Confirmation of CHD7 as a cause of CHARGE association identified by mapping a balanced chromosome translocation in affected monozygotic twins

Chromatin remodelling complexes in cerebral cortex development and neurodevelopmental disorders

The diverse number of neurons in the cerebral cortex are generated during development by neural stem cells lining the ventricle, and they continue maturing postnatally. Dynamic chromatin regulation in these neural stem cells is a fundamental determinant of the emerging property of the functional neural network, and the chromatin remodellers are critical determinants of this process. Chromatin remodellers participate in several steps of this process from proliferation, differentiation, migration leading to complex network formation which forms the basis of higher-order functions of cognition and behaviour. Here we review the role of these ATP-dependent chromatin remodellers in cortical development in health and disease and highlight several key mouse mutants of the subunits of the complexes which have revealed how the remodelling mechanisms control the cortical stem cell chromatin landscape for expression of stage-specific transcripts. Consistent with their role in cortical development, several putative risk variants in the subunits of the remodelling complexes have been identified as the underlying causes of several neurodevelopmental disorders. A basic understanding of the detailed molecular mechanism of their action is key to understating how mutations in the same networks lead to disease pathologies and perhaps pave the way for therapeutic development for these complex multifactorial disorders.

Enhancers: bridging the gap between gene control and human disease

Enhancers are a class of regulatory elements essential for precise spatio-temporal control of gene expression during development and in terminally differentiated cells. This review highlights signature features of enhancer elements as well as new advances that provide mechanistic insights into enhancer-mediated gene control in the context of three-dimensional chromatin. We detail the various ways in which non-coding mutations can instigate aberrant gene control and cause a variety of Mendelian disorders, common diseases and cancer.

Chronic mild corticosterone exposure during adolescence enhances behaviors and upregulates neuroplasticity-related proteins in rat hippocampus

Adolescence is a critical period with ongoing maturational processes in stress-sensitive systems. It remains unknown how adolescent individuals would be affected by chronic exposure to corticosterone (the major stress hormone in rodents, CORT) at the doses that are usually not detrimental in adults. In this study, male Sprague-Dawley rats were injected with CORT (5 mg/kg) or vehicle for 21 days during adolescence (postnatal day (PND) 29-49) or adulthood (PND 71-91) and then subjected to behavioral testing or sacrifice for neurobiological analyses. Shortly after treatment cessation, different from CORT-treated adults showing increased anxiety-like behaviors, CORT-treated adolescents exhibited enhanced prepulse inhibition and spatial learning. They also showed increased expression of hippocampal neuroplasticity-related proteins, including BDNF, nectin3, and AMPA receptor subunits. These effects became undetectable after a four-week washout period when CORT-treated adolescents exhibited improved reversal learning. Together, these findings demonstrate that chronic CORT exposure at the dose of 5 mg/kg endows adolescent individuals with enhanced cognitive capacities, possibly supported by increased hippocampal neuroplasticity. This study also highlights mild elevation of CORT levels during adolescence as a potential approach of promoting adaptive behaviors.

Breakpoint mapping and haplotype analysis of translocation t(1;12)(q43;q21.1) in two apparently independent families with vascular phenotypes

BACKGROUND

The risk of serious congenital anomaly for de novo balanced translocations is estimated to be at least 6%. We identified two apparently independent families with a balanced t(1;12)(q43;q21.1) as an outcome of a "Systematic Survey of Balanced Chromosomal Rearrangements in Finns." In the first family, carriers (n = 6) manifest with learning problems in childhood, and later with unexplained neurological symptoms (chronic headache, balance problems, tremor, fatigue) and cerebral infarctions in their 50s. In the second family, two carriers suffer from tetralogy of Fallot, one from transient ischemic attack and one from migraine. The translocation cosegregates with these vascular phenotypes and neurological symptoms.

