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1.  Chromosome 8p23.1 Deletions as a Cause of Complex Congenital Heart Defects and Diaphragmatic Hernia 
Recurrent interstitial deletion of a region of 8p23.1 flanked by the low copy repeats 8p-OR-REPD and 8p-OR-REPP is associated with a spectrum of anomalies that can include congenital heart malformations and congenital diaphragmatic hernia (CDH). Haploinsufficiency of GATA4 is thought to play a critical role in the development of these birth defects. We describe two individuals and a monozygotic twin pair discordant for anterior CDH all of whom have complex congenital heart defects caused by this recurrent interstitial deletion as demonstrated by array comparative genome hybridization. To better define the genotype/phenotype relationships associated with alterations of genes on 8p23.1, we review the spectrum of congenital heart and diaphragmatic defects that have been reported in individuals with isolated GATA4 mutations and interstitial, terminal, and complex chromosomal rearrangements involving the 8p23.1 region. Our findings allow us to clearly define the CDH minimal deleted region on chromosome 8p23.1 and suggest that haploinsufficiency of other genes, in addition to GATA4, may play a role in the severe cardiac and diaphragmatic defects associated with 8p23.1 deletions. These findings also underscore the importance of conducting a careful cytogenetic/molecular analysis of the 8p23.1 region in all prenatal and postnatal cases involving congenital defects of the heart and/or diaphragm.
doi:10.1002/ajmg.a.32896
PMCID: PMC2765374  PMID: 19606479
Congenital heart defects; 8p23.1 deletion syndrome; Diaphragmatic hernia; Array comparative genomic hybridization; GATA4; Prenatal diagnosis
2.  Multiplex Ligation-Dependent Probe Amplification Analysis of GATA4 Gene Copy Number Variations in Patients with Isolated Congenital Heart Disease 
Disease markers  2010;28(5):287-292.
GATA4 mutations are found in patients with different isolated congenital heart defects (CHDs), mostly cardiac septal defects and tetralogy of Fallot. In addition, GATA4 is supposed to be the responsible gene for the CHDs in the chromosomal 8p23 deletion syndrome, which is recognized as a malformation syndrome with clinical symptoms of facial anomalies, microcephaly, mental retardation, and congenital heart defects. Thus far, no study has been carried out to investigate the role of GATA4 copy number variations (CNVs) in non-syndromic CHDs. To explore the possible occurrence of GATA4 gene CNVs in isolated CHDs, we analyzed by multiplex ligation-dependent probe amplification (MLPA) a cohort of 161 non-syndromic patients with cardiac anomalies previously associated with GATA4 gene mutations. The patients were mutation-negative for GATA4, NKX2.5, and FOG2 genes after screening with denaturing high performance liquid chromatography. MLPA analysis revealed that normalized MLPA signals were all found within the normal range values for all exons in all patients, excluding a major contribution of GATA4 gene CNVs in CHD pathogenesis.
doi:10.3233/DMA-2010-0703
PMCID: PMC3833239  PMID: 20592452
CHD; MLPA; GATA4; CNV
3.  Rare copy number variants in isolated sporadic and syndromic atrioventricular septal defects 
Atrioventricular septal defects (AVSDs) are a frequent but not universal component of Down syndrome (DS), while AVSDs in otherwise normal individuals have no well-defined genetic basis. The contribution of copy number variation (CNV) to specific congenital heart disease (CHD) phenotypes including AVSD is unknown. We hypothesized that de novo CNVs on chromosome 21 might cause isolated sporadic AVSDs, and separately that CNVs throughout the genome might constitute an additional genetic risk factor for AVSD in patients with DS. We utilized a custom oligonucleotide arrays targeted to CNV hotspots that are flanked by large duplicated segments of high sequence identity. We assayed 29 euploid and 50 DS individuals with AVSD, and compared to general population controls. In patients with isolated-sporadic AVSD we identified two large unique deletions outside of chromosome 21 not seen in the expanded set of 8,635 controls, each overlapping with larger deletions associated with similar CHD reported in the DECIPHER database. There was a small duplication in one patient with DS and AVSD. We conclude that isolated sporadic AVSDs may be occasionally associated with large de novo genomic structural variation outside of chromosome 21. The absence of CNVs on chromosome 21 in patients with isolated sporadic AVSD suggests that sub-chromosomal duplications or deletions of greater than 150 kbp on chromosome 21 do not cause sporadic AVSDs. Large CNVs do not appear to be an additive risk factor for AVSD in the DS population.
