Are all cases of low-grade mosaic trisomy 13 in amniotic fluid with no fetal malformation in fact confined placental mosaicism? A case report

Low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a positive NIPT result suspicious of trisomy 13, a CVS result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a positive non-invasive prenatal testing (NIPT) result suspicious of trisomy 13, a chorionic villus sampling (CVS) result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome.

CASE REPORT

A 29-year-old, gravida 2, para 1, woman underwent amniocentesis at 20 weeks of gestation because of a positive NIPT result (Z-score = 20.9, positive ≥3) suspicious of trisomy 13 at 11 weeks of gestation and a CVS result of mosaic trisomy 13 at 14 weeks of gestation. At 14 weeks of gestation, CVS revealed the multiplex ligation-dependent probe amplification (MLPA) result of rea X,Y (P095) × 1, 13 (P095) × 3, 18,21 (P095) × 2/X,Y (P095) × 1, 13,18,21 (P095) × 2 and a karyotype of 48,XY,+13,+mar [9]/47,XY,+mar[16]. She was referred to the hospital for genetic counseling at 15 weeks of gestation, and cytogenetic analysis of parental blood revealed 47,XY,+mar in the father and 46, XX in the mother. Fluorescence in situ hybridization (FISH) analysis on the paternal blood showed that the extra dicentric marker was derived from chromosome 15 without the locus SNRPN (15q11.2), and the result was 47,XY,+mar.ish dic(15) (D15Z1++, SNRPN-, PML-)[20]. Amniocentesis at 20 weeks of gestation revealed a karyotype of 47,XY,+mar pat (20/20). Simultaneous interphase FISH analysis on uncultured amniocytes revealed 32% (32/100 cells) mosaicism for trisomy 13. Quantitative fluorescence polymerase chain reaction (QF-PCR) analysis using the DNA extracted from the parental bloods and uncultured amniocytes excluded uniparental disomy (UPD) 13. Prenatal ultrasound findings were normal. The woman was advised to continue the pregnancy, and a phenotypically normal 2708-g male baby was delivered at 38 weeks of gestation, The cord blood, umbilical cord and placenta had the karyotypes of 47,XY,+mar pat and did not have UPD 13. When follow-up at age two months, the neonate was phenotypically normal. FISH analysis on buccal mucosal cells detected 5.3% (5/95 cells) mosaicism for trisomy 13, compared with 0% in the normal control.

CONCLUSION

Low-level mosaic trisomy 13 at amniocentesis can be associated with a positive NIPT result suspicious of trisomy 13, a CVS result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome.

Low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a favorable fetal outcome and cytogenetic discrepancy in various tissues

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with associated with a favorable fetal outcome and cytogenetic discrepancy in various tissues.

CASE REPORT

A 38-year-old, gravida 3, para 0, woman underwent amniocentesis at 19 weeks of gestation because of advanced maternal age. This pregnancy was conceived by in vitro fertilization and embryo transfer. Amniocentesis revealed a karyotype of 47,XX,+13[2]/ 46,XX[20] in co-twin A and a karyotype of 46,XY in co-twin B. In co-twin A, among 22 colonies of cultured amniocytes, two colonies had a karyotype of 47,XX,+13, whereas the rest 20 colonies had the karyotype of 46,XX. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from cultured amniocytes revealed arr (1-22,X) × 2, Y × 0 and detected no genomic imbalance. Prenatal ultrasound and parental karyotypes were normal. Quantitative fluorescence polymerase chain reaction (QF-PCR) analysis on the DNA extracted from the parental bloods and cultured amniocytes excluded uniparental disomy (UPD) 13. The woman was encouraged to continue the pregnancy. At 37 weeks of gestation, a normal 2410-g female co-twin A and a normal 2360-g male co-twin B were delivered without any phenotypic abnormality. The karyotypes of cord blood, umbilical cord and placenta of co-twin A were 46,XX (40/40 cells), 47,XX,+13 [1]/46,XX[39] and 47,XX,+13[36]/46,XX [4], respectively. QF-PCR analysis on cord blood of co-twin A excluded UPD 13. When follow-up at age 1½ years, the neonate of co-twin A was normal in physical and psychomotor development.

CONCLUSION

Low-level true mosaic trisomy 13 at amniocentesis can be associated with a favorable fetal outcome and cytogenetic discrepancy in various tissues.

Low-level mosaic trisomy 13 at amniocentesis associated with a favorable outcome in a pregnancy

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis associated with a favorable outcome in a pregnancy.

CASE REPORT

A 39-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XY,+13[8]/46,XY[20]. The woman underwent cord blood sampling at 22 weeks of gestation. Cytogenetic analysis of cord blood revealed a karyotype of 47,XY,+13[2]/46,XY[98]. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from cord blood revealed 10% gene dosage increase in chromosome 13. Prenatal ultrasound findings were unremarkable. After genetic counseling, the parents decided to continue the pregnancy, and a 2,280-g healthy male baby was delivered at 38 weeks of gestation. The parental karyotypes were normal. The cord blood at birth had a karyotype of 47,XY,+13[1]/46,XY[49]. At age one month, interphase fluorescence in situ hybridization (FISH) analysis revealed no trisomy 13 signals in 100/100 buccal mucosal cells, and trisomy 13 signals in 2/54 (3.7%) urinary cells compared with 0/60 cells in the normal control. The neonate was doing well and presented neither phenotypic abnormalities nor psychomotor disorders at age two months.

CONCLUSION

Low-level true mosaic trisomy 13 at amniocentesis without ultrasound abnormalities can be associated with a favorable outcome.