Identification of Two Disease-causing Genes TJP2 and GJB2 in a Chinese Family with Unconditional Autosomal Dominant Nonsyndromic Hereditary Hearing Impairment

Genotype correlates with clinical course and outcome of children with tight junction protein 2 (TJP2) deficiency-related cholestasis

BACKGROUND AND AIMS

The study aimed to describe the clinical course and outcomes, and analyze the genotype-phenotype correlation in patients with tight junction protein 2 (TJP2) deficiency.

APPROACH AND RESULTS

Data from all children with chronic cholestasis and either homozygous or compound heterozygous mutations in TJP2 were extracted and analyzed. The patients were categorized into 3 genotypes: TJP2-A (missense mutations on both alleles), TJP2-B (missense mutation on one allele and a predicted protein-truncating mutation [PPTM] on the other), and TJP2-C (PPTMs on both alleles). A total of 278 cases of genetic intrahepatic cholestasis were studied, with TJP2 deficiency accounting for 44 cases (15.8%). Of these, 29 were homozygous and 15 were compound heterozygous variants of TJP2 . TJP2-A genotype was identified in 21 (47.7%), TJP2-B in 7 cases (15.9%), and TJP2-C in 16 cases (36.4%), respectively. Patients with the TJP2-C genotype were more likely to experience early infantile cholestasis (87.5% vs. 53.5%, p =0.033), less likely to clear jaundice (12.5% vs. 52.2%, p =0.037), more likely to develop ascites, and had higher serum bile acids. Patients with the TJP2-C genotype were more likely to die or require liver transplantation (native liver survival: 12.5% vs. 78.6%, p <0.001), with a median age at death/liver transplantation of 2.5 years. Cox regression analysis revealed that TJP2-C mutations ( p =0.003) and failure to resolve jaundice ( p =0.049) were independent predictors of poor outcomes.

CONCLUSIONS

Patients with the TJP2-C genotype carrying PPTMs in both alleles had a rapidly progressive course, leading to early decompensation and death if they did not receive timely liver transplantation.

Gene regulation analysis of patient-derived iPSCs and its CRISPR-corrected control provides a new tool for studying perturbations of ELMOD3 c.512A>G mutation during the development of inherited hearing loss

The ELMOD3 gene is implicated in causing autosomal recessive/dominant non-syndromic hearing loss in humans. However, the etiology has yet to be completely elucidated. In this study, we generated a patient-derived iPSC line carrying ELMOD3 c.512A>G mutation. In addition, the patient-derived iPSC line was corrected by CRISPR/Cas9 genome editing system. Then we applied RNA sequencing profiling to compare the patient-derived iPSC line with different controls, respectively (the healthy sibling-derived iPSCs and the CRISPR/Cas9 corrected iPSCs). Functional enrichment and PPI network analysis revealed that differentially expressed genes (DEGs) were enriched in the gene ontology, such as sensory epithelial development, intermediate filament cytoskeleton organization, and the regulation of ion transmembrane transport. Our current work provided a new tool for studying how disruption of ELMOD3 mechanistically drives hearing loss.

Zonula Occludens Proteins Signaling in Inflammation and Tumorigenesis

Tight junction (TJ) is the barrier of epithelial and endothelial cells to maintain paracellular substrate transport and cell polarity. As one of the TJ cytoplasmic adaptor proteins adjacent to cell membrane, zonula occludens (ZO) proteins are responsible for connecting transmembrane TJ proteins and cytoplasmic cytoskeleton, providing a binding platform for transmembrane TJ proteins to maintain the barrier function. In addition to the basic structural function, ZO proteins play important roles in signal regulation such as cell proliferation and motility, the latter including cell migration, invasion and metastasis, to influence embryonic development, tissue homeostasis, damage repair, inflammation, tumorigenesis, and cancer progression. In this review, we will focus on the signal regulating function of ZO proteins in inflammation and tumorigenesis, and discuss the limitations of previous research and future challenges in ZO protein research.

Clinical outcomes of surgical management for rare types of progressive familial intrahepatic cholestasis: a case series

Background

Progressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of genetic autosomal recessive diseases that cause severe cholestasis, which progresses to cirrhosis and liver failure, in infancy or early childhood. We herein report the clinical outcomes of surgical management in patients with four types of PFIC.

