PCR analysis of DBS sample 2 in Table
, a female with a large premutation allele and a highly methylated normal allele. A: Capillary electrophoresis profile of PCR analysis. Arrows indicate alleles of 30, 161 and 167 CGG repeats. The 161 and 167 repeat alleles (arrows at right) represent a premutation allele. (Somatic mosaicism is presumably responsible for the bifurcation). B: Methylation analysis reference (no Hpa II digestion) PCR profile of DBS DNA. C: Methylation analysis PCR profile of Hpa II-digested DBS DNA. Comparison of B and C illustrates how each allele is protected from HpaII digestion by methylation. The premutation was split into two alleles and the analysis suggests that the larger, 167 repeat had a lower level of methylation than the smaller, 161 repeat allele. The 2 PCR products at approximately 0 CGG repeats represent internal controls for the methylation analysis.