METHODS AND RESULTS

We narrowed down the breakpoint regions using mate pair sequencing. We observed conserved haplotypes around the breakpoints, pointing out that this translocation has arisen only once. The chromosome 1 breakpoint truncates a CHRM3 processed transcript, and is flanked by the 5' end of CHRM3 and the 3' end of RYR2. TRHDE, KCNC2, and ATXN7L3B flank the chromosome 12 breakpoint.

CONCLUSIONS

This study demonstrates a balanced t(1;12)(q43;q21.1) with conserved haplotypes on the derived chromosomes. The translocation seems to result in vascular phenotype, with or without neurological symptoms, in at least two families. We suggest that the translocation influences the positional expression of CHRM3, RYR2, TRHDE, KCNC2, and/or ATXN7L3B.

Three novel mutations of CHD7 gene in two turkish patients with charge syndrome; A double point mutation and an insertion

The CHARGE (coloboma, heart defects, atresia, retardation, genital, ear) syndrome is a genetic disease characterized by ocular coloboma, choanal atresia or stenosis and semicircular canal abnormalities. Most of the patients clinically diagnosed with CHARGE syndrome have mutations in chromodomain helicase DNA-binding protein 7 (CHD7) gene. The CHD7 gene is located on chromosome 8q12.1, and up to now, there are more than 500 pathogenic mutations identified in the literature. We report two patients diagnosed with CHARGE syndrome with two novel mutations in the CHD7 gene: the first patient has double consecutive novel mutations in three adjacent codons, and the other has a novel insertion.

Practice parameter for the diagnosis and management of primary immunodeficiency

The American Academy of Allergy, Asthma & Immunology (AAAAI) and the American College of Allergy, Asthma & Immunology (ACAAI) have jointly accepted responsibility for establishing the "Practice parameter for the diagnosis and management of primary immunodeficiency." This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.

CHARGE syndrome: a review

CHARGE syndrome is a complex genetic syndrome, owing to the wide range of tissues/systems affected by mutations in the CHD7 gene. In this review, we discuss the diagnosis, clinical features and management of CHARGE syndrome.

Identification of a novel mutation in the CHD7 gene in a patient with CHARGE syndrome

CHARGE syndrome has been estimated to occur in 1:10,000 births worldwide and shows various clinical manifestations. It is a genetic disorder characterized by a specific and a recognizable pattern of anomalies. The major clinical features are ocular coloboma, heart malformations, atresia of the choanae, growth retardation, genital hypoplasia, and ear abnormalities. The chromodomain helicase DNA-binding protein 7 (CHD7) gene, located on chromosome 8q12.1, causes CHARGE syndrome. The CHD7 protein is an adenosine triphosphate (ATP)-dependent chromatin remodeling protein. A total of 67% of patients clinically diagnosed with CHARGE syndrome have CHD7 mutations. Five hundred twenty-eight pathogenic and unique CHD7 alterations have been identified so far. We describe a patient with a CHARGE syndrome diagnosis who carried a novel de novo mutation, a c.3896T>C (p. leu1299Pro) missense mutation, in the CHD7 gene. This finding will provide more information for genetic counseling and expand our understanding of the pathogenesis and development of CHARGE syndrome.

Descriptive and risk factor analysis for choanal atresia: The National Birth Defects Prevention Study, 1997-2007