Case presentation

Six patients diagnosed with PFIC who underwent surgical treatment between 1998 and 2020 at our institution were retrospectively assessed. Living-donor liver transplantation (LDLT) was performed in 5 patients with PFIC. The median age at LDLT was 4.8 (range: 1.9–11.4) years. One patient each with familial intrahepatic cholestasis 1 (FIC1) deficiency and bile salt export pump (BSEP) deficiency died after LDLT, and the four remaining patients, one each with deficiency of FIC1, BSEP, multidrug resistance protein 3 (MDR3), and tight junction protein 2 (TJP2), survived. One FIC1 deficiency recipient underwent LDLT secondary to deterioration of liver function, following infectious enteritis. Although he underwent LDLT accompanied by total external biliary diversion, the patient died because of PFIC-related complications. The other patient with FIC1 deficiency had intractable pruritus and underwent partial internal biliary diversion (PIBD) at 9.8 years of age, pruritus largely resolved after PIBD. One BSEP deficiency recipient, who had severe graft damage, experienced recurrence of cholestasis due to the development of antibodies against BSEP after LDLT, and eventually died due to graft failure. The other patient with BSEP deficiency recovered well after LDLT and there was no evidence of posttransplant recurrence of cholestasis. In contrast, recipients with MDR3 or TJP2 deficiency showed good courses and outcomes after LDLT.

Conclusions

Although LDLT was considered an effective treatment for PFIC, the clinical courses and outcomes after LDLT were still inadequate in patients with FIC1 and BSEP deficiency. LDLT accompanied by total biliary diversion may not be as effective for patients with FIC1 deficiency.

Zonula occludens 2 and Cell-Cell Contacts Are Required for Normal Nuclear Shape in Epithelia

MAGUK protein ZO-2 is present at tight junctions (TJs) and nuclei. In MDCK ZO-2 knockdown (KD) cells, nuclei exhibit an irregular shape with lobules and indentations. This condition correlates with an increase in DNA double strand breaks, however cells are not senescent and instead become resistant to UV-induced senescence. The irregular nuclear shape is also observed in isolated cells and in those without TJs, due to the lack of extracellular calcium. The aberrant nuclear shape of ZO-2 KD cells is not accompanied by a reduced expression of lamins A/C and B and lamin B receptors. Instead, it involves a decrease in constitutive and facultative heterochromatin, and microtubule instability that is restored with docetaxel. ZO-2 KD cells over-express SUN-1 that crosses the inner nuclear membrane and connects the nucleoskeleton of lamin A to nesprins, which traverse the outer nuclear membrane. Nesprins-3 and -4 that indirectly bind on their cytoplasmic face to vimentin and microtubules, respectively, are also over-expressed in ZO-2 KD cells, whereas vimentin is depleted. SUN-1 and lamin B1 co-immunoprecipitate with ZO-2, and SUN-1 associates to ZO-2 in a pull-down assay. Our results suggest that ZO-2 forms a complex with SUN-1 and lamin B1 at the inner nuclear membrane, and that ZO-2 and cell–cell contacts are required for a normal nuclear shape.

High Prevalence of MYO6 Variants in an Austrian Patient Cohort With Autosomal Dominant Hereditary Hearing Loss

INTRODUCTION

Genetic hearing loss (HL) is often monogenic. Whereas more than half of autosomal recessive (AR) cases in Austria are caused by mutations in a single gene, no disproportionately frequent contributing genetic factor has been identified in cases of autosomal dominant (AD) HL. The genetic characterization of HL continues to improve diagnosis, genetic counseling, and lays a foundation for the development of personalized medicine approaches.

METHODS

Diagnostic HL panel screening was performed in an Austrian multiplex family with AD HL, and segregation was tested with polymerase chain reaction and Sanger sequencing. In an independent approach, 18 unrelated patients with AD HL were screened for causative variants in all known HL genes to date and segregation was tested if additional family members were available. The pathogenicity of novel variants was assessed based on previous literature and bioinformatic tools such as prediction software and protein modeling.

RESULTS

In six of the 19 families under study, candidate pathogenic variants were identified in MYO6, including three novel variants (p.Gln441Pro, p.Ser612Tyr, and p.Gln650ValfsTer7). Some patients carried more than one likely pathogenic variant in known deafness genes.

CONCLUSION

These results suggest a potential high prevalence of MYO6 variants in Austrian cases of AD HL. The presence of multiple rare HL variants in some patients highlights the relevance of considering multiple-hit diagnoses for genetic counseling and targeted therapy design.

Phenotypic Heterogeneity of Post-lingual and/or Milder Hearing Loss for the Patients With the GJB2 c.235delC Homozygous Mutation

Objective

To report the phenotypic heterogeneity of GJB2 c.235delC homozygotes associated with post-lingual and/or milder hearing loss, and explore the possible mechanism of these unconditional phenotypes.

