CAG

Since the CAG repeat expansion is the sole mutation
responsible for all HD cases, molecular genetic analysis
concentrates on this single region. Small CAG expansions can
be detected using PCR amplification of the repeat region.
The PCR products are then sized using polyacrylamide gel
electrophoresis. Samples with known repeat sizes may be used
as controls to determine the size of the expansion. Larger
expansions cannot be detected by PCR and the time-consuming
Southern blotting method must be used in cases where two
normal sized repeat alleles are not detected by PCR.