Prenatal diagnosis of partial trisomy 12 and partial trisomy 21 due to a 3:1 segregation of maternal reciprocal translocation t(12;21) (p13.3;q21).

We describe the prenatal diagnosis and fetal phenotype of partial trisomy 12 (p13.3-pter) and partial trisomy 21 (pter-q21) due to a 3:1 segregation with tertiary aneuploidy transmitted from a maternal reciprocal translocation 12;21. Genetic amniocentesis of a 39-year-old gravida 2, para 1 woman at 19 weeks' gestation due to advanced maternal age revealed an unusual karyotype of 47,XY,+der(21)t(12;21)(p13.3;q21)mat. The pregnancy was terminated at 24 gestational weeks. The proband postnatally displayed by dysmorphic features of a round flat face with prominent cheeks and high forehead, upward slanting palpebral fissures, epicanthic folds, hypertelorism, a short nose, a broad and depressed nasal bridge, anteverted nares, a deformed philtrum, an open mouth, thin upper vermilion and broad everted lower lip, low-set ears with prominent anthelix and deep concha, broad hands with simian creases, a short neck, and cryptorchidism. The association of the involved chromosomal segments with the phenotype of Down's syndrome and trisomy 12p syndrome is discussed.