Non-mosaic trisomy 16 in a third-trimester fetus.

ABSTRACT

BACKGROUND: Trisomy 16 in the most common trisomy first-trimester spontaneous abortions, suggesting a high rate of non-disjunction of this chromosome. Deoxyribonucleic acid studies in aborted conceptuses with trisomy 16 have demonstrated a maternal origin in all cases. There have been cases of confined placental mosaicism, fetal mosaicism, and partial trisomy involving chromosome 16 reported in term fetuses. However, to our knowledge, there have been no previous reports of a near-term fetus with full trisomy 16 since the advent of modern chromosomal banding techniques. CASE A 25-year-old Filipino woman underwent obstetric sonographic evaluation at 32 weeks' gestation; results were remarkable for oligohydramnios, severe growth restriction, and multiple dysmorphic features. Percutaneous umbilical blood sampling was performed for rapid karyotyping, viral serology, and blood profiles. The fetal karyotype was 47, XY+16; the remainder of the laboratory analysis was unremarkable. The patient went into spontaneous labor at 35 weeks' gestation and delivered a stillborn female fetus (birth weight 783 g). Chromosomes from skin, brain, and chorionic villi were examined and all demonstrated trisomy 16 (47, XX,+16). Deoxyribonucleic acid primers for known polymorphic regions of chromosome 16 were used and determined the origin of the extra chromosome to be non-disjunction during paternal meiosis. CONCLUSION: Previously, full trisomy 16 has been thought to be incompatible with fetal survival past the early second trimester. This case also contrasts with previously reported experience with trisomy 16 in that parental origin studies determined that the extra chromosome 16 originated from the father, suggesting that paternal derivation of the additional chromosome may play a role in the ultimate phenotypic expression.