An unusual case of X-15 translocation: evidence for the presence of an 'activator' region on Xpter of man.

A case of an X-autosome rearrangement is presented in which part of the Xpter is deleted but the STS and MIC2X loci are retained. The normal X is late replicating in 97/100 lymphocytes and 50/50 fibroblasts examined. It is assumed that the initial X-inactivation in the embryo is random, but that cells with the rearranged X inactivated are selected against because inactivation spreads into the attached autosomal segment. This spreading, through the normally active STS locus, is hypothesised to be caused by deletion of a part of Xpter which is critical for the maintenance of activity of the Xpter region as a whole.