Results of HUMARA assay on DNA from ECs of control infants’ skin, hemangioma lesions, and unbound fibroblast-like cells. Amplification was performed before (–) or after (+) HhaI digestion. For each cell sample shown, the individual is heterozygous for CAG repeat size and has two different alleles before HhaI digestion, represented by two major PCR products on gel. Fainter (“stutter”) bands are products of slippage by DNA polymerase in STR region. (a) Amplification of DNA from ECs cultured at P4 to P7 from skin of two control female infants HFSEC-3 (left) and HFSEC-11 (right). In each sample, two alleles are equally amplifiable both before and after digestion. (b) Amplification of DNA from cultured hemECs from patient 1 (left) at P4 and P6 and patient 21 (right) at P5, P6, and P7. In both cases, one allele completely disappears after HhaI digestion. This selective amplification of one allele indicates that it is always methylated and not subject to digestion by HhaI and, therefore, is the only inactive allele in cell population. C is a positive control for the HUMARA assay. (c) Amplification of DNA from cultured unbound, fibroblast-like cells of hemangioma 10 at P4 (UB-P4). For comparison, DNA from cultured hemEC-10 at P5 (EC-P5) is shown at right.