doi:10.1002/ajmg.a.35315
PMCID: PMC3564951  PMID: 22529060
Down syndrome; atrioventricular septal defects; copy number variation; array CGH; congenital heart disease
4.  Rare Copy Number Variants in Isolated Sporadic and Syndromic Atrioventricular Septal Defects 
Atrioventricular septal defects (AVSDs) are a frequent but not universal component of Down syndrome (DS), while AVSDs in otherwise normal individuals have no well-defined genetic basis. The contribution of copy number variation (CNV) to specific congenital heart disease (CHD) phenotypes including AVSD is unknown. We hypothesized that de novo CNVs on chromosome 21 might cause isolated sporadic AVSDs, and separately that CNVs throughout the genome might constitute an additional genetic risk factor for AVSD in patients with DS. We utilized a custom oligonucleotide arrays targeted to CNV hotspots that are flanked by large duplicated segments of high sequence identity. We assayed 29 euploid and 50 DS individuals with AVSD, and compared to general population controls. In patients with isolated-sporadic AVSD we identified two large unique deletions outside of chromosome 21 not seen in the expanded set of 8,635 controls, each overlapping with larger deletions associated with similar CHD reported in the DECIPHER database. There was a small duplication in one patient with DS and AVSD. We conclude that isolated sporadic AVSDs may be occasionally associated with large de novo genomic structural variation outside of chromosome 21. The absence of CNVs on chromosome 21 in patients with isolated sporadic AVSD suggests that sub-chromosomal duplications or deletions of greater than 150 kbp on chromosome 21 do not cause sporadic AVSDs. Large CNVs do not appear to be an additive risk factor for AVSD in the DS population. © 2012 Wiley Periodicals, Inc.
doi:10.1002/ajmg.a.35315
PMCID: PMC3564951  PMID: 22529060
Down syndrome; atrioventricular septal defects; copy number variation; array CGH; congenital heart disease
5.  Novel GATA6 Mutations Associated with Congenital Ventricular Septal Defect or Tetralogy of Fallot 
DNA and Cell Biology  2012;31(11):1610-1617.
Congenital heart disease (CHD) is the most common form of developmental malformation and is the leading noninfectious cause of infant mortality. Emerging evidence indicates that genetic defects are involved in the pathogenesis of CHD. Nevertheless, CHD is genetically heterogeneous, and the molecular basis for CHD in a majority of patients remains unknown. In this study, the whole coding region of GATA6, a gene encoding a zinc-finger transcription factor crucial for normal cardiogenesis, was sequenced in 380 unrelated patients with CHD. The relatives of the index patients harboring the identified mutations and 200 unrelated control individuals were subsequently genotyped. The functional effect of the mutations was characterized using a luciferase reporter assay system. As a result, two novel heterozygous GATA6 mutations, p.D404Y and p.E460X, were identified in two families with ventricular septal defect and tetralogy of Fallot, respectively. The mutations co-segregated with CHD in the families with complete penetrance, and were absent in 400 control chromosomes. Functional analysis demonstrated that the mutated GATA6 proteins were associated with significantly decreased transactivational activity in comparison with their wild-type counterpart. These findings provide novel insight into the molecular mechanism implicated in CHD, suggesting potential implications for the early prophylaxis and personalized treatment of CHD.
The transcription factor GATA6 is a zinc finger DNA-binding protein that has been shown to be essential for cardiac development. In this article, two novel heterologous polymorphisms were associated with two cardiac malformations in families.
doi:10.1089/dna.2012.1814
PMCID: PMC3482375  PMID: 23020118
6.  Detailed mapping of a congenital heart disease gene in chromosome 3p25 
Journal of Medical Genetics  2000;37(8):581-587.
Distal deletion of chromosome 3p25-pter (3p− syndrome) produces a distinct clinical syndrome characterised by low birth weight, mental retardation, telecanthus, ptosis, and micrognathia. Congenital heart disease (CHD), typically atrioventricular septal defect (AVSD), occurs in about a third of patients. In total, approximately 25 cases of 3p− syndrome have been reported world wide. We previously analysed five cases and showed that (1) the 3p25-pter deletions were variable and (2) the presence of CHD correlated with the proximal extent of the deletion, mapping a CHD gene centromeric to D3S18. To define the molecular pathology of the 3p− syndrome further, we have now proceeded to analyse the deletion region in a total of 10 patients (five with CHD), using a combination of FISH analysis and polymorphic markers, for up to 21 loci from 3p25-p26. These additional investigations further supported the location of an AVSD locus within 3p25 and refined its localisation. Thus, the critical region was reduced to an interval between D3S1263 and D3S3594. Candidate 3p25 CHD genes, such as PMCA2 (ATP2B2), fibulin 2, TIMP4, and Sec13R, were shown to map outside the target interval. Additionally, the critical region for the phenotypic features of the 3p− phenotype was mapped to D3S1317 to D3S17 (19-21 cM). These findings will accelerate the identification of the 3p25 CHD susceptibility locus and facilitate investigations of the role of this locus in non-syndromic AVSDs, which are a common form of familial and isolated CHD.


