Mutations In NKX2 Research Articles

Genetic study of TSHR, PAX8 and NKX2-5 genes in Tunisian patients with congenital hypothyroidism

Introduction Thyroid dysgenesis is reported to be associated to mutations in TSHR, PAX8 and NKX2-5 genes. In fact, mutation in TSHR gene is responsible for non-syndromic thyroid dysgenesis while mutations in PAX8 and NKX2-5 generate thyroid dysgenesis, which could be associated to renal abnormality and congenital heart disease respectively. Patients and methods The aim of the current study is to present the clinical features of eleven Tunisian patients with congenital hypothyroidism and thyroid dysgenesis, and to search for mutations or variants in TSHR, PAX8 and NKX2-5 genes. The clinical, molecular and bioinformatics investigation were performed in the eleven recruited patients. Results According to clinical data, eight patients were diagnosed with non-syndromic thyroid dysgenesis and three Tunisian patients with syndromic thyroid dysgenesis. The mutational analyses of the three candidate genes showed only known polymorphisms and we noticed that polymorphisms in PAX8 and NKX2-5 genes are especially associated with syndromic thyroid dysgenesis in our patients. Bioinformatic tools showed the putative impact of the identified polymorphisms on ESE elements and on mRNA structure. Conclusions The obtained results are suggestive of potential effects of the described polymorphisms on thyroid dysgenesis in our studied patients and are highlighted the utility of the bioinformatics tools.

Chorea in children: etiology, diagnostic approach and management.

Chorea is defined by the presence of abnormal, involuntary, continuous, random movements that results from a number of autoimmune, hereditary, vascular, metabolic, drug-induced and functional (psychogenic) causes. Chorea may present at all stages of life, from newborns to elderly individuals. While Huntington disease is the main suspicion in adults presenting with chorea, once a drug-induced or parkinsonian dyskinesia have been ruled out; Huntington disease exceptionally presents with chorea in children. Sydenham chorea is considered the most common cause of acute childhood-onset chorea, but its prevalence has decreased in Western countries. However, in younger children other etiologies such as dyskinetic cerebral palsy, anti-NMDAR receptor encephalitis, other autoimmune conditions, or mutations in NKX2-1, ADCY-5, FOXG1, GNAO1, GPR88, SLC2A1, SQSTM1, ATP8A2, or SYT-1 should be considered. In this manuscript, we review the main causes, diagnosis and management of chorea in children.

Levodopa-Responsive Chorea: A Review.

Background:Chorea is one of the disabling movement disorders, and the number of drugs which can treat this disorder effectively is limited. Tetrabenazine and deutetrabenazine are the two drugs approved by the US-FDA for the treatment of chorea associated with HD. Levodopa can improve chorea in some disorders, and this review aims to provide information on the use of levodopa in chorea.Methods:A literature search was performed in February 2019 using the following terms “levodopa chorea,” “levodopa TITF-1,” levodopa brain-lung-thyroid syndrome,” and “levodopa Huntington's Disease.” The information regarding the etiology, outcome, and dose of levodopa was collected.Results:We found a total of 18 cases in the literature where the benefit was reported with levodopa. Majority of the cases were brain-thyroid-lung (BTL) syndrome (50%). Another 5 cases were HD (Huntington's Disease), one with PCH type 2 (Pontocerebellar hypoplasia type 2), one with meningovascular syphilis, and two patients with Sydenham chorea. The patients with BTL syndrome responded to a very low dose of levodopa.Discussion:This review suggests that levodopa has the potential to improve chorea in BTL syndrome while its use in chorea due to other disorders requires further study. BTL syndrome due to NKX2-1 mutation responded to levodopa while we did not find any case of chorea due to ADCY-5 mutation responding to levodopa.

Analysis of NKX2-5 in 439 Chinese Patients with Sporadic Atrial Septal Defect.

