Abstract：
OBJECTIVE: We present low-level mosaic trisomy 21 at amniocentesis associated with a favorable fetal outcome.
METHODS: A 31-year-old primigravid woman underwent non-invasive prenatal testing (NIPT) at 12 weeks of gestation, and the result was normal. She underwent amniocentesis at 16 weeks of gestation because of fetal choroid plexus cyst, and the result was 47,XX,+21[5]/46,XX[32]. Repeat amniocentesis was performed at 19 weeks of gestation, and the result was 47,XX,+21[5]/46,XX[15]. Simultaneous array comparative genomic hybridization (aCGH) analysis on uncultured amniocytes revealed the result of arr (21) × 3 [0.10], consistent with 10% mosaicism for trisomy 21. Prenatal ultrasound findings were unremarkable. She was referred for genetic counseling at 22 weeks of gestation, and the third amniocentesis was performed at 25 weeks of gestation, and the result was 46,XX (20/20 colonies). The parental karyotypes were normal. Simultaneous quantitative fluorescence polymerase chain reaction (QF-PCR) analysis on the DNA extracted from uncultured amniocytes and parental bloods excluded uniparental disomy (UPD) 21. aCGH analysis on uncultured amniocytes revealed arr 21q11.2q22.3 × 2.1 (log2 ratio = 0.1), consistent with 10-15% mosaicism for trisomy 21. Fluorescence in situ hybridization (FISH) analysis on uncultured amniocytes revealed 30% (30/100 cells) mosaicism for trisomy 21. The woman was advised to continue the pregnancy, and a phenotypically normal 2800-g female baby was delivered at 38 weeks of gestation. The karyotype of cord blood, umbilical cord and placenta were 47,XX,+21[1]/46,XX[39]. 47,XX,+21[4]/46,XX[36] and 46,XX (40/40 cells), respectively. When follow-up at age two months, the neonate was phenotypically normal. The peripheral blood had a karyotype of 47,XX,+21[1]/46,XX[39], and FISH analysis on buccal mucosal cells revealed 8.4% (7/83 cells) mosaicism for trisomy 21, compared with 0% in the normal control.
CONCLUSIONS: Low-level mosaic trisomy 21 at amniocentesis can be associated with a negative NIPT result, cytogenetic discrepancy in various tissues, perinatal progressive decrease of the aneuploid cell line and a favorable fetal outcome.
METHODS: A 31-year-old primigravid woman underwent non-invasive prenatal testing (NIPT) at 12 weeks of gestation, and the result was normal. She underwent amniocentesis at 16 weeks of gestation because of fetal choroid plexus cyst, and the result was 47,XX,+21[5]/46,XX[32]. Repeat amniocentesis was performed at 19 weeks of gestation, and the result was 47,XX,+21[5]/46,XX[15]. Simultaneous array comparative genomic hybridization (aCGH) analysis on uncultured amniocytes revealed the result of arr (21) × 3 [0.10], consistent with 10% mosaicism for trisomy 21. Prenatal ultrasound findings were unremarkable. She was referred for genetic counseling at 22 weeks of gestation, and the third amniocentesis was performed at 25 weeks of gestation, and the result was 46,XX (20/20 colonies). The parental karyotypes were normal. Simultaneous quantitative fluorescence polymerase chain reaction (QF-PCR) analysis on the DNA extracted from uncultured amniocytes and parental bloods excluded uniparental disomy (UPD) 21. aCGH analysis on uncultured amniocytes revealed arr 21q11.2q22.3 × 2.1 (log2 ratio = 0.1), consistent with 10-15% mosaicism for trisomy 21. Fluorescence in situ hybridization (FISH) analysis on uncultured amniocytes revealed 30% (30/100 cells) mosaicism for trisomy 21. The woman was advised to continue the pregnancy, and a phenotypically normal 2800-g female baby was delivered at 38 weeks of gestation. The karyotype of cord blood, umbilical cord and placenta were 47,XX,+21[1]/46,XX[39]. 47,XX,+21[4]/46,XX[36] and 46,XX (40/40 cells), respectively. When follow-up at age two months, the neonate was phenotypically normal. The peripheral blood had a karyotype of 47,XX,+21[1]/46,XX[39], and FISH analysis on buccal mucosal cells revealed 8.4% (7/83 cells) mosaicism for trisomy 21, compared with 0% in the normal control.
