Adeno-associated viruses (AAV): they are from the parvovirus
family and are small viruses with a genome of single stranded
DNA. The wild type AAV can insert genetic material at a
specific site on chromosome 19 with near 100% certainty. But
the recombinant AAV, which does not contain any viral genes
and only the therapeutic gene, does not integrate into the
genome. Instead the recombinant viral genome fuses at its
ends via the ITR (inverted terminal repeats) recombination to
form circular, episomal forms which are predicted to be the
primary cause of the long term gene expression