BackgroundThe NKX2 gene family is made up of core transcription factors that are involved in the morphogenesis of the vertebrate heart. NKx2-5 plays a pivotal role in mouse cardiogenesis, and mutations in NKx2-5 result in an abnormal structure and function of the heart, including atrial septal defect and cardiac electrophysiological abnormalities.Material/MethodsTo investigate the genetic variation of NKX2-5 in Chinese patients with sporadic atrial septal defect, we sequenced the full length of the NKX2-5 gene in the participants of the study. Four hundred thirty-nine patients and 567 healthy unrelated individuals were recruited. Genomic DNA was extracted from the peripheral blood leukocytes of the participants. DNA samples from the participants were amplified by multiplex PCR and sequenced on an Illumina HiSeq platform. Variations were detected by comparison with a standard reference genome and annotation with a variant effect predictor.ResultsThirty variations were detected in Chinese patients with sporadic atrial septal defect, and 6 single nucleotide polymorphisms (SNPs) had a frequency greater than 1%. Among the 30 variations, the SNPs rs2277923 and rs3729753 were extremely prominent, with a high frequency and odds ratio in patients.ConclusionsSingle nucleotide variations are the prominent genetic variations of NKX2-5 in Chinese patients with sporadic atrial septal defect. The SNPs rs2277923 and rs3729753 are prominent single nucleotide variations (SNVs) in Chinese patients with sporadic atrial septal defect.

High-resolution computed tomography findings of thyroid transcription factor 1 deficiency (NKX2-1 mutations).

The expression of the NKX2-1 gene and its encoded protein, thyroid transcription factor 1 (TTF-1), plays a role in pulmonary surfactant homeostasis and lung development. NKX2-1 mutations have been associated with neonatal respiratory distress, hypotonia, choreoathetosis and congenital hypothyroidism. These clinical findings have been coined brain-lung-thyroid syndrome, although not all three organs are always involved. While many of these children develop interstitial lung disease, no systematic review of chest high-resolution CT (HRCT) findings has been reported. To summarize the clinical presentations, pathology and HRCT imaging findings of children with NKX2-1 mutations. We identified six children with NKX2-1 mutations, deletions or duplications confirmed via genetic testing at our institution. Three pediatric radiologists reviewed the children's HRCT imaging findings and ranked the dominant findings in order of prevalence via consensus. We then correlated the imaging findings with histopathology and clinical course. All children in the study were heterozygous for NKX2-1 mutations, deletions or duplications. Ground-glass opacities were the most common imaging feature, present in all but one child. Consolidation was also a prevalent finding in 4/6 of the children. Architectural distortion was less common. HRCT findings of TTF-1 deficiency are heterogeneous and evolve over time. There is significant overlap between the HRCT findings of TTF-1 deficiency, other surfactant dysfunction mutations, and pulmonary interstitial glycogenosis. TTF-1 deficiency should be considered in term infants presenting with interstitial lung disease, especially if hypotonia or hypothyroidism is present.

A comprehensive in silico analysis, distribution and frequency of human Nkx2-5 mutations; A critical gene in congenital heart disease.

Introduction: Congenital heart disease (CHD) affects 1% to 2 % of live births. The Nkx2-5 gene, is known as the significant heart marker during embryonic evolution and it is also necessary for the survival of cardiomyocytes and homeostasis in adulthood. In this study, Nkx2-5 mutations are investigated to identify the frequency, distribution, functional consequences of mutations by using computational tools. Methods: A complete literature search was conducted to find Nkx2-5 mutations using the following key words: Nkx2-5 and/or CHD and mutations. The mutations were in silico analyzed using tools which predict the pathogenicity of the variants. A picture of Nkx2-5 protein and functional or structural effects of its variants were also figured using I-TASSER and STRING. Results: A total number of 105 mutations from 18 countries were introduced. The most (24.1%) and the least (1.49%) frequency of Nkx2-5 mutations were observed in Europe and Africa, respectively. The c.73C>T and c.533C>T mutations are distributed worldwide. c.325G>T (62.5%) and c.896A>G (52.9%) had the most frequency. The most numbers of Nkx2-5 mutations were reported from Germany. The c.541C>T had the highest CADD score (Phred score = 38) and the least was for c.380C>A (Phred score=0.002). 41.9% of mutations were predicted as potentially pathogenic by all prediction tools. Conclusion: This is the first report of the Nkx2-5 mutations evaluation in the worldwide. Given that the high frequency of mutation in Germany, and also some mutations were seen only in this country, therefore, presumably the main origin of Nkx2-5 mutations arise from Germany.

