Char syndrome, an inherited disorder with patent ductus arteriosus, maps to chromosome 6p12-p21

Crucial role of TFAP2B in the nervous system for regulating NREM sleep

The AP-2 transcription factors are crucial for regulating sleep in both vertebrate and invertebrate animals. In mice, loss of function of the transcription factor AP-2β (TFAP2B) reduces non-rapid eye movement (NREM) sleep. When and where TFAP2B functions, however, is unclear. Here, we used the Cre-loxP system to generate mice in which Tfap2b was specifically deleted in the nervous system during development and mice in which neuronal Tfap2b was specifically deleted postnatally. Both types of mice exhibited reduced NREM sleep, but the nervous system-specific deletion of Tfap2b resulted in more severe sleep phenotypes accompanied by defective light entrainment of the circadian clock and stereotypic jumping behavior. These findings indicate that TFAP2B in postnatal neurons functions at least partly in sleep regulation and imply that TFAP2B also functions either at earlier stages or in additional cell types within the nervous system.

Human Genetics of Ventricular Septal Defect

Ventricular septal defects (VSDs) are recognized as one of the commonest congenital heart diseases (CHD), accounting for up to 40% of all cardiac malformations, and occur as isolated CHDs as well as together with other cardiac and extracardiac congenital malformations in individual patients and families. The genetic etiology of VSD is complex and extraordinarily heterogeneous. Chromosomal abnormalities such as aneuploidy and structural variations as well as rare point mutations in various genes have been reported to be associated with this cardiac defect. This includes both well-defined syndromes with known genetic cause (e.g., DiGeorge syndrome and Holt-Oram syndrome) and so far undefined syndromic forms characterized by unspecific symptoms. Mutations in genes encoding cardiac transcription factors (e.g., NKX2-5 and GATA4) and signaling molecules (e.g., CFC1) have been most frequently found in VSD cases. Moreover, new high-resolution methods such as comparative genomic hybridization enabled the discovery of a high number of different copy number variations, leading to gain or loss of chromosomal regions often containing multiple genes, in patients with VSD. In this chapter, we will describe the broad genetic heterogeneity observed in VSD patients considering recent advances in this field.

A human embryonic limb cell atlas resolved in space and time

Human limbs emerge during the fourth post-conception week as mesenchymal buds, which develop into fully formed limbs over the subsequent months1. This process is orchestrated by numerous temporally and spatially restricted gene expression programmes, making congenital alterations in phenotype common2. Decades of work with model organisms have defined the fundamental mechanisms underlying vertebrate limb development, but an in-depth characterization of this process in humans has yet to be performed. Here we detail human embryonic limb development across space and time using single-cell and spatial transcriptomics. We demonstrate extensive diversification of cells from a few multipotent progenitors to myriad differentiated cell states, including several novel cell populations. We uncover two waves of human muscle development, each characterized by different cell states regulated by separate gene expression programmes, and identify musculin (MSC) as a key transcriptional repressor maintaining muscle stem cell identity. Through assembly of multiple anatomically continuous spatial transcriptomic samples using VisiumStitcher, we map cells across a sagittal section of a whole fetal hindlimb. We reveal a clear anatomical segregation between genes linked to brachydactyly and polysyndactyly, and uncover transcriptionally and spatially distinct populations of the mesenchyme in the autopod. Finally, we perform single-cell RNA sequencing on mouse embryonic limbs to facilitate cross-species developmental comparison, finding substantial homology between the two species.

KCTD1 and Scalp-Ear-Nipple ('Finlay-Marks') syndrome may be associated with myopia and Thin basement membrane nephropathy through an effect on the collagen IV α3 and α4 chains

INTRODUCTION

Scalp-Ear-Nipple syndrome is caused by pathogenic KCTD1 variants and characterised by a scalp defect, prominent ears, and rudimentary breasts. We describe here further clinical associations in the eye and kidney.

METHODS

Fifteen affected members from two unrelated families with p.(Ala30Glu) or p.(Pro31Leu) in KCTD1 were examined for ocular and renal abnormalities. The relevant proteins were studied in the eye and kidney, and the mutation consequences determined from mouse knockout models.

RESULTS

Five males and 10 females with a median age of 40 years (range 1-70) with pathogenic variants p.(Ala30Glu) (n = 12) or p.(Pro31Leu) (n = 3) in KCTD1 were studied. Of the 6 who underwent detailed ophthalmic examination, 5 (83%) had low myopic astigmatism, the mean spherical equivalent of 10 eyes was 2.38D, and one (17%) had hypermetropic astigmatism. One female had a divergent strabismus.Five individuals had renal cysts (5/15, 33%), with renal biopsy in one demonstrating a thinned glomerular basement membrane identical to that seen in Thin basement membrane nephropathy (AD Alport syndrome).In the eye, KCTD1 and its downstream targets, TFAP2, and the collagen IV α3 and α4 chains localised to the cornea and near the retinal amacrine cells. In the kidney, all these proteins except TFAP2 were expressed in the podocytes and distal tubules. TFAP2B and COL4A4 knockout mice also had kidney cysts, and COL4A3 and COL4A4 knockout mice had myopia.