Keywords: congenital heart disease; chromosome 3p25
doi:10.1136/jmg.37.8.581
PMCID: PMC1734659  PMID: 10922384
7.  Congenital Diaphragmatic Hernia Interval on Chromosome 8p23.1 Characterized by Genetics and Protein Interaction Networks 
Chromosome 8p23.1 is a common hotspot associated with major congenital malformations, including congenital diaphragmatic hernia (CDH) and cardiac defects. We present findings from high-resolution arrays in patients who carry a loss (n =18) or a gain (n =1) of sub-band 8p23.1. We confirm a region involved in both diaphragmatic and heart malformations. Results from a novel CNVConnect algorithm, prioritizing protein–protein interactions between products of genes in the 8p23.1 hotspot and products of previously known CDH causing genes, implicated GATA4, NEIL2, and SOX7 in diaphragmatic defects. Sequence analysis of these genes in 226 chromosomally normal CDH patients, as well as in a small number of deletion 8p23.1 patients, showed rare unreported variants in the coding region; these may be contributing to the diaphragmatic phenotype. We also demonstrated that two of these three genes were expressed in the E11.5–12.5 primordial mouse diaphragm, the developmental stage at which CDH is thought to occur. This combination of bioinformatics and expression studies can be applied to other chromosomal hotspots, as well as private microdeletions or microduplications, to identify causative genes and their interaction networks.
doi:10.1002/ajmg.a.35665
PMCID: PMC3761361  PMID: 23165946
congenital diaphragmatic hernia; congenital heart defect; DNA copy number variants; deletion 8p23 1; duplication 8p23 1; CNVConnect; GATA4; SOX7; NEIL2
8.  Implications of copy number variation in people with chromosomal abnormalities: potential for greater variation in copy number state may contribute to variability of phenotype 
The HUGO Journal  2010;4(1-4):1-9.
Copy number variation is common in the human genome with many regions, overlapping thousands of genes, now known to be deleted or amplified. Aneuploidies and other forms of chromosomal imbalance have a wide range of adverse phenotypes and are a common cause of birth defects resulting in significant morbidity and mortality. “Normal” copy number variants (CNVs) embedded within the regions of chromosome imbalance may affect the clinical outcomes by altering the local copy number of important genes or regulatory regions: this could alleviate or exacerbate certain phenotypes. In this way CNVs may contribute to the clinical variability seen in many disorders caused by chromosomal abnormalities, such as the congenital heart defects (CHD) seen in ~40% of Down’s syndrome (DS) patients. Investigation of CNVs may therefore help to pinpoint critical genes or regulatory elements, elucidating the molecular mechanisms underlying these conditions, also shedding light on the aetiology of such phenotypes in people without major chromosome imbalances, and ultimately leading to their improved detection and treatment.
doi:10.1007/s11568-010-9144-z
PMCID: PMC3051043  PMID: 22132061
Copy number variation; Chromosomal abnormalities; Aneuploidy; Phenotypic variability
9.  Karyotypic and Molecular Genetic Changes Associated With Fetal Cardiovascular Abnormalities: Results of a Retrospective 4-Year Ultrasonic Diagnosis Study 
Objective: To investigate the incidence of aneuploidy in fetuses with congenital heart defects (CHDs) and to further identify submicroscopic changes and global DNA methylation levels as potential biomarkers in complex CHD cases.
Methods: Fetuses at high risk for birth defects or with obvious sonographic anomalies were recruited at the Prenatal Diagnosis Center and Ultrasonic Diagnosis Center. Elective fetal karyotyping and DNA copy number and promoter methylation analyses were carried out following parental consent. G-banded karyotyping was performed to detect fetal aneuploidy. Copy number variations (CNVs) were detected using the Affymetrix SNP Array 6.0 and validated by real time PCR. Global DNA methylation analyses were conducted using a Roche NimbleGen Human DNA Methylation 3x720K Array, and DNA methylation differences were assayed by a Sequenom MassARRAY EpiTYPER.
Results: Conventional karyotyping identified 30 cases with aneuploidy in 179 CHD fetuses. Various CNVs were found in two aneuploid fetuses and in five euploid CHD fetuses. Verified segmental deletion or duplications were not directly associated with cardiovascular malformations except in DAAM1 and GATA6. Verifiable aberrant DNA methylation could not be identified in three complex CHD fetuses.
Conclusions: In this study, Trisomy 18, Trisomy 21 and 45,XO were the most common aneuploidies identified in CHD fetuses. In the affected samples, only DAAM1 deletion and GATA6 amplification could be associated with cardiovascular biological processes.
doi:10.7150/ijbs.5404
PMCID: PMC3654495  PMID: 23678296
Congenital heart defect; Karyotyping; Copy number variants; Methylation level.
