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Abstract
Although trisomy 18 (Edwards' syndrome) or the terminal deletion syndromes of 18p and 18q have been occasionally detected, pseudoisodicentric chromosome 18 is a very rare constitutional chromosomal abnormality. We describe a case of pseudoisodicentric chromosome 18q without mosaicism, which was confirmed from fetal cells in the amniotic fluid used for prenatal diagnosis of multiple congenital anomalies. A 23-yr-old pregnant woman was suspected of having a fetal anomaly at 18+3 weeks gestation. In sonography, the fetus showed multiple anomalies: bilateral overt ventriculomegaly in the brain, ventricular septal defect and valve anomaly in the heart, bilateral club foot, polydactyly, meningocele, and a single umbilical artery. The pregnancy was terminated and a conventional G-banded chromosome study was performed using amniotic fluid. Twenty metaphase cells among the cultured amniocytes showed a 46,XX,psu idic(18)(q22). Consequently, the fetus had partial trisomy (18pter→q22) and partial monosomy (18q22→qter). Both parents were confirmed to have a normal karyotype.
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Fig. 1.
Prenatal sonographic findings of pseudoisodicentric 18q at 18+3 weeks gestation. (A) Transaxial plane of the fetal brain shows bilateral overt ventriculomegaly. (B) Fetal echocardiography shows pulmonary stenosis (2 m/s). (C) 3D ultrasonography shows bilateral club foot. (D) Coronal plane of the fetal spine shows meningocele.
Fig. 3.
Karyotype showing pseudoisodicentric chromosome 18 by G-banding analysis. Chromosome 18 shows a breakpoint at 18q22 and has 2 centromeres, the upper one of which has a primary constriction, whereas the lower one lacks a primary constriction.
Table 1.
Summary of clinical findings for the present case, compared with two other cases of psu idic 18q without mosaicism
| Cases of psu idic 18q without mosaicism | ||||
|---|---|---|---|---|
| Findings of pure trisomy 18 | 1st case [Meins et al.8] | 2nd case [Lin et al.1] | Present study [Cho et al.] | |
| 1. Karyotype | 47,XX,+18, or 47,XY,+18 | 46,XX,psu dic(18)(q22.1) | 46,XX,psu dic(18) | 46,XX,psu idic(18)(q22) |
| 2. Intrauterine growth retardation | Detected | Detected | NC | Detected |
| 3. Brain | Ventriculomegaly | Normal | Normal | Ventriculomegaly |
| 4. Face | Cleft lip and palate, micrognathia, small and low-set ears | Cleft lip and palate | Cleft lip and palate, anotia Rt. ear), low-set left ear, micrognathia | Normal |
| 5. Neck | No special anomaly | Short | NC | Normal |
| 6. Thorax | No special anomaly | Narrow | NC | Normal |
| 7. Heart | VSD, ASD, PDA | VSD and ASD | Normal | VSD and valve anomaly |
| 8. Kidney | Hydronephrosis, horseshoe kidney | Real hypoplasia | Normal | Normal |
| 9. Spinal cord | Neural tube defect | NC | NC | Meningocele |
| 10. Skin | Cutis laxa | Redundant skin | NC | Normal |
| 11. Extremities | Club feet, rocker-bottom feet | Club foot and hand, thumb aplasia | Rocker-bottom feet, abnormal finger∗ and toe† | Club feet and polydactyly |
| 12. Umbilical artery | Single umbilical artery | NC | NC | Single umbilical artery |
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