CONCLUSION

Individuals with a pathogenic KCTD1 variant may have low myopic astigmatism and represent a further rare genetic cause for a thinned glomerular basement membrane.

Focused Strategies for Defining the Genetic Architecture of Congenital Heart Defects

Congenital heart defects (CHD) are malformations present at birth that occur during heart development. Increasing evidence supports a genetic origin of CHD, but in the process important challenges have been identified. This review begins with information about CHD and the importance of detailed phenotyping of study subjects. To facilitate appropriate genetic study design, we review DNA structure, genetic variation in the human genome and tools to identify the genetic variation of interest. Analytic approaches powered for both common and rare variants are assessed. While the ideal outcome of genetic studies is to identify variants that have a causal role, a more realistic goal for genetic analytics is to identify variants in specific genes that influence the occurrence of a phenotype and which provide keys to open biologic doors that inform how the genetic variants modulate heart development. It has never been truer that good genetic studies start with good planning. Continued progress in unraveling the genetic underpinnings of CHD will require multidisciplinary collaboration between geneticists, quantitative scientists, clinicians, and developmental biologists.

Functional Divergence of Mammalian TFAP2a and TFAP2b Transcription Factors for Bidirectional Sleep Control

Sleep is a conserved behavioral state. Invertebrates typically show quiet sleep, whereas in mammals, sleep consists of periods of nonrapid-eye-movement sleep (NREMS) and REM sleep (REMS). We previously found that the transcription factor AP-2 promotes sleep in Caenorhabditiselegans and Drosophila In mammals, several paralogous AP-2 transcription factors exist. Sleep-controlling genes are often conserved. However, little is known about how sleep genes evolved from controlling simpler types of sleep to govern complex mammalian sleep. Here, we studied the roles of Tfap2a and Tfap2b in sleep control in mice. Consistent with our results from C. elegans and Drosophila, the AP-2 transcription factors Tfap2a and Tfap2b also control sleep in mice. Surprisingly, however, the two AP-2 paralogs play contrary roles in sleep control. Tfap2a reduction of function causes stronger delta and theta power in both baseline and homeostasis analysis, thus indicating increased sleep quality, but did not affect sleep quantity. By contrast, Tfap2b reduction of function decreased NREM sleep time specifically during the dark phase, reduced NREMS and REMS power, and caused a weaker response to sleep deprivation. Consistent with the observed signatures of decreased sleep quality, stress resistance and memory were impaired in Tfap2b mutant animals. Also, the circadian period was slightly shortened. Taken together, AP-2 transcription factors control sleep behavior also in mice, but the role of the AP-2 genes functionally diversified to allow for a bidirectional control of sleep quality. Divergence of AP-2 transcription factors might perhaps have supported the evolution of more complex types of sleep.

Genetic Basis of Human Congenital Heart Disease

Congenital heart disease (CHD) is the most common major congenital anomaly with an incidence of ∼1% of live births and is a significant cause of birth defect-related mortality. The genetic mechanisms underlying the development of CHD are complex and remain incompletely understood. Known genetic causes include all classes of genetic variation including chromosomal aneuploidies, copy number variants, and rare and common single-nucleotide variants, which can be either de novo or inherited. Among patients with CHD, ∼8%-12% have a chromosomal abnormality or aneuploidy, between 3% and 25% have a copy number variation, and 3%-5% have a single-gene defect in an established CHD gene with higher likelihood of identifying a genetic cause in patients with nonisolated CHD. These genetic variants disrupt or alter genes that play an important role in normal cardiac development and in some cases have pleiotropic effects on other organs. This work reviews some of the most common genetic causes of CHD as well as what is currently known about the underlying mechanisms.

Genetic variants associated with patent ductus arteriosus in extremely preterm infants

OBJECTIVE

Patent ductus arteriosus (PDA) is a commonly observed condition in preterm infants. Prior studies have suggested a role for genetics in determining spontaneous ductal closure. Using samples from a large neonatal cohort we tested the hypothesis that common genetic variations are associated with PDA in extremely preterm infants.

STUDY DESIGN

Preterm infants (n = 1013) enrolled at NICHD Neonatal Research Network sites were phenotyped for PDA. DNA was genotyped for 1634 single nucleotide polymorphisms (SNPs) from candidate genes. Analyses were adjusted for ancestral eigenvalues and significant epidemiologic variables.

RESULTS

SNPs in several genes were associated with the clinical diagnosis of PDA and with surgical ligation in extremely preterm neonates diagnosed with PDA (p < 0.01). None of the associations were significant after correction for multiple comparisons.

