An atypically mild case of ethylmalonic encephalopathy with pathogenic ETHE1 variant.

Ethylmalonic encephalopathy (EE) is a rare, severe, autosomal recessive condition caused by pathogenic variants in ETHE1 leading to progressive encephalopathy, hypotonia evolving to dystonia, petechiae, orthostatic acrocyanosis, diarrhea, and elevated ethylmalonic acid in urine. In this case report, we describe a patient with only mild speech and gross motor delays, subtle biochemical abnormalities, and normal brain imaging found to be homozygous for a pathogenic ETHE1 variant (c.586G>A) via whole exome sequencing. This case highlights the clinical heterogeneity of ETHE1 mutations and the utility of whole-exome sequencing in diagnosing mild cases of EE.

Genomic Landscape and Mutational Signatures of Deafness-Associated Genes.

The classification of genetic variants represents a major challenge in the post-genome era by virtue of their extraordinary number and the complexities associated with ascribing a clinical impact, especially for disorders exhibiting exceptional phenotypic, genetic, and allelic heterogeneity. To address this challenge for hearing loss, we have developed the Deafness Variation Database (DVD), a comprehensive, open-access resource that integrates all available genetic, genomic, and clinical data together with expert curation to generate a single classification for each variant in 152 genes implicated in syndromic and non-syndromic deafness. We evaluate 876,139 variants and classify them as pathogenic or likely pathogenic (more than 8,100 variants), benign or likely benign (more than 172,000 variants), or of uncertain significance (more than 695,000 variants); 1,270 variants are re-categorized based on expert curation and in 300 instances, the change is of medical significance and impacts clinical care. We show that more than 96% of coding variants are rare and novel and that pathogenicity is driven by minor allele frequency thresholds, variant effect, and protein domain. The mutational landscape we define shows complex gene-specific variability, making an understanding of these nuances foundational for improved accuracy in variant interpretation in order to enhance clinical decision making and improve our understanding of deafness biology.

Comprehensive genetic testing in the clinical evaluation of 1119 patients with hearing loss.

Hearing loss is the most common sensory deficit in humans, affecting 1 in 500 newborns. Due to its genetic heterogeneity, comprehensive diagnostic testing has not previously been completed in a large multiethnic cohort. To determine the aggregate contribution inheritance makes to non-syndromic hearing loss, we performed comprehensive clinical genetic testing with targeted genomic enrichment and massively parallel sequencing on 1119 sequentially accrued patients. No patient was excluded based on phenotype, inheritance or previous testing. Testing resulted in identification of the underlying genetic cause for hearing loss in 440 patients (39%). Pathogenic variants were found in 49 genes and included missense variants (49%), large copy number changes (18%), small insertions and deletions (18%), nonsense variants (8%), splice-site alterations (6%), and promoter variants (<1%). The diagnostic rate varied considerably based on phenotype and was highest for patients with a positive family history of hearing loss or when the loss was congenital and symmetric. The spectrum of implicated genes showed wide ethnic variability. These findings support the more efficient utilization of medical resources through the development of evidence-based algorithms for the diagnosis of hearing loss.

Navigating genetic diagnostics in patients with hearing loss.

PURPOSE OF REVIEW: In the age of targeted genomic enrichment and massively parallel sequencing, there is no more efficient genetic testing method for the diagnosis of hereditary hearing loss. More clinical tests are on the market, which can make choosing good tests difficult. RECENT FINDINGS: More and larger comprehensive genetic studies in patients with hearing loss have been published recently. They remind us of the importance of looking for both single nucleotide variation and copy number variation in all genes implicated in nonsyndromic hearing loss. They also inform us of how a patient's history and phenotype provide essential information in the interpretation of genetic data. SUMMARY: Choosing the most comprehensive genetic test improves the chances of a genetic diagnosis and thereby impacts clinical care.

Characterising the spectrum of autosomal recessive hereditary hearing loss in Iran.

BACKGROUND: Countries with culturally accepted consanguinity provide a unique resource for the study of rare recessively inherited genetic diseases. Although hereditary hearing loss (HHL) is not uncommon, it is genetically heterogeneous, with over 85 genes causally implicated in non-syndromic hearing loss (NSHL). This heterogeneity makes many gene-specific types of NSHL exceedingly rare. We sought to define the spectrum of autosomal recessive HHL in Iran by investigating both common and rarely diagnosed deafness-causing genes. DESIGN: Using a custom targeted genomic enrichment (TGE) panel, we simultaneously interrogated all known genetic causes of NSHL in a cohort of 302 GJB2-negative Iranian families. RESULTS: We established a genetic diagnosis for 67% of probands and their families, with over half of all diagnoses attributable to variants in five genes: SLC26A4, MYO15A, MYO7A, CDH23 and PCDH15. As a reflection of the power of consanguinity mapping, 26 genes were identified as causative for NSHL in the Iranian population for the first time. In total, 179 deafness-causing variants were identified in 40 genes in 201 probands, including 110 novel single nucleotide or small insertion-deletion variants and three novel CNV. Several variants represent founder mutations. CONCLUSION: This study attests to the power of TGE and massively parallel sequencing as a diagnostic tool for the evaluation of hearing loss in Iran, and expands on our understanding of the genetics of HHL in this country. Families negative for variants in the genes represented on this panel represent an excellent cohort for novel gene discovery.

