Malignant myeloid transformation with isochromosome 7q in Shwachman-Diamond syndrome.

Shwachman-Diamond syndrome is an autosomal recessive disorder characterized by exocrine pancreatic dysfunction, bony metaphyseal dysostosis, various degrees of cytopenia, and a striking tendency to develop myelodysplastic syndrome and acute myeloblastic leukemia. Isochromosome 7 [i(7q)] is a rare non-random cytogenetic abnormality of myeloid cells in hematological malignancy. We report two cases of Shwachman-Diamond syndrome in which patients developed myelodysplastic syndrome and i(7q), detected by G-banding karyotype analysis and fluorescence in situ hybridization. Three other children have been previously reported to have myelodysplastic syndrome in association with i(7q); two of them had Shwachman-Diamond syndrome. Isochromosome 7q may be a fairly specific marker of myeloid malignant transformation in this syndrome and play a role in its pathogenesis.