PRENATAL DIAGNOSIS, VOL. 13, 767-774 (1993)

LETTERS TO THE EDITOR

How accurate does rapid fetal karyotyping need to be? Case of unbalanced t(13;18)

Since the advent of clinical cytogenetics, the major thrust of research and development has been to achieve greater accuracy of diagnosis. Advances have included banding and high resolution techniques and recently in situ hybridization. In prenatal diagnosis, the need to obtain a speedy result must be weighed against any extra time taken to achieve greater accuracy. Using fetal blood specimens, rapid karyotyping for abnormal- ities detected on ultrasound has been pro- moted to aid in the subsequent management of the pregnancy (Nicolaides et al., 1988). Even though these samples are of necessity small, and banding is frequently subopti- mal, useful information can be obtained in 2-3 days. Just how accurate does this rapid karyotyping need to be? We present a recent case which centred around this point.

Ultrasound at 33 weeks’ gestation in the third pregnancy of a 27-year-old woman showed marked polyhydramnios (the deep- est verticle pool of amniotic fluid was 11.5 cm) and intrauterine growth retarda- tion. In addition, ultrasound showed an absent stomach bubble, a perimembraneous ventriculo-septa1 defect, and dysmorphic fa- cial features (micrognathia, hypotelorism). Aneuploidy was suspected and 1 ml of fetal blood was collected by cordocentesis. Cyto- genetic results were obtained with very good GTG banding from a 48 h synchronized fetal blood lymphocyte culture. The result showed 46 chromosomes with the absence of one normal chromosome 13 and the presence of an additional chromosome, con- sisting of a translocation between chromo- somes 13 and 18. It was not possible with G banding alone to determine the origin of the centromere of this translocation chromo- some and hence accurate breakpoints, but it was evident that the karyotype was mark- edly unbalanced with trisomy for the long

Addressee for correspondence: A. Smith, Cyto- genetics Unit, Royal Alexandra Hospital for Children, Pyrmont Bridge Road, Camperdown, NSW 2050, Australia.

0 1993 by John Wiley & Sons, Ltd.

arm of chromosome 18. Parental blood was requested and these tests showed that both parents had normal karyotypes.

The obstetrician wanted a more precise cytogenetic result so that more accurate information on the survival of this fetus could be given. Fluorescence in situ hybrid- ization (FISH) was undertaken with bio- tinylated probes for the centromeres of chromosomes 18 and 13, and a human telomere-specific probe. Metaphase spreads were aged for 72 h prior to overnight hy- bridization (Smith et al., 1993). The deriva- tive chromosome gave a positive signal with the chromosome 18 centromere probe (Figure 1) and both the 13 centromere and the telomere probes were negative with FISH. On the basis of these results, the karyotype was considered to be 46,XX, - 13, +der( 18),t( 13;18)(q12;pl1.2) (Figure 2). FISH resolved the origin of the cen- tromere and made it possible to assign more accurately the breakpoint to the short arm of chromosome 18. The imbalance consisted of virtually complete trisomy 18 with a small monosomy of proximal 13q.

Subsequently, a stillborn female child with a birth weight of 1500 g (<third centile for gestational age) was delivered spontane- ously at 36 weeks’ gestation. Post-mortem pathological examination revealed multiple congenital anomalies confirming trisomy 18 (Figure 3). No evidence of rocker-bottom feet or limb abnormalities were seen but X-ray demonstrated bilateral cervical ribs and poor skeletal ossification. There was a persistent septum pellucidum anteriorly. The cardiovascular system showed an iso- lated small membraneous ventricular septa1 defect. There was a wider type C tracheo- oesophageal fistula with proximal oesoph- ageal atresia. There was a thin fibrous band over the second part of the duodenum. Microscopic examination of the brain, thy- roid, thymus, lungs, liver, spleen, pancreas, adrenal, bowel, kidney, and bone did not reveal any abnormality.

Assessing phenotypic features in cases of partial trisomy 18 due to translocation is difficult because of the monosomy of the ‘other’ chromosome (Schwanitz et al.,

Figure 1 . Metaphase with FISH and chromosome 18 centromere probe. Thin arrows indicate the free chromosome 18, and the thick arrow indicates the translocation chromosome

Figure 2. GTG partial karyotype showing one chromosome 13, two chromosomes 18, and the translocation chromosome

LETTERS TO THE EDITOR 769

Figure 3. Facial appearance of the 36-week-old fetus at post-mortem. Note micrognathia (mandible recessed 5 mm), hypotelorism, and microstomia; the right ear was set 8 mm lower than the left ear

1975). Monosomy of proximal 13q is a poorly defined syndrome with rather few consistent features which are non-specific, e.g., short stature and asymmetry of the body and skull (Schinzel, 1983; Suzuki et al., 1987; Colley et al., 1992). There appears to be no straightforward correlation be- tween phenotypic manifestations and tripli- cated loci along chromosome 18 (Wilson et aL, 1991). Our case is indistinguishable from a full trisomy 18 and there were no features which could not be accounted for by trisomy 18.

