Paternal nondisjunction in trisomy 21: excess of male patients

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Abstract
Paternal nondisjunction accounts for approximately 5% of cases of trisomy 21. We have studied 36 cases of free trisomy 21, in which the supernumerary chromosome was of paternal origin, with DNA markers in the pericentromeric region and along the long arm of chromosome 21. Fifteen of the paternal cases were consistent with melosis II errors, 8 with mitotic errors and only 7 with melosis I nondisjunction. This contrasts markedly with maternally derived trisomy 21, in which meiosis I errors predominate. An excess of males was observed in the melotic cases (21 maies:6 females), highly significantly different from a 1.06 ratio. A significant difference in mean maternal age was found between cases of paternal origin (28.1 years) and those of maternal origin (31.8 years, n=429). This indicates that the maternal age effect is confined to maternal nondisjunction.

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