Down's syndrome in twins

Abstract

Male twins concordant for Down's syndrome and female twins discordant for Down's syndrome were investigated. Both males have trisomy 21 (47, XY, 21 +), and their parents are normal. One of the female twins is mosaic for trisomy 21 (46, XX/47, XX, 21 +) and the other is normal (46, XX). On the basis of multiple parameters, it is suggested that both pairs of twins are mono‐zygous, including the female twins discordant for Down's syndrome. Once the underlying cytogenetic mechanisms are understood and elucidated, genetic counselling can be undertaken.