Methods

Mutation screening of GJB2 was performed on all ascertained members from Family 1006983 and three sporadic patients by polymerase chain reaction (PCR) amplification and Sanger sequencing. Next generation sequencing (NGS) was successively performed on some of the affected members and normal controls from Family 1006983 to explore additional possible genetic codes. Reverse transcriptase–quantitative PCR was conducted to test the expression of Connexin30.

Results

We identified a Chinese autosomal recessive hearing loss family with the GJB2 c.235delC homozygous mutation, affected members from which had post-lingual moderate to profound hearing impairment, and three sporadic patients with post-lingual moderate hearing impairment, instead of congenital profound hearing loss. NGS showed no other particular variants. Overexpression of Connexin30 in some of these cases was verified.

Conclusion

Post-lingual and/or moderate hearing impairment phenotypes of GJB2 c.235delC homozygotes are not the most common phenotype, revealing the heterogeneity of GJB2 pathogenic mutations. To determine the possible mechanism that rescues part of the hearing or postpones onset age of these cases, more cases are required to confirm both Connexin30 overexpression and the existence of modifier genes.

New paradigms of USP53 disease: normal GGT cholestasis, BRIC, cholangiopathy, and responsiveness to rifampicin

Biallelic variants in the USP53 gene have recently been reported to segregate with normal gamma glutamyltransferase (GGT) cholestasis. Using whole-exome sequencing (WES), we detected two USP53 homozygous variants (c.951delT; p. Phe317fs and c.1744C>T; p. Arg582*) in five additional cases, including an unpublished cousin of a previously described family with intractable itching and normal GGT cholestasis. Three patients, a child and two adults, presented with recurrent episodes of normal GGT cholestasis, consistent with a diagnosis of benign recurrent intrahepatic cholestasis (BRIC). Cholangiopathic changes, possibly autoimmune in origin, were recognized in some patients. Additional phenotypic details in one patient included an enlarged left kidney, and speech/developmental delay. Notably, two patients exhibited a complete response to rifampicin, and one responded to ursodeoxycholic acid (UDCA). Two adult patients were suspected to have autoimmune liver disease and treated with steroids. This report describes new cases of USP53 disease presenting with normal GGT cholestasis or BRIC in three children and two adults. We also describe the novel finding of a dramatic response to rifampicin. The association of cholangiopathy with normal GGT cholestasis provides a diagnostic challenge and remains poorly understood.

Low-GGT intrahepatic cholestasis associated with biallelic USP53 variants: Clinical, histological and ultrastructural characterization

BACKGROUND & AIMS

In about 20% of children with cholestasis and normal or low serum gamma-glutamyltransferase (GGT) activity, no aetiology is identified. We sought new genes implicated in paediatric hepatobiliary disease.

METHODS

We conducted whole-exome sequencing in 69 children evaluated at our centre from 2011 to 2018 who had low-GGT cholestasis and in whom homozygous/compound heterozygous predictedly pathogenic variants (PPVs) in ATP8B1, ABCB11, NR1H4, MYO5B or TJP2 were not found. Clinical records and findings on light microscopy and transmission electron microscopy of liver biopsy materials were reviewed.

RESULTS

In seven patients from seven unrelated families, biallelic PPVs (10 in total) were found in USP53, recently associated with intrahepatic cholestasis. Seven variants were classified as pathogenic: one canonical splicing, c.569 + 2T > C, and six nonsense or frameshifting: c.169C > T (p.Arg57Ter), c.581delA (p.Arg195GlufsTer38), c.831_832insAG (p.Val279GlufsTer16), c.1012C > T (p.Arg338Ter), c.1426C > T (p.Arg476Ter) and c.1558C > T (p.Arg520Ter). Three were likely pathogenic: c.297G > T (p.Arg99Ser), c.395A > G (p.His132Arg) and c.878G > T (p.Gly293Val). In all patients, jaundice began at age <7 months. Cholestasis was transient, with documented resolution of hyperbilirubinaemia in all (oldest patient now aged 5 years) except one, who was lost to follow-up. Light microscopy identified intralobular cholestasis, giant-cell change of hepatocytes and perisinusoidal-perihepatocytic and portal-tract fibrosis. Ultrastructural study revealed elongated hepatocyte-hepatocyte tight junctions. One patient was deaf.

CONCLUSION

USP53 interacts with the tight junction constituent TJP2. TJP2 mutation can cause low-GGT intrahepatic cholestasis, with elongated hepatocyte-hepatocyte tight junctions, as well as deafness. Our findings extend a preliminary report of USP53 disease and indicate that USP53 mutation may generate a partial phenocopy of TJP2 disease.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

New tight junction protein 2 variant causing progressive familial intrahepatic cholestasis type 4 in adults: A case report

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) encompasses a group of autosomal recessive disorders with high morbidity and mortality. Variants in the gene encoding tight junction protein-2 (TJP2) have been linked to PFIC type 4 (PFIC4), which predominantly presents in childhood. However, there are only limited data from adults with TJP2-related PFIC4. We report a family with an autosomal recessive disorder with a novel variant in the TJP2 gene in adults with very variable expression of PFIC4.

