Research Letter
Discrepancy in the trisomy mosaicism level between cultured amniocytes and
uncultured amniocytes in prenatally detected mosaic trisomy 20
Chih-Ping Chen a,b,c,d,e,f,g*, Shuenn-Dyh Chang h, Ho-Yen Chueh h, Yi-Ning Su i, Schu-Rern Chern b, Jun-Wei Su a,j, Yu-Ting Chen b, Wen-Lin Chen a, Meng-Shan Lee a and Wayseen Wang b,k
a Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan b Department of Medical Research, Mackay Memorial Hospital, Taipei, Taiwan
c Department of Medicine, Mackay Medical College, New Taipei City, Taiwan d Department of Biotechnology, Asia University, Taichung, Taiwan
e School of Chinese Medicine, College of Chinese Medicine, China Medical University, Taichung, Taiwan f Institute of Clinical and Community Health Nursing, National Yang-Ming University, Taipei, Taiwan g Department of Obstetrics and Gynecology, School of Medicine, National Yang-Ming University, Taipei,
Taiwan
h Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital, Lin-Kou Medical Center,
Chang Gung University, Tao-Yuan, Taiwan
i Department of Obstetrics and Gynecology, School of Medicine, Taipei Medical University, Taipei,
Taiwan
j Department of Obstetrics and Gynecology, China Medical University Hospital, Taichung, Taiwan k Department of Bioengineering, Tatung University, Taipei, Taiwan
* Correspondence to: Chih-Ping Chen, MD
Department of Obstetrics and Gynecology, Mackay Memorial Hospital 92, Section 2, Chung-Shan North Road, Taipei, Taiwan
Tel: +886-2-25433535; Fax: +886-2-25433642, +886-2-25232448 E-mail: [email protected]
A 35-year-old, gravida 2, para 1, woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Cytogenetic analysis of cultured amniocytes revealed a karyotype of 47,XY,+20[26]/46,XY[9]. Among 35 colonies of cultured amniocytes investigated by in situ cultured method, 26 colonies had a karyotype of 47,XY,+20, while 9 colonies had a karyotype of 46,XY. The level of trisomy in the cultured amniocytes was 74.3% (26/35). She was referred to the hospital for rapid positive confirmation of mosaic trisomy 20 at 23 weeks of gestation, and repeated amniocentesis was performed. Interphase fluorescence in situ hybridization (FISH) analysis using the bacterial artificial chromosome (BAC) clone probe RP11-2E8 (20p12.2) showed three 20p-specific signals in 10% (5/50) of the uncultured amniocytes and two 20p-specific signals in 90% (45/50) of the uncultured amniocytes, indicating 10% mosaicism for trisomy 20 in uncultured amniocytes (Fig. 1). Quantitative fluorescent polymerase chain reaction analysis on the uncultured amniocytes showed equal fluorescent activity from two different parental alleles. Array comparative genomic hybridization (aCGH) analysis on the uncultured amniocytes revealed no gene dosage change on chromosome 20. The cultured amniocytes in the repeated amniocentesis had a karyotype of 47,XY,+20[16]/46,XY[19]. Among 35 colonies of cultured amniocytes investigated by in situ cultured method, 16 colonies had a karyotype of 47,XY,+20, while 19 colonies had a karyotype of 46,XY. The level of trisomy in the cultured amniocytes of the repeated amniocentesis was 45.7% (16/35). Prenatal ultrasound findings were unremarkable. After genetic counseling, the parents elected to continue the pregnancy. A 3,290-g healthy male baby was delivered at 38 weeks of gestation. Postnatal cytogenetic analysis revealed a karyotype of 46,XY in 60/60 of cord blood lymphocytes, 40/40 of umbilical cord fibroblasts, 40/40 of chorionic villi cells and 40/40 of amniotic membrane fibroblasts. Interphase FISH analysis of the uncultured urinary cells using the BAC clone probe showed two 20p-specific signals in 100% (27/27) of urinary cells, indicating 0% of trisomy 20 in the urine. The baby was doing well, and there was no phenotypic abnormality at the age of 10 months.
Application of molecular cytogenetic techniques on uncultured amniocytes in prenatal diagnosis of trisomy mosaicism has been well described [1-6]. The present case additionally demonstrates the usefulness of interphase FISH, QF-PCR and aCGH on uncultured amniocytes in rapid positive confirmation of trisomy 20 mosaicism. The present case provides evidence for
discrepancy in the trisomy mosaicism level between cultured amniocytes and uncultured amniocytes in prenatally detected mosaic trisomy 20.
Mosaic trisomy 20 is one of the most commonly observed mosaic trisomies at amniocentesis and has been reported to be associated with grossly normal phenotype in approximately 90% of the cases [7]. Genetic counseling of mosaic trisomy 20 at amniocentesis remains a challenge despite various suggested considerations, because all the reported suggestions have been based on observations of the trisomy mosaicism levels in cultured amniocytes [8-11]. In a study of 152 cases with mosaic trisomy 20 at amniocentesis, Wallerstein et al [8] found abnormal outcome in 20% (4/20) of the pregnancies with greater than 50% trisomy 20 cells and in 4.5% (6/132) of the pregnancies with less than 50% trisomy 20 cells. In a meta-analysis of published cases, Robinson et al [9] concluded that there is a clear association with the trisomy mosaicism level at amniocentesis and fetal outcome. Robinson et al [9] found that 50% (5/10) of the cases with greater than 80% trisomy 20 cells had abnormal outcome, 28% (17/61) of the cases with greater than 40% trisomy 20 cells had abnormal outcome, and 4% (8/201) of the cases with less than 40% trisomy 20 cells had abnormal outcome. However, Bianca et al [10,11] suggested a contradictory proposal that trisomy mosaicism levels do not influence the outcome in prenatally detected mosaic trisomy 20, and a second amniocentesis would add little value in genetic counseling.
The present case shows that the mosaic level may change after long-term tissue cultures in amniotic fluid with trisomy 20 amniocytes. The present case also suggests that uncultured amniocytes can be considered as a useful tool for confirmation of the presence of a true fetal mosaicism, and there may exist a correlation of low level trisomy 20 mosaicism of uncultured amniocytes with favorable fetal outcome in pregnancies with prenatally detected mosaic trisomy 20.
Acknowledgements
This work was supported by research grants NSC-99-2628-B-195-001-MY3 and NSC-101-2314-B-195-011-MY3 from the National Science Council and MMH-E-101-04 from Mackay Memorial Hospital, Taipei, Taiwan.
References
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Figure Legend
Fig. 1. Interphase fluorescence in situ hybridization analysis on uncultured amniocytes using a bacterial artificial chromosome clone probe RP11-2E8 (20p12.2) (spectrum green) shows (A) three green signals in an abnormal cell with trisomy 20 and (B) two green signals in a normal cell with disomy 20.
