Copy number variants are a common cause of non-syndromic hearing loss

Genome Medicine (Impact Factor: 5.34). 05/2014; 6(5):37. DOI: 10.1186/gm554
Source: PubMed


Copy number variants (CNVs) are a well-recognized cause of genetic disease; however, methods for their identification are often gene-specific, excluded as ‘routine’ in screens of genetically heterogeneous disorders, and not implemented in most next-generation sequencing pipelines. For this reason, the contribution of CNVs to non-syndromic hearing loss (NSHL) is most likely under-recognized. We aimed to incorporate a method for CNV identification as part of our standard analysis pipeline and to determine the contribution of CNVs to genetic hearing loss.

We used targeted genomic enrichment and massively parallel sequencing to isolate and sequence all exons of all genes known to cause NSHL. We completed testing on 686 patients with hearing loss with no exclusions based on type of hearing loss or any other clinical features. For analysis we used an integrated method for detection of single nucleotide changes, indels and CNVs. CNVs were identified using a previously published method that utilizes median read-depth ratios and a sliding-window approach.

Of 686 patients tested, 15.2% (104) carried at least one CNV within a known deafness gene. Of the 38.9% (267) of individuals for whom we were able to determine a genetic cause of hearing loss, a CNV was implicated in 18.7% (50). We identified CNVs in 16 different genes including 7 genes for which no CNVs have been previously reported. CNVs of STRC were most common (73% of CNVs identified) followed by CNVs of OTOA (13% of CNVs identified).

CNVs are an important cause of NSHL and their detection must be included in comprehensive genetic testing for hearing loss.

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    • "SIFT) assuming an autosomal recessive mode of inheritance. Samples were also analyzed for copy number variations (CNVs) using a sliding-window method to assess read-depth ratios [Shearer et al., 2014]. Validation and segregation of candidate variants was completed by Sanger sequencing on an ABI 3730 Sequencer (Perkin Elmer, Waltham, MA). "
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    ABSTRACT: Deafness is the most frequent sensory disorder. With over 90 genes and 110 loci causally implicated in non-syndromic hearing loss, it is phenotypically and genetically heterogeneous. Here, we investigate the genetic etiology of deafness in four families of Iranian origin segregating autosomal recessive non-syndromic hearing loss (ARNSHL). We used a combination of linkage analysis, homozygosity mapping, and a targeted genomic enrichment platform to simultaneously screen 90 known deafness-causing genes for pathogenic variants. Variant segregation was confirmed by Sanger sequencing. Linkage analysis and homozygosity mapping showed segregation with the DFNB57 locus on chromosome 10 in two families. Targeted genomic enrichment with massively parallel sequencing identified causal variants in PDZD7: a homozygous missense variant (p.Gly103Arg) in one family and compound heterozygosity for missense (p.Met285Arg) and nonsense (p.Tyr500Ter) variants in the second family. Screening of two additional families identified two more variants: (p.Gly228Arg) and (p.Gln526Ter). Variant segregation with the hearing loss phenotype was confirmed in all families by Sanger sequencing. The missense variants are predicted to be deleterious, and the two nonsense mutations produce null alleles. This report is the first to show that mutations in PDZD7 cause ARNSHL, a finding that offers addition insight into the USH2 interactome. We also describe a novel likely disease-causing mutation in CIB2 and illustrate the complexity associated with gene identification in diseases that exhibit large genetic and phenotypic heterogeneity. © 2015 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 09/2015; DOI:10.1002/ajmg.a.37274 · 2.16 Impact Factor
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    • "Role of copy number variants (CNVs) in human genetic disorders are well-recognized. Copy number variation plays major role particularly in the genetic etiology of many developmental disorders including autism, intellectual disability (ID) and hearing loss [Marshall and Scherer, 2012; Asadollahi et al., 2014; Bademci et al., 2014; Shearer et al., 2014]. "
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    ABSTRACT: X-linked intellectual disability is the most common form of neurological disorder in male and accounts for 5-10% of incidence in the population. Copy number variants (CNVs) have been studied extensively to identify genomic regions responsible for neurological disorders. Array CGH and SNP genotyping have identified several CNVs on X-chromosome in patients with X-linked intellectual disability. We genotyped 2.5 million SNPs in 10 individuals of a 4 generation family segregating X-linked intellectual disability using Illumina Infinium BeadChip assay. Whole genome genotyping data analysis identified a single duplication of 3.95 Mb on X-chromosome in all five affected male individuals. This CNV is inherited from a healthy mother. All five affected individuals manifest moderate to severe intellectual disability, seizures and behavioral abnormalities. X-chromosome inactivation analysis showed that X-chromosome of the mother with duplication is completely inactivated which has also been found in daughters. © 2015 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 09/2015; DOI:10.1002/ajmg.a.37372 · 2.16 Impact Factor
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    ABSTRACT: Background Copy number variations (CNVs) are the major type of structural variation in the human genome, and are more common than DNA sequence variations in populations. CNVs are important factors for human genetic and phenotypic diversity. Many CNVs have been associated with either resistance to diseases or identified as the cause of diseases. Currently little is known about the role of CNVs in causing deafness. CNVs are currently not analyzed by conventional genetic analysis methods to study deafness. Here we detected both DNA sequence variations and CNVs affecting 80 genes known to be required for normal hearing. Methods Coding regions of the deafness genes were captured by a hybridization-based method and processed through the standard next-generation sequencing (NGS) protocol using the Illumina platform. Samples hybridized together in the same reaction were analyzed to obtain CNVs. A read depth based method was used to measure CNVs at the resolution of a single exon. Results were validated by the quantitative PCR (qPCR) based method. Results Among 79 sporadic cases clinically diagnosed with sensorineural hearing loss, we identified previously-reported disease-causing sequence mutations in 16 cases. In addition, we identified a total of 97 CNVs (72 CNV gains and 25 CNV losses) in 27 deafness genes. The CNVs included homozygous deletions which may directly give rise to deleterious effects on protein functions known to be essential for hearing, as well as heterozygous deletions and CNV gains compounded with sequence mutations in deafness genes that could potentially harm gene functions. Conclusions We studied how CNVs in known deafness genes may result in deafness. Data provided here served as a basis to explain how CNVs disrupt normal functions of deafness genes. These results may significantly expand our understanding about how various types of genetic mutations cause deafness in humans.
    BMC Ear Nose and Throat Disorders 09/2014; 14(1):9. DOI:10.1186/1472-6815-14-9
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