PRENATAL-DIAGNOSIS AND OUTCOME OF MOSAICISM FOR A DE-NOVO UNBALANCED TRANSLOCATION IDENTIFIED IN AMNIOCYTES

Mosaicism for an unbalanced reciprocal translocation was identified in cultured amniocytes of a 16-week-old fetus; mos46,XX,der(4)t(4; 5)(q3 4;q12)/46,XX. Parental karyotypes were normal, indicating a de novo or igin of the unbalanced translocation in the fetus. The additional chro mosomal material on the der(il) was derived from chromosome 5 as demon strated by both GTG banding and fluorescence in situ hybridization wit h a chromosome 5 paint. Two subsequent amniocenteses, at 18 and 20 wee ks, confirmed the presence of the abnormal cell line. A percutaneous u mbilical blood sample (PUBS) contained only normal cells, 46,XX, and a high resolution ultrasound revealed no fetal abnormalities or growth retardation. The pregnancy was continued and a normal female was born at term. No evidence of the unbalanced translocation cell line was fou nd in cord blood or placental samples at birth. The finding of mosaici sm for an unbalanced translocation at amniocentesis is rare, and is as sociated with a high risk of fetal abnormality. This case illustrates the importance of follow-up studies by PUBS and high-resolution ultras ound for further assessing the risk of phenotypic abnormality. (C) 199 8 John Wiley & Sons, Ltd.