CONCLUSION

We identified several common genetic variants associated with PDA. These findings may inform further studies on genetic risk factors for PDA in preterm infants.

Char Syndrome a novel mutation and new insights: A clinical report

Transcription Factor AP-2 Beta (TFAP2B) functions in the differentiation of neural crest cell derivatives and contributes to the embryogenesis of the ductus arteriosus. Mutations of TFAP2B produces Char syndrome. Char syndrome is an autosomal dominant disorder comprising facial dysmorphism, hand anomalies, and patent ductus arteriosus (PDA). In this report, we describe a proband with a de novo TFAP2B frameshift mutation c.650delG p.(Gly217Alafs*32) in the basic domain. The proband presented mainly with musculoskeletal features of Char syndrome. No PDA was identified at presentation suggesting that this syndrome may prove to be phenotypically heterogeneous. This report will help illustrate the genotype/phenotype correlation of TAFB2 mutations and better delineate the clinical features in Char syndrome.

A study of familial Char syndrome involving the TFAP2B gene with a focus on facial shape characteristics

In this case study, we investigate a child presenting with patent ductus arteriosus, short philtrum, duck-bill lips, strabismus, a flat nasal bridge, a broad forehead, low-set ears, hypertelorism, up-slanting palpebral fissures, almond-shaped eyes, and hypodontia, all leading to the clinical diagnosis of Char syndrome. Genetic analysis showed heterozygosity for the novel variant c.851T>C, p. Leu284Ser in the TFAP2B gene. Family analysis suggested that at least 20 members, extending six generations back, were affected. All 10 members available for genetic testing were heterozygous for the novel pathogenic variant. Qualitative analysis of the facial dysmorphology in the proband and three of the affected family members using three-dimensional surface scanning showed that the major deviations were observed in the forehead/eyebrow, nose, upper lip, and chin regions with, for example, a flattened nose and reduced height of the upper lip and the face. Furthermore, it is suggested that Char syndrome is associated with disturbances of tooth formation and eruption.

Genetics of patent ductus arteriosus susceptibility and treatment

The ductus arteriosus is a vital fetal structure designed to close shortly after birth. Although many physiologic and pharmacologic investigations have characterized the closure of this structure, genetic studies of persistent patency of the ductus arteriosus (patent ductus arteriosus, PDA) are relatively recent. Progress in the identification of specific genes associated with PDA is well behind that of many adult-onset diseases because of several reasons ranging from the lack of large biorepositories for this unique population to the belief that any genetic contribution to PDA is minimal. Viewing the PDA as a complex, developmentally influenced disease with both genetic and environmental risk factors has resulted in initial successes in some genetic studies. We will introduce several genetic approaches, which have been or are currently being applied to the study of PDA, that have been successful in identifying polymorphisms associated with adult diseases. Genetic investigations of PDA will be discussed with respect to heritability, in general, and to specific risk genes. Several animal models that have been used to study PDA-related genes will also be presented. Further advances in discovering genetic variation causing PDA will drive the more rational use of current therapies, and may help identify currently unknown targets for future therapeutic manipulation.

Current Perspectives on Pathobiology of the Ductus Arteriosus

The ductus arteriosus (DA) shunts blood away from the lungs during fetal life, but at birth this shunt is no longer needed and the vessel rapidly constricts. Postnatal persistence of the DA, patent ductus arteriosus (PDA), is predominantly a detrimental condition for preterm infants but is simultaneously a condition required to maintain systemic blood flow for infants born with certain severe congenital heart defects. Although PDA in preterm infants is associated with significant morbidities, there is controversy regarding whether PDA is truly causative. Despite advances in our understanding of the pathobiology of PDA, the optimal treatment strategy for PDA in preterm infants is unclear. Here we review recent studies that have continued to elucidate the fundamental mechanisms of DA development and pathogenesis.

