IVS8+1 DelG, a Novel Splice Site Mutation Causing DFNA5 Deafness in a Chinese Family

Gain-of-function variants in GSDME cause pyroptosis and apoptosis associated with post-lingual hearing loss

Gasdermin E (GSDME), a member of the gasdermin protein family, is associated with post-lingual hearing loss. All GSDME pathogenic mutations lead to skipping exon 8; however, the molecular mechanisms underlying hearing loss caused by GSDME mutants remain unclear. GSDME was recently identified as one of the mediators of programmed cell death, including apoptosis and pyroptosis. Therefore, in this study, we injected mice with GSDME mutant (MT) and examined the expression levels to assess its effect on hearing impairment. We observed loss of hair cells in the organ of Corti and spiral ganglion neurons. Further, the N-terminal release from the GSDME mutant in HEI-OC1 cells caused pyroptosis, characterized by cell swelling and rupture of the plasma membrane, releasing lactate dehydrogenase and cytokines such as interleukin-1β. We also observed that the N-terminal release from GSDME mutants could permeabilize the mitochondrial membrane, releasing cytochromes and activating the mitochondrial apoptotic pathway, thereby generating possible positive feedback on the cleavage of GSDME. Furthermore, we found that treatment with disulfiram or dimethyl fumarate might inhibit pyroptosis and apoptosis by inhibiting the release of GSDME-N from GSDME mutants. In conclusion, this study elucidated the molecular mechanism associated with hearing loss caused by GSDME gene mutations, offering novel insights for potential treatment strategies.

The gasdermin family: emerging therapeutic targets in diseases

The gasdermin (GSDM) family has garnered significant attention for its pivotal role in immunity and disease as a key player in pyroptosis. This recently characterized class of pore-forming effector proteins is pivotal in orchestrating processes such as membrane permeabilization, pyroptosis, and the follow-up inflammatory response, which are crucial self-defense mechanisms against irritants and infections. GSDMs have been implicated in a range of diseases including, but not limited to, sepsis, viral infections, and cancer, either through involvement in pyroptosis or independently of this process. The regulation of GSDM-mediated pyroptosis is gaining recognition as a promising therapeutic strategy for the treatment of various diseases. Current strategies for inhibiting GSDMD primarily involve binding to GSDMD, blocking GSDMD cleavage or inhibiting GSDMD-N-terminal (NT) oligomerization, albeit with some off-target effects. In this review, we delve into the cutting-edge understanding of the interplay between GSDMs and pyroptosis, elucidate the activation mechanisms of GSDMs, explore their associations with a range of diseases, and discuss recent advancements and potential strategies for developing GSDMD inhibitors.

[Splicing mutations of GSDME cause late-onset non-syndromic hearing loss]

Objective:To dentify the genetic and audiological characteristics of families affected by late-onset hearing loss due to GSDMEgene mutations, aiming to explore clinical characteristics and pathogenic mechanisms for providing genetic counseling and intervention guidance. Methods:Six families with late-onset hearing loss from the Chinese Deafness Genome Project were included. Audiological tests, including pure-tone audiometry, acoustic immittance, speech recognition scores, auditory brainstem response, and distortion product otoacoustic emission, were applied to evaluate the hearing levels of patients. Combining with medical history and physical examination to analyze the phenotypic differences between the probands and their family members. Next-generation sequencing was used to identify pathogenic genes in probands, and validations were performed on their relatives by Sanger sequencing. Pathogenicity analysis was performed according to the American College of Medical Genetics and Genomics Guidelines. Meanwhile, the pathogenic mechanisms of GSDME-related hearing loss were explored combining with domestic and international research progress. Results:Among the six families with late-onset hearing loss, a total of 30 individuals performed hearing loss. The onset of hearing loss in these families ranged from 10 to 50 years（mean age: 27.88±9.74 years）. In the study, four splicing mutations of the GSDME were identified, including two novel variants: c. 991－7C>G and c. 1183+1G>T. Significantly, the c. 991－7C>G was a de novo variant. The others were previously reported variants: c. 991-1G>C and c. 991-15_991-13del, the latter was identified in three families. Genotype-phenotype correlation analysis revealed that probands with the c. 991－7C>G and c. 1183+1G>T performed a predominantly high-frequency hearing loss. The three families carrying the same mutation exhibited varying degrees of hearing loss, with an annual rate of hearing deterioration exceeding 0.94 dB HL/year. Furthermore, follow-up of interventions showed that four of six probands received intervention（66.67%）, but the results of intervention varied. Conclusion:The study analyzed six families with late-onset non-syndromic hearing loss linked to GSDME mutations, identifying four splicing variants. Notably, c. 991－7C>G is the first reported de novo variant of GSDME globally. Audiological analysis revealed that the age of onset generally exceeded 10 years,with variable effectiveness of interventions.