A Not So Benign Family Pedigree With Hereditary Chorea: A Broader Phenotypic Expression or Additional Picture?

NKX2-1 mutations have been usually associated with a non-progressive neurological disease. Recent reports revealed a vast variability regarding its clinical expressivity. Aim of this work was widening the Benign Hereditary Chorea neurological, cognitive and behavioral phenotype through the description of a child and her family pedigree. Molecular analysis focused on NKX2-1 gene revealed a novel frameshift mutation in the three-generation members described. Cognitive scales detected a relevant developmental delay, and the clinical observation and Autism Diagnostic Observation Schedule -2 administration allowed the diagnosis of autism spectrum disorder in the proband. Microarray testing, further executed to exclude a double hit contextually provoking the complex neurodevelopmental disorder, revealed the 22q11.2 Duplication Syndrome. This paper may contribute to enlarge Benign Hereditary Chorea variable expressivity and, together with other studies reported in the literature, underlines the need to reconsider the term “benign,” verifying the opportunity of more a complex diagnosis.

Is Benign Hereditary Chorea Really Benign? Brain-Lung-Thyroid Syndrome Caused by NKX2-1 Mutations.

Since its localization to the NKX2-1 gene in 2002, the phenotype of the disorder historically called "benign hereditary chorea" has been expanding beyond chorea. The phenomenology of movement disorders and other symptomatology associated with mutations in NKX2-1 were characterized after a detailed evaluation of consecutive patients evaluated in our clinic over the past 3 years. We studied 5 patients (3 females), ages 2 to 31 years, with confirmed pathogenic variants in NKX2-1. All patients exhibited chorea, gross motor delay, and gait impairment. Other symptoms included neonatal respiratory failure (n = 4), cognitive deficits (n = 3), hypothyroidism (n = 4), joint laxity (n = 2), myoclonus (n = 1), hypotonia (n = 3), and seizures (n = 1). Chorea often proved refractory to medical therapies. The phenotype associated with pathogenic variants in NKX2-1 frequently includes disabling and often medically refractory neurological and non-neurological abnormalities. We therefore suggest that the term benign hereditary chorea be abandoned in favor of its genetic designation as NKX2-1-related disorder.

Restless Legs Syndrome in NKX2-1-related chorea: An expansion of the disease spectrum

BackgroundMolecular technologies are expanding our knowledge about genetic variability underlying early-onset non-progressive choreic syndromes. Focusing on NKX2-1-related chorea, the clinical phenotype and sleep related disorders have been only partially characterized. MethodsWe propose a retrospective and longitudinal observational study in 7 patients with non-progressive chorea due to NKX2-1 mutations. In all subjects sleep and awake EEG, brain MRI with study of pituitary gland, chest X-rays, endocrinological investigations were performed. Movement disorders, pattern of sleep and related disorders were investigated using structured clinical evaluation and several validated questionnaires. ResultsIn patients carrying NKX2-1 mutations, chorea was mainly distributed in the upper limbs and tended to improve with age. All patients presented clinical or subclinical hypothyroidism and delayed motor milestones. Three subjects had symptoms consistent with Restless Legs Syndrome (RLS) that improved with Levodopa. ConclusionsPatients with NKX2-1 gene mutations should be investigated for RLS, which, similarly to chorea, can sometimes be ameliorated by Levodopa.