Familial nonsyndromic patent ductus arteriosus caused by mutations in TFAP2B

Patent ductus arteriosus (PDA) is a common congenital heart disease that develops soon after birth when the arterial duct does not remodel. Mutations in TFAP2B, which encodes a neural crest-derived transcription factor, can cause Char syndrome, characterized by PDA, facial dysmorphism, and skeletal abnormalities of the hand. The TFAP2B mutations result in a great amount of phenotypic variability, and a novel TFAP2B mutation has been found in patients with nonsyndromic PDA. Therefore, this study investigated whether TFAP2B mutations can cause familial nonsyndromic PDA. Clinical data and peripheral blood specimens were collected from two kindreds (A and B) and from a cohort of 100 unrelated subjects with PDA. Kindred A spanned three generations, in which 5 of the 16 individuals had PDA, and kindred B spanned three generations, in which 2 of the 13 individuals had PDA. The study enrolled 100 unrelated healthy individuals as control subjects. Polymerase chain reaction (PCR) was used to amplify seven exons and flanking introns of the TFAP2B gene. A few exons of the TFAP2B gene were amplified using reverse transcription polymerase chain reaction (RT-PCR), and direct forward and reverse sequencing of the PCR products was performed. The acquired sequences were aligned with those in GenBank by using a basic local alignment search tool (BLAST). The following two types of mutations were identified in TFAP2B: c.601+5G>A and c.435_438delCCGG. The mutation c.601+5G>A was detected in the affected members of kindred A. Nested PCR showed a splice junction in intron 3 and a 61-bp deletion in exon 3. The mutation c.435_438delCCGG, found in the affected members of kindred B, was caused by a four-base deletion in exon 2, which in turn caused a frame shift that resulted in the formation of a premature stop codon, p.Arg145Argfsx45. None of these mutations was detected in the unaffected members of the kindred or in the control group. Furthermore, two novel single-nucleotide polymorphisms (SNPs), c.1-34G>A and c.539+62G>C, were detected in the introns. The variant c.1-34G>A was identified 34 bp upstream of the transcription initiation site in the TFAP2B gene. Significant differences in the prevalence of the alleles G and A were observed in the control subjects and PDA patients (Z = -2.513, P = 0.012). The study identified that another variant was c.539+62G>C but that the frequency of this variant was similar between the control subjects and the PDA patients (Z = -0.332, P = 0.74). The TFAP2B mutations may be associated with isolated nonsyndromic, hereditary PDA in Chinese families. The authors propose that a TFAP2B mutation should be considered a risk factor for isolated PDA. However, the detailed genetic mechanism underlying nonsyndromic the PDA-causing TFAP2B mutation is yet to be elucidated.

A heart-hand syndrome gene: Tfap2b plays a critical role in the development and remodeling of mouse ductus arteriosus and limb patterning

BACKGROUND

Patent ductus arteriosus (PDA) is one of the most common forms of congenital heart disease. Mutations in transcription factor TFAP2B cause Char syndrome, a human disorder characterized by PDA, facial dysmorphysm and hand anomalies. Animal research data are needed to understand the mechanisms. The aim of our study was to elucidate the pathogenesis of Char syndrome at the molecular level.

METHODOLOGY/PRINCIPAL FINDINGS

Gene expression of Tfap2b during mouse development was studied, and newborns of Tfap2b-deficient mice were examined to identify phenotypes. Gel shift assays had been carried out to search for Tfap2 downstream genes. Promoters of candidate genes were cloned into a reporter construct and used to demonstrate their regulation by Tfap2b in cell transfection. In situ hybridizations showed that the murine transcription factor Tfap2b was expressed during the entire development of mouse ductus arteriosus. Histological examination of ductus arteriosus from Tfap2b knockout mice 6 hours after birth revealed that they were not closed. Consequently, the lungs of Tfap2b(-/-) mice demonstrated progressive congestion of the pulmonary capillaries, which was postulated to result secondarily from PDA. In addition, Tfap2b was expressed in the limb buds, particularly in the posterior limb field during development. Lack of Tfap2b resulted in bilateral postaxial accessory digits. Further study indicated that expressions of bone morphogenetic protein (Bmp) genes, which are reported to be involved in the limb patterning and ductal development, were altered in limb buds of Tfap2b-deficient embryos, due to direct control of Bmp2 and Bmp4 promoter activity by Tfap2b.

CONCLUSIONS/SIGNIFICANCE

Tfap2b plays important roles in the development of mouse ductus arteriosus and limb patterning. Loss of Tfap2b results in altered Bmp expression that may cause the heart-limb defects observed in Tfap2b mouse mutants and Char syndrome patients. The Tfap2b knockout mouse may add to the very limited available animal models of PDA.

Unicuspid aortic valve, hand anomalies: a heart-hand syndrome

Embryonic heart and limb development are closely related with >100 known inherited disorders affecting both. Common limb defects include duplication, deficiencies, and hypoplasia. Ventricular septal defects and atrial septal defects are the commonest associated cardiac conditions. A positive association exists between heart defects and limb disorders when these disorders are analyzed separately. Closer associations exist between heart defects and upper limb defects compared with lower limb defects. The majority of limb defects occur in the more distal parts of the affected limb. Genes expressed in both the heart and limb development include TGF-beta, BMP4, Msx transcription factor, HAND gene, retinoic acid receptor, and sonic hedgehog gene. Radial ray-heart syndromes are better described than ulnar ray-hand syndromes. There is significant variability of malformations. Partial phenocopies that are not genetically linked are well documented. An appreciation of ulnar anomalies should always provoke an evaluation of the heart for potential abnormalities. Although heart-hand syndromes are rare, valvular abnormalities and aortic aneurysms can lead to significant complications unless identified in time. The presence of radial or ulnar ray anomalies merit a detailed cardiac examination and a low threshold for cardiac imaging.

