A short piece of genetic material (DNA or RNA) which can bind to a specific gene and change how the code is read. They can be used as a "molecular patch" to mask errors in the genetic code, this is known as exon skipping and this is in clinical trial for Duchenne muscular dystrophy. Certain types of antisense oligonucleotides are also being investigated in the laboratory for their ability to completely switch off genes, this is known as gene silencing.