Choanal atresia causes serious posterior nasal obstruction. This defect is the leading cause of nasal surgery in newborns, although its etiology is largely unknown. Data from the National Birth Defects Prevention Study, a population-based case-control study, were used to examine associations between maternal self-reports of exposures and occurrence of choanal atresia in their offspring. Overall, 117 case and 8350 control mothers with deliveries from 1997 through 2007 provided telephone interview reports of pre-pregnancy (one year before conception) and periconceptional (one month before through three months after conception) exposures. The exposures analyzed were pre-pregnancy dietary intake, pre-pregnancy and periconceptional caffeine consumption, and periconceptional cigarette smoking, alcohol drinking, and medication use. Independent associations between each exposure and all choanal atresia cases combined (n = 117) and isolated choanal atresia cases (those without additional unrelated major defects; n = 61) were examined. Odds ratios (ORs), both unadjusted (uORs) and adjusted (aORs) for potential confounders, and 95% confidence intervals (CIs) were estimated using unconditional logistic regression analysis. For all choanal atresia cases combined, positive associations were observed with maternal pre-pregnancy intake in the highest quartile for vitamin B-12 (aOR = 1.9; CI = 1.1,3.1), zinc (aOR = 1.7; CI = 1.0,3.1), and niacin (aOR = 1.8; CI = 1.0,3.1), and intake in the lowest quartile for methionine (aOR = 1.6; CI = 1.0,2.6) and vitamin D (aOR = 1.6; CI = 1.0,2.4) compared to intake in the two intermediate quartiles combined. Further, a positive association was observed with periconceptional use of thyroid medications (uOR = 2.6; CI = 1.0,6.3) compared to no use of such medications. Among isolated choanal atresia cases, negative associations were observed for pantothenic acid (aOR = 0.4; CI = 0.2,0.9) and fat (aOR = 0.5; 95% CI = 0.2,1.0) intake in the lowest quartile compared to that in the intermediate quartiles, and positive associations were observed for periconceptional cigarette smoking (aOR = 2.3; CI = 1.1,4.7) compared to no smoking and pre-pregnancy daily coffee intake of 3 or more cups (aOR = 2.5; CI = 1.1,5.6) compared to intake of less than 1 cup per day. The positive association for periconceptional exposure to thyroid medications also persisted for isolated choanal atresia cases (uOR = 4.0; CI = 1.1,11.2). Because of the large number of associations tested, these findings may be due to chance. Alternatively, they may contribute new hypotheses regarding the etiology of choanal atresia; thus, requiring replication in additional studies.

The role of genetics in the establishment and maintenance of the epigenome

Epigenetic mechanisms play an important role in gene regulation during development. DNA methylation, which is probably the most important and best-studied epigenetic mechanism, can be abnormally regulated in common pathologies, but the origin of altered DNA methylation remains unknown. Recent research suggests that these epigenetic alterations could depend, at least in part, on genetic mutations or polymorphisms in DNA methyltransferases and certain genes encoding enzymes of the one-carbon metabolism pathway. Indeed, the de novo methyltransferase 3B (DNMT3B) has been recently found to be mutated in several types of cancer and in the immunodeficiency, centromeric region instability and facial anomalies syndrome (ICF), in which these mutations could be related to the loss of global DNA methylation. In addition, mutations in glycine-N-methyltransferase (GNMT) could be associated with a higher risk of hepatocellular carcinoma and liver disease due to an unbalanced S-adenosylmethionine (SAM)/S-adenosylhomocysteine (SAH) ratio, which leads to aberrant methylation reactions. Also, genetic variants of chromatin remodeling proteins and histone tail modifiers are involved in genetic disorders like α thalassemia X-linked mental retardation syndrome, CHARGE syndrome, Cockayne syndrome, Rett syndrome, systemic lupus erythematous, Rubinstein-Taybi syndrome, Coffin-Lowry syndrome, Sotos syndrome, and facioescapulohumeral syndrome, among others. Here, we review the potential genetic alterations with a possible role on epigenetic factors and discuss their contribution to human disease.

