X-CHROMOSOME INACTIVATION AND MICRONUCLEI IN NORMAL AND TURNER INDIVIDUALS

Studies on aneuploidy have shown that the X is the most frequently los t chromosome in females, and that the number of X chromosome-positive micronuclei increases with age in women. Recently, we showed that the inactive X chromosome is incorporated preferentially in micronuclei. T he objectives of the current study were, firstly, to determine the inc idence of X chromosome incorporation into micronuclei in males and, se condly, to determine the incidence of X chromosome incorporation into micronuclei of females with Turner syndrome, Blood samples were obtain ed from 18 male newborns and 35 normal adult males ranging in age from 22 to 79 years and from seven women with non-mosaic Turner syndrome a ged 11-39 years. Isolated lymphocytes were cultured in the presence of cytochalasin B and 2000 binucleated cells per subject were scored for micronuclei, Cells were then hybridized with the biotinylated X centr omere-specific probe, pBamX7, and visualized with fluorescein-conjugat ed avidin. All micronucleated cells were relocated and evaluated for t he presence or absence of the X chromosome, Of the 335 micronuclei obs erved, 6.6% (22/335) contained an X chromosome. Analysis of variance s hows a statistically significant increase, for both males and Turner f emales, in the number of X chromosome-positive micronuclei with age (P < 0.001). These data also show that the X chromosome is included in m icronuclei from males more often than would be expected by chance (P < 0.005; chi(2) analysis, 15 df). Here we show that there is a tenfold d ifference in the frequency of X chromosome-positive micronuclei in 46, XX females compared to 46,XY males and 45,X females, providing further support to our previous finding that the X chromosome in micronuclei is the inactive chromosome.