly A, and are flanked by target site duplications. Until recently, very few polymorphic processed pseudogenes had been discovered in mammalian genomes. Now several studies have found a number of polymorphic processed pseudogenes in humans. Moreover, processed pseudogenes can occur in somatic cells, including in various cancers and in early fetal development. One recent somatic insertion of a processed pseudogene has caused a Mendelian X-linked disease, chronic granulomatous disease.