CONCLUSIONS: Low-level mosaic trisomy 21 at amniocentesis can be associated with a negative NIPT result, cytogenetic discrepancy in various tissues, perinatal progressive decrease of the aneuploid cell line and a favorable fetal outcome.
摘要：
目的：我们介绍了羊膜穿刺术中低水平镶嵌三体性21与良好的胎儿结局相关。
方法：一名31岁的初产妇在妊娠12周时接受了非侵入性产前检测（NIPT），结果很正常.由于胎儿脉络丛囊肿，她在妊娠16周时接受了羊膜穿刺术，结果是47，XX，+21[5]/46,XX[32]。在妊娠19周时重复进行羊膜穿刺术，结果是47，XX，+21[5]/46,XX[15]。对未培养的羊膜细胞进行的同时阵列比较基因组杂交（aCGH）分析显示了arr（21）×3[0.10]的结果，与21三体的10%镶嵌性一致。产前超声检查结果无明显变化。她在妊娠22周时被转介接受遗传咨询，第三次羊膜穿刺术是在妊娠25周时进行的，结果为46,XX(20/20菌落)。亲本核型正常。对从未培养的羊膜细胞和亲本血液中提取的DNA进行同时定量荧光聚合酶链反应（QF-PCR）分析，排除了亲本单倍体（UPD）21。未培养羊膜细胞的aCGH分析显示ARR21q11.2q22.3×2.1（log2比率=0.1），与21三体的10-15%镶嵌性一致。对未培养的羊膜细胞的荧光原位杂交（FISH）分析显示，三体性21具有30％（30/100细胞）的镶嵌性。建议该妇女继续怀孕，在妊娠38周时分娩了表型正常的2800-g女婴。脐带血的核型,脐带和胎盘分别为47，XX，+21[1]/46,XX[39]。47,XX,+21[4]/46,XX[36]和46,XX(40/40细胞),分别。当在两个月的年龄进行随访时，新生儿表型正常.外周血核型为47,XX,+21[1]/46,XX[39],颊粘膜细胞的FISH分析显示，三体性21为8.4％（7/83细胞）镶嵌性，而正常对照组为0％。
结论：羊膜穿刺术中低水平镶嵌三体21可能与NIPT阴性结果相关，各种组织的细胞遗传学差异，围产期非整倍体细胞系的进行性减少和有利的胎儿结局。
方法：一名31岁的初产妇在妊娠12周时接受了非侵入性产前检测（NIPT），结果很正常.由于胎儿脉络丛囊肿，她在妊娠16周时接受了羊膜穿刺术，结果是47，XX，+21[5]/46,XX[32]。在妊娠19周时重复进行羊膜穿刺术，结果是47，XX，+21[5]/46,XX[15]。对未培养的羊膜细胞进行的同时阵列比较基因组杂交（aCGH）分析显示了arr（21）×3[0.10]的结果，与21三体的10%镶嵌性一致。产前超声检查结果无明显变化。她在妊娠22周时被转介接受遗传咨询，第三次羊膜穿刺术是在妊娠25周时进行的，结果为46,XX(20/20菌落)。亲本核型正常。对从未培养的羊膜细胞和亲本血液中提取的DNA进行同时定量荧光聚合酶链反应（QF-PCR）分析，排除了亲本单倍体（UPD）21。未培养羊膜细胞的aCGH分析显示ARR21q11.2q22.3×2.1（log2比率=0.1），与21三体的10-15%镶嵌性一致。对未培养的羊膜细胞的荧光原位杂交（FISH）分析显示，三体性21具有30％（30/100细胞）的镶嵌性。建议该妇女继续怀孕，在妊娠38周时分娩了表型正常的2800-g女婴。脐带血的核型,脐带和胎盘分别为47，XX，+21[1]/46,XX[39]。47,XX,+21[4]/46,XX[36]和46,XX(40/40细胞),分别。当在两个月的年龄进行随访时，新生儿表型正常.外周血核型为47,XX,+21[1]/46,XX[39],颊粘膜细胞的FISH分析显示，三体性21为8.4％（7/83细胞）镶嵌性，而正常对照组为0％。
结论：羊膜穿刺术中低水平镶嵌三体21可能与NIPT阴性结果相关，各种组织的细胞遗传学差异，围产期非整倍体细胞系的进行性减少和有利的胎儿结局。
