A fast polymerase chain reaction-mediated strategy for introducing repeat expansions into CAG-repeat containing genes.

We describe a simple method for expanding CAG trinucleotides in CAG-repeat containing genes which, in contrast to other techniques, leaves the original gene sequence intact. Here, we expanded the CAG stretches of a plasmid clone containing the cDNA of the SCA3/MJD gene from 22 CAG up to > 130 CAG repeats using polymerase chain reaction (PCR)-mediated mutagenesis. The method reported in this article requires minimal resources, is very fast, and enables to construct recombinant plasmids carrying large CAG expansions.