FIGURE 1.

The principle of the modified TP-PCR. Two PCR procedures, conventional PCR and TP-PCR are simultaneously carried out. The conventional PCR primers, P1-F and P2-R bind to the gene specific regions that closely flank the CTG repeat, generating the smaller alleles. Primer P4(CTG)₆-R has two parts: 6 CAG trinucleotides at the 3′-end sequence and an artificial sequence with no homology to the human genome at the 5′-end sequence. By the triplet priming from its 3′-end sequence, a ladder of PCR fragments differing by 1 CTG unit is produced.