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A functional assay to study the pathogenicity of CHD7 protein variants encountered in CHARGE syndrome patients.

ABSTRACT: CHARGE syndrome is a rare genetic disease characterized by numerous congenital abnormalities, mainly caused by de novo alterations of the CHD7 gene. It encodes a chromodomain protein, involved in the ATP-dependent remodeling of chromatin. The vast majority of CHD7 alterations consists in null alleles like deletions, nonsense substitutions or frameshift-causing variations. The aim of this study was to develop a biological test of CHD7 protein, to study the impact upon protein functionality of rare allelic variants in the CHD7 gene that elicits changes in the amino acid sequence. Using an expression vector encoding CHD7, three amino acid substitutions and one five-amino acid insertion were generated via site-directed mutagenesis. Then CHD7 proteins, either wild-type (WT) or variants, were overexpressed in HeLa cell line. Protein expression was highlighted by western blot and immunofluorescence. We then used real-time RT-PCR to study CHD7 functionality by evaluating the transcript amounts of five genes whose expression is regulated by CHD7 according to the literature. These reporter genes are 45S rDNA, SOX4, SOX10, ID2, and MYRF. We observed that, upon WT-CHD7 expression, the reporter gene transcriptions were downregulated, whereas the four variant alleles of CHD7 had no impact. This suggests that these alleles are not polymorphisms because the variant proteins appeared nonfunctional. Therefore, these variations can be considered as disease-causing of CHARGE syndrome.

SUBMITTER: Brajadenta GS

PROVIDER: S-EPMC6871090 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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A functional assay to study the pathogenicity of CHD7 protein variants encountered in CHARGE syndrome patients.

Brajadenta Gara Samara GS Bilan Frédéric F Gilbert-Dussardier Brigitte B Kitzis Alain A Thoreau Vincent V

European journal of human genetics : EJHG 20190709 11

CHARGE syndrome is a rare genetic disease characterized by numerous congenital abnormalities, mainly caused by de novo alterations of the CHD7 gene. It encodes a chromodomain protein, involved in the ATP-dependent remodeling of chromatin. The vast majority of CHD7 alterations consists in null alleles like deletions, nonsense substitutions or frameshift-causing variations. The aim of this study was to develop a biological test of CHD7 protein, to study the impact upon protein functionality of rar ...[more]

PMID: 31289371

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Project description:Background: CHARGE syndrome (CS) is a single-gene genetic disorder with multiple organ malformations caused by a variant of the chromodomain helicase DNA-binding protein 7 (CHD7) gene on chromosome 8q12.1. In this study, we aimed to investigate new variants that have emerged in these cases compared with typical CS and the relationship between the genes and phenotypes. Methods: Patients with suspected genetic diseases were subjected to Whole Exome Sequencing (WES) at a genetics laboratory in Guangzhou. The average sequencing coverage depth was >200 ×, and 96% was >20 ×. The variant interpretation was manipulated according to the American College of Medical Genetics (ACMG) guidelines. Molecular data on databases for ClinVar and CHD7 were also collected and collated. We reviewed the currently described CHD7 variants and analyzed the genetic variation and phenotypic heterogeneity. Results: Data of 12 patients with CS from four hospitals in China were collected. According to gestational age, most of them (8/12) were near-term babies with a lower birth weight than their peers, averaging 2.62 kg. In this study, the most common phenotypes were respiratory tract malformations (11/12), heart malformations (10/12), and central nervous system malformations (9/12). Two fetuses were confirmed to have brain or heart abnormalities during prenatal testing, while 10/12 were found to have abnormalities during prenatal testing. The maximum Acute Physiology and Chronic Health Evaluation (APACHE II) score at admission was 19, and the average was 11.58. Five variants in the CHD7 gene c.7012C > T (p.Q2338*), c.7868delC (p.P2623Rfs*16), c.5405-3C > G, c.6936 + 2T > C, and c.8077-2A > G) were novel and were located in exons 33, 36, and introns 25, 32, and 37, respectively. There may be a positive correlation between exon location and phenotype. Conclusion: Five novel variants were discovered. These expanded the mutational spectrum of the CHD7 gene and the phenotype of CS. There may be a correlation between the new mutation sites and the phenotype, which has some reference value for the evaluation of mutation sites.

Project description:BackgroundOtologic manifestations are one of the most consistent findings of CHARGE syndrome found in more than 90%. Since genetic analysis of the CHD7 gene has rarely been performed in previous reports dealing with ear abnormalities, the genotypic spectrum of CHD7 mutations was analyzed in deaf patients with CHARGE syndrome, and the clinical considerations concerning auditory rehabilitation were investigated.MethodsNine Korean patients with CHARGE syndrome showing profound hearing loss and semicircular canal aplasia were included. All 38 exons of CHD7 were analyzed by direct sequencing. For splice site variations, in silico and exon-trapping analyses were performed to verify the pathogenicity of nucleotide variations. Clinical features and the outcome of auditory rehabilitation were also analyzed.ResultsEight of 9 patients revealed alterations of the CHD7 gene including 3 frameshift, 2 nonsense, 2 splice site, and 1 missense mutations. Five of 9 patients were clinically diagnosed as atypical CHARGE syndrome but demonstrated various mutations of the CHD7 gene. One familial case showed intra-familial variability. Radiologic findings suggesting cochleovestibular nerve deficiency were identified in most of the patients. Of the 8 patients who underwent cochlear implantation, 5 patients demonstrated favorable outcome. Larger diameter of the cochleovestibular nerve on imaging and absence of severe mental retardation were factors related to better outcome after cochlear implantation rather than the type of CHD7 mutations. Auditory brainstem implantation was performed in two patients who did not benefit from cochlear implantation.ConclusionsGenetic analysis of the CHD7 gene should be performed in cases with semicircular canal aplasia even when other typical features of CHARGE syndrome are absent. For auditory rehabilitation in CHARGE syndrome, cochlear implantation should be strongly recommended in selected cases with favorable prognostic factors. Auditory brainstem implantation may be a viable option in patients with CHARGE syndrome who have failed to benefit from cochlear implantation.

Dataset Information

A functional assay to study the pathogenicity of CHD7 protein variants encountered in CHARGE syndrome patients.

Publications

A functional assay to study the pathogenicity of CHD7 protein variants encountered in CHARGE syndrome patients.

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