Current development of patient-specific induced pluripotent stem cells harbouring mitochondrial gene mutations and their applications in the treatment of sensorineural hearing loss

Of all the human body's sensory systems, the auditory system is perhaps its most intricate. Hearing loss can result from even modest damage or cell death in the inner ear, and is the most common form of sensory loss. Human hearing is made possible by the sensory epithelium, the lateral wall, and auditory nerves. The most prominent functional cells in the sensory epithelium are outer hair cells (OHCs), inner hair cells (IHCs), and supporting cells. Different sound frequencies are processed by OHCs and IHCs in different cochlear regions, with those in the apex responsible for low frequencies and those in the basal region responsible for high frequencies. Hair cells can be damaged or destroyed by loud noise, aging process, genetic mutations, ototoxicity, infection, and illness. As such, they are a primary target for treating sensorineural hearing loss. Other areas known to affect hearing include spiral ganglion neurons (SGNs) in the auditory nerve. Age-related degradation of HCs and SGNs can also cause hearing loss. The aim of this review is to introduce the roles of mitochondria in human auditory system and the inner ear's main cell types and cellular functions, before going on to detail the likely health benefits of iPSC technology. We posit that patient-specific iPSCs with mitochondrial gene mutations will be an important aspect of regenerative medicine and will lead to significant progress in the treatment of SNHL.

Alternative splicing in shaping the molecular landscape of the cochlea

The cochlea is a complex organ comprising diverse cell types with highly specialized morphology and function. Until now, the molecular underpinnings of its specializations have mostly been studied from a transcriptional perspective, but accumulating evidence points to post-transcriptional regulation as a major source of molecular diversity. Alternative splicing is one of the most prevalent and well-characterized post-transcriptional regulatory mechanisms. Many molecules important for hearing, such as cadherin 23 or harmonin, undergo alternative splicing to produce functionally distinct isoforms. Some isoforms are expressed specifically in the cochlea, while some show differential expression across the various cochlear cell types and anatomical regions. Clinical phenotypes that arise from mutations affecting specific splice variants testify to the functional relevance of these isoforms. All these clues point to an essential role for alternative splicing in shaping the unique molecular landscape of the cochlea. Although the regulatory mechanisms controlling alternative splicing in the cochlea are poorly characterized, there are animal models with defective splicing regulators that demonstrate the importance of RNA-binding proteins in maintaining cochlear function and cell survival. Recent technological breakthroughs offer exciting prospects for overcoming some of the long-standing hurdles that have complicated the analysis of alternative splicing in the cochlea. Efforts toward this end will help clarify how the remarkable diversity of the cochlear transcriptome is both established and maintained.

Mutation analysis of the GSDME gene in a Chinese family with non-syndromic hearing loss

Background

Hearing loss is considered one of the most common sensory nervous system defects, about 60% of which are caused by genetic factors. Mutations in the GSDME gene are responsible for post-lingual, progressive, autosomal dominant hearing loss. This study aimed to characterize the genetic mutations and clinical features of a Chinese GSDME family.

Methods

After clinical evaluations, high-throughput DNA sequencing was conducted using DNA samples from this family. Sanger sequencing was performed to verify the suspected variants. A detailed genotype and phenotype analysis were carried out. Gene set enrichment analysis (GSEA) was performed to identify the signaling pathway associated with GSDME expression.

Results

A known hotspot heterozygous splice-site variation (c.991-15_991_13delTTC) was identified and shown to segregate with the hearing loss phenotype in the family. This pathogenic splice-site variant results in skipping of exon 8. GSEA analysis identified changes in regulation of the cell cycle checkpoint, peroxisome, and amino acid metabolism signaling pathways.

