Korean J Lab Med.  2010 Aug;30(4):440-443. 10.3343/kjlm.2010.30.4.440.

A Case of Pseudoisodicentric Chromosome 18q Detected at Prenatal Diagnosis

• Cho SY
• Lim G
• Kim SY
• Kim MJ
• Lee KA
• Choi JR
• Lee HJ
• Suh JT
• Park TS
• Jung E

• KMID: 1781652
• DOI: http://doi.org/10.3343/kjlm.2010.30.4.440

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.

Keyword

Pseudoisodicentric; Isodicentric; Trisomy 18

MeSH Terms

Abnormalities, Multiple/diagnosis/*genetics
Centromere
*Chromosomes, Human, Pair 18
Female
Gestational Age
Humans
Karyotyping
Pregnancy
Prenatal Diagnosis/*methods
Trisomy
Ultrasonography, Prenatal
Young Adult

Figure

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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.

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  Fig. 2. Photograph of terminated fetus showing bilateral club foot and meningocele.

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  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.

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