TRUE TRISOMY-15 MOSAICISM, DETECTED BY AMNIOCENTESIS AT 12 WEEKS OF GESTATION AND FETAL ECHOCARDIOGRAPHY

A case of mosaicism of trisomy 15, with two-thirds of the cells trisom ic, was detected at 12 weeks of gestation in amniotic fluid cell cultu res obtained with the filtration technique. Ultrasound examination at 13 weeks showed a nodule protruding into the amniotic cavity which was speculated to be remnants of a co-twin, causing the trisomic cell lin e. At 20 weeks of gestation, a malformation scan (level III) was norma l, but supplementary fetal echocardiography revealed a severe cardiac defect (mitral atresia and a ventricular septal defect). Fetal lymphoc ytes obtained by cordocentesis showed trisomy 15 mosaicism, but only i n 5 per cent of the mitoses. After termination, the same percentage of trisomy 15 mosaicism was found in cells from skin and tendon as in th e original early amniocentesis. No sign of earlier twinning was found in the placenta or membranes. We conclude that mosaicism in early amni otic fluid obtained by the filter technique in this case reflected the true karyotype accurately and that supplementary echocardiography add ed significantly to the interpretation of the clinical implications.