Intracytoplasmic sperm injection (ICSI) has given some patients with Klinef
elter's syndrome (ie, men with an XXY sex-chromosome profile) the chance to
become fathers, but the genetic makeup of the spermatozoa used for the inj
ection is a concern. We studied the segregation of the sex chromosomes and
chromosomes 1 and 21 by multicolour fluorescence in-situ hybridisation in a
patient with non-mosaic Klinefelter's syndrome who was a candidate for ICS
I. As other workers have found, we saw a higher rate of 24,XX and 24,XY spe
rmatozoa in the patient than in controls. However, we also found a much hig
her frequency of disomy 21 in the spermatozoa of this patient than in contr
ols (6.2 vs 0.4%). Any child conceived by ICSI using this man's sperm will
thus have a proportionally higher risk of trisomy 21.