The origin of 47, XXY and 47, XXX aneuploidy: heterogeneous mechanisms and role of aberrant recombination

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Abstract
We Investigated the parent and cell division of origin of the additional sex chromosome in 142 males with a 47,XXY constitution and 50 females with a 47,XXX constitution. In 66 of the 47,XXY males the additional chromosome was paternal In origin and in 76 It was maternal in origin, while among the 47, XXX females only 5 had an additional paternal X chromosome, the remaining 45 having an additional maternal chromosome. Among the 107 maternally derived aneuploids for whom It was possible to determine the cell division of origin, 73 were the result of a mat Ml error, 24 the result of a mat Mil error and 10 the result of a post zygotlc mitotlc (PZM) error Involving the maternal X chromosome. Among those In which the non-disjunction was attributable to an error at the first melotlc division (Ml) we observed three different mechanisms of origin. Approximately 30% were associated with complete absence of recombination (nullichiasmate); approximately 24% were associated with a normal number of recombinant events but an abnormal distribution of exchanges (perturbed recombination), while approximately 45% were associated with a normal number and distribution of recombinant events (normochiasmate). Non-disjunction due to an error at the second melotic division (Mll) was associated with a slight reduction in the total number of recomblnant events and an abnormal distribution of exchanges. Thus of the four different meiotic mechanisms of origin, three were associated with an abnormal number and/or distribution of exchange events. There was no evidence of an Increased paternal age in the aneuploids of paternal origin. Among those of maternal origin there was a significantly increased maternal age In the aneuplofds resulting from an error of mat Ml, but this was restricted to the nullichiasmate and the normochiasmate sub groups. The maternal ages of the Ml perturbed recombination sub group, the Mil and the PZM group were not increased.