New trends in chromosomal investigation in children with cardiovascular malformations

Genome-wide association studies of Down syndrome associated congenital heart defects

Congenital heart defects (CHDs) are the most common structural birth defect and are present in 40-50% of children born with Down syndrome (DS). To characterize the genetic architecture of DS-associated CHD, we sequenced genomes of a multiethnic group of children with DS and a CHD (n=886: atrioventricular septal defects (AVSD), n=438; atrial septal defects (ASD), n=122; ventricular septal defects (VSD), n=170; other types of CHD, n=156) and DS with a structurally normal heart (DS+NH, n=572). We performed four GWAS for common variants (MAF>0.05) comparing DS with CHD, stratified by CHD-subtype, to DS+NH controls. Although no SNP achieved genome-wide significance, multiple loci in each analysis achieved suggestive significance (p<2×10-6). Of these, the 1p35.1 locus (near RBBP4) was specifically associated with ASD risk and the 5q35.2 locus (near MSX2) was associated with any type of CHD. Each of the suggestive loci contained one or more plausible candidate genes expressed in the developing heart. While no SNP replicated (p<2×10-6) in an independent cohort of DS+CHD (DS+CHD: n=229; DS+NH: n=197), most SNPs that were suggestive in our GWASs remained suggestive when meta-analyzed with the GWASs from the replication cohort. These results build on previous work to identify genetic modifiers of DS-associated CHD.

Prenatal Diagnosis of DNA Copy Number Variations by Genomic Single-Nucleotide Polymorphism Array in Fetuses with Congenital Heart Defects

Objectives: To evaluate the usefulness of single-nucleotide polymorphism (SNP) array for prenatal genetic diagnosis of congenital heart defect (CHD), we used this approach to detect clinically significant copy number variants (CNVs) in fetuses with CHDs. Methods: A HumanCytoSNP-12 array was used to detect genomic samples obtained from 39 fetuses that exhibited cardiovascular abnormalities on ultrasound and had a normal karyotype. The relationship between CNVs and CHDs was identified by using genotype-phenotype comparisons and searching of chromosomal databases. All clinically significant CNVs were confirmed by real-time PCR. Results: CNVs were detected in 38/39 (97.4%) fetuses: variants of unknown significance were detected in 2/39 (5.1%), and clinically significant CNVs were identified in 7/39 (17.9%). In 3 of the 7 fetuses with clinically significant CNVs, 3 rare and previously undescribed CNVs were detected, and these CNVs encompassed the CHD candidate genes FLNA (Xq28 dup), BCOR (Xp11.4 dup), and RBL2 (16q12.2 del). Conclusion: Compared with conventional cytogenetic genomics, SNP array analysis provides significantly improved detection of submicroscopic genomic aberrations in pregnancies with CHDs. Based on these results, we propose that genomic SNP array is an effective method which could be used in the prenatal diagnostic test to assist genetic counseling for pregnancies with CHDs.

Chromosomal abnormalities in patients with congenital heart disease

Background

Chromosomal abnormalities (CAs) are an important cause of congenital heart disease (CHD).

Objective

Determine the frequency, types and clinical characteristics of CAs identified in a sample of prospective and consecutive patients with CHD.

Method

Our sample consisted of patients with CHD evaluated during their first hospitalization in a cardiac intensive care unit of a pediatric referral hospital in Southern Brazil. All patients underwent clinical and cytogenetic assessment through high-resolution karyotype. CHDs were classified according to Botto et al. Chi-square, Fisher exact test and odds ratio were used in the statistical analysis (p < 0.05).

Results

Our sample consisted of 298 patients, 53.4% males, with age ranging from 1 day to 14 years. CAs were observed in 50 patients (16.8%), and 49 of them were syndromic. As for the CAs, 44 (88%) were numeric (40 patients with +21, 2 with +18, 1 with triple X and one with 45,X) and 6 (12%) structural [2 patients with der(14,21), +21, 1 with i(21q), 1 with dup(17p), 1 with del(6p) and 1 with add(18p)]. The group of CHDs more often associated with CAs was atrioventricular septal defect.

Conclusions

CAs detected through karyotyping are frequent in patients with CHD. Thus, professionals, especially those working in Pediatric Cardiology Services, must be aware of the implications that performing the karyotype can bring to the diagnosis, treatment and prognosis and for genetic counseling of patients and families.

Of mice and men: molecular genetics of congenital heart disease

Congenital heart disease (CHD) affects nearly 1 % of the population. It is a complex disease, which may be caused by multiple genetic and environmental factors. Studies in human genetics have led to the identification of more than 50 human genes, involved in isolated CHD or genetic syndromes, where CHD is part of the phenotype. Furthermore, mapping of genomic copy number variants and exome sequencing of CHD patients have led to the identification of a large number of candidate disease genes. Experiments in animal models, particularly in mice, have been used to verify human disease genes and to gain further insight into the molecular pathology behind CHD. The picture emerging from these studies suggest that genetic lesions associated with CHD affect a broad range of cellular signaling components, from ligands and receptors, across down-stream effector molecules to transcription factors and co-factors, including chromatin modifiers.

