Free proximal trisomy 21 in the mother and malformation syndrome in the son.

[monosomy 21]

We report on a new case of duplication of the proximal part of the long arm of chromosome 21 . The proposita presents normal mental development , no trisomy 21 manifestations ; on the contrary , she had a few monosomy 21 -like stigmata . She gave birth to a severely malformed infant with a pattern of malformations suggesting a partial 21 -monosomy syndrome , but with a 46 ,XY normal karyotype in his peripheral blood lymphocytes . The findings are explained in the following way : the infant probably had originally a 47 ,XY ,+21 q- karyotype like his mother . Post zygotic nondisjunctional events produced a prevalent 46 ,XY ,21 q- line responsible for the severe malformations and the normal 46 ,XY line found in his blood lymphocytes .