Conclusions

We identified a reported mutation in the GSDME gene. Our findings support the 3 bp deletion (c.991-15_991-13del) was a hotspot variation, and it emerged as an essential contributor to autosomal dominant progressive hearing loss in East Asians. GSDME gene is closely associated with a range of signaling pathways. These characterized findings may provide new evidence for pathogenesis.

A novel splice site variant c.1183 + 1 G > C in DFNA5 causing autosomal dominant nonsyndromic hearing loss in a Chinese family

BACKGROUND

The most frequent clinical presentation of autosomal dominant nonsyndromic hearing loss (ADNSHL) is bilateral, symmetrical, postlingual progressive sensorineural hearing loss, which begins with impairment at high frequencies and eventually progresses to hearing loss at all frequencies. Autosomal dominant deafness-5 (DFNA5) is a subtype of ADNSHL caused by heterozygous variants in the gasdermin E (GSDME, also known as DFNA5) gene.

METHODS

Deafness gene NGS panel analysis were performed on the proband of a six-generation Chinese family with hearing loss. The co-segregation analysis between the hearing loss and the novel variant was analyzed by Sanger sequencing and pure-tone audiometry. The minigene splicing assay was performed to evaluate the potential effect of the variant on messenger RNA splicing in vitro.

RESULTS

The family exhibited autosomal dominant, progressive, postlingual, nonsyndromic sensorineural hearing loss, which was similar to that of the previously reported DFNA5 families. A novel heterozygous splice site variant in GSDME gene intron 8 was identified, which co-segregated with the hearing loss phenotype of the family. The variant caused skipping of exon 8 in the mutant transcript, leading to the direct linking of exons 7 and 9.

CONCLUSIONS

We identified a novel GSDME splice site variant c.1183 + 1 G > C in an extended Chinese family, which led to the skipping of exon 8. The results extended the pathogenic variants spectrum of the GSDME gene, provided further support for the 'gain-of-function' mechanism of DFNA5, and afforded a molecular interpretation for these patients with ADNSHL.

Modulation of Autoimmune and Autoinflammatory Diseases by Gasdermins

Autoimmune diseases and autoinflammatory diseases are two types of the immune system disorders. Pyroptosis, a highly inflammatory cell death, plays an important role in diseases of immune system. The gasdermins belong to a pore-forming protein gene family which are mainly expressed in immune cells, gastrointestinal tract, and skin. Gasdermins are regarded as an executor of pyroptosis and have been shown to possess various cellular functions and pathological effects such as pro-inflammatory, immune activation, mediation of tumor, etc. Except for infectious diseases, the vital role of gasdermins in autoimmune diseases, autoinflammatory diseases, and immune-related neoplastic diseases has been proved recently. Therefore, gasdermins have been served as a potential therapeutic target for immune disordered diseases. The review summarizes the basic molecular structure and biological function of gasdermins, mainly discusses their role in autoimmune and autoinflammatory diseases, and highlights the recent research on gasdermin family inhibitors so as to provide potential therapeutic prospects.

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

Identification of a novel DFNA5 mutation, IVS7-2 a > G, in a Chinese family with non-syndromic sensorineural hearing loss

BACKGROUND

To date, seven DFNA5 mutations have been reported in families with autosomal dominant non-syndromic hearing loss worldwide. All the mutations cause exon 8 skipping at the mRNA level, that led to the protein truncated and the protein could exert a gain of ototoxic function.

OBJECTIVE

In this study, we found an autosomal-dominant non-syndromic hearing loss Chinese pedigree which spanned four generations and comprised 43 members. We want to identify the causative gene and mutation.

METHODS

Application of microsatellite markers on DFNA 23 loci preliminary screening of 25 genes, data were analyzed by linkage analysis.

RESULTS

We mapped the locus to the region between D7S629 and D7S516 (two-point lod-score of 5.39) with the application of 8 microsatellite markers. By direct sequencing of candidate genes in mapping region, we identified a novel missense mutation ivs7-2 A > G in DFNA5 gene, which was faithfully cosegregated with hearing loss in the family.

