A case of myelodysplasia with eosinophilia having a translocation t(5;12) (q31;q13) restricted to myeloid cells but not involving eosinophils.

A chromosomally abnormal clone characterized by a translocation, t(5;12)(q31;q13), was detected in the marrow of a child with myelodysplasia and associated eosinophilia which included a generalized skin infiltration. Combined immunophenotyping and fluorescence in situ hybridization on interphase bone marrow cells showed that the chromosomal rearrangement was restricted to the granulocyte lineage but was not present in the eosinophils. If the chromosome rearrangement is important in the overproduction of eosinophils in this case, the lineage restriction found suggests that its effect must be indirect.