We obtained a meaningful result in this case within 2 days of receiving the fetal blood specimen. The original cytogenetic request, coupled with the ultrasound find- ings, provided sufficient information to manage the case further had the pregnancy continued. FISH took another 4 days, but the time factor here was not so crucial because the parents were being tested as well during this time. In our case, FISH did provide more accurate information but the main indication for the extra work was to meet the expectations of the providers of the

770 LETTERS TO THE EDITOR

prenatal service. To gain as much accurate information as possible in a given case is an admirable objective. However, expectations should be tempered by the resources avail- able. Even when resources are available, discussion between those concerned with the patient’s management needs to take place to justify any extra work.

J. JACKSON*, L. ROBSON*,

G. WATSON$ AND A. SMITH

*Cytogenetics Unit, Royal Alexandra Hospital for Children,

Pyrmont Bridge Road, Camperdown,

NS W 2050, Australia

TFetaI Medicine Unit, King George V Hospital for Mothers and

Babies, Missenden Road,

Camperdo wn. N S W 2050,

Australia $ Anatomica I Patho logy,

Royal Prince Alfred Hospital, Missenden Road,

Camperdown, NS W 2050,

Australia

s. MEAGHER?,

REFERENCES Colley, A,, Thakker, Y., Ward, H., Donnai, D.

(1992). Unbalanced 13;18 translocation and Williams syndrome, J. Med. Genet., 29, 63-65.

Nicolaides, K.H., Rodeck, C.H., Gosden, C.M. (1986). Rapid karyotyping in non-lethal fetal malformations, Lancet, i, 283-287.

Schinzel, A. (1983). Chromosome 13. In: Cutu- logue of Unbalanced Chromosome Aberrations in Man, Berlin: Gruyter Press, 477-535.

Schwanitz, G., Reither, M., Grosse, G., Hagele, C., Grosse, K.A., Gutfried, U. (1975). Partial monosomy 13 as the result of a balanced translocation 3/13 pat, Humangenetik, 28, 93-96.

Smith, A,, Robson, L., Neumann, A., Mulcahy, M., Chabros, V., Deng, Z.M., Woodage, T., Trent, R.J. (1993). Fluorescence in-situ hybrid- isation and molecular studies used in the char- acterisation of a Robertsonian translocation (13ql5q) in Prader-Willi syndrome, Clin. Genet., 43, 5-8.

Suzuki, Y., Ono, K., Ota, S., Matsubara, T., Arima, M., Nakagome, Y. (1987). A case of

(13q;18q) translocation with proximal 13q monosomy, Hum. Genet., 38, 337-341.

Wilson, G.N., Hellen, K.B., Eherman, R.D., Schnider, N.R. (1991). Partial trisomy 18 with minimal anomalies: lack of correspondence between phenotypic manifestations and tripli- cated loci along chromosome 18, Am. J. Med. Genet., 36, 506-510.

Fetal karyotype from cystic hygroma fluid diploidltetraploid mosaicism

In a recent issue of this journal, Ville et al. (1992) described a new method of fetal sampling by analysing cells from cystic hygroma fluid. We fully agree with the authors when they say that karyotyping fetuses with cystic hygroma is essential to the prognosis and further genetic counsel- ling. At the Centre of Prenatal Diagnosis in Marseilles, we routinely perform direct puncture of cystic hygroma fluid when oli- gohydramnios andor hydrops fetalis makes it difficult to obtain amniotic fluid or fetal blood specimens. We would like to report a recent experience in this field.

A 24-year-old woman (gravida I, para 0) underwent systematic ultrasonographic sur- vey at 19 weeks of gestation. Fetal echogra- phy showed a large cystic hygroma with oligohydramnios, and bilateral pleural and pericardial effusion. Amniocentesis was impossible because of the lack of amniotic fluid. Transabdominal puncture under echography provided two samples. The first specimen was removed from the pleural cavity and the second one from the nuchal cyst.

Cytogenetic analysis was carried out according to the routine method used for amniotic cells and was successful in both cultures. The two samples were highly dis- crepant: a normal 46,XY karyotype in all the pleural cells (24 cells examined) and 92,XXYY in all 46 cells from the cystic hygroma fluid.

The pregnancy was terminated. Post- mortem examination of the fetus confirmed the presence of a large cystic hygroma of the neck in an otherwise normal fetus.

Human tetraploidy is now admitted to be a true chromosomal abnormality rather

Addressee for correspondence: Dr. C. Piquet, Centre de Diagnostic Prtnatal, Hopital d’enfants de la Timone, 13385 Marseille cedex 5, France.