10.  ISL1 Common Variant rs1017 Is Not Associated with Susceptibility to Congenital Heart Disease in a Chinese Population 
Background: ISL1, as a member of the LIM homeodomain transcription factor family, is expressed in a distinct population of undifferentiated cardiac progenitors and plays a pivotal role in cardiogenesis. Lacking ISL1 expression results in growth arrest or displays profound defects in heart development, including atria, ventricle, and the inflow and outflow tracts, which constitute a major form of congenital heart disease (CHD). Recently, an important study by Stevens et al. found that genetic variation in ISL1 is associated with risk of CHD in white and black/African American populations; this observation led us to hypothesize that ISL1 common variants might influence susceptibility to sporadic CHD in our Chinese population. Methods: We conducted a case–control study of CHD in Chinese to test our hypothesis by genotyping ISL1 common variant rs1017 in 1003 CHD cases and 1012 non-CHD controls. Results: We found that rs1017 was not associated with the risk of CHD (p=0.213). When we performed stratified analyses according to subjects' age, sex, and CHD classifications, we found no overall heterogeneity of risk in different subgroups. Conclusions: This is the first study which indicates that ISL1 common variant rs1017 may not play a role in sporadic CHD susceptibility in the Chinese population.
doi:10.1089/gtmb.2011.0249
PMCID: PMC3396000  PMID: 22480195
11.  A novel autosomal dominant condition consisting of congenital heart defects and low atrial rhythm maps to chromosome 9q 
Congenital heart defects (CHDs) occur mostly sporadic, but familial CHD cases have been reported. Mutations in several genes, including NKX2.5, GATA4 and NOTCH1, were identified in families and patients with CHD, but the mechanisms underlying CHD are largely unknown. We performed genome-wide linkage analysis in a large four-generation family with autosomal dominant CHD (including atrial septal defect type I and II, tetralogy of Fallot and persistent left superior vena cava) and low atrial rhythm, a unique phenotype that has not been described before. We obtained phenotypic information including electrocardiography, echocardiography and DNA of 23 family members. Genome-wide linkage analysis on 12 affected, 5 unaffected individuals and 1 obligate carrier demonstrated significant linkage only to chromosome 9q21–33 with a multipoint maximum LOD score of 4.1 at marker D9S1690, between markers D9S167 and D9S1682. This 48-c critical interval corresponds to 39 Mb and contains 402 genes. Sequence analysis of nine candidate genes in this region (INVS, TMOD1, TGFBR1, KLF4, IPPK, BARX1, PTCH1, MEGF9 and S1PR3) revealed no mutations, nor were genomic imbalances detected using array comparative genomic hybridization. In conclusion, we describe a large family with CHD and low atrial rhythm with a significant LOD score to chromosome 9q. The phenotype is representative of a mild form of left atrial isomerism or a developmental defect of the sinus node and surrounding tissue. Because the mechanisms underlying CHD are largely unknown, this study represents an important step towards the discovery of genes implied in cardiogenesis.
doi:10.1038/ejhg.2011.33
PMCID: PMC3137501  PMID: 21386876
atrium; congenital heart defects; sinus node
12.  Differences in Copy Number Variation between Discordant Monozygotic Twins as a Model for Exploring Chromosomal Mosaicism in Congenital Heart Defects 
Molecular Syndromology  2012;2(2):81-87.
Studies addressing the role of somatic copy number variation (CNV) in the genesis of congenital heart defects (CHDs) are scarce, as cardiac tissue is difficult to obtain, especially in non-affected individuals. We explored the occurrence of copy number differences in monozygotic (MZ) twins discordant for the presence of a CHD, as an illustrative model for chromosomal mosaicism in CHDs. Array comparative genomic hybridization was performed on peripheral blood-derived DNA obtained from 6 discordant MZ twin pairs and on sex-matched reference samples. To identify CNV differences between both twin members as well as potential CNVs in both twins contributing to the phenotype, DNA from each twin was hybridized against its co-twin, and against a normal control. Three copy number differences in 1 out of 6 MZ twin pairs were detected, confirming the occurrence of somatic CNV events in MZ twins. Further investigation by copy number and (epi)genome sequencing analyses in MZ twins, discordant for the presence of CHDs, is required to improve our knowledge on how postzygotic genetic, environmental and stochastic factors can affect human heart development.
