  Extreme deformations of the DNA double helix attracted a lot of attention
during the past decades. Particularly, the determination of the persistence
length of DNA with extreme local disruptions, or kinks, has become a crucial
problem in the studies of many important biological processes. In this paper we
review an approach to calculate the persistence length of the double helix by
taking into account the formation of kinks of arbitrary configuration. The
reviewed approach improves the Kratky--Porod model to determine the type and
nature of kinks that occur in the double helix, by measuring a reduction of the
persistence length of the kinkable DNA.
