XIST FISH and results of the X chromosome inactivation assay. A-C: FISH analysis using a XIST probe (red signal) demonstrates the presence of two XIST loci in 46,X,der(X) and one XIST locus in cell lines 46,X,r(X) and 45,X. The green signal represents a centromere probe (Cen X). D: X chromosome inactivation study shows two AR alleles in the peripheral lymphocytes without Hpa II digestion. E: XCI analysis shows only one AR allele after digestion with a methylation-sensitive restriction enzyme Hpa II.