CHARGE Association

We present here a case of 17-year-old boy from Kolkata presenting with obesity, bilateral gynecomastia, mental retardation, and hypogonadotrophic hypogonadism. The patient weighed 70 kg and was of 153 cm height. Facial asymmetry (unilateral facial palsy), gynecomastia, decreased pubic and axillary hair, small penis, decreased right testicular volume, non-palpable left testis, and right-sided congenital inguinal hernia was present. The patient also had disc coloboma, convergent squint, microcornea, microphthalmia, pseudohypertelorism, low set ears, short neck, and choanalatresia. He had h/o VSD repaired with patch. Laboratory examination revealed haemoglobin 9.9 mg/dl, urea 24 mg/dl, creatinine 0.68 mg/dl. IGF1 77.80 ng/ml (decreased for age), GH <0.05 ng/ml, testosterone 0.25 ng/ml, FSH-0.95 μIU/ml, LH 0.60 ΅IU/ml. ACTH, 8:00 A.M cortisol, FT3, FT4, TSH, estradiol, DHEA-S, lipid profile, and LFT was within normal limits. Prolactin was elevated at 38.50 ng/ml. The patient's karyotype was 46XY. Echocardiography revealed ventricularseptal defect closed with patch, grade 1 aortic regurgitation, and ejection fraction 67%. Ultrasound testis showed small right testis within scrotal sac and undescended left testis within left inguinal canal. CT scan paranasal sinuses revealed choanalatresia and deviation of nasal septum to the right. Sonomammography revealed bilateral proliferation of fibroglandular elements predominantly in subareoalar region of breasts. MRI of brain and pituitary region revealed markedly atrophic pituitary gland parenchyma with preserved infundibulum and hypothalamus and widened suprasellar cistern. The CHARGE association is an increasingly recognized non-random pattern of congenital anomalies comprising of coloboma, heart defect, choanal atresia, retarded growth and development, genital hypoplasia, ear abnormalities, and/or deafness.[1] These anomalies have a higher probability of occurring together. In this report, we have described a boy with CHARGE association.

8q12.1q12.3 de novo microdeletion involving the CHD7 gene in a patient without the major features of CHARGE syndrome: case report and critical review of the literature

CHARGE syndrome is an autosomal dominant inherited disorder characterized by a specific and recognizable pattern of anomalies. De novo mutations or deletions of the gene encoding chromodomain helicase DNA binding protein 7 (CHD7) are the major cause of CHARGE syndrome. In this report, we describe a patient with a typical phenotype characterized by psychomotor retardation, hypertrichosis, facial asymmetry, synophria, failure to thrive, developmental delay and gastro-esophageal reflux, carrying a de novo 6.04Mb interstitial deletion in 8q12.1q12.3 detected by single nucleotide polymorphism (SNP) array analysis. Despite the deletion includes CHD7 and although the patient shares some of the clinical features of the CHARGE syndrome, she does not fulfill the clinical criteria for this syndrome. To the best of our knowledge, this is the second case with an entire deletion of the CHD7 gene not leading to CHARGE syndrome and, for this reason, useful to expand and further delineate the clinical features associated with the 8q12.1q12.3 deletion. Furthermore, the literature review revealed that the phenotype secondary to duplications of the same region partially overlaps with the phenotype reported in this study. Selected genes that are present in the hemizygous state and which might be important for the phenotype of this patient, are discussed in context of the clinical features.

Immunological aspects of 22q11.2 deletion syndrome

Chromosome 22q11 deletion is the most common chromosomal deletion syndrome and is found in the majority of patients with DiGeorge syndrome and velo-cardio-facial syndrome. Patients with CHARGE syndrome may share similar features. Cardiac malformations, speech delay, and immunodeficiency are the most common manifestations. The immunological phenotype may vary widely between patients. Severe T lymphocyte immunodeficiency is rare-thymic transplantation offers a new approach to treatment, as well as insights into thymic physiology and central tolerance. Combined partial immunodeficiency is more common, leading to recurrent sinopulmonary infection in early childhood. Autoimmunity is an increasingly recognized complication. New insights into pathophysiology are reviewed.