Advances in the study of susceptible genes related to tetralogy of Fallot

Congenital heart disease(CHD) is a class of cardiovascular malformation caused by abnormal development of cardiovascular system, developmental disorders, or degenerative tissue which should be degenerated after birth during embryonic development, and tetralogy of Fallot is one of the most serious types of CHD, including ventricular septal defect (VSD), overriding aorta (OA), pulmonic stenosis (PS) and right ventricular hypertrophy (RVH). Up to now, a series of clinical evidence shows that genetic factors have been involved in the occurrence of TOF, and some gene mutations are associated with the occurrence of TOF, of which NKX2-5, GATA4, TBX5 and TBX20 have been confirmed to be highly correlated with TOF.Based on the existing research results, this paper expounds the relationship between etiology and pathogenesis of tetralogy of Fallot and the mutations of NKX2-5, GATA4, TBX5 and TBX20. Key words: Congenital heart disease; tetralogy of Fallot; Susceptibility gene

Search of Somatic Mutations of NKX2-5 and GATA4 Genes in Chinese Patients with Sporadic Congenital Heart Disease.

Congenital heart disease (CHD) usually occurs sporadically, with only a minority of cases associated with a known genetic mechanism. Cardiac-specific transcription factors NKX2-5 and GATA4 play key roles in the mammalian heart development, and the affected cardiac tissues of CHD patients are prone to somatic mutations which thus participate in the pathogenesis of CHD. We collected 98 patients with sporadic CHD, extracted genomic DNA from cardiac tissues and blood, and then screened NKX2-5 and GATA4 genes using PCR-direct sequence analysis. A novel heterozygous missense mutation (c.907G>A, p.V303I) of NKX2-5 gene was identified in a patient with tetralogy of Fallots. Functional assay revealed that this mutant was associated with significantly reduced transcriptional activity. In addition, we found two known single-nucleotide polymorphisms (SNPs) (rs2277923, rs3729753) in NKX2-5 and two known SNPs (rs56166237, rs3729856) in GATA4. All variations identified in cardiac tissues were consistent with those of peripheral blood, and no somatic mutations were found in cardiac tissues. Our study shows no evidence of NKX2-5 and GATA4 somatic mutations playing a role in the pathogenesis of sporadic CHD.

Mutations in the thyroid transcription factor gene NKX2-1 result in decreased expression of SFTPB and SFTPC

Mutations in the NK2 homeobox 1 (NKX2-1) gene are associated with lung disease in infants and children. We hypothesize that disruption of normal surfactant gene expression with these mutations contributes to the respiratory phenotypes observed. To assess transactivational activity, cotransfection of luciferase reporter vectors containing surfactant protein B or C (SFTPB or SFTPC) promoters with NKX2-1 plasmids was performed and luciferase activity was measured. To assess the binding of mutated proteins to target DNA, electrophoretic mobility shift assays (EMSA) were performed using nuclear protein labeled with oligonucleotide probes representing NKX2-1 consensus binding sequences followed by gel electrophoresis. The effect of overexpression of wild-type (WT) and mutant NKX2-1 on SFTPB and SFTPC was evaluated with quantitative real-time PCR. Decreased transactivation of the SFTPB promoter by both mutants and decreased transactivation of the SFTPC promoter by the L197P mutation was observed. EMSA demonstrated decreased DNA binding of both mutations to NKX2-1 consensus binding sequences. Transfection of A549 cells with NKX2-1 expression vectors demonstrated decreased stimulation of SFTPB and SFTPC expression by mutant proteins compared with that of WT. Disruption of transcriptional activation of surfactant protein genes by these DNA-binding domain mutations is a plausible biological mechanism for disruption of surfactant function and subsequent respiratory distress.

