A chronic myeloproliferative disorder associated with monosomy 7 in the bone marrow cells; normal karyotype in acute transformation.

A chronic myeloproliferative disorder associated with monosomy 7 of the bone marrow cells is described in a male infant. After nearly 4 years, during which time no drug therapy was given, the disease transformed to a 'blast crisis' and at this stage the karyotypes of the marrow and unstimulated blood cells were shown to be normal. It is proposed that the development of the myeloproliferative disorder associated with monosomy 7 is a multistage process and the acquisition of the chromosomal abnormality is a secondary event.