CHARACTERIZATION BY FLUORESCENCE AND ELECTRON-MICROSCOPY IN-SITU HYBRIDIZATION OF A DOUBLE Y-ISOCHROMOSOME

A patient with mixed gonadal dysgenesis and Y isochromosomes i(Y) is d escribed, Lymphocyte cultures from peripheral blood contained a high p roportion of 45,X cells and several other cell lines with two differen t marker chromosomes (mars). These markers had either a monocentric (m arl) or a dicentric appearance (mar2). Following high-resolution GTG, RBG, QFQ, and CBG bandings, five cell lines were identified; 45, X/46, X, +mar1/46, X, +mar2/47, X, + mar1x2/47, X, +mar2x2. The percentages were 66/6/26/1/1%, respectively, Chromosome banding analyses were ins ufficient for characterization of the markers, In situ hybridization o f specific probes for the Y centromere and its short arm showed, both in fluorescence and electron microscopy (EM), two different Y rearrang ements, Marl is an isochromosome for the short arm i(Yp) and mar2 is a dicentric which was shown by EM to be a double isochromosome Yp, inv dup i(Yp), The breakpoint producing marl is within the centromere and the one producing mar2 is within one of the short arms of the Y isochr omosome. The findings of different cell populations in peripheral bloo d lymphocytes indicate the postzygotic instability of this i(Yp). (C) 1996 Wiley-Liss, Inc.