Temporal requirement of Nkx2-5 during cardiac conduction system development

During cardiac development, transient invaginations of the myocardium, termed trabeculae, appear at the inner surface of the ventricles, which disappeared by compaction to form a functional ventricular wall. Trabeculae also contain progenitor cells of the ventricular conduction system (VCS), a complex network of Purkinje fibers driving the rapid propagation of electrical activity in the ventricles. Defects in ventricular compaction and conduction have been observed in patients and mutant mice carrying mutations in NKX2-5, encoding a key transcriptional regulator of heart development. In order to analyze the link between trabecular fate and VCS differentiation, we carried out genetic tracing and prospective clonal analyses of trabeculae using Cx40-CreERT2 mice and Rosa26-Confetti mice. Our results show that the peripheral VCS segregates progressively during embryonic development. Cells exclusively fated to give rise to the VCS are present in the trabecular compartment as early as E9.5. Specification of new conductive myocytes within the trabecular compartment during subsequent development contributes to the formation of a complex Purkinje fiber network at birth. We performed the same lineage tracing experiments in Nkx2-5 heterozygous mice with severe hypoplasia of the Purkinje fiber network at adult stages. The number of Purkinje fibers originating from early Nkx2-5 hapolinsufficient progenitors is identical to control. In contrast, at later stages of development, we observed an increase in the number of trabecular cells that do not give rise to Purkinje fibers. This suggests that Nkx2-5 controls the progressive recruitment of trabecular cells into the VCS as well as the later maintenance of the conductive phenotype. Overall our study highlights the early segregation of the VCS lineage at the onset of trabeculation and the later role of Nkx2-5 in formation of the Purkinje fiber network.

His-Purkinje system defects induced by Nkx2-5 deletion leads to progressive conduction defects and heart failure

The synchronization of heartbeats is triggered by electric impulses delivered by specialized cardiomyocytes of the conduction system. In the ventricles, the His-Purkinje system mediates rapid propagation of electrical activity such that contractions propagate from the apex to the base of the heart to increase the efficiency of blood expulsion to the great arteries. Human heterozygous mutations of NKX2-5 are associated with a large spectrum of congenital heart diseases and atrioventricular conduction block. In agreement with these observations, mouse genetics has revealed the complexity of the role of Nkx2-5 during cardiac development. Germline deletion of Nkx2-5 results in cardiac lethality at early stages, while Nkx2-5± embryos and mice appear normal and reproduce the phenotype observed in patients, including atrial septal defects and conduction disturbances. These mice display ventricular conduction defects that can be correlated with hypoplastic development of the His-Purkinje system. To further decipher the role of this transcription factor in the conduction system, we conditionally inactivated Nkx2-5 in the His-Purkinje system using a Cx40-CreERT2 mouse line. Postnatal deletion of Nkx2-5 in the His-Purkinje system induced a progressive loss of expression of conduction markers and hypoplasia of the Purkinje fiber network. These mice develop conduction defects with enlarged QRS intervals and left bundle branch block. Long-term follow-up of cardiac function recorded by MRI and echocardiography shows a progressive reduction of ejection fraction correlated with strain defects. These results highlight the importance of Nkx2-5-dependent maintenance of the His-Purkinje system in preserving cardiac function.

Molecular Analysis of Congenital Hypothyroidism in Saudi Arabia: SLC26A7 Mutation Is a Novel Defect in Thyroid Dyshormonogenesis.

Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder, affecting one in 3000 to 4000 newborns. Since the introduction of a newborn screening program in 1988, more than 300 cases have been identified. The underlying genetic defects have not been systematically studied. To identify the mutation spectrum of CH-causing genes. Fifty-five patients from 47 families were studied by next-generation exome sequencing. Mutations were identified in 52.7% of patients (29 of 55) in the following 11 genes: TG, TPO, DUOX2, SLC26A4, SLC26A7, TSHB, TSHR, NKX2-1, PAX8, CDCA8, and HOXB3. Among 30 patients with thyroid dyshormonogenesis, biallelic TG mutations were found in 12 patients (40%), followed by biallelic mutations in TPO (6.7%), SLC26A7 (6.7%), and DUOX2 (3.3%). Monoallelic SLC26A4 mutations were found in two patients, one of them coexisting with two tandem biallelic deletions in SLC26A7. In 25 patients with thyroid dysgenesis, biallelic mutations in TSHR were found in six patients (24%). Biallelic mutations in TSHB, PAX 8, NKX2-1, or HOXB3 were found once in four different patients. A monoallelic CDCA8 mutation was found in one patient. Most mutations were novel, including three TG, two TSHR, and one each in DUOX2, TPO, SLC26A7, TSHB, NKX2-1, PAX8, CDCA8, and HOXB3. SLC26A7 and HOXB3 were novel genes associated with thyroid dyshormonogenesis and dysgenesis, respectively. TG and TSHR mutations are the most common genetic defects in Saudi patients with CH. The prevalence of other disease-causing mutations is low, reflecting the consanguineous nature of the population. SLC26A7 mutations appear to be associated with thyroid dyshormonogenesis.

