Letters to the Editor

Indian Pediatrics 1999;36:321-322

Single Cell Translocations: Is it coincidental or Causal?

Single cell abnormality is defined as the chromosome abnormality which occurs in one metaphase plate, the same is not seen when more metaphases are scored(1). Single cell translocations have been previously reported to occur in normal lymphocyte cultures. A number of investigators have reported the frequent occurrence of translocation involving chromosome 7 and 14(1,2). We have observed this single cell abnormality involving chromosomes 7 and 14 in PHA stimulated blood from a 1-year-old male child. The child had a history of mental retardation and seizure disorder. The single cell translocation was first detected in 25 cells and when 75 additional cells were analyzed no further occurrence of translocation was observed. The break points were identified to be on 7p 12 and 14q 12 regions (Fig. 1). The pathogenesis of these abnormalities has not yet been clearly understood(3,4). In our routine cytogenetic screening, single cell abnormality was found as random chromosome loss or gain in cases such as bad obstetric history and spontaneous repeated abortions. To rule out the occurrence of single cell translocations, we have set up two, different blood lymphocyte cultures, namely, blood ,culture induced with high dose of PHA, and long hypotmic treatment. In the latter random chromosome loss or gain was observed. Our in vitro study results suggest that the random chomosome loss gain sometimes may be accidental or due to a technical artefact, but the structural abnormalities occurring in single cells may have a definite role in the disease development as mosaic, where a greater number cells may need,to be analyzed or cells from fibroblasts may need to be cultured to identify mosaicism. Single cell abnormalities might indicate the presence of parental mosaicism. Hence there is an urgent need to rule out parental mosaicism in such a case to enable appropriate genetic counseling to the family.

 

Fig. 1. Partial metaphase showing translocation between 7 and 14 chromosome, i.e., t (7;14) (p12;q11) and deleted part of7p.

 

 

                            V. Babu Rao,
                              Bibhas Kar,
   Insiitute afGenetic Studies,
                Rajkamal Complex,
                Panchsheel Square,
                                Nagpur-10,
                                          India

4. Murre C, Waldmann R, Morton .c, Bongiovanni K, Waldmann T, Shows T, et al. Human gammachain genes are rearranged in leukaemic T cells and map to the short arm of chromosome 7. Nature 1985; 316: 549-552.