Cranial neural crest cells on the move: their roles in craniofacial development

The craniofacial region is assembled through the active migration of cells and the rearrangement and sculpting of facial prominences and pharyngeal arches, which consequently make it particularly susceptible to a large number of birth defects. Genetic, molecular, and cellular processes must be temporally and spatially regulated to culminate in the three-dimension structures of the face. The starting constituent for the majority of skeletal and connective tissues in the face is a pluripotent population of cells, the cranial neural crest cells (NCCs). In this review we discuss the newest scientific findings in the development of the craniofacial complex as related to NCCs. Furthermore, we present recent findings on NCC diseases called neurocristopathies and, in doing so, provide clinicians with new tools for understanding a growing number of craniofacial genetic disorders.

CHARGE: an association or a syndrome?

INTRODUCTION

CHARGE "association" is a rare clinical entity with multiple congenital anomalies that necessitates a multidisciplinary approach. Its diagnosis is important not only for the pediatric surgery practice but also for the otorhinolaryngology practice as it complicates with a number of major surgical anomalies. The aim of this paper is to present the latest evidences on the genetic basis of the disease.

MATERIALS AND METHODS

In order to evaluate, a computed literature review was undertaken using PubMed and OMIM databases.

RESULTS

Heterozygous mutations within the chromodomain helicase DNA binding protein 7 (CHD7) were reported in every two of three CHARGE patients. CHD protein family is located on chromosome 8q11.2 and is known to regulate chromatin remodeling which plays an essential role in the developmental gene expression. That is why the haploinsufficiency of CHD7 gene due to heterozygous mutations results in not only the postnatal but also the prenatal developmental regulation errors. The wide expression of this gene in the prenatal period overlaps with the broad spectrum of the phenotypic symptoms of the disease.

CONCLUSION

CHD7 gene haploinsufficiency is expected to be the underlying basis of CHARGE. Even though the genetic basis is unsolved in one-third of the patients, the current evidence supports the term "syndrome" rather than an "association" should be more appropriate for CHARGE.

Molecular and phenotypic aspects of CHD7 mutation in CHARGE syndrome

CHARGE syndrome [coloboma of the eye, heart defects, atresia of the choanae, retardation of growth and/or development, genital and/or urinary abnormalities, and ear abnormalities (including deafness)] is a genetic disorder characterized by a specific and a recognizable pattern of anomalies. De novo mutations in the gene encoding chromodomain helicase DNA binding protein 7 (CHD7) are the major cause of CHARGE syndrome. Here, we review the clinical features of 379 CHARGE patients who tested positive or negative for mutations in CHD7. We found that CHARGE individuals with CHD7 mutations more commonly have ocular colobomas, temporal bone anomalies (semicircular canal hypoplasia/dysplasia), and facial nerve paralysis compared with mutation negative individuals. We also highlight recent genetic and genomic studies that have provided functional insights into CHD7 and the pathogenesis of CHARGE syndrome.

Chromodomain proteins in development: lessons from CHARGE syndrome

In humans, heterozygous mutations in the adenosine triphosphate-dependent chromatin remodeling gene CHD7 cause CHARGE syndrome, a common cause of deaf-blindness, balance disorders, congenital heart malformations, and olfactory dysfunction with an estimated incidence of approximately 1 in 10,000 newborns. The clinical features of CHARGE in humans and mice are highly variable and incompletely penetrant, and most mutations appear to result in haploinsufficiency of functional CHD7 protein. Mice with heterozygous loss of function mutations in Chd7 are a good model for CHARGE syndrome, and analyses of mouse mutant phenotypes have begun to clarify a role for CHD7 during development and into adulthood. Chd7 heterozygous mutant mice have postnatal delayed growth, inner ear malformations, anosmia/hyposmia, and craniofacial defects, and Chd7 homozygous mutants are embryonic lethal. A central question in developmental biology is how chromodomain proteins like CHD7 regulate important developmental processes, and whether they directly activate or repress downstream gene transcription or act more globally to alter chromatin structure and/or function. CHD7 is expressed in a wide variety of tissues during development, suggesting that it has tissue-specific and developmental stage-specific roles. Here, we review recent and ongoing analyses of CHD7 function in mouse models and cell-based systems. These studies explore tissue-specific effects of CHD7 deficiency, known CHD7 interacting proteins, and downstream target sites for CHD7 binding. CHD7 is emerging as a critical regulator of important developmental processes in organs affected by human CHARGE syndrome.

