The 5q- chromosome in preleukaemia and acute leukaemia.

13 patients with the 5q- chromosome are described. In 6 patients the 5q- chromosome was the sole aberration. 10 patients had preleukaemia, 1 a preleukaemia-like syndrome after treatment of polycythaemia vera, a 2 acute myeloid leukaemia. The prognosis was especially poor in terms of survival in preleukaemic patients with 3 or more affected chromosomes: none of these 6 patients survived for more than 6 months. In 4 patients the haematological picture resembled 'the 5q- syndrome'. In the long arm of chromosome No 5 deletions of 3 different kinds were detected. They were named according to the size of the 5q- marker: the short type (10 patients), the intermediate type (1 patient) and the long type (2 patients). There was no clear correlation between the clinical picture and the type of deletion. While the break points cannot always be exactly defined, our data and those reviewed from the literature suggest that the loss of a segment of regions 5q2 or 5q3 is common to all or most deletions.