Patent arterial duct

Patent arterial duct (PAD) is a congenital heart abnormality defined as persistent patency in term infants older than three months. Isolated PAD is found in around 1 in 2000 full term infants. A higher prevalence is found in preterm infants, especially those with low birth weight. The female to male ratio is 2:1. Most patients are asymptomatic when the duct is small. With a moderate-to-large duct, a characteristic continuous heart murmur (loudest in the left upper chest or infraclavicular area) is typical. The precordium may be hyperactive and peripheral pulses are bounding with a wide pulse pressure. Tachycardia, exertional dyspnoea, laboured breathing, fatigue or poor growth are common. Large shunts may lead to failure to thrive, recurrent infection of the upper respiratory tract and congestive heart failure. In the majority of cases of PAD there is no identifiable cause. Persistence of the duct is associated with chromosomal aberrations, asphyxia at birth, birth at high altitude and congenital rubella. Occasional cases are associated with specific genetic defects (trisomy 21 and 18, and the Rubinstein-Taybi and CHARGE syndromes). Familial occurrence of PAD is uncommon and the usual mechanism of inheritance is considered to be polygenic with a recurrence risk of 3%. Rare families with isolated PAD have been described in which the mode of inheritance appears to be dominant or recessive. Familial incidence of PAD has also been linked to Char syndrome, familial thoracic aortic aneurysm/dissection associated with patent arterial duct, and familial patent arterial duct and bicuspid aortic valve associated with hand abnormalities. Diagnosis is based on clinical examination and confirmed with transthoracic echocardiography. Assessment of ductal blood flow can be made using colour flow mapping and pulsed wave Doppler. Antenatal diagnosis is not possible, as PAD is a normal structure during antenatal life. Conditions with signs and symptoms of pulmonary overcirculation secondary to a left-to-right shunt must be excluded. Coronary, systemic and pulmonary arteriovenous fistula, peripheral pulmonary stenosis and ventricular septal defect with aortic regurgitation and collateral vessels must be differentiated from PAD on echocardiogram. In preterm infants with symptomatic heart failure secondary to PAD, treatment may be achieved by surgical ligation or with medical therapy blocking prostaglandin synthesis (indomethacin or ibuprofen). Transcatheter closure of the duct is usually indicated in older children. PAD in preterm and low birth weight infants is associated with significant co-morbidity and mortality due to haemodynamic instability. Asymptomatic patients with a small duct have a normal vital prognosis but have a lifetime risk of endocarditis. Patients with moderate-to-large ducts with significant haemodynamic alterations may develop irreversible changes to pulmonary vascularity and pulmonary hypertension.

Determination of genetic predisposition to patent ductus arteriosus in preterm infants

OBJECTIVE

Patent ductus arteriosus is a common morbidity associated with preterm birth. The incidence of patent ductus arteriosus increases with decreasing gestational age to approximately 70% in infants born at 25 weeks' gestation. Our major goal was to determine if genetic risk factors play a role in patent ductus arteriosus seen in preterm infants.

METHODOLOGY

We investigated whether single-nucleotide polymorphisms in genes that regulate smooth muscle contraction, xenobiotic detoxification, inflammation, and other processes are markers for persistent patency of ductus arteriosus. Initially, 377 single-nucleotide polymorphisms from 130 genes of interest were evaluated in DNA samples collected from 204 infants with a gestational age of <32 weeks. A family-based association test was performed on genotyping data to evaluate overtransmission of alleles.

RESULTS

P values of <.01 were detected for genetic variations found in 7 genes. This prompted additional analysis with an additional set of 162 infants, focusing on the 7 markers with initial P values of <.01, and 1 genetic variant in the angiotensin II type I receptor previously shown to be related to patent ductus arteriosus. Of the initial positive signals, single-nucleotide polymorphisms in the transcription factor AP-2 beta and tumor necrosis factor receptor-associated factor 1 genes remained significant. Additional haplotype analysis revealed genetic variations in prostacyclin synthase to be associated with patent ductus arteriosus. An angiotensin II type I receptor polymorphism previously reported to be associated with patent ductus arteriosus after prophylactic indomethacin administration was not associated with the presence of a patent ductus arteriosus in our population.

CONCLUSIONS

Overall, our data support a role for genetic variations in transcription factor AP-2 beta, tumor necrosis factor receptor-associated factor 1, and prostacyclin synthase in the persistent patency of the ductus arteriosus seen in preterm infants.

Transcription factors and congenital heart defects

Although there have been important advances in diagnostic modalities and therapeutic strategies for congenital heart defects (CHD), these malformations still lead to significant morbidity and mortality in the human population. Over the past 10 years, characterization of the genetic causes of CHD has begun to elucidate some of the molecular causes of these defects. Linkage analysis and candidate-gene approaches have been used to identify gene mutations that are associated with both familial and sporadic cases of CHD. Complementation of the human studies with developmental studies in mouse models provides information for the roles of these genes in normal development as well as indications for disease pathogenesis. Biochemical analysis of these gene mutations has provided further insight into the molecular effects of these genetic mutations. Here we review genetic, developmental, and biochemical studies of six cardiac transcription factors that have been identified as genetic causes for CHD in humans.

