Eteplirsen is an oligonucleotide (roughly speaking, its chemistry resembles that of DNA).

FORBES: In A First, An Experimental Drug May Help Boys With Muscular Dystrophy

In order to work out where an oligonucleotide has stuck, an extra, fluorescent, component is added to it when it is made.

ECONOMIST: Finding fault with genes

The novel antisense oligonucleotide works by inhibiting the synthesis of apo-B and is under development in the United States and Europe for the treatment of familial hypercholesterolemia.

FORBES: CHMP Recommends Against Approval For Mipomersen In Europe