Ring F chromosome mosaicism (46,XY,20r-46,XY) in an epileptic child without apparent haematological disease.

they were present in the peripheral blood of the mother, they either did not survive for more than 4 weeks, or at least they disappeared from the circulation. They were not selected out in a long term leucocyte culture. The latter fact however is not surprising as we have been unable to detect the marker chromosome specific of the leukaemic cells in established long term leucocyte cultures in 12 patients with Ph' positive CML and in 2 other patients with acute leukaemia (H. van den Berghe, unpublished data).