The transcription factor AP-2beta causes cell enlargement and insulin resistance in 3T3-L1 adipocytes

We have reported the association of variations in the activating protein-2beta (AP-2beta) transcription factor gene with type 2 diabetes. This gene was preferentially expressed in 3T3-L1 adipocytes in a differentiation stage-dependent manner, and preliminary experiments showed that subjects with the disease-susceptible allele showed stronger expression in adipose tissue than those without the susceptible allele. Thus, we overexpressed the AP-2beta gene in 3T3-L1 adipocytes to clarify whether AP-2beta might play a crucial role in the pathogenesis of type 2 diabetes through dysregulation of adipocyte function. In cells overexpressing AP-2beta, cells increased in size by accumulation of triglycerides accompanied by enhanced glucose uptake. On the contrary, suppression of AP-2beta expression by small interfering RNA inhibited glucose uptake. Enhancement of glucose uptake by AP-2beta overexpression was attenuated by inhibitors of phospholipase C (PLC) and atypical protein kinase Czeta/lambda (PKCzeta/lambda), but not by a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Consistently, we found activation of PLC and atypical PKC, but not PI3-K, by AP-2beta expression. Furthermore, overexpression of PLCgamma enhanced glucose uptake, and this activation was inhibited by an atypical PKC inhibitor, suggesting that the enhanced glucose uptake may be mediated through PLC and atypical PKCzeta/lambda, but not PI3-K. Moreover, we observed the increased tyrosine phosphorylation of Grb2-associated binder-1 (Gab1) and its association with PLCgamma, indicating that Gab1 may be involved in AP-2beta-induced PLCgamma activation. Finally, AP-2beta overexpression was found to relate to the impaired insulin signaling. We propose that AP-2beta is a candidate gene for producing adipocyte hypertrophy and may relate to the abnormal characteristics of adipocytes observed in obesity.

A case of long QT syndrome associated with familial occurrence of persistent patency of the arterial duct

We describe an occurrence of long QT syndrome in association with persistent patency of the arterial duct in members of a family. Patency of the arterial duct was diagnosed in family members of 4 successive generations. The index case had long QT syndrome associated with such a patent duct. Another patient had long QT syndrome, but associated with a ventricular septal defect. We postulate that there may be a common genetic mechanism for long QT syndrome and persistent patency of the arterial duct.

Syndromic patent ductus arteriosus: evidence for haploinsufficient TFAP2B mutations and identification of a linked sleep disorder

Patent ductus arteriosus (PDA) is a common congenital heart disease that results when the ductus arteriosus, a muscular artery, fails to remodel and close after birth. A syndromic form of this disorder, Char syndrome, is caused by mutation in TFAP2B, the gene encoding a neural crest-derived transcription factor. Established features of the syndrome are PDA, facial dysmorphology, and fifth-finger clinodactyly. Disease-causing mutations are missense and are proposed to be dominant negative. Because only a small number of families have been reported, there is limited information on the spectrum of mutations and resulting phenotypes. We report the characterization of two kindreds (K144 and K145) with Char syndrome containing 22 and 5 affected members, respectively. Genotyping revealed linkage to TFAP2B in both families. Sequencing of TFAP2B demonstrated mutations in both kindreds that were not found among control chromosomes. Both mutations altered highly conserved bases in introns required for normal splicing as demonstrated by biochemical studies in mammalian cells. The abnormal splicing results in mRNAs containing frameshift mutations that are expected to be degraded by nonsense-mediated mRNA decay, resulting in haploinsufficiency; even if produced, the protein in K144 would lack DNA binding and dimerization motifs and would likely result in haploinsufficiency. Examination of these two kindreds for phenotypes that segregate with TFAP2B mutations identified several phenotypes not previously linked to Char syndrome. These include parasomnia and dental and occipital-bone abnormalities. The striking sleep disorder in these kindreds implicates TFAP2B-dependent functions in the normal regulation of sleep.

Identification and embryonic expression of a new AP-2 transcription factor, AP-2 epsilon