doi:10.1159/000335284
PMCID: PMC3326280  PMID: 22511896
Array comparative genomic hybridization; Congenital heart defects; Copy number variation; Monozygotic twins
13.  A variant in the carboxyl-terminus of connexin 40 alters GAP junctions and increases risk for tetralogy of Fallot 
GJA5 gene (MIM no. 121013), localized at 1q21.1, encodes for the cardiac gap junction protein connexin 40. In humans, copy number variants of chromosome 1q21.1 have been associated with variable phenotypes comprising congenital heart disease (CHD), including isolated TOF. In mice, the deletion of Gja5 can cause a variety of complex CHDs, in particular of the cardiac outflow tract, corresponding to TOF in many cases. In the present study, we screened for mutations in the GJA5 gene 178 unrelated probands with isolated TOF. A heterozygous nucleotide change (c.793C>T) in exon 2 of the gene leading to the p.Pro265Ser variant at the carboxyl-terminus of the protein was found in two unrelated sporadic patients, one with classic anatomy and one with pulmonary atresia. This GJA5 missense substitution was not observed in 1568 ethnically-matched control chromosomes. Immunofluorescent staining and confocal microscopy revealed that cells expressing the mutant protein form sparse or no visible gap-junction plaques in the region of cell–cell contact. Moreover, analysis of the transfer of the gap junction permanent tracer lucifer yellow showed that cells expressing the mutant protein have a reduced rate of dye transfer compared with wild-type cells. Finally, use of a zebrafish model revealed that microinjection of the GJA5-p.Pro265Ser mutant disrupts overall morphology of the heart tube in the 37% (22/60) of embryos, compared with the 6% (4/66) of the GJA5 wild-type-injected embryos. These findings implicate GJA5 gene as a novel susceptibility gene for TOF.
doi:10.1038/ejhg.2012.109
PMCID: PMC3533258  PMID: 22713807
congenital heart disease; tetralogy of Fallot; 1q21.1;  GJA5 ; connexin 40
14.  Reproductive dysfunction and decreased GnRH neurogenesis in a mouse model of CHARGE syndrome 
Human Molecular Genetics  2011;20(16):3138-3150.
CHARGE is a multiple congenital anomaly disorder and a common cause of pubertal defects, olfactory dysfunction, growth delays, deaf-blindness, balance disorders and congenital heart malformations. Mutations in CHD7, the gene encoding chromodomain helicase DNA binding protein 7, are present in 60–80% of individuals with the CHARGE syndrome. Mutations in CHD7 have also been reported in the Kallmann syndrome (olfactory dysfunction, delayed puberty and hypogonadotropic hypogonadism). CHD7 is a positive regulator of neural stem cell proliferation and olfactory sensory neuron formation in the olfactory epithelium, suggesting that the loss of CHD7 might also disrupt development of other neural populations. Here we report that female Chd7Gt/+ mice have delays in vaginal opening and estrus onset, and erratic estrus cycles. Chd7Gt/+ mice also have decreased circulating levels of luteinizing hormone and follicle-stimulating hormone but apparently normal responsiveness to gonadotropin-releasing hormone (GnRH) agonist and antagonist treatment. GnRH neurons in the adult Chd7Gt/+ hypothalamus and embryonic nasal region are diminished, and there is decreased cellular proliferation in the embryonic olfactory placode. Expression levels of GnRH1 and Otx2 in the hypothalamus and GnRHR in the pituitary are significantly reduced in adult Chd7Gt/+ mice. Additionally, Chd7 mutant embryos have CHD7 dosage-dependent reductions in expression levels of Fgfr1, Bmp4 and Otx2 in the olfactory placode. Together, these data suggest that CHD7 has critical roles in the development and maintenance of GnRH neurons for regulating puberty and reproduction.
doi:10.1093/hmg/ddr216
PMCID: PMC3140819  PMID: 21596839
15.  Daam1a mediates asymmetric habenular morphogenesis by regulating dendritic and axonal outgrowth 
Development (Cambridge, England)  2013;140(19):3997-4007.
Although progress has been made in resolving the genetic pathways that specify neuronal asymmetries in the brain, little is known about genes that mediate the development of structural asymmetries between neurons on left and right. In this study, we identify daam1a as an asymmetric component of the signalling pathways leading to asymmetric morphogenesis of the habenulae in zebrafish. Daam1a is a member of the Formin family of actin-binding proteins and the extent of Daam1a expression in habenular neuron dendrites mirrors the asymmetric growth of habenular neuropil between left and right. Local loss and gain of Daam1a function affects neither cell number nor subtype organisation but leads to a decrease or increase of neuropil, respectively. Daam1a therefore plays a key role in the asymmetric growth of habenular neuropil downstream of the pathways that specify asymmetric cellular domains in the habenulae. In addition, Daam1a mediates the development of habenular efferent connectivity as local loss and gain of Daam1a function impairs or enhances, respectively, the growth of habenular neuron terminals in the interpeduncular nucleus. Abrogation of Daam1a disrupts the growth of both dendritic and axonal processes and results in disorganised filamentous actin and α-tubulin. Our results indicate that Daam1a plays a key role in asymmetric habenular morphogenesis mediating the growth of dendritic and axonal processes in dorsal habenular neurons.
doi:10.1242/dev.091934
PMCID: PMC3775416  PMID: 24046318
Asymmetry; Nervous system; Morphogenesis; Daam1; Habenula; Zebrafish
16.  Genetic Modifiers Predisposing to Congenital Heart Disease in the Sensitized Down Syndrome Population 
Background
About half of people with Down syndrome (DS) exhibit some form of congenital heart disease (CHD). However, trisomy for human chromosome 21 (Hsa21) alone is insufficient to cause CHD as half of all people with DS have a normal heart, suggesting that genetic modifiers interact with dosage sensitive gene(s) on Hsa21 to result in CHD. We hypothesize that a threshold exists in both Down syndrome and euploid populations for the number of genetic perturbations that can be tolerated before CHD results.
