22q11 deletions and cardiac disease

Prevalence of 22q11.2 microdeletion in 146 patients with cardiac malformation in a referral hospital of North India

Background

The 22q11.2 microdeletion syndrome is a common condition that is associated with cardiac as well as extra-cardiac manifestations. Its prevalence and manifestations from north India has not been reported. This study was designed to determine the prevalence and ability of clinical criteria to predict 22q11.2 microdeletion.

Methods

A total of 146 cases of cardiac malformation requiring tertiary care at a teaching hospital were prospectively screened for 22q11.2 microdeletion using fluorescence in situ hybridization test. Detailed clinical information was obtained as per guidelines of Tobias, et al (1999).

Results

Nine out of 146 patients (6.16%) was found to have 22q11.2 microdeletion. All the positive patients showed the presence of extra-cardiac features of 22q11.2 microdeletion syndrome. None of the cases with isolated cardiac defect were positive for microdeletion.

Conclusions

It seems that 22q11.2 microdeletion syndrome is over-suspected in children with isolated congenital heart defects. Screening for 22q11.2 microdeletion should be considered in those cardiac malformation cases which have extra-cardiac manifestations in the form of facial dysmorphism and hypocalcaemia.

Prevalence of 22q11 deletion in fetuses with conotruncal cardiac defects: a 6-year prospective study

OBJECTIVES

Conotruncal malformations (CTMs) are a major feature of 22q11 microdeletion (22qdel). The prevalence of 22qdel in fetuses harboring these defects is unknown. We assessed the prevalence of 22qdel in a population of fetuses with conotruncal cardiac defects.

STUDY DESIGN

Consecutive fetuses (n = 261) with a CTM and a normal karyotype were included in the study. All fetuses were screened for 22qdel by means of fluorescent in situ hybridization.

RESULTS

A 22qdel was found in 54 fetuses (20.7%). The proportion of 22qdel for each CTM was: tetralogy of Fallot (14/100), pulmonary atresia with ventricular septal defect (11/61), tetralogy of Fallot with absent pulmonary valves (6/16), interrupted aortic arch (10/22), truncus arteriosus (9/29), and complex transpositions of the great arteries (4/33). Additional vascular anomalies were present in 75%. Typical abnormal facial appearance at birth or at autopsy was observed in 80%, and thymus hypoplasia, in 76%. The pregnancy was terminated in 41 of 54 cases, including an intrauterine death in one case. The 22qdel was inherited in 7.7%.

CONCLUSION

Prevalence of the 22qdel is high in fetuses with CTMs. The risk of mental retardation associated with the respective risk of cardiac surgery for each type of CTM may strongly influence prenatal counseling.

Prenatal detection of a tetralogy of Fallot with origin of the left pulmonary artery from the ascending aorta in a familial 22q11 microdeletion

Here we report a case of prenatal diagnosis of anomalous origin of the left pulmonary artery from the ascending aorta associated with a tetralogy of Fallot in a familial form of 22q11 deletion. The mother, who had a normal heart and a velo-cardio-facial syndrome, had a first child with a pulmonary atresia plus ventricular septal defect associated with a 22q11 deletion. Prenatal diagnosis during the second pregnancy identified the above-described cono-truncal anomaly and FISH study showed a recurrent 22q11 deletion. This case illustrates the intrafamilial variability of cardiac involvement in 22q11 deletion as well as the possibility of diagnosing complex cono-truncal malformations during fetal life.

Congenital heart defects and 22q11 deletions: which genes count?

Hemizygous deletions on the long arm of chromosome 22 (del22q11) are a relatively common cause of congenital heart disease. For some specific heart defects such as interrupted aortic arch type B and tetralogy of Fallot with absent pulmonary valve, del22q11 is probably the most frequent genetic cause. Although extensive gene searches have been successful in discovering many novel genes in the deleted segment, standard positional cloning has so far failed to demonstrate a role for any of these genes in the disease. We show how the use of experimental animal models is beginning to provide an insight into the developmental role of some of these genes, while novel genome manipulation technologies promise to dissect the genetic aspects of this complex syndrome.

A genetic etiology for interruption of the aortic arch type B

Interrupted aortic arch (IAA) type B is a congenital heart defect believed to be caused by an anomaly of bronchial arch mesenchymal development. IAA type B has been associated with DiGeorge syndrome (DGS), which includes conotruncal heart defects, T-cell immunodeficiency, hypocalcemia, and facial abnormalities. The great majority of DGS cases are associated with hemizygous deletions at the chromosome 22q11 locus. The present study was designed to establish the involvement of the 22q11 locus in the etiology of IAA type B, independently from the typical DGS phenotype. An evaluation was performed on 73 patients with conotruncal heart defects using fluorescence in situ hybridization (FISH) analysis with probes from the 22q11 DGS locus. From this group, 7 patients were deleted (including 4 of the 11 patients with IAA type B). FISH analysis was extended to a total of 22 patients with IAA type B and 11 of these (50%) were deleted. FISH and Southern blot analyses using additional markers within the DiGeorge chromosomal region were performed on patients found not to be deleted in the initial FISH screening. No small deletions or rearrangements were detected. In our patient population, a single, specific genetic defect is the basis for one half of the IAA type B cases. These data suggest that IAA type B is one of the most etiologically homogeneous congenital heart defects. A 22q11 deletion in IAA type B may or may not be associated with the typical DGS phenotype. Therefore, IAA type B, per se, should be an indication for 22q11 deletion testing.

Cloning and comparative mapping of a gene from the commonly deleted region of DiGeorge and Velocardiofacial syndromes conserved in C. elegans

We have identified and cloned a gene, ES2, encoding a putative 476 amino acid protein with a predicted Mr of 52,568. The gene is localized within the DiGeorge/Velocardiofacial syndrome locus on 22q11.2 and is deleted in all the patients in which a deletion within 22q11 could be demonstrated, with the exception of one patient. ES2 is expressed in all the tissues studied. Sequence comparison showed identity with five ESTs and at the amino acid level the sequence was highly similar to, and collinear with, a hypothetical C. elegans protein of unknown function. Mutation analysis was performed in 16 patients without deletion, but no mutation has been found. The cDNA sequence is conserved in mouse and is localized on MMU16B1-B3, known to contain a syntenic group in common with HSA 22q11.2.