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An adaptation of the standard fluorescence in situ hybridization (FISH) technique allowing rapid analysis (4 h) has been used to study the prevalence of trisomy 12 in 33 patients with B-CLL, of whom 54% have been shown to have this abnormality. The presence of trisomy 12 has been compared with clinical parameters, and there may be a relationship between the prevalence of trisomy 12 in B-CLL and duration of disease.

Coelomic fluid (n = 32), amniotic fluid (n = 26) and placental tissue were obtained from 32 women undergoing termination of pregnancy at 7–11 weeks of gestation. Fluorescence in situ hybridisation (FISH) was performed to determine fetal sex using a heterochromatic Y probe and an alpha satellite repeat probe for chromosome X. In each case there was concordance in the fetal sex from the three compartments. However, no result could be obtained from 4 of the 32 coelomic fluids and 4 of the 26 amniotic fluid samples. The hybridisation efficiency was significantly lower in coelomic and amniotic fluid compared with placental tissue.

Objective Evaluation of fluorescence in situ hybridisation in the detection of numerical aberrations involving chromosomes X, Y, 13, 18 and 21. Setting Harris Birthright Research Centre for Fetal Medicine. Subjects and methods Chorionic villi (n= 45) or fetal blood (n= 34) were obtained from 79 pregnancies undergoing fetal karyotyping at 10 to 39 weeks of gestation because of ultrasonographic markers of fetal chromosomal abnormality. Karyotyping was performed by both traditional cytogenetics and fluorescence in situ hybridisation, using commercially available kits which utilise a heterochromatic Y probe and the alpha satellite repeat probes for chromosomes X, 18, and 13/21. The frequency distributions of the number of signals obtained by fluorescence in situ hybridisation in the chromosomally normal and abnormal fetuses were compared. Results Traditional cytogenetic analysis demonstrated that the fetal karyotype was normal in 47 cases and abnormal in 32 (including 24 with trisomies 21, 18 or 13, three with triploidy, one with Turners syndrome and four with translocations, deletions or mosaicism). With fluorescence in situ hybridisation it was possible to obtain accurate diagnosis of trisomy 18, Turners or triploidy within six hours of sampling; signal distributions with these chromosomal abnormalities were very different from those of normals. However, for trisomies 21 and 13 there was an overlap in values with those from normals. Conclusions In detection of fetal numerical chromosomal abnormalities the use of the combined 13/21 probe cannot provide sufficiently accurate results to justify abandonment of traditional cytogenetics in favour of fluorescence in situ hybridisation.

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