Methods and Results
We ascertained a group of individuals with DS and complete atrioventricular septal defect (AVSD) and sequenced two candidate genes for CHD, CRELD1, which is associated with AVSD in people with or without DS, and HEY2, whose mouse ortholog produces septal defects when mutated. Several deleterious variants were identified but the frequency of these potential modifiers was low. We crossed mice with mutant forms of these potential modifiers to the Ts65Dn mouse model of Down syndrome. Crossing loss-of-function alleles of either Creld1 or Hey2 onto the trisomic background caused a significant increase in the frequency of CHD, demonstrating an interaction between the modifiers and trisomic genes. We showed further that although either of these mutant modifiers is benign by itself, they interact to affect heart development when inherited together.
Conclusions
Using mouse models of Down syndrome and of genes associated with congenital heart disease we demonstrate a biological basis for an interaction that supports a threshold hypothesis for additive effects of genetic modifiers in the sensitized trisomic population.
doi:10.1161/CIRCGENETICS.111.960872
PMCID: PMC3386785  PMID: 22523272
congenital heart disease; genetic modifier; Down syndrome
17.  Variants of Folate Metabolism Genes and the Risk of Conotruncal Cardiac Defects 
Background
Although congenital heart defects (CHD) are the most common, serious group of birth defects, relatively little is known about the causes of these conditions and there are no established prevention strategies. There is evidence suggesting that the risk of CHD in general, and conotruncal and ventricular septal defects in particular, may be related to maternal folate status as well as genetic variants in folate-related genes. However, efforts to establish the relationships between these factors and CHD risk have been hampered by a number of factors including small study sample sizes and phenotypic heterogeneity.
Methods and Results
The present study examined the relationships between variation in nine folate-related genes and a subset of CHD phenotypes (i.e. conotruncal defects, perimembranous and malalignment type ventricular septal defects, and isolated aortic arch anomalies) in a cohort of over 700 case-parent triads. Further, both maternal and embryonic genetic effects were considered. Analyses of the study data confirmed a previously reported association between embryonic genotype for MTHFR A1298C and disease risk (unadjusted p=0.002).
Conclusions
These results represent the most comprehensive and powerful analysis of the relationship between CHD and folate-related genes reported to date, and provide additional evidence that, similar to neural tube defects, this subset of CHD is folate-related.
doi:10.1161/CIRCGENETICS.108.796342
PMCID: PMC3035562  PMID: 20031554
pediatrics; heart defects; congenital; genetics
18.  Phenotypic manifestations of copy number variation in chromosome 16p13.11 
The widespread clinical utilization of array comparative genome hybridization, has led to the unraveling of many new copy number variations (CNVs). Although some of these CNVs are clearly pathogenic, the phenotypic consequences of others, such as those in 16p13.11 remain unclear. Whereas deletions of 16p13.11 have been associated with multiple congenital anomalies, the relevance of duplications of the region is still being debated. We report detailed clinical and molecular characterization of 10 patients with duplication and 4 patients with deletion of 16p13.11. We found that patients with duplication of the region have varied clinical features including behavioral abnormalities, cognitive impairment, congenital heart defects and skeletal manifestations, such as hypermobility, craniosynostosis and polydactyly. These features were incompletely penetrant. Patients with deletion of the region presented with microcephaly, developmental delay and behavioral abnormalities as previously described. The CNVs were of varying sizes and were likely mediated by non-allelic homologous recombination between low copy repeats. Our findings expand the repertoire of clinical features observed in patients with CNV in 16p13.11 and strengthen the hypothesis that this is a dosage sensitive region with clinical relevance.
doi:10.1038/ejhg.2010.184
PMCID: PMC3061988  PMID: 21150890
CNV; 16p13.11; cognitive impairment; behavioral abnormality
19.  Great vessel development requires biallelic expression of Chd7 and Tbx1 in pharyngeal ectoderm in mice  
The Journal of Clinical Investigation  2009;119(11):3301-3310.