The contribution of chromosomal abnormalities to congenital heart defects: a population-based study

We aimed to assess the frequency of chromosomal abnormalities among infants with congenital heart defects (CHDs) in an analysis of population-based surveillance data. We reviewed data from the Metropolitan Atlanta Congenital Defects Program, a population-based birth-defects surveillance system, to assess the frequency of chromosomal abnormalities among live-born infants and fetal deaths with CHDs delivered from January 1, 1994, to December 31, 2005. Among 4430 infants with CHDs, 547 (12.3%) had a chromosomal abnormality. CHDs most likely to be associated with a chromosomal abnormality were interrupted aortic arch (type B and not otherwise specified; 69.2%), atrioventricular septal defect (67.2%), and double-outlet right ventricle (33.3%). The most common chromosomal abnormalities observed were trisomy 21 (52.8%), trisomy 18 (12.8%), 22q11.2 deletion (12.2%), and trisomy 13 (5.7%). In conclusion, in our study, approximately 1 in 8 infants with a CHD had a chromosomal abnormality. Clinicians should have a low threshold at which to obtain testing for chromosomal abnormalities in infants with CHDs, especially those with certain types of CHDs. Use of new technologies that have become recently available (e.g., chromosomal microarray) may increase the identified contribution of chromosomal abnormalities even further.

Síndrome de deleção 22q11.2 e cardiopatias congênitas

OBJETIVO: Revisar as características clínicas, etiológicas e diagnósticas da síndrome de deleção 22q11 e sua associação com as cardiopatias congênitas. FONTES DOS DADOS: Foram pesquisados artigos científicos presentes nos portais Medline, Lilacs e SciELO, utilizando-se descritores específicos como "22q11", "DiGeorge syndrome", "velocardiofacial syndrome", "congenital heart defects" e "cardio-vascular malformations". O período adotado para a revisão foi de 1980 a 2009. SÍNTESE DOS DADOS: As malformações cardíacas são os defeitos congênitos observados mais frequentemente ao nascimento e representam um problema importante de Saúde Pública. Dentre suas principais causas conhecidas destaca-se a síndrome de deleção 22q11, também chamada de síndrome de DiGeorge, síndrome velocardiofacial e CATCH22. Trata-se de uma doença autossômica domi-nante caracterizada por um fenótipo altamente variável, o que dificulta em muito seu reconhecimento clínico. Além disso, a maior parte dos pacientes apresenta uma microdeleção identificada principalmente por técnicas de citogenética molecular, como a hibridização in situ fluorescente, pouco disponíveis em nosso meio. De forma similar a outras síndromes, a síndrome de deleção 22q11 associa-se a certos defeitos cardíacos específicos, no caso os do tipo conotruncal. Apesar disso, não há ainda na literatura um consenso sobre quais os pacientes com car-diopatia congênita que deveriam ser investigados para a síndrome de deleção 22q11. CONCLUSÕES: Cardiologistas e cirurgiões cardíacos, espe-cialmente pediátricos, devem estar cientes das peculiaridades e dos cuidados dispensados à síndrome de deleção 22q11. Os indivíduos com a síndrome apresentam comumente alterações envolvendo vários sistemas, o que pode levar a dificuldades e a complicações durante seu manejo clínico e cirúrgico.

Unrelated chromosomal anomalies found in patients with suspected 22q11.2 deletion

Screening for 22q11.2 deletions has not an easy approach due to the wide variability of their associated phenotype. Many clinical features overlap with those of other known syndromes and reported loci. Patients referred to exclude a 22q11.2 deletion are usually tested with a locus-specific FISH probe, with 10% positive cases depending on the selection criteria, but patients testing negative for FISH at 22q11.2 may have other chromosomal aberrations in routine cytogenetic analysis. We tested 819 patients suspected of having a 22q11.2 deletion. Eighty-eight patients (10.7%) were positive for 22q11.2 deletion, whereas 30 patients (3.7%) showed other chromosomal abnormalities involving deletions and duplications, derivative chromosomes, marker chromosomes, apparently balanced and unbalanced translocations and sex chromosome aneuploidies. Of these alterations, 28 did not involve region 22q11 and most had not been associated with 22q11.2 deletion phenotype before. We discuss the similarity of DiGeorge/velocardiofacial syndrome with other known clinical entities and suggest correlations between the new loci and the observed clinical features. The frequency of unrelated chromosomal anomalies reported in this study and in other previous reports highlights the importance of conventional cytogenetic analysis as an initial genome-wide screening tool in all referred patients, and provides useful data to optimize diagnostic and screening protocols according to the most frequent chromosomal findings.

Genetic basis for congenital heart defects: current knowledge: a scientific statement from the American Heart Association Congenital Cardiac Defects Committee, Council on Cardiovascular Disease in the Young: endorsed by the American Academy of Pediatrics

The intent of this review is to provide the clinician with a summary of what is currently known about the contribution of genetics to the origin of congenital heart disease. Techniques are discussed to evaluate children with heart disease for genetic alterations. Many of these techniques are now available on a clinical basis. Information on the genetic and clinical evaluation of children with cardiac disease is presented, and several tables have been constructed to aid the clinician in the assessment of children with different types of heart disease. Genetic algorithms for cardiac defects have been constructed and are available in an appendix. It is anticipated that this summary will update a wide range of medical personnel, including pediatric cardiologists and pediatricians, adult cardiologists, internists, obstetricians, nurses, and thoracic surgeons, about the genetic aspects of congenital heart disease and will encourage an interdisciplinary approach to the child and adult with congenital heart disease.