CRYPTIC DELETIONS AND INVERSIONS OF CHROMOSOME-21 IN A PHENOTYPICALLYNORMAL INFANT WITH TRANSIENT ABNORMAL MYELOPOIESIS - A MOLECULAR CYTOGENETIC STUDY

A case of transient abnormal myelopoiesis in a normal newborn without features of Down syndrome is described. The majority of bone marrow ce lls analysed belonged to a chromosomally abnormal clone with trisomy f or chromosomes 18 and 21, Complex intrachromosomal rearrangements of o ne chromosome 21, demonstrated by fluorescence in situ hybridization u sing locus-specific probes, were found in a minor population of the cl onal cells. These rearrangements involved loci previously shown to be rearranged in the leukaemic cells from patients with Down syndrome and leukaemia. However, the child's myeloproliferation resolved rapidly w ith disappearance of the abnormal clone, and 3.5 years later she remai ns well.