Aortic arch artery patterning defects account for approximately 20% of congenital cardiovascular malformations and are observed frequently in velocardiofacial syndrome (VCFS). In the current study, we screened for chromosome rearrangements in patients suspected of VCFS, but who lacked a 22q11 deletion or TBX1 mutation. One individual displayed hemizygous CHD7, which encodes a chromodomain protein. CHD7 haploinsufficiency is the major cause of coloboma, heart defect, atresia choanae, retarded growth and development, genital hypoplasia, and ear anomalies/deafness (CHARGE) syndrome, but this patient lacked the major diagnostic features of coloboma and choanal atresia. Because a subset of CHARGE cases also display 22q11 deletions, we explored the embryological relationship between CHARGE and VCSF using mouse models. The hallmark of Tbx1 haploinsufficiency is hypo/aplasia of the fourth pharyngeal arch artery (PAA) at E10.5. Identical malformations were observed in Chd7 heterozygotes, with resulting aortic arch interruption at later stages. Other than Tbx1, Chd7 is the only gene reported to affect fourth PAA development by haploinsufficiency. Moreover, Tbx1+/–;Chd7+/– double heterozygotes demonstrated a synergistic interaction during fourth PAA, thymus, and ear morphogenesis. We could not rescue PAA morphogenesis by restoring neural crest Chd7 expression. Rather, biallelic expression of Chd7 and Tbx1 in the pharyngeal ectoderm was required for normal PAA development.
doi:10.1172/JCI37561
PMCID: PMC2769172  PMID: 19855134
20.  DAAM Is Required for Thin Filament Formation and Sarcomerogenesis during Muscle Development in Drosophila 
PLoS Genetics  2014;10(2):e1004166.
During muscle development, myosin and actin containing filaments assemble into the highly organized sarcomeric structure critical for muscle function. Although sarcomerogenesis clearly involves the de novo formation of actin filaments, this process remained poorly understood. Here we show that mouse and Drosophila members of the DAAM formin family are sarcomere-associated actin assembly factors enriched at the Z-disc and M-band. Analysis of dDAAM mutants revealed a pivotal role in myofibrillogenesis of larval somatic muscles, indirect flight muscles and the heart. We found that loss of dDAAM function results in multiple defects in sarcomere development including thin and thick filament disorganization, Z-disc and M-band formation, and a near complete absence of the myofibrillar lattice. Collectively, our data suggest that dDAAM is required for the initial assembly of thin filaments, and subsequently it promotes filament elongation by assembling short actin polymers that anneal to the pointed end of the growing filaments, and by antagonizing the capping protein Tropomodulin.
Author Summary
Sarcomeres, the smallest contractile units of muscle, are formed by two major filament systems, the myosin containing thick and the actin containing thin filaments. Although it is well established that sarcomerogenesis involves the formation of novel actin filaments, so far it remained largely unclear how these filaments form. In this study, we show that the Drosophila and mouse members of the DAAM formin subfamily are sarcomere associated actin assembly factors. Genetic analysis revealed that dDAAM plays an essential role in thin filament formation and sarcomere organization. In addition, we demonstrate that mDaam1 is an early determinant of myofibrillogenesis. Our data suggest that besides a role at the barbed end of the thin filaments, dDAAM also functions at the pointed end where it antagonizes the capping protein Tropomodulin. Based on these observations, we propose that DAAM family formins are very good candidates for being the long sought-after muscle actin nucleators, that also promote filament elongation by assembling short actin polymers that anneal to the Z-disc anchored growing filament. Given that cardiomyopathies, muscular dystrophies and the cardiovascular disease related heart muscle degenerations belong to the major health problems worldwide, understanding the mechanism of how muscles normally form is of immense biomedical relevance.
doi:10.1371/journal.pgen.1004166
PMCID: PMC3937221  PMID: 24586196
21.  Recurrent reciprocal 1q21.1 deletions and duplications associated with microcephaly or macrocephaly and developmental and behavioral abnormalities 
Nature genetics  2008;40(12):1466-1471.
Chromosome region 1q21.1 contains extensive and complex low-copy repeats, and copy number variants (CNVs) in this region have recently been reported in association with congenital heart defects1, developmental delay2,3, schizophrenia and related psychoses4,5. We describe 21 probands with the 1q21.1 microdeletion and 15 probands with the 1q21.1 microduplication. These CNVs were inherited in most of the cases in which parental studies were available. Consistent and statistically significant features of microcephaly and macrocephaly were found in individuals with micro-deletion and microduplication, respectively. Notably, a paralog of the HYDIN gene located on 16q22.2 and implicated in autosomal recessive hydrocephalus6 was inserted into the 1q21.1 region during the evolution of Homo sapiens7; we found this locus to be deleted or duplicated in the individuals we studied, making it a probable candidate for the head size abnormalities observed. We propose that recurrent reciprocal microdeletions and microduplications within 1q21.1 represent previously unknown genomic disorders characterized by abnormal head size along with a spectrum of developmental delay, neuropsychiatric abnormalities, dysmorphic features and congenital anomalies. These phenotypes are subject to incomplete penetrance and variable expressivity.
doi:10.1038/ng.279
PMCID: PMC2680128  PMID: 19029900
22.  22q11.2 Distal Deletion Syndrome: Description of a New Case with Truncus Arteriosus Type 2 and Review 
Molecular Syndromology  2011;2(1):35-44.