Is it Usher syndrome? Collaborative diagnosis and molecular genetics of patients with visual impairment and hearing loss.

Background: Usher syndrome is the most common hereditary syndrome combining deafness and blindness. In the 2017 National Child Count of Children and Youth who are Deaf-Blind, Usher syndrome represented 329 of 10,000 children, but there were also at least 70 other etiologies of deaf-blindness documented. The purpose of this study was to analyze the work-up and ultimate diagnoses of 21 consecutive families who presented to the Genetic Eye-Ear Clinic (GEEC) at the University of Iowa. Our hypothesis was that most families referred to the GEEC would have initial and final diagnoses of Usher syndrome.Materials and Methods: Patients were identified through an IRB approved retrospective chart review of referrals to the GEEC between 2012 and 2019. Details about each patient's history, exam, and clinical and genetic work-up were recorded.Results: From 2012 to 2019, 21 families (25 patients) were referred to the collaborative GEEC. Overall molecular diagnostic rate in this cohort was 14/21 (67%). Evaluation resulted in a change of diagnosis in 11/21 (52%) families. Ultimately, there were eleven unique diagnoses including hereditary, non-hereditary, and independent causes of combined visual impairment and hearing loss. The most common diagnosis was Usher syndrome, which represented 6/21 (29%) families.Conclusions: Providing a correct diagnosis for patients with visual impairment and hearing loss can be challenging for clinicians and their patients, but it can greatly improve clinical care and outcomes. We recommend an algorithm that includes multidisciplinary collaboration, careful clinical evaluation, strategic molecular testing, and consideration of a broad differential diagnosis.

Genetic variants in the peripheral auditory system significantly affect adult cochlear implant performance.

BACKGROUND: Cochlear implantation is an effective habilitation modality for adults with significant hearing loss. However, post-implant performance is variable. A portion of this variance in outcome can be attributed to clinical factors. Recent physiological studies suggest that the health of the spiral ganglion also impacts post-operative cochlear implant outcomes. The goal of this study was to determine whether genetic factors affecting spiral ganglion neurons may be associated with cochlear implant performance. METHODS: Adults with post-lingual deafness who underwent cochlear implantation at the University of Iowa were studied. Pre-implantation evaluation included comprehensive genetic testing for genetic diagnosis. A novel score of genetic variants affecting genes with functional effects in the spiral ganglion was calculated. A Z-scored average of up to three post-operative speech perception tests (CNC, HINT, and AzBio) was used to assess outcome. RESULTS: Genetically determined spiral ganglion health affects cochlear implant outcomes, and when considered in conjunction with clinically determined etiology of deafness, accounts for 18.3% of the variance in postoperative speech recognition outcomes. Cochlear implant recipients with deleterious genetic variants that affect the cochlear sensory organ perform significantly better on tests of speech perception than recipients with deleterious genetic variants that affect the spiral ganglion. CONCLUSION: Etiological diagnosis of deafness including genetic testing is the single largest predictor of postoperative speech outcomes in adult cochlear implant recipients. A detailed understanding of the genetic underpinning of hearing loss will better inform pre-implant counseling. The method presented here should serve as a guide for further research into the molecular physiology of the peripheral auditory system and cochlear implants.

Detection and Confirmation of Deafness-Causing Copy Number Variations in the STRC Gene by Massively Parallel Sequencing and Comparative Genomic Hybridization.

OBJECTIVE: Copy number variations (CNVs), a major cause of genetic hearing loss, most frequently involve the STRC gene, located on chr15q15.3 and causally related to autosomal recessive non-syndromic hearing loss (ARNSHL) at the DFNB16 locus. The interpretation of STRC sequence data can be challenging due to the existence of a virtually identical pseudogene, pSTRC, that promotes complex genomic rearrangements in this genomic region. Targeted genomic enrichment with massively parallel sequencing (TGE+MPS) has emerged as the preferred method by which to provide comprehensive genetic testing for hearing loss. We aimed to identify CNVs in the STRC region using established and validated bioinformatics methods. METHODS: We used TGE+MPS to identify the genetic cause of hearing loss. The CNV results were confirmed with customized array comparative genomic hybridization (array CGH). RESULTS: Three probands with progressive mild to moderate hearing loss were found among 40 subjects with ARNSHL to segregate homozygous STRC deletions and gene to pseudogene conversion. Array CGH showed that the deletions/conversions span multiple genes outside of the exons captured by TGE+MPS. CONCLUSION: These data further validate the necessity to integrate the detection of both simple variant changes and complex genomic rearrangements in the clinical diagnosis of genetic hearing loss.