PRENATAL-DIAGNOSIS OF AN INFANT WITH MOSAIC TRISOMY-16 OF PATERNAL ORIGIN

We present the first case of an infant with paternally-derived mosaic trisomy 16. Amniocentesis following an elevated maternal serum alpha-f etoprotein level and early fetal growth restriction at 19 weeks detect ed a high level of mosaicism with 25/33 colonies demonstrating trisomy 16 and 8/33 colonies with a normal 46,XX karyotype. Molecular studies revealed a paternal origin of the trisomy which was present in amniot ic fluid cells, representing either a post-zygotic error or a meiosis II non-disjunction without crossing-over. In addition, there was norma l biparental inheritance in the normal cell fine. The symmetrically gr owth-restricted fetus was closely monitored for the remainder of the g estation. Decreased fetal movements at 36 weeks in conjunction with el ectronic fetal monitoring showing evidence of fetal distress necessita ted abdominal delivery. Severe growth restriction, mild facial dysmorp hism, and cardiac anomalies were identified. Microsatellite analysis d emonstrated biparental inheritance in skin fibroblasts with a paternal origin for the trisomy in the placenta. Follow-up cytogenetic studies of additional tissues revealed 85 per cent trisomy 16 mosaicism in th e placenta, yet only cytogenetically normal cells in lymphocytes and f ibroblasts.