The Principles of Clinical Cytogenetics - Extra Materials - Springer

292 Linda Marie Randolph
Fig. 4. Ultrasound image of a ventricular septal defect (indicated as VSD by arrows) in a 17-week-gestation
fetus. RV = right ventricle; LV = left ventricle; RA = right atrium; LA = left atrium. (Courtesy of Greggory
DeVore, M.D.)
abnormal (153–155). The difference between prenatal and postnatal data probably reflects the high
incidence of in utero demise in fetuses with chromosome abnormalities.
The most frequent prenatally and postnatally diagnosed heart abnormality is the ventricular septal
defect (VSD) (see Fig. 4), followed by tetralogy of Fallot (TOF), right or left hypoplastic heart, and
transposition of the great arteries. Many investigators use the four-chamber view to evaluate the fetal
heart, with an 80–92% sensitivity claimed by this method (154). However, the four-chamber view
alone will not detect TOF or transposition of the great arteries and only detects approximately 59% of
heart abnormalities.
Extracardiac abnormalities are seen, depending on the gestational ages at which the ultrasound
evaluations are performed and what is considered an abnormality, in 36–71% of fetuses with heart
abnormalities (153–155). The presence of extracardiac abnormalities increases the risk of a chromosome
abnormality from 32–48% to 50–71%.
Conotruncal heart abnormalities are those related to faulty conotruncal septation, or division, of
the single primitive heart tube into two outflow tracts that, in turn, result from the fusion of two
swellings that arise in the truncal region at 30 days’ gestation. With increasing awareness of the
strong association between conotruncal heart abnormalities and chromosome 22q11 deletions or
microdeletions, it is now recommended that FISH analysis of this region be performed when a
conotruncal heart abnormality is seen on fetal ultrasound and fetal chromosomes are normal. In five
patients whose fetuses had fetal cardiac abnormalities and a prenatal diagnosis of 22q11 deletion
[del(22)(q11.2)], the heart abnormalities included TOF with absent pulmonary valve, pulmonary atresia
with VSD, truncus arteriosus, and left atrial isomerism with double-outlet right ventricle. One of
the fetuses had an absent kidney and the others had isolated cardiac abnormalities (156).
A population-based study of the 22q11.2 deletion was undertaken by a group from Atlanta, GA.
They evaluated data on babies born from 1994 to 1999 in the Atlanta area and matched those records
with the Metropolitan Atlanta Congenital Defects Program, a local heart center, and the genetics
division at Emory University in Atlanta. Among 255,849 births, 43 children were found to have
22q11.2 deletions for an overall prevalence of 1 in 5950 births (157). Thirty-five of the children had