No abstract

A significant problem associated with cytogenetic prenatal diagnosis is distinguishing between true and pseudomosaicism. This becomes a diagnostic dilemma when fetal mosaicism corresponds with a known clinical entity. True mosaicism reportedly occurs with a frequency of 0.2 per cent and pseudomosaicism in 0.7 per cent to 2.7 per cent of cases. In the past 12 months, our laboratory has completed 522 fetal karyotypes. Nine cases were found to demonstrate mosaicism, 4 true mosaics (0.8 per cent) and 6 pseudomosaics (1.1 per cent). One case demonstrated both true and pseudomosaicism. In all cases of true mosaicism, the pregnancy was continued and karyotypes completed at birth. Our results demonstrate a danger of' rigid adherence to the criteria for true and pseudomosaicism in the examination of amniotic fluids. It is suggested that the criteria established for true and pseudomosaicism may not be valid when an aberrant cell line is found in a single flask and when that aberrant cell line is compatible with a known clinical entity due to a chromosome anomaly.

We report chromosome rearrangements and/or duplication of chromosomes 11 and/or 22. This investigation was prompted by propositi with multiple congenital anomalies and an apparently identical chromosome abnormality - ie, 47, +der(22)t(11;22)(q23;q11.2)mat in two unrelated families. The propositi had failure to thrive, development delay, cleft palate, congenital heart disease, meningomyelocele, and hydrocephaly. The breakage points identified on chromosomes 11 and 22 are site-specific and occur in a nonrandom fashion. Band 11q23 corresponds to the gap produced in some individuals by special treatment of the chromosome preparation with mercaptoethanol and may provide a method to identify individuals at risk for chromosome breakage and rearrangements during gametogenesis.