Mutations in CHD7 in patients with CHARGE syndrome cause T-B + natural killer cell + severe combined immune deficiency and may cause Omenn-like syndrome

More than 11 genetic causes of severe combined immunodeficiency (SCID) have been identified, affecting development and/or function of T lymphocytes, and sometimes B lymphocytes and natural killer (NK) cells. Deletion of 22q11.2 is associated with immunodeficiency, although less than 1% of cases are associated with T-B + NK + SCID phenotype. Severe immunodeficiency with CHARGE syndrome has been noted only rarely Omenn syndrome is a rare autosomal recessive form of SCID with erythroderma, hepatosplenomegaly, lymphadenopathy and alopecia. Hypomorphic recombination activating genes 1 and 2 mutations were first described in patients with Omenn syndrome. More recently, defects in Artemis, RMRP, IL7Ralpha and common gamma chain genes have been described. We describe four patients with mutations in CHD7, who had clinical features of CHARGE syndrome and who had T-B + NK + SCID (two patients) or clinical features consistent with Omenn syndrome (two patients). Immunodeficiency in patients with DiGeorge syndrome is well recognized--CHARGE syndrome should now be added to the causes of T-B + NK + SCID, and mutations in the CHD7 gene may be associated with Omenn-like syndrome.

CHD7 mutation spectrum in 28 Swedish patients diagnosed with CHARGE syndrome

CHARGE syndrome is a disorder characterized by Coloboma, Heart defect, Atresia choanae, Retarded growth and/or development, Genital hypoplasia and Ear anomalies. Heterozygous mutations in the chromodomain helicase DNA-binding protein 7 (CHD7) gene have been identified in about 60% of individuals diagnosed with CHARGE syndrome. We performed a CHD7 mutation screening by direct exon sequencing in 28 index patients (26 sporadic cases, 1 familial case consisting of a brother and sister and 1 case consisting of monozygotic twins) diagnosed with CHARGE syndrome in order to determine the mutations in a cohort of Swedish CHARGE syndrome patients. The patients without a detectable CHD7 mutation, or with a missense mutation, were further investigated by multiplex ligation-dependent probe amplification (MLPA) in order to search for intragenic deletions or duplications. Thirteen novel mutations and five previously reported mutations were detected. The mutations were scattered throughout the gene and included nonsense, frameshift and missense mutations as well as intragenic deletions. In conclusion, CHD7 mutations were detected in a large proportion (64%) of cases diagnosed with CHARGE syndrome. Screening for intragenic deletions with MLPA is recommended in cases where mutations are not found by sequencing. In addition, a CDH7 mutation was found in an individual without temporal bone malformation.

Breakpoint mapping and array CGH in translocations: comparison of a phenotypically normal and an abnormal cohort

We report the analyses of breakpoints in 31 phenotypically normal and 14 abnormal carriers of balanced translocations. Our study assesses the differences between balanced translocations in normal carriers and those in abnormal carriers, focusing on the presence of genomic imbalances at the breakpoints or elsewhere in the genome, presence of cryptic chromosome rearrangements, and gene disruption. Our hypothesis is that all four features will be associated with phenotypic abnormalities and absent or much less frequent in a normal population. In the normal cohort, we identified neither genomic imbalances at the breakpoints or elsewhere in the genome nor cryptic chromosome rearrangements. In contrast, we identified candidate disease-causing imbalances in 4/14 abnormal patients. These were three breakpoint associated deletions and three deletions unrelated to the breakpoints. All six de novo deletions originated on the paternally inherited chromosome. Additional complexity was also present in one of these cases. Gene disruption by the breakpoints was present in 16/31 phenotypically normal individuals and in 5/14 phenotypically abnormal patients. Our results show that translocations in phenotypically abnormal patients are molecularly distinct from those in normal individuals: the former are more likely to be associated with genomic imbalances at the breakpoints or elsewhere and with chromosomal complexity, whereas the frequency of gene disruption is similar in both normal and abnormal translocation carriers.

