Inactive normal X in a female leukaemic patient with an acquired X/autosome translocation.

An X;9;22 translocation was detected in bone marrow cells of a female patient with blastic crisis of CML. A dynamic study following 5-BrdU treatment showed that the inactive late-replicating X chromosome was the normal one. This pattern of X-chromosome replication appears to be superimposable on the most usual model found in congenital X/autosome translocations. It is suggested that preferential autosome translocation onto the active X chromosome could be the general rule in acquired X/autosome translocations associated with long survival.