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Trisomy is the most common type of chromosome abnormality, affecting 4% of clinically recognised pregnancies, of which, trisomies 16, 21 and 22 are the most prevalent. It has been suggested that a large proportion of maternally derived trisomic pregnancies, specifically trisomy 21, are the result of low-level ovarian mosaicism. In this study, we aimed to reproduce these previously published results on trisomy 21 and investigate the other common maternally derived trisomies (i.e. trisomies 16 and 22) by determining chromosome copy number in fetal ovarian and control skin cells.Ovarian and control skin tissue was collected from eight karyotypically normal female fetuses of between 10 and 14 weeks gestation, which were terminated for social reasons. Tissues were dissociated and fluorescence in situ hybridisation was performed with break-apart probes: CBFβ (16q22), RUNX1 (21q22) and EWSR1 (22q12).A small number of trisomic cells, 13 out of 51,146 cells examined (0.025%), were identified in both ovarian and control skin samples. Only three of these trisomic cells were present in the fetal ovarian tissue.This study found no evidence of fetal ovarian mosaicism for trisomies 16, 21 and 22.

Deficiency of amylo-1,6–glucosidase activity was expressed in parallel in liver and skin fibroblasts from a patient with type III glycogenosis. In crude extracts of control liver and muscle, amylo-1, 6–glucosidase (M.W. 164000) was identified by immunoprecipitation; no cross-reacting material was found in the patient's liver. Assay of amylo-1,6–glucosidase activity in cultured skin fibroblasts from the affected family revealed less than 10 per cent of control value in mutant homozygous cells whereas in cells from the parents, activity was reduced to 40–60 per cent of the control value. Activity in cultured amniotic fluid cells was similar to that of control fibroblasts. In cultured amniotic fluid cells obtained during the mother's subsequent pregnancy, the normal amylo–1,6–glucosidase activity measured, predicted correctly the outcome of this pregnancy prior to the 20th week of gestation.