X chromosomes attached by their long arm: replication autonomy of the short arm adjacent to the inactive centromere.

A 16 years old girl with Turner syndrome was found to have a 45,X/46,X,t(XqXq)?(q27q23) constitution. The two X chromosomes are attached by their long arms with loss of chromosome material and have one active and one inactive centromere. Analysis of replication patterns with autoradiography and BrdU treatment showed that the abnormal X is always the late replicating one and that the short arm of the second X which is adjacent to the inactive centromere maintains a degree of replication autonomy from the rest of the long arm.