Abstract
A 31 years old women underwent amniocentesis because of increased risk for Down syndrome on biochemical screen. Her previous pregnancy ended in a spontaneous abortion.The Karyotype was 46, XY/47, XY, +21, inv(9) with a mosaicism rate of 45%. The husband, which was known to have oligo-terato-asteno-spermia on semen analysis, had a karyotype 46, XY, inv(9)(q11; 13)9qh+.Mono and dual color FISH was applied to his sperm as well as to sperm of normal controls, using centromer probes for 8, 9, 18, 21, X and Y.In this man with inv9 and 9qh+ the rate of disomy was significantly higher then in normal controls for all probes tested (p<0.001).These findings represent interference in the first meiotic division. The disomy in this man's sperm can be explained by the difference in length of the hetrochromatic region in the two 9 chromosomes. This difference leads to incomplete pairing of chromosomes 9 and may be of the other chromosomes and to disturbance in the meiotic division especially meiosis I.We assume that the 21 mosaicism might have occurred in the same mechanism.
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