Characterization of apparently balanced chromosomal rearrangements from the developmental genome anatomy project

Apparently balanced chromosomal rearrangements in individuals with major congenital anomalies represent natural experiments of gene disruption and dysregulation. These individuals can be studied to identify novel genes critical in human development and to annotate further the function of known genes. Identification and characterization of these genes is the goal of the Developmental Genome Anatomy Project (DGAP). DGAP is a multidisciplinary effort that leverages the recent advances resulting from the Human Genome Project to increase our understanding of birth defects and the process of human development. Clinically significant phenotypes of individuals enrolled in DGAP are varied and, in most cases, involve multiple organ systems. Study of these individuals' chromosomal rearrangements has resulted in the mapping of 77 breakpoints from 40 chromosomal rearrangements by FISH with BACs and fosmids, array CGH, Southern-blot hybridization, MLPA, RT-PCR, and suppression PCR. Eighteen chromosomal breakpoints have been cloned and sequenced. Unsuspected genomic imbalances and cryptic rearrangements were detected, but less frequently than has been reported previously. Chromosomal rearrangements, both balanced and unbalanced, in individuals with multiple congenital anomalies continue to be a valuable resource for gene discovery and annotation.

Defects in vestibular sensory epithelia and innervation in mice with loss of Chd7 function: implications for human CHARGE syndrome

CHD7 is a chromodomain gene mutated in CHARGE syndrome, a multiple anomaly condition characterized by ocular coloboma, heart defects, atresia of the choanae, retarded growth and development, genital hypoplasia, and ear defects including deafness and semicircular canal dysgenesis. Mice with heterozygous Chd7 deficiency have circling behavior and semicircular canal defects and are an excellent animal model for exploring the pathogenesis of CHARGE features. Inner ear vestibular defects have been characterized in heterozygous Chd7-deficient embryos and early postnatal mice, but it is not known whether vestibular defects persist throughout adulthood in Chd7-deficient mice or whether the vestibular sensory epithelia and their associated innervation and function are intact. Here we describe a detailed analysis of inner ear vestibular structures in mature mice that are heterozygous for a Chd7-deficient, gene-trapped allele (Chd7(Gt/+)). Chd7(Gt/+) mice display variable asymmetric lateral and posterior semicircular canal malformations, as well as defects in vestibular sensory epithelial innervation despite the presence of intact hair cells in the target organs. These observations have important functional implications for understanding the clinical manifestations of CHD7 mutations in humans and for designing therapies to treat inner ear vestibular dysfunction.

CHARGE syndrome: an update

CHARGE syndrome is a rare, usually sporadic autosomal dominant disorder due in 2/3 of cases to mutations within the CHD7 gene. The clinical definition has evolved with time. The 3C triad (Coloboma-Choanal atresia-abnormal semicircular Canals), arhinencephaly and rhombencephalic dysfunctions are now considered the most important and constant clues to the diagnosis. We will discuss here recent aspects of the phenotypic delineation of CHARGE syndrome and highlight the role of CHD7 in its pathogeny. We review available data on its molecular pathology as well as cytogenetic and molecular evidences for genetic heterogeneity within CHARGE syndrome.