22q11.2 deletion syndrome is mainly characterized by conotruncal congenital heart defects, velopharyngeal insufficiency, hypocalcemia and a characteristic craniofacial appearance. The etiology in the majority of patients is a 3-Mb recurrent deletion in region 22q11.2. Nevertheless, recently some cases of infrequent deletions with various sizes have been reported with a different phenotype. We report on a patient with congenital heart disease (truncus arteriosus type 2) in whom a de novo 1.3-Mb 22q11.2 deletion was detected by array comparative genomic hybridization. The deletion described corresponds to an atypical and distal deletion which spans low copy repeat (LCR) 4 and is associated with breakpoint sites that do not correspond to known LCRs of 22q11.2. We examine the clinical phenotype of our case and compare our findings with those published in the literature. The most prevalent clinical features in this type of deletion are a history of prematurity, pre-natal and post-natal growth retardation, slight facial dysmorphic features, microcephaly and developmental delay, with a speech defect in particular. These are clearly different from those found in the classic 22q11.2 deletion syndrome, and we believe that the main differential diagnosis should be with Silver-Russel syndrome. In our case we observe the cardiac phenotype with truncus arteriosus communis usually seen in the classic 22q11.2 deletion syndrome, and so far associated with the TBX1 gene. Significantly, however, TBX1 is not included in our patient's deletion. The possible roles of a position effect or other genes are discussed.
doi:10.1159/000334262
PMCID: PMC3343753  PMID: 22582037
22q11.2 distal deletion syndrome; Pre- and post-natal growth retardation; TBX1; Truncus arteriosus
23.  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.
doi:10.1007/s00018-013-1430-1
PMCID: PMC3958813  PMID: 23934094
Congenital heart disease; CHD; Disease genes; Copy number variants; CNVs
24.  DAAM family members leading a novel path into formin research 
Formins are an important and evolutionarily well conserved class of actin binding proteins with essential biological functions. Although their molecular roles in actin regulation have been clearly demonstrated in vitro, their functions at the cellular or organism levels are still poorly understood. To illustrate this problem, but also to demonstrate potential ways forward, we focus here on the DAAM group of formins. In vertebrates, DAAM group members have been demonstrated to be important regulators of cellular and tissue morphogenesis but, as for all formins, the molecular mechanisms underlying these morphogenetic functions remain to be uncovered. The genome of the fruitfly Drosophila encodes a single DAAM gene that is evolutionarily highly conserved. Recent work on dDAAM has already provided a unique combination of observations and experimental opportunities unrivalled by any other Drosophila formin. These comprise in vitro actin polymerisation assays, subcellular studies in culture and in vivo, and a range of developmental phenotypes revealing a role in tracheal morphogenesis, axonal growth and muscle organization. At all these levels, future work on dDAAM will capitalize on the power of fly genetics, raising unique opportunities to advance our understanding of dDAAM at the systems level, with obvious implications for other formins.
doi:10.4161/cib.4.5.16511
PMCID: PMC3204122  PMID: 22046456
formin; actin cytoskeleton; DAAM; drosophila; axon growth; filopodia formation
25.  Chromosomal imbalance letter: Phenotypic consequences of combined deletion 8pter and duplication 15qter 
Exact breakpoint determination by oligonucleotide array-CGH has improved the analysis of genotype-phenotype correlations in cases with chromosome aberrations allowing a more accurate definition of relevant genes, particularly their isolated or combined impact on the phenotype in an unbalanced state. Chromosomal imbalances have been identified as one of the major causes of mental retardation and/or malformation syndromes and they are observed in ~2-5% of the cases. Here we report a female child born to non-consanguineous parents and having multiple congenital anomalies such as atrial septal defect and multiple ventricular septal defects, convergent strabismus, micropthalmia, seizures and mental retardation, with her head circumference and stature normal for her age. Cytogenetic study suggested 46,XX,add(8)(p23). Further analysis by array-CGH using 44K oligonucleotide probe confirmed deletion on 8p23.3p23.1 of 7.1 Mb and duplication involving 15q23q26.3 of 30 Mb size leading to 46,XX,der(8)t(8;15)(p23.3;q23)pat.arr 8p23.3p23.1(191,530-7,303,237)x1,15q23q26.3(72,338,961-102,35,195)x3. The unique phenotypic presentation in our case may have resulted from either loss or gain of a series of contiguous genes which may have resulted in a direct phenotypic effect and/or caused a genetic regulatory disturbance. Double segmental aberrations may have conferred phenotypic variability, as in our case, making it difficult to predict the characteristics that evolved as a result of the global gene imbalance, caused by the concomitant deletion and duplication.
doi:10.1186/1755-8166-6-24
PMCID: PMC3750467  PMID: 23815819
Chromosomal imbalance; 8p23 deletion; 15q23 duplication; IGF1R; GATA4; MCPH1

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