Amplification Refractory Mutation System (ARMS)

also called allele-specific PCR (ASP)
to amplify or detect mutant DNA, use 3 primers

ARMS has the ability to isolate low levels of a mutant sequence in a background of wild-type DNA. The system depends on the specificity of a primer for the normal sequence and another primer for the mutation.

In ARMS, the primer pair is designed so that one of the 3' ends coincides with a variant nucleotide in the target sequence. When the primer mismatches the template the frequency of extension is very low and consequently the effective number of sequence copies available for amplification is greatly reduced.

The principle of ARMS. Primers are designed to amplify wild-type and mutant sequence. The difference between these two primers is the 3' base, where one matches wild-type sequence and the other the mutant. The reaction containing the mutant primer will only extend mutant template and wild-type template will not be extended by this primer. (3' base of primer is where extension begins, therefore need specificity)

http://www.horizonpress.com/pcr/pdf/rtpcr/rtpcr09.pdf
http://clincancerres.aacrjournals.org/content/12/13/3875/F1.large.jpg