PARENTAL ORIGIN OF CHROMOSOMES INVOLVED IN THE TRANSLOCATION T(9 22)

FUNCTIONALLY equivalent genetic material can be labelled by an epigenetic marking process and used differentially depending on whether its origin is maternal or paternal1. This phenomenon is known as genomic imprinting and is manifested at either the chromosomal or gene level. Genomic imprinting seems to play an important role in cancer predisposition syndromes2-5 , and phenotypic consequences are evident in constitutional deletion syndromes and uniparental disomies1. Moreover, there seems to be a preferential retention of paternal alleles in sporadic tumours such as Wilms' tumour6, rhabdomyosarcoma7, osteosarcoma8 and retinoblastoma9. To investigate whether chromosomes involved in acquired abnormalities of haematologic neoplasms show a similar 'parent of origin' bias, we studied the inheritance of the translocated chromosomes 9 and 22 in cases of Philadelphia-chromosome-positive leukaemia, using unique specific chromosome band polymorphisms. Here we show that the translocated chromosome 9 was of paternal origin, whereas the translocated chromosomes 22 were derived exclusively from the maternal copy, in 11 cases with reliable polymorphisms. Our data therefore provide evidence that imprinting phenomena may play an important role in acquired tumour-specific chromosome rearrangements.