Fetal phenotype in a case of partial trisomy 21 and partial monosomy 22 detected prenatally.

Prenatal diagnosis was performed in a woman whose previous pregnancy resulted in a girl with probable Down syndrome who died soon after delivery. The mother was found to be a carrier of a reciprocal balanced translocation between chromosomes 21 and 22, and the fetus was found to have an unbalanced translocation involving chromosomes 21 and 22: 46,XX, -22, +t(21;22)(q22;q11)(21 pter leads to 21q22::22q11 leads to 22qter). Despite partial monosomy for the proximal segment of 22 and trisomy for proximal 21, the fetus did not have gross external abnormalities, but several internal malformations were found. To our knowledge, this is the first time that this unbalanced karyotype has been described.