CONCLUSION AND SIGNIFICANCE

The missense mutation in intron 7 of DFNA5 causes skipping of exon 8, resulting in premature termination of the open reading frame. This type of mutation has repeatedly confirmed that it provides more evidence for the previous view and provides a more solid foundation for future research.

AudioGene: refining the natural history of KCNQ4, GSDME, WFS1, and COCH-associated hearing loss

Autosomal dominant non-syndromic hearing loss (ADNSHL) displays gene-specific progression of hearing loss, which is amenable to sequential audioprofiling. We sought to refine the natural history of ADNSHL by examining audiometric data in 5-year increments. 2175 audiograms were included from four genetic causes of ADNSHL-KCNQ4 (DFNA2), GSDME (DFNA5), WFS1 (DFNA6/14/38), and COCH (DFNA9). Annual threshold deterioration (ATD) was calculated for each gene: for the speech-frequency pure tone average, the ATD, respectively, was 0.72 dB/year, 0.94 dB/year, 0.53 dB/year, and 1.41 dB/year, with the largest drops occurring from ages 45-50 (0.89 dB/year; KCNQ4), 5-10 (1.42 dB/year; GSDME), 40-45 (0.83 dB/year; WFS1), and 50-55 (2.09 dB/year; COCH). 5-year interval analysis of audiograms reveals the gene specific natural history of KCNQ4, GSDME, WFS1 and COCH-related progressive hearing loss. Identifying ages at which hearing loss is most rapid informs clinical care and patient expectations. Natural history data are also essential to define outcomes of clinical trials that test novel therapies designed to correct or ameliorate these genetic forms of hearing loss.

Identification of the First Single GSDME Exon 8 Structural Variants Associated with Autosomal Dominant Hearing Loss

GSDME, also known as DFNA5, is a gene implicated in autosomal dominant nonsyndromic hearing loss (ADNSHL), affecting, at first, the high frequencies with a subsequent progression over all frequencies. To date, all the GSDME pathogenic variants associated with deafness lead to skipping of exon 8. In two families with apparent ADNSHL, massively parallel sequencing (MPS) integrating a coverage-based method for detection of copy number variations (CNVs) was applied, and it identified the first two causal GSDME structural variants affecting exon 8. The deleterious impact of the c.991-60_1095del variant, which includes the acceptor splice site sequence of exon 8, was confirmed by the study of the proband’s transcripts. The second mutational event is a complex rearrangement that deletes almost all of the exon 8 sequence. This study increases the mutational spectrum of the GSDME gene and highlights the crucial importance of MPS data for the detection of GSDME exon 8 deletions, even though the identification of a causal single-exon CNV by MPS analysis is still challenging.

Pyroptosis in Cancer: Friend or Foe?

Simple Summary

Pyroptosis is a new form of programmed cell death that differs from apoptosis in terms of its release of inflammatory factors and its characteristic bubble-like morphology. Pyroptosis was first discovered in the process of immune defense against bacterial infection, but the field of research soon spread to other inflammatory diseases and cancer. As cancer constitutes a serious risk for public health, numerous studies investigating pyroptosis in cancer have been carried out during these years. Tumorigenesis and new therapeutic treatments have been the focus of much recent research. This review discusses the role of pyroptosis in tumorigenesis and its influence on tumor immunity.

Abstract

Pyroptosis is an inflammatory form of programmed cell death that is mediated by pore-forming proteins such as the gasdermin family (GSDMs), including GSDMA-E. Upon cleavage by activated caspases or granzyme proteases, the N-terminal of GSDMs oligomerizes in membranes to form pores, resulting in pyroptosis. Though all the gasdermin proteins have been studied in cancer, the role of pyroptosis in cancer remains mysterious, with conflicting findings. Numerous studies have shown that various stimuli, such as pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs), and chemotherapeutic drugs, could trigger pyroptosis when the cells express GSDMs. However, it is not clear whether pyroptosis in cancer induced by chemotherapeutic drugs or CAR T cell therapy is beneficial or harmful for anti-tumor immunity. This review discusses the discovery of pyroptosis as well as its role in inflammatory diseases and cancer, with an emphasis on tumor immunity.

