Paternal sex chromosome aneuploidy as a possible origin of Turner syndromein monozygotic twins

The meiotic or mitotic origin of most cases of Turner syndrome remains unkn own, due to the difficulty in detecting hidden mosaicisms and to the lack o f meiotic segregation studies. We have had the opportunity to study one pai r of monozygotic twins concordant for Turner syndrome of paternal origin. T he paternal origin of the single X chromosome was determined by polymerase chain reaction (PCR) amplification. No mosaicism was detected for the X or Y chromosome. In this case, a meiotic error during gametogenesis would be a likely origin of X monosomy. To determine if meiotic errors are more frequ ent in the father of these monozygotic twins concordant for Turner syndrome of paternal origin, molecular studies in spermatozoa were conducted to ana lyse sex chromosome numerical abnormalities. A total of 12520 sperm nuclei from the twins' father and 85338 sperm nuclei from eight normal donors were analysed using three-colour fluorescent in-situ hybridization, There were significant differences between the twins' father and control donors for XY disomy (0.22 versus 0.11%, P < 0.001) and total sex chromosome disomy (0.3 8 versus 0.21%, P < 0.001). These results could indicate an increased tende ncy to meiotic sex chromosome non-disjunction in the father of the Turner t wins.