Trisomy 16 mosaicism in amniotic fluid cell cultures.

Trisomy 16 mosaicism was found in amniotic fluid cells in a patient undergoing amniocentesis because of elevated second-trimester maternal serum alpha-fetoprotein (MSAFP) (2.80 MOM), a markedly elevated human chorionic gonadotropin level (hCG) (12.02 MOM), and a Down syndrome risk of 1:55. Ultrasound evaluation of the fetus indicated the presence of an atrial septal defect and clinodactyly. Cytogenetic analyses of various fetal tissues using fluorescence in situ hybridization (FISH) failed to detect substantial numbers of trisomy 16 cells; however, trisomy 16 mosaicism was identified in placental tissue. Molecular genetic analysis at five different loci [four analysed by polymerase chain reaction (PCR) and one by Southern blot analysis] failed to show any evidence for uniparental disomy. Although trisomy 16 cells could not be clearly demonstrated in the fetus, the presence of a clinically significant proportion of aneuploid cells early in development could not be excluded and it therefore cannot be assumed that a 'confined placental mosaicism' existed. The markedly elevated hCG and elevated MSAFP levels are consistent with abnormal placental function in trisomy 16 mosaicism. Serial ultrasound evaluation (to detect any late-onset growth retardation) and fetal echocardiography may be indicated for patients with extraordinarily high levels of hCG, especially if MSAFP is also elevated.

Comparison of high resolution chromosome banding and fluorescence in situ hybridization (FISH) for the laboratory evaluation of Prader-Willi syndrome and Angelman syndrome.

The development of probes containing segments of DNA from chromosome region 15q11-q13 provides the opportunity to confirm the diagnosis of Prader-Willi syndrome (PWS) and Angelman syndrome (AS) by fluorescence in situ hybridization (FISH). We have evaluated FISH studies and high resolution chromosome banding studies in 14 patients referred to confirm or rule out PWS and five patients referred to confirm or rule out AS. In four patients (three from the PWS category and 1 from the AS group) chromosome analysis suggested that a deletion was present but FISH failed to confirm the finding. In one AS group patient, FISH identified a deletion not detectable by high resolution banding. Review of the clinical findings in the discrepant cases suggested that the FISH results were correct and high resolution findings were erroneous. Studies with a chromosome 15 alpha satellite probe (D15Z) on both normal and abnormal individuals suggested that incorrect interpretation of chromosome banding may occasionally be attributable to alpha satellite polymorphism but other variation of 15q11-q13 chromosome bands also contributes to misinterpretation. We conclude that patients who have been reported to have a cytogenetic deletion of 15q11-q13 and who have clinical findings inconsistent with PWS and AS should be re-evaluated by molecular genetic techniques.

Chromosome 7p--syndrome: craniosynostosis with preservation of region 7p2.

Deletion of a portion of the short arm of chromosome 7 is associated with a recognizable phenotype which often includes craniosynostosis. Recent reports have suggested that craniosynostosis occurs only if there is a deletion involving band 7p21 or the segment distal to that band. We report on a boy who had an interstitial deletion of 7p, not involving band 7p21 or the segment distal to that band, who nevertheless had craniosynostosis. Thus, it appears that the determination of craniosynostosis in this syndrome is more complicated than has been suggested previously.

Diploid/tetraploid mosaicism in a liveborn infant demonstrable only in the bone marrow: case report and literature review.

A case of a multiply malformed liveborn infant with mosaic tetraploidy on examination of bone marrow but not of peripheral lymphocytes or skin fibroblasts is presented. The literature is reviewed and the clinical features of our patient are compared with those of the nine previously reported cases. We suggest that when the clinical suspicion of polyploidy is strong, it may be prudent to expand the search for the abnormality to include cytogenetic studies of the bone marrow, despite a normal karyotype in peripheral blood.