Monochorionic diamniotic twin with a Down syndrome in one of the fetuses

Abstract

A clinical observation of monochorionic diamniotic twins with discordance of cytogenetic and clinical manifestations of Down syndrome is presented. Pregnancy was complicated by feto-fetal transfusion syndrome at 17 weeks of gestation. An ultrasound scan revealed a ventriculomegaly in a donor. Laser coagulation of anastomoses was performed. Karyotype 46, XY was established in the recipient amniocytes. The pregnancy ended in childbirth at 33 weeks with newborn boys weighing 1789 and 2080g. One of the newborns (donor) had phenotypic signs of Down syndrome. When karyotyping peripheral blood lymphocytes of a child with clinical manifestations of Down syndrome, karyotype mos 47,XY,+21[12]/46,XY [88] was established, and a child with a normal phenotype was mos 47,XY,+21[14]/46,XY [86]. No malformations of internal organs were found. When analyzing the buccal epithelium by the FISH method, it was found that in all the analyzed interphase nuclei obtained from a child without clinical manifestations (recipient fetus), trisomy 21 was not detected. In 78% of the interphase nuclei of cells of a child with Down syndrome (fetus-donor), trisomy 21 was established. Thus, the presence of a clone of cells with trisomy 21 in the recipient is associated with twin chimerism.