Channelling inflammation: gasdermins in physiology and disease

Gasdermins were recently identified as the mediators of pyroptosis - inflammatory cell death triggered by cytosolic sensing of invasive infection and danger signals. Upon activation, gasdermins form cell membrane pores, which release pro-inflammatory cytokines and alarmins and damage the integrity of the cell membrane. Roles for gasdermins in autoimmune and inflammatory diseases, infectious diseases, deafness and cancer are emerging, revealing potential novel therapeutic avenues. Here, we review current knowledge of the family of gasdermins, focusing on their mechanisms of action and roles in normal physiology and disease. Efforts to develop drugs to modulate gasdermin activity to reduce inflammation or activate more potent immune responses are highlighted.

Mini-Review: GSDME-Mediated Pyroptosis in Diabetic Nephropathy

Pyroptosis is a recently identified type of lytic programmed cell death, in which pores form in the plasma membrane, and cells swell, rupture, and then release their contents, including inflammatory cytokines. Molecular studies indicated that pyroptosis may occur via a gasdermin D (GSDMD) and caspase-1 (Casp1) -dependent classical pathway, a GSDMD and Casp11/4/5-dependent non-classical pathway, or a gasdermin E (GSDME) and Casp3-dependent pathway. Studies of animal models and humans indicated that pyroptosis can exacerbate several complications of diabetes, including diabetic nephropathy (DN), a serious microvascular complication of diabetes. Many studies investigated the mechanism mediating the renoprotective effect of GSDMD regulation in the kidneys of patients and animal models with diabetes. As a newly discovered regulatory mechanism, GSDME and Casp3-dependent pyroptotic pathway in the progression of DN has also attracted people's attention. Z-DEVD-FMK, an inhibitor of Casp3, ameliorates albuminuria, improves renal function, and reduces tubulointerstitial fibrosis in diabetic mice, and these effects are associated with the inhibition of GSDME. Studies of HK-2 cells indicated that the molecular and histological features of secondary necrosis were present following glucose stimulation due to GSDME cleavage, such as cell swelling, and release of cellular contents. Therefore, therapies targeting Casp3/GSDME-dependent pyroptosis have potential for treatment of DN. A novel nephroprotective strategy that employs GSDME-derived peptides which are directed against Casp3-induced cell death may be a key breakthrough. This mini-review describes the discovery and history of research in this pyroptosis pathway and reviews the function of proteins in the gasdermin family, with a focus on the role of GSDME-mediated pyroptosis in DN. Many studies have investigated the impact of GSDME-mediated pyroptosis in kidney diseases, and these studies used multiple interventions, in vitro models, and in vivo models. We expect that further research on the function of GDSME in DN may provide valuable insights that may help to improve treatments for this disease.

GSDME and its role in cancer: From behind the scenes to the front of the stage

Gasdermin E (GSDME), a gene originally involved in hereditary hearing loss, has been associated with several types of cancer in the last two decades. Recently, GSDME was identified as a pore-forming molecule, which is activated following caspase-3-mediated cleavage resulting in so-called secondary necrosis following apoptotic cell death, or in primary necrotic cell death without an apoptotic phase, so-called pyroptosis-like. This implication in cell death execution suggests its potential role as a tumor suppressor. GSDME also exhibited a cancer type-specific differential methylation pattern between tumor tissues and normal cells, implying GSDME gene methylation as both a pan-cancer and cancer type-specific detection biomarker. A bit paradoxically, GSDME protein expression is considered to be less suited as biomarker, and although its ablation does not protect the cell against eventual cell death, its protein expression might still operate in tumor immunogenicity due to its capacity to induce (secondary) necrotic cell death, which has enhanced immunogenic properties. Additionally, GSDME gene expression has been shown to be associated with favorable prognosis following chemotherapy, and it could therefore be a potential predictive biomarker. We provide an overview of the different associations between GSDME gene methylation, gene expression and tumorigenesis, and explore their potential use in the clinic. Our review only focuses on GSDME and summarizes the current knowledge and most recent advances on GSDME's role in cancer formation, its potential as a biomarker in cancer and on its promising role in immunotherapies and antitumor immune response.

