Twenty-eight laboratories evaluated a new fluorescence in situ hybridization (FISH) strategy for chronic myeloid leukemia. In a three-part study, bcr/abl1 D-FISH probes were used to study bone marrow specimens. First, laboratories familiarized themselves with the strategy by applying it to known normal and abnormal specimens. Then, collectively the laboratories studied 20 normal and 20 abnormal specimens blindly and measured workload. Finally, each laboratory and two experts studied six serial dilutions with 98–0% abnormal nuclei. Using the reported normal cutoff of <1% abnormal nuclei, participants reported no false-negative cases and 15 false-positive cases (1–6.6% abnormal nuclei). Results provided by participants for serial dilutions approximated the expected percentages of abnormal nuclei, but those from the experts exhibited greater precision. The clinical sensitivity, precision, nomenclature, workload, recommendations for training, and quality assurance in methods using D-FISH in clinical practice are discussed.

We report two cases of mosaic trisomy 16 diagnosed by amniocentesis, with dysmorphic findings in both cases evident upon delivery. Following elective termination, case 1 demonstrated a trisomy 16 cell line in fetal skin (4 per cent) and placental tissue (64 per cent). Molecular studies on the disomic cell line indicated that both chromosome 16s were maternal in origin, suggesting loss of the paternal chromosome 16 from a trisomic zygote (uniparental heterodisomy). At birth, case 2 demonstrated only disomic cells in skin and blood, with trisomy 16 present in 4 per cent of cells from the amnion. Molecular studies confirmed both maternal and paternal contributions of the chromosome 16s. We analysed DNA from one previously reported case of mosaic trisomy 16 (Williams et al., 1992) and failed to find signs of uniparental disomy in this child with congenital heart defects. These cases had distinctive but different dysmorphic features. We suggest that trisomy 16 embryos may revert to disomy during the course of pregnancy, allowing for longer survival with various abnormalities in growth and morphogenesis. The clinical significance of prenatally detected mosaic trisomy 16 may not be completely defined by additional cytogenetic, molecular, and ultrasound studies.