This paper reports a case of chromosomal mosaicism for trisomy 5 recovered from amniotic fluid cells and from skin fibroblasts of a liveborn dysmorphic male. Routine amniocentesis was performed at 16 weeks' gestation because of parental concern. Trisomy 5 cells were measured from 25 per cent of amniocytes from two culture vessels. No further invasive testing was performed until 32 weeks' gestation, at which time ultrasound examination showed a fetus with intrauterine growth retardation. Fetal blood sampling was then performed, with only karyotypically normal cells recovered. At birth, the child was found to have multiple dysmorphic features and congenital anomalies, including an eventration of the diaphragm and ventricular septal defect, both of which required surgical correction. Chromosomal analysis of cord blood lymphocytes indicated 46,XY; however, 20 per cent of the cultured fibroblasts obtained from the chest skin at the incision site for diaphragmatic repair had a 47,XY, +5 karyotype. Trisomy 5 mosaicism may be another example of tissue-limited mosaicism. Fetal blood sampling can then be falsely reassuring. Furthermore, because some cell lines rarely appear in lymphocyte populations, cytogenetic analysis of multiple tissues is warranted as part of the evaluation of individuals with developmental delay and dysmorphic features.

A child with a 7q+ chromosome abnormality had a father with 0.5% mosaicism for a balanced 7;14 translocation. This mosaicism was not found in 100 fibroblasts. This degree of mosaicism is well below the limits usually detected by standard clinical cytogenetic protocols. However, the one abnormal cell cannot be disregarded in this case, since it can serve as an explanation of the child's genotype. This case serves to illustrate the need for detecting subtle degrees of mosaicism for structural anomalies in humans and brings to question the true population frequencies of mosaic balanced translocation carriers.

The purpose of this study was to determine the rate of utilization of Tay Sachs disease screening by the Ashkenazi Jewish population. Pregnant women who were referred to one of three genetic centers in New Jersey for amniocentesis unrelated to Tay Sachs screening were the study population. 4490 charts were reviewed retrospectively to determine the at risk population for Tay Sachs disease (Ashkenazi Jews) and whether or not patients and their spouses had elected Tay Sachs screening prior to referral. A group of 25 patients who did not elect screening were questioned as to their specific reason for declining Tay Sachs screening. Overall community utilization was 90%. Of the couples who did not elect screening, 64% felt that their risk to have an affected child was too small, 16% could not recall Tay Sachs screening being offered to them, 8% felt that screening was inconvenient. Tay Sachs screening as a voluntary preventive health care program has a high utilization rate in our study group.