PMC4255715_01
Abnormal sonographic features of fetus at 19th week. A. strawberry-shaped head. B. Four-chamber view of the fetal heart showing a ventricular septal defect (0.6 cm diameter).
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F1
Ultrasound scan at 19+3 week showed strawberry-shaped head and ventricular septal defect (VSD) (Figure  1).
Conventional karyotype analysis of cultured amniocytes shows the fetal karyotype as 47, XX, +18 (trisomy 18).
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F2
G-banding of amniocytes cultivation identified the fetal karyotyping result as 47, XX, +18 (Figure  2) and implied that the NIPT had given a false negative result of T18.
The MPS results of maternal peripheral blood DNA, fetal DNA, placental DNA. A-B. The maternal information of chromosome 18 and X, based on the sequencing result of maternal peripheral blood DNA, suggests a euploid status of the maternal background. C-D. The sequencing results of fetal DNA, where the copy ratio (1.5) of chromosome 18 in C indicated the trisomy 18 status in the fetus, the copy ratio (1.0) of chromosome X in D indicated the euploid status of chromosome X in the fetus. E-F. The sequencing results of the placental DNA, where the copy ratio (1.0-1.5) of chromosome 18 in E indicated a low level of mosacism of trisomy 18, the copy ratio (0.5-1.0) in F indicated a low level of mosaicism of monosomy X.
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F3
Sequencing results of NIPT (Figure  3) identified the aborted fetal tissue as T18 condition, while the placental tissue as a status of mosaic T18 (mosaic ratio nearly 30%) and 45, X (mosaic ratio nearly 60%), which was in agreement with the amniocentesis result.
FISH analysis results of placental tissue showed the combination status of 45, X and trisomy 18 mosaicism, with DNA of chromosome 18 marked as aqua (A) and chromosome X as green (G). The cells with karyotype 47, XX, +18 were indicated as 2G3A, while the 45, X cells were indicated as 1G2A. Two additional chromatin segments attached to a chromosome 18 were observed in a cell (2G3A) on the left, suggesting partial duplications in addition to trisomy 18.
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F4
T18 cells (30%, 28/92) in total (Figure  4). Notably, the result indicated partial duplication for the distal section of 18q represented in 17% of the cells, which was evidenced by the observation of two additional chromatin segments attached to a chromosome 18 in the FISH results (Figure  4).
Illumina SNP array result showing the presence of mosaicism of placental tissue. A. A view of normal chromosome 18 as control of SNP array (Illumina HumanCytoSNP-12). The upper axis indicates the value of B allele frequency (BAF, blue dots). BAF may have three values (1 for BB, 0.5 for AB and 0 for AA) in a diploid individual. Additionally, the lower axis indicates the logR ratio (red line), where R illustrates the ratio of each SNP compared to diploid individuals in chromosome 18 (a logR ratio of 0 means an actual ratio of 1). B. A SNP array of placental tissue with mosaic trisomy 18. The BAF values (1 for BBB and BB; 0.6 for ABB and AB; 0.4 for AAB and AB; and 0 for AAA and AA) and the increased logR ratio indicated a mosaicism. Partial duplication in distal region of 18q was also observed. C. A view of normal chromosome X as control of SNP array (Illumina HumanCytoSNP-12). D. A SNP array of placental tissue with mosaic monosomy X. The BAF values (1 for BB; 0.75 for BB and BO; 0.25 for AA and AO; 0 for AA) and the decreased logR ratio indicated a mosaicism.
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F5
T18 mosaicism. The SNP-array results (Figure  5) with the signal intensity (logR) and genotyping (B allele frequency, BAF) value plots indicated the mosaic rearrangements. The increased logR and altered BAF value (Figure  5B) suggested a mosaic trisomy of chromosome 18 in 50% of the cells. The level of mosaicism was determined based on both logR and BAF value . On the other hand, large mosaic deletion ranging in size from 31.05 to 93.16 Mb of chromosome X was illustrated in Figure  5C.