Mutation of the SNF2 family member Chd2 affects mouse development and survival

The chromodomain helicase DNA-binding domain (Chd) proteins belong to the SNF2-like family of ATPases that function in chromatin remodeling and assembly. These proteins are characterized by the presence of tandem chromodomains and are further subdivided based on the presence or absence of additional structural motifs. The Chd1-Chd2 subfamily is distinguished by the presence of a DNA-binding domain that recognizes AT-rich sequence. Currently, there are no reports addressing the function of the Chd2 family member. Embryonic stem cells containing a retroviral gene-trap inserted at the Chd2 locus were utilized to generate mice expressing a Chd2 protein lacking the DNA-binding domain. This mutation in Chd2 resulted in a general growth delay in homozygous mutants late in embryogenesis and in perinatal lethality. Animals heterozygous for the mutation showed decreased neonatal viability and increased susceptibility to non-neoplastic lesions affecting most primary organs. In particular, approximately 85% of the heterozygotes showed gross kidney abnormalities. Our results demonstrate that mutation of Chd2 dramatically affects mammalian development and long-term survival.

CHARGE syndrome

CHARGE syndrome was initially defined as a non-random association of anomalies (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, Ear anomalies/deafness). In 1998, an expert group defined the major (the classical 4C's: Choanal atresia, Coloboma, Characteristic ears and Cranial nerve anomalies) and minor criteria of CHARGE syndrome. Individuals with all four major characteristics or three major and three minor characteristics are highly likely to have CHARGE syndrome. However, there have been individuals genetically identified with CHARGE syndrome without the classical choanal atresia and coloboma. The reported incidence of CHARGE syndrome ranges from 0.1-1.2/10,000 and depends on professional recognition. Coloboma mainly affects the retina. Major and minor congenital heart defects (the commonest cyanotic heart defect is tetralogy of Fallot) occur in 75-80% of patients. Choanal atresia may be membranous or bony; bilateral or unilateral. Mental retardation is variable with intelligence quotients (IQ) ranging from normal to profound retardation. Under-development of the external genitalia is a common finding in males but it is less apparent in females. Ear abnormalities include a classical finding of unusually shaped ears and hearing loss (conductive and/or nerve deafness that ranges from mild to severe deafness). Multiple cranial nerve dysfunctions are common. A behavioral phenotype for CHARGE syndrome is emerging. Mutations in the CHD7 gene (member of the chromodomain helicase DNA protein family) are detected in over 75% of patients with CHARGE syndrome. Children with CHARGE syndrome require intensive medical management as well as numerous surgical interventions. They also need multidisciplinary follow up. Some of the hidden issues of CHARGE syndrome are often forgotten, one being the feeding adaptation of these children, which needs an early aggressive approach from a feeding team. As the child develops, challenging behaviors become more common and require adaptation of educational and therapeutic services, including behavioral and pharmacological interventions.

Multiple mutations in mouse Chd7 provide models for CHARGE syndrome

Mouse ENU mutagenesis programmes have yielded a series of independent mutations on proximal chromosome 4 leading to dominant head-bobbing and circling behaviour due to truncations of the lateral semicircular canal of the inner ear. Here, we report the identification of mutations in the Chd7 gene in nine of these mutant alleles including six nonsense and three splice site mutations. The human CHD7 gene is known to be involved in CHARGE syndrome, which also shows inner ear malformations and a variety of other features with varying penetrance and appears to be due to frequent de novo mutation. We found widespread expression of Chd7 in early development of the mouse in organs affected in CHARGE syndrome including eye, olfactory epithelium, inner ear and vascular system. Closer inspection of heterozygous mutant mice revealed a range of defects with reduced penetrance, such as cleft palate, choanal atresia, septal defects of the heart, haemorrhages, prenatal death, vulva and clitoral defects and keratoconjunctivitis sicca. Many of these defects mimic the features of CHARGE syndrome. There were no obvious features of the gene that might make it more mutable than other genes. We conclude that the large number of mouse mutants and human de novo mutations may be due to the combination of the Chd7 gene being a large target and the fact that many heterozygous carriers of the mutations are viable individuals with a readily detectable phenotype.