Case Report: Novel Heterozygous DFNA5 Splicing Variant Responsible for Autosomal Dominant Non-syndromic Hearing Loss in a Chinese Family

Autosomal dominant non-syndromic hearing loss (ADNSHL) has a broad phenotypic spectrum which includes bilateral, symmetrical, and high-frequency sensorineural hearing loss, that eventually progresses into hearing loss at all frequencies. Several genetic variations have been identified as causal factors underlying deafness, autosomal dominant 5 (DFNA5) gene-related hearing loss. Here, we report a novel mutation (c.991-1G > C) in DFNA5, which co-segregated with late-onset ADNSHL in a Chinese family and was identified via exome sequencing and Sanger sequencing of DNA from peripheral blood of the family members. Further sequencing of cDNA derived from peripheral blood mRNA revealed that the c.991-1G >C mutation led to the skipping of exon 8, which is a known pathogenic mechanism for DFNA5-related hearing loss.

DFNA5 (GSDME) c.991-15_991-13delTTC: Founder Mutation or Mutational Hotspot?

Deafness due to mutations in the DFNA5 gene is caused by the aberrant splicing of exon 8, which results in a constitutively active truncated protein. In a large family of European descent (MORL-ADF1) segregating autosomal dominant nonsyndromic hearing loss, we used the OtoSCOPE platform to identify the genetic cause of deafness. After variant filtering and prioritization, the only remaining variant that segregated with the hearing loss in the family was the previously described c.991-15_991-13delTTC mutation in DFNA5. This 3-base pair deletion in the polypyrimidine of intron 7 is a founder mutation in the East Asian population. Using ethnicity-informative markers and haplotype reconstruction within the DFNA5 gene, we confirmed family MORL-ADF1 is of European ancestry, and that the c.991-15_991-13delTTC mutation arose on a unique haplotype, as compared to that of East Asian families segregating this mutation. In-depth audiometric analysis showed no statistical difference between the audiometric profile of family MORL-ADF1 and the East Asian families. Our data suggest the polypyrimidine tract in intron 7 may be a hotspot for mutations.

Gasdermins: pore-forming activities and beyond

Gasdermins (GSDMs) belong to a protein superfamily that is found only in vertebrates and consists of GSDMA, GSDMB, GSDMC, GSDMD, DFNA5 (a.k.a. GSDME) and DFNB59 (a.k.a. Pejvakin (PJVK)) in humans. Except for DFNB59, all members of the GSDM superfamily contain a conserved two-domain structure (N-terminal and C-terminal domains) and share an autoinhibitory mechanism. When the N-terminal domain of these GSDMs is released, it possesses pore-forming activity that causes inflammatory death associated with the loss of cell membrane integrity and release of inflammatory mediators. It has also been found that spontaneous mutations occurring in the genes of GSDMs have been associated with the development of certain autoimmune disorders, as well as cancers. Here, we review the current knowledge of the expression profile and regulation of GSDMs and the important roles of this protein family in inflammatory cell death, tumorigenesis and other related diseases.

The deafness gene GSDME: its involvement in cell apoptosis, secondary necrosis, and cancers

Gasdermin E (GSDME), also called DFNA5, is a member of the gasdermin family. GSDME is involved in the regulation of apoptosis and necrosis. The N-terminal domain of GSDME displays an apoptosis-inducing activity while the C-terminal domain may serve as an apoptosis-inhibiting regulator by shielding the N-terminal domain. Besides its function in the regulation of apoptosis, GSDME was recently reported to be a substrate of caspase-3 and cleavage of GSDME by caspase-3 into necrotic N-terminal fragment leads to the induction of secondary necrosis. GSDME was first identified as a deafness gene because its mutation was associated with a specific form of autosomal dominant progressive sensorineural hearing loss. Furthermore, GSDME has been considered a tumor suppressor implicated in several types of cancer. This mini-review summarized recent reports relevant to the functions of GSDME in the regulation of apoptosis and necrosis as well as its clinical relevance.

