Department of Obstetrics and Gynecology, Department of Fetal Medicine and Prenatal Diagnosis, Key Laboratory for Major Obstetric Diseases of Guangdong Province, The Third Affiliated Hospital of Guangzhou Medical University, 63 Duobao Road, Liwan District, Guangzhou, 510150, China.
BMC Pregnancy Childbirth. 2021 Jan 30;21(1):101. doi: 10.1186/s12884-021-03587-x.
Monozygotic twins are nearly identical in genotype and phenotype because monozygotic twins arise from one fertilized oocyte. In all cases of discordant karyotype in monozygotic twins, trisomy 21 accounts for about one in 385,000. Monozygotic twins discordant for Robertsonian translocation trisomy 21 of the der (21;21)(q10;q10), in which the additional chromosome originates from the father is rare.
A 28-year-old parous woman, G3P1A0, came to our institution for a dating scan at 8 weeks of gestation. The transvaginal ultrasound examination demonstrated a monochorionic diamniotic pregnancy. She and her husband were healthy, with no family history of trisomy 21 or other congenital diseases. The ultrasound examination of nuchal translucency thickness was discordant in twins at 13 weeks (twin A, NT 1.4 mm with CRL being 65 mm; twin B, NT 7.8 mm with CRL being 69 mm). At 17 weeks, twin A was normal, but ventricular septal defect and the hypoplastic left heart was detected in twin B. The deepest vertical pocket was 18 mm in twin A (oligohydramnios) and 102 mm in Twin B (polyhydramnios). The bladder in twin A was absent. Ultrasound findings indicated TTTS Stage II. Amniocentesis was performed for the two fetuses. The karyotyping results revealed 46, XX in twin A but 46,XX,+ 21,der (21;21)(q10;q10) in twin B. For twin B, the parents opted for selective fetal termination by radiofrequency ablation. The procedure was uneventful. At 40 weeks, twin A was born with a birth weight of 4120 g by vaginal delivery.
The early detection of discordant karyotype and twin-to-twin transfusion syndrome is beneficial to the early intervention. In monozygotic twins with a discordant anomaly, the discordant karyotype should be considered.
同卵双胞胎在基因型和表型上几乎完全相同，因为同卵双胞胎是由一个受精卵发育而来。在所有同卵双胞胎的核型不一致的情况下，21 三体约占 385000 分之一。同卵双胞胎中罗伯逊易位导致的 21 三体不一致的情况非常罕见，其中额外的染色体来自父亲。
一位 28 岁经产妇，G3P1A0，在妊娠 8 周时来到我们机构进行妊娠检查。经阴道超声检查显示为单绒毛膜双羊膜妊娠。她和她的丈夫身体健康，没有 21 三体或其他先天性疾病的家族史。双胞胎的颈项透明层厚度超声检查在 13 周时不一致（双胞胎 A，NT 1.4mm，CRL 为 65mm；双胞胎 B，NT 7.8mm，CRL 为 69mm）。在 17 周时，双胞胎 A 正常，但双胞胎 B 被发现存在室间隔缺损和左心发育不良。双胞胎 A 的最深垂直囊袋为 18mm（羊水过少），双胞胎 B 的为 102mm（羊水过多）。双胞胎 A 的膀胱缺失。超声检查结果表明 TTTS 二期。对两个胎儿进行了羊膜穿刺术。核型分析结果显示双胞胎 A 为 46，XX，但双胞胎 B 为 46，XX，+21，der（21；21）（q10；q10）。对于双胞胎 B，父母选择通过射频消融术进行选择性胎儿终止。手术过程顺利。在 40 周时，双胞胎 A 通过阴道分娩，出生体重为 4120g。
早期发现核型不一致和双胎输血综合征有利于早期干预。在核型不一致的同卵双胞胎中，应考虑不一致的核型。
