Fig. 3.

Current molecular diagnostic methods. Flow chart shows an example of two current diagnostic methods for diagnosing STR expansions: Southern blot and repeat-primed PCR. The sample analysis shown in both diagnostic methods was taken from a patient with Friedrich’s ataxia with a heterozygous ‘GAA’ expansion in the FXN gene (approximately 90 and 900 repeats). The RP-PCR graph shows the characteristic tailing/stuttering pattern of expanded alleles caused by the repeat-primed probes binding to more sites within the STR expansion. For sizing, Southern blot is performed. The larger 900-repeat ‘GAA’ allele cannot be seen using the Southern blot sizing ladder shown above