Mosaic Tetrasomy 12P With Discrepancy Between Fetal Tissues and Extraembryonic Tissues: Molecular Analysis and Possible Mechanism of Formation

A healthy 40-year-old, gravida 2, para 1, woman underwent amniocentesis at 16 weeks of gestation because of her advanced maternal age.Cytogenetic analysis of cultured amniocytes revealed mosaicism for tetrasomy 12p, or 47,XX,+i(12p)/46,XX (64%/36%; 16 colonies/9 colonies).The parental karyotypes were normal and the pregnancy was subsequently terminated.A 399 g fetus was delivered with a craniofacial appearance characteristic of Pallister-Killian syndrome (PKS).The clinical findings for this case were described previously [1].Postnatal cytogenetic analysis revealed a 47,XX,+i(12p) karyotype in 100% (30 of 30) of cultured umbilical cord cells and a 47,XX,+i(12p)/46,XX karyotype in the cultured cells of fetal skin and liver.The level of cells with tetrasomy 12p was 53% (16 of 30) and 60% (18 of 30) in skin and liver, respectively.Genomic DNAs were isolated from parental blood, umbilical cord blood and the uncultured tissues of umbilical cord, placental chorionic villi, amniotic membrane, liver, and skin.Quantitative fluorescent polymerase chain reaction and polymorphic short tandem repeat markers specific for chromosome 12p and chromosome 12q were used for determination of aneuploidy, possible mechanism of formation and parental origin of the isochromosome 12p (Table, Figure 1).