AP-2 proteins comprise a family of highly related transcription factors, which are expressed during mouse embryogenesis in a variety of ectodermal, neuroectodermal, and mesenchymal tissues. AP-2 transcription factors were shown to be involved in morphogenesis of craniofacial, urogenital, neural crest-derived, and placental tissues. By means of a partial cDNA fragment identified during an expressed sequence tag search for AP-2 genes, we identified a fifth, previously unknown AP-2-related gene, AP-2 epsilon. AP-2 epsilon encodes an open reading frame of 434 amino acids, which reveals the typical modular structure of AP-2 transcription factors with highly conserved C-terminal DNA binding and dimerization domains. Although the N-terminally localized activation domain is less homologous, position and identity of amino acids essential for transcriptional transactivation are conserved. Reverse transcriptase-polymerase chain reaction analyses of murine embryos revealed AP-2 epsilon expression from gestational stage embryonic day 7.5 throughout all later embryonic stages until birth. Whole-mount in situ hybridization using a specific AP-2 epsilon cDNA fragment demonstrated that during embryogenesis, expression of AP-2 epsilon is mainly restricted to neural tissue, especially the midbrain, hindbrain, and olfactory bulb. This expression pattern was confirmed by immunohistochemistry with an AP-2 epsilon-specific antiserum. By using this antiserum, we could further localize AP-2 epsilon expression in a hypothalamic nucleus and the neuroepithelium of the vomeronasal organ, suggesting an important function of AP-2 epsilon for the development of the olfactory system.

Novel TFAP2B mutations that cause Char syndrome provide a genotype-phenotype correlation

To elucidate further the role, in normal development and in disease pathogenesis, of TFAP2B, a transcription factor expressed in neuroectoderm, we studied eight patients with Char syndrome and their families. Four novel mutations were identified, three residing in the basic domain, which is responsible for DNA binding, and a fourth affecting a conserved PY motif in the transactivation domain. Functional analyses of the four mutants disclosed that two, R225C and R225S, failed to bind target sequence in vitro and that all four had dominant negative effects when expressed in eukaryotic cells. Our present findings, combined with data about two previously identified TFAP2B mutations, show that dominant negative effects consistently appear to be involved in the etiology of Char syndrome. Affected individuals in the family with the PY motif mutation, P62R, had a high prevalence of patent ductus arteriosus but had only mild abnormalities of facial features and no apparent hand anomalies, a phenotype different from that associated with the five basic domain mutations. This genotype-phenotype correlation supports the existence of TFAP2 coactivators that have tissue specificity and are important for ductal development but less critical for craniofacial and limb development.

Molecular determinants of atrial and ventricular septal defects and patent ductus arteriosus

Septation defects and patent ductus arteriosus are the most common human cardiovascular malformations (CVMs). Genetic factors play a major part in the origin of these malformations. Recent molecular analyses have shed light on several mendelian forms. In the autosomal dominant Holt-Oram syndrome, both atrial and ventricular septal defects are inherited in association with limb deformity as a result of mutations in the gene encoding the TBX5 transcription factor. Mutations in the NKX2.5 transcription factor gene cause autosomal dominant familial atrial septal defects in association with progressive atrioventricular block as well as complex congenital heart disease. Common atrial syndromes in autosomal dominant Ellis-van Creveld syndrome arise in the context of axial skeletal and limb malformation as a result of mutations in the EVC gene, whose function is unknown. Patent ductus arteriosus occurs in several syndromic forms of congenital heart disease, including Holt-Oram syndrome. Recent analyses of autosomal dominant Char syndrome, which includes, with variable penetrance, patent ductus arteriosus as well as craniofacial and hand malformations, have shown that the syndrome is caused by mutations in the TFAP2B transcription factor gene. Ongoing analyses are poised to determine the contribution of these genes as well as others yet to be identified to common, sporadic forms of congenital heart disease.

Genetic basis of syndromes associated with congenital heart disease

Numerous syndromes affecting patients have phenotypes that include congenital heart defects (CHDs). These disorders have fascinated physicians for many years, raising questions about how seemingly disparate aspects of human development can be perturbed together in striking, but consistent, ways. Paralleling the major advances in human genetics during recent decades, we have come to understand that some of these syndromes arise from gross defects in chromosomal number, some from subtler alterations in genomic regions, and still others from point mutations in specific genes. These disorders, largely mendelian in nature, have provided researchers with the wherewithal to discover disease genes underlying CHD. Although some of these medical conditions are relatively rare, their solution has often provided insights that could be applied toward understanding the basis of nonsyndromic CHD. In this review, recent progress toward uncovering the molecular basis of several forms of syndromic CHD is discussed.

Aortic dissection and patent ductus arteriosus in three generations

Aortic dissection was found in a woman, her 2 sons, and 1 of her 3 daughters, and the 3 affected children and a granddaughter had patent ductus arteriosus. The pattern of inheritance of this unique syndrome probably is an autosomal dominant one.