In Vitro Modeling of Congenital Heart Defects Associated with an NKX2-5 Mutation Revealed a Dysregulation in BMP/Notch-Mediated Signaling.

The Nkx2-5 gene codes for a transcription factor that plays a critical role in heart development. Heterozygous mutations in NKX2-5 in both human and mice result in congenital heart defects (CHDs). However, the molecular mechanisms by which these mutations cause the disease are still unknown. Recently, we have generated the heterozygous mouse model of the human CHDs associated mutation NKX2-5 R142C (Nkx2-5R141C/+ mouse ortholog of human NKX2-5 R142C variant) that developed septal and conduction defects. This study generated a heterozygous Nkx2-5 R141C mouse embryonic stem cell line (Nkx2-5R141C/+ mESCs) to model CHDs in vitro. We observed that Nkx2-5R141C/+ mESCs display an alteration in the expression of genes that are essential for normal heart development. Furthermore, the reduced cardiomyogenesis is paralleled by a reduction in nuclear import of Nkx2-5 protein. Examination of the Nkx2-5R141C/+ embryos at E8.5 revealed a transient loss of cardiomyogenesis, which is consistent with the phenotype observed in vitro. Moreover, gene expression profiling of Nkx2-5R141C/+ cells at an early stage of cardiac differentiation revealed pronounced deregulation of several cardiac differentiation and function genes. Collectively, our data showed that heterozygosity for the R141C mutation results in disruption of the cellular distribution of Nkx2-5 protein, a transient reduction in cardiomyogenesis that may disrupt the early patterning of the heart, and this, in turn, affects the intricate orchestration of signaling pathways leading to downregulation of Bone morphogenetic protein (BMP) and Notch signaling. Therefore, we have developed mESCs model of a human CHD, providing an in vitro system to examine early stages of heart development, which are otherwise difficult to study in vivo. Stem Cells 2018;36:514-526.

NKX2-1 Is Required in the Embryonic Septum for Cholinergic System Development, Learning, and Memory

SummaryThe transcription factor NKX2-1 is best known for its role in the specification of subsets of cortical, striatal, and pallidal neurons. We demonstrate through genetic fate mapping and intersectional focal septal deletion that NKX2-1 is selectively required in the embryonic septal neuroepithelium for the development of cholinergic septohippocampal projection neurons and large subsets of basal forebrain cholinergic neurons. In the absence of NKX2-1, these neurons fail to develop, causing alterations in hippocampal theta rhythms and severe deficiencies in learning and memory. Our results demonstrate that learning and memory are dependent on NKX2-1 function in the embryonic septum and suggest that cognitive deficiencies that are sometimes associated with pathogenic mutations in NKX2-1 in humans may be a direct consequence of loss of NKX2-1 function.

