[Tetralogy of Fallot in monozygotic twins]

Could submicroscopical chromosomal imbalances cause cono-truncal malformations in twins?

The course of normal heart formation in the embryo has been known for decades, but little is known about the genes that control its development. To further improve our understanding of the molecular and genetic mechanisms involved in congenital heart disease, we screened for submicroscopic chromosomal aberrations using bacterial artificial chromosome-based array comparative genomic hybridization analysis in two Danish twin pairs, one pair of monozygotic twins with tetralogy of Fallot, and one twin pair of unknown zygosity with pulmonary valve stenosis. We did not find any major chromosome defects, although a number of submicroscopic copy number variations were present. The question of whether these submicroscopic chromosomal imbalances alone or in conjunction with unknown intrauterine factors causes the observed cono-truncal malformations remains unanswered.

A study to determine the incidence of structural congenital heart disease in monochorionic twins

OBJECTIVE

To determine the incidence of structural heart disease in at least one of a monochorionic (MC) twin pair excluding any cardiac effects of twin-twin transfusion syndrome (TTTS).

METHOD

A cohort study of 165 sets of MC twins undergoing detailed fetal echocardiography in a tertiary unit over a 4-year period.

RESULTS

The overall risk of at least one of a MC twin pair having a structural congenital cardiac anomaly was 9.1% (15/165); for monochorionic diamniotic (MC/DA) twins, this figure was 7.0% (11/158) but for monochorionic-monoamniotic (MC/MA) twins the risk for at least one affected twin was 57.1% (4/7). If one of a pair of MC twins was affected, the risk to the other twin for a structural cardiac anomaly was 26.7% (4/15).

CONCLUSIONS

The incidence of structural heart disease in MC twins is increased, independent of TTTS. This justifies referral of these pregnancies for detailed fetal echocardiography as part of their assessment. If one twin is affected, the risk to the other twin is increased further.

Congenital heart diseases in twin pregnancies

OBJECTIVE

To find connection between the type of congenital heart malformations and twin pregnancies.

METHOD

Retrospective analysis of data of fetal cardiology database between 1 January 1996 and 30 November 2003.

RESULTS

In single pregnancies 455 and in twin pregnancies 31 severe congenital heart malformations were diagnosed prenatally. In monozygotic twin pregnancies 36% of heart malformations were pulmonary stenosis and 45% endocardial fibroelastosis, which is significantly higher than in single pregnancies. In dizygotic twin pregnancies Ebstein malformation was significantly more frequent than in single pregnancies. With the exception of Ebstein malformation in dichorionic and dizygotic twin pregnancies the cardiac malformations were similar to the ones in single pregnancies.

CONCLUSIONS

The twin pregnancy alone can be considered as indication for fetal echocardiography. The type of congenital heart malformations detected in monochorial twin pregnancies was different from those found in single, dizygotic or dichorionic twin pregnancies. Chorionicity seems to be more important than zygosity.