IMMUNOGLOBULIN AND T-CELL RECEPTOR DELTA-GENE REARRANGEMENTS ARE RARELY FOUND IN MYELODYSPLASTIC SYNDROMES IN CHRONIC PHASE

Clonality, in MDS, can only be assessed in patients with chromosomal r earrangements or in fem ales heterozygote for X chromosome restricted polymorph isms. ''Illegitimate'' rearrangements of the immunoglobulin heavy chain (Ig H) gene and incomplete rearrangements involving V delt a(2) and D delta(3) segments of the T-cell receptor delta (TcR delta) gene are seen in some cases of AML, and AML post-SMD, and can be detec ted by a sensitive PCR method. in order to analyse clonality in additi onal cases in MDS, we looked for Ig H and TcR delta gene rearrangement by PCR in 95 cases of MDS. A rearrangement of the Ig H gene was seen in 2 of the 95 patients: in the circulating blood of 2 of the 36 cases of chronic myelomonocytic leukaemia (CMML) and in none of the marrow samples of the other 59 MDS. A rearrangement of the TcR delta gene (in volving V delta(2) and D delta(3) segments) was seen in three cases (i n the circulating blood of two other CMLL patients, and in the bone ma rrow of another MDS patient). Twenty-five of the 90 cases of MDS with negative PCR findings, in addition to the five cases with positive PCR findings underwent Southern blot analysis of Ig H and TcR delta genes , and PCR analysis of V delta(1) and J delta(1) segments of the TcR de lta gene. Those examinations were normal in all the cases tested. in p atients with positive PCR findings for Ig H or V delta(2)D delta(3) re arrangements, the proportion of rearranged cells was evaluated at 1-5% in four cases, and 5-20% in the remaining patient. Because the analys is was performed on total circulating leukocytes or total nucleated ma rrow cells, the nature of the clonal population in positive cases (lym phoid cells ? myeloid cells ? blasts ?) could not be determined. From a practical point of view, Ig H and TcR delta gene rearrangements seem to very rare in MDS, and cannot be used as clonality markers in most cases.