Novel recessive PDZD7 biallelic mutations associated with hereditary hearing loss in a Chinese pedigree

BACKGROUND

Autosomal recessive non-syndromic hearing loss (ARNSHL) is a highly heterogeneous genetic disease. PDZD7 is a new ARNSHL associated gene. Until now, nine PDZD7 biallelic mutation families with ARNSHL have been reported. Here we report a case of Chinese patient with ARNSHL linked to novel mutations in PDZD7 genes.

METHOD

The pathogenic mutations were detected by whole exome sequencing for hereditary deafness-related genes of both the proband and his parents. We used kinship detection, mutational hazard prediction, genotype-phenotype correlation analysis and variation screening for potential pathogenic mutations. Re-sequencing was used to confirm the mutations by Sanger sequence. Real time quantitative PCR (RT-qPCR) was used to analyze the PDZD7 gene expression. Population-based screening for variation frequency, evolutionary conservation comparisons, pathogenicity evaluation, and protein structure prediction were conducted to assess the pathogenicity of the novel mutations of PDZD7 gene.

RESULTS

We determined three variants of the PDZD7 gene that contributed to the deafness of the patient (PDZD7 c.192G > A, p. Met64Ile; c.1648C > T p. Gln550* and c.2341_2352delCGCAGCCGCAGCp. Arg781_Ser 784del). Pathogenic analysis in accordance with the ACMG/AMP Standards and Guidelines identified two novel mutations as Likely Pathogenic. The expression level of PDZD7 gene in the patient was decreased compared to the normal control (P < 0.001).

CONCLUSION

Three mutations in PDZD7 gene linked to ARNSHL were identified in a Chinese pedigree. The findings expand not only our knowledge of genetic causes of ARNSHL, but also PDZD7 genes mutation spectrum of the disease. They will aid personalized genetic counseling, molecular diagnostics and clinical management of this condition.

Further evidence for "gain-of-function" mechanism of DFNA5 related hearing loss

To report two DFNA5 pathogenic splice-site variations and a novel benign frameshift variation to further support the gain-of-function mechanism of DFNA5 related hearing impairment, targeted genes capture and next generation sequencing were performed on selected members from Family 1007208, 1007081 and a sporadic case with sensorineural hearing loss. Reverse transcriptase polymerase chain reaction was conducted on the proband from Family 1007208 to test how the splice-site variation affects the transcription in RNA level. A novel heterozygous splice-site variation c.991-3 C > A in DFNA5 was found in Family 1007208; a known hotspot heterozygous splice-site variation c.991-15_991_13delTTC was identified in Family 1007081. Both the splice-site variations were segregated with the late onset hearing loss phenotype, leading to the skipping of exon 8 at RNA level. In addition, a novel DFNA5 frameshift variation c.116_119delAAAA was found in the sporadic case, but was not segregated with the hearing impairment phenotype. In conclusion, we identified one novel and one known pathogenic DFNA5 splice-site variation in two Chinese Families, as well as a novel DFNA5 frameshift variation c.116_119delAAAA in a sporadic case, which does not the cause for the hearing loss case. Both the two pathogenic splice-site variations and the nonpathogenic frameshift variation provide further support for the specific gain-of-function mechanism of DFNA5 related hearing loss.

Exonic mutations and exon skipping: Lessons learned from DFNA5

Dysregulation of splicing is a common factor underlying many inherited diseases including deafness. For one deafness-associated gene, DFNA5, perturbation of exon 8 splicing results in a constitutively active truncated protein. To date, only intronic mutations have been reported to cause exon 8 skipping in patients with DFNA5-related deafness. In five families with postlingual progressive autosomal dominant non-syndromic hearing loss, we employed two next-generation sequencing platforms-OtoSCOPE and whole exome sequencing-followed by variant filtering and prioritization based on both minor allele frequency and functional consequence using a customized bioinformatics pipeline to identify three novel and two recurrent mutations in DFNA5 that segregated with hearing loss in these families. The three novel mutations are all missense variants within exon 8 that are predicted computationally to decrease splicing efficiency or abolish it completely. We confirmed their functional impact in vitro using mini-genes carrying each mutant DFNA5 exon 8. In so doing, we present the first exonic mutations in DFNA5 to cause deafness, expand the mutational spectrum of DFNA5-related hearing loss, and highlight the importance of assessing the effect of coding variants on splicing.