Analysis of the structure and expression pattern of MRP7 (ABCC10), a new member of the MRP subfamily

The MRP subfamily of ABC transporters currently consists of at least six members, several of which have been demonstrated to transport amphipathic anions and to confer in vitro resistance to chemotherapeutic agents. In searching the data bases we identified the product of a cDNA sequencing project that bears significant similarity to MRP subfamily transporters. In this report the predicted coding sequence, protein product and expression pattern of this cDNA, termed MRP7, are analyzed. The MRP7 cDNA sequence encodes a 1492 amino acid ABC transporter whose structural architecture resembles that of MRP1, MRP2, MRP3, and MRP6, in that its transmembrane helices are arranged in three membrane spanning domains. However, in contrast to the latter transporters, a conserved N-linked glycosylation site is not found at the N-terminus of MRP7. Comparisons of the MRP7 amino acid sequence indicated that while it is most closely related to other MRP subfamily members, its degree of relatedness is the lowest of any of the known MRP-related transporters. The integrity of the predicted MRP7 coding sequence was confirmed by the synthesis of an approximately 158 kDa protein in reticulocyte lysates programmed with the MRP7 cDNA. While MRP7 transcript was detected in a variety of tissues by RT/PCR, it was not readily detectable by RNA blot analysis, suggesting that it is expressed at low levels in these tissues. Fluorescence in situ hybridization indicated that MRP7 maps to chromosome 6p12-21, in proximity to several genes associated with glutathione conjugation and synthesis. On the basis of these findings and evolutionary cluster analysis, we conclude that MRP7 is a member of the MRP subfamily of amphipathic anion transporters.

Regulatory roles of AP-2 transcription factors in vertebrate development, apoptosis and cell-cycle control

AP-2 transcription factors represent a family of three closely related and evolutionarily conserved sequence-specific DNA-binding proteins, AP-2alpha, -beta and -gamma. Subsequent studies have identified spatially and temporally regulated embryonic expression patterns in a number of different tissues including neural crest derivatives, neural, epidermal and urogenital tissues. Here, we review the current understanding of developmental defects in AP-2-deficient mice and consider regulatory functions of AP-2 in control of apoptosis, cell cycle, and gene expression. Recently, the first inherited human disorder, Char syndrome, was identified to be caused by AP-2beta missense mutations. In light of the manifold and essential functions of AP-2 proteins in cell growth, differentiation and programmed death, mutations or changes in precisely programmed expression patterns are likely to contribute to other congenital malformations or neoplastic diseases.

Char syndrome: an additional family with polythelia, a new finding

This report describes a father and daughter with Char syndrome, a rare autosomal dominant disorder. Both affected individuals had typical face, strabismus, and foot anomalies. The girl also had a patent ductus arteriosus. In addition, both patients had polythelia (supernumerary nipples), a finding not described before in the Char syndrome.

Mutations in TFAP2B cause Char syndrome, a familial form of patent ductus arteriosus

Char syndrome is an autosomal dominant trait characterized by patent ductus arteriosus, facial dysmorphism and hand anomalies. Using a positional candidacy strategy, we mapped TFAP2B, encoding a transcription factor expressed in neural crest cells, to the Char syndrome critical region and identified missense mutations altering conserved residues in two affected families. Mutant TFAP2B proteins dimerized properly in vitro, but showed abnormal binding to TFAP2 target sequence. Dimerization of both mutants with normal TFAP2B adversely affected transactivation, demonstrating a dominant-negative mechanism. Our work shows that TFAP2B has a role in ductal, facial and limb development and suggests that Char syndrome results from derangement of neural-crest-cell derivatives.

Familial patent ductus arteriosus and bicuspid aortic valve with hand anomalies: a novel heart-hand syndrome

The association between cardiac and limb defects, particularly those affecting the hand, has been well documented by the delineation of several heart-hand syndromes. Based on observations with a three-generation family with seven affected individuals, we describe a novel heart-hand syndrome comprising patent ductus arteriosus, bicuspid aortic valve, 5th metacarpal hypoplasia, and brachydactyly. The inheritance pattern was consistent with autosomal dominance, although X-linked dominance could not be excluded. Penetrance appeared to be complete, but there was variability of the cardiac and hand phenotypes. Because this new syndrome closely resembled Char syndrome (patent ductus arteriosus, 5th finger middle phalangeal hypoplasia, and minor facial anomalies), multipoint linkage analysis was performed using polymorphic DNA markers spanning the recently identified Char syndrome critical region at chromosomal bands 6p12-p21.1. This analysis formally excluded this 3-cM region, documenting that the two traits are not allelic. In sum, a novel heart-hand syndrome involving left ventricular outflow and aortic arch as well as an ulnar ray derivative has been identified. Because the hand anomalies can be subtle, thorough evaluation is suggested for families inheriting these cardiac defects as a mendelian trait.

Advances in the molecular genetics of congenital structural heart disease

Molecular genetic analyses have generated significant advances in our understanding of congenital heart disease. Techniques of genetic mapping with polymorphic microsatellites and fluorescence in situ hybridization (FISH) have provided informative tools for localization and identification of disease genes. Some cardiovascular diseases have proven to result from single gene defects. Others relate to more complex etiologies involving several genes and their interactions. Elucidation of the molecular genetic etiologies of congenital heart disease prompts consideration of DNA testing for cardiac disorders. Future integration of these diagnostic modalities with improved treatments may ultimately decrease morbidity and mortality from congenital heart diseases.