X-chromosome inactivation patterns in EPCs from MM patients. (A) X-chromosome inactivation status in a MM patient (Case 5, Table 1). XCI patterns were determined at least twice for each sample by incorporating α-[33P]-dCTP into the PCR reaction. For each sample, DNA was either undigested (-) or digested (+) with the methylation-sensitive restriction enzyme HpaII. The PCR products were separated on 8% sequencing gels and subjected to autoradiography. Intensity of the specific bands corresponding to the AR gene demonstrates a skewed pattern of XCI (predominance of a single band) in EPCs, and a random pattern of XCI (presence of two bands of similar intensity) in hair root cells. A clonal population was defined as a cell population with greater than 77% expression of either one of the X-linked alleles. (B) Distribution of XCI patterns in MM patients and healthy controls. XCI patterns were determined in DNA from EPCs in MM patients (filled triangles), and PBMCs in healthy controls (open triangles) (*p = .05). For clarity, the y-axis begins at 40%.