Heterogeneity of lung disease associated with NK2 homeobox 1 mutations

We retrospectively studied the clinical presentation, treatment modalities and outcome in 16 patients with heterozygous NKX2-1 mutation associated with chronic lung disease.Twelve different NKX2-1 mutations, including 4 novel mutations, were identified in the 16 patients. Nine patients presented with brain-lung-thyroid syndrome, 3 had neurological and lung symptoms and 4 had only pulmonary symptoms. Ten patients had neonatal respiratory distress, and 6 of them developed infiltrative lung disease (ILD). The other patients were diagnosed with ILD in childhood (n = 3) or in adulthood (n = 3). The median age at diagnosis was 36 months (IQ 3.5–95). Patient testing included HRCT (n = 13), BALF analysis (n = 6), lung biopsies (n = 3) and lung function tests (n = 6). Six patients required supplemental oxygen support with a median duration of 18 months (IQ 2.5–29). All symptomatic ILD patients (n = 12) benefited from a treatment consisting of steroids, azithromycin (n = 9), and/or hydroxychloroquine (n = 4). The median follow-up was 36 months (IQ 24–71.5). One patient died of respiratory failure at 18 months and another is waiting for lung transplantation.In summary, the initial diagnosis was based on clinical presentation and radiological features, but the presentation was heterogeneous. Definitive diagnosis required genetic analysis, which should be performed, even in absence of neurological or thyroid symptoms.

Nkx2-5 and Sarcospan genetically interact in the development of the muscular ventricular septum of the heart

The muscular ventricular septum separates the flow of oxygenated and de-oxygenated blood in air-breathing vertebrates. Defects within it, termed muscular ventricular septal defects (VSDs), are common, yet less is known about how they arise than rarer heart defects. Mutations of the cardiac transcription factor NKX2-5 cause cardiac malformations, including muscular VSDs. We describe here a genetic interaction between Nkx2-5 and Sarcospan (Sspn) that affects the risk of muscular VSD in mice. Sspn encodes a protein in the dystrophin-glycoprotein complex. Sspn knockout (SspnKO) mice do not have heart defects, but Nkx2-5+/−/SspnKO mutants have a higher incidence of muscular VSD than Nkx2-5+/− mice. Myofibers in the ventricular septum follow a stereotypical pattern that is disrupted around a muscular VSD. Subendocardial myofibers normally run in parallel along the left ventricular outflow tract, but in the Nkx2-5+/−/SspnKO mutant they commonly deviate into the septum even in the absence of a muscular VSD. Thus, Nkx2-5 and Sspn act in a pathway that affects the alignment of myofibers during the development of the ventricular septum. The malalignment may be a consequence of a defect in the coalescence of trabeculae into the developing ventricular septum, which has been hypothesized to be the mechanistic basis of muscular VSDs.

122 - Temporal deletions of Nkx2-5 induce hypertrabeculation and progressive conduction defects and heart failure

Left ventricular non-compaction (LVNC), characterized by hypertrabeculation and deep trabecular recesses in the left ventricle, is the most common cardiomyopathy with a spectrum ranging from extreme normal variants to a pathological phenotype. In all forms, heart failure and sudden cardiac death represent the most severe complications related with non-compaction and arrhythmias. Defects in ventricular compaction and conduction are traits observed in patients and mutant mice carrying mutations in NKX2-5, encoding a key transcriptional regulator of cardiac development. In order to dissect the role of this gene in the apparition of the pathological outcomes of LVNC, we established a LVNC mouse model by inactivating Nkx2-5 in a time and tissue specific manner. Nkx2-5 was conditionally knockout in atria and trabecular cardiomyocytes at embryonic stages, when trabeculae arise, or during fetal stage, when they start to compact, or at neonatal stages, when the ventricles are mature. Our results show that the loss of Nkx2-5 at embryonic stages provokes a hypertrabeculation associated with important subendocardial fibrosis and Purkinje fibers hypoplasia in adult mice. These phenotypes are milder when the deletion occurred at fetal stages. Deletion only in the ventricular conduction system, at neonatal stage, leads to a progressive hypoplasia of this tissue without signs of hypertrabeculation nor fibrosis. However, all these mice develop progressively conduction defects and heart failure. The analysis of molecular pathways associated to these phenotypes, demonstrated that Nkx2-5 plays pleiotropic roles during trabecular development. Thus, deletion of Nkx2-5 during trabecular development represents a good model for studying the cellular and molecular mechanisms associated with LVNC, and the more pronounced disorder is provoked by a deletion at earlier stages.