Apparent C Trisomy in Bone Marrow Cells: Report of Two Cases

A supernumerary chromosome belonging to group C was encountered in bone marrow cells from two patients. One patient, suffering from an atypical myeloproliferative syndrome resembling chronic myeloid leukaemia, has had the apparent C trisomy in 100% of his dividing bone marrow cells for over a year. The other patient, who died of acute myelomonocytic leukaemia, had a mixture of normal and apparently C trisomic cells in his bone marrow. In both instances, phytohaemagglutininstimulated lymphocytes as well as fibroblasts of skin origin showed normal karyotypes. Clinical investigations, including cytochemical characterization of abnormal cells and quantitation and fractionation of vitamin B12-binding proteins, are reported. The results failed to reveal any common clinical entity. Previous case reports are reviewed. The trisomic condition has been discovered in disorders affecting the myeloid, monocytoid and erythroid, but not the lymphoid, cells. The significance of C trisomy in haematological disorders remains obscure.