CASE SUMMARY

The index patient presented at 19 years old with liver cirrhosis and variceal bleeding and was treated with endoscopic banding and beta-blockers. In 2018, he developed primary liver cancer that was treated with radiofrequency ablation followed by liver transplantation in 2019. Genetic testing revealed a novel homozygous TJP2 variant causing PFIC4 (TJP2([NM_004817.3]:c.[3334C>T]; [3334C>T])). The consanguineous family consists of the father and mother (both heterozygous) and their 12 children, of which five carry the variant in a homozygous state; however, these five siblings have highly variable expression of PFIC4. Two homozygous brothers had cirrhosis and portal hypertension at diagnosis at the ages of 19 and 36. Two other homozygous brothers, age 23 and 19, and the homozygous sister, age 21, have elevated liver enzymes but presently no cirrhosis, which may suggest an age-dependent penetrance. In addition, five sisters had severe and mild intrahepatic cholestasis of pregnancy and carry the TJP2 variant in a homozygous and heterozygous state, respectively.

CONCLUSION

This novel TJP2 variant is associated with PFIC4 causing severe liver disease with cirrhosis and primary liver cancer in adolescents/adults.

ZO-2 Is a Master Regulator of Gene Expression, Cell Proliferation, Cytoarchitecture, and Cell Size

ZO-2 is a cytoplasmic protein of tight junctions (TJs). Here, we describe ZO-2 involvement in the formation of the apical junctional complex during early development and in TJ biogenesis in epithelial cultured cells. ZO-2 acts as a scaffold for the polymerization of claudins at TJs and plays a unique role in the blood–testis barrier, as well as at TJs of the human liver and the inner ear. ZO-2 movement between the cytoplasm and nucleus is regulated by nuclear localization and exportation signals and post-translation modifications, while ZO-2 arrival at the cell border is triggered by activation of calcium sensing receptors and corresponding downstream signaling. Depending on its location, ZO-2 associates with junctional proteins and the actomyosin cytoskeleton or a variety of nuclear proteins, playing a role as a transcriptional repressor that leads to inhibition of cell proliferation and transformation. ZO-2 regulates cell architecture through modulation of Rho proteins and its absence induces hypertrophy due to inactivation of the Hippo pathway and activation of mTOR and S6K. The interaction of ZO-2 with viral oncoproteins and kinases and its silencing in diverse carcinomas reinforce the view of ZO-2 as a tumor regulator protein.

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.

ELMOD3, a novel causative gene, associated with human autosomal dominant nonsyndromic and progressive hearing loss

Autosomal dominant nonsyndromic hearing loss (ADNSHL) is a highly genetically heterogeneous disorder. Up to date only approximately 37 ADNSHL-causing genes have been identified. The goal of this study was to determine the causative gene in a five-generation Chinese family with ADNSHL. A Chinese family was ascertained. Simultaneously, two affected individuals and one normal hearing control from the family were analyzed by whole exome capture sequencing. To assess the functional effect of the identified variant, in-vitro studies were performed. novel missense variant, c.512A>G (p.His171Arg) in exon 8 of the ELMO domain-containing 3 (ELMOD3) gene, was identified as a causative variant in this family affected by late-onset and progressive ADNSHL. The variant was validated by Sanger sequencing and found to co-segregate with the phenotype within the pedigree and was absent in 500 ethnically matched unrelated normal hearing control subjects. To our knowledge, this is the first report of a family with ADNSHL caused by ELMOD3 mutation. Western blots and immunofluorescence staining demonstrated that p.His171Arg resulted in abnormal expression levels of ELMOD3 and abnormal subcellular localization. Furthermore, the analysis of the stability of the wild-type (WT) and mutant ELMOD3 protein shows that the decay of p.His171Arg is faster than that of the WT, suggesting a shorter halflife of the c.512A > G variant. A novel variant in the ELMOD3 gene, encoding a member of the engulfment and cell motility (ELMO) family of GTPase-activating proteins, was identified for the first time as responsible for ADNSHL.

Hearing impairment caused by mutations in two different genes responsible for nonsyndromic and syndromic hearing loss within a single family

Usher syndrome is rare genetic disorder impairing two human senses, hearing and vision, with the characteristic late onset of vision loss. This syndrome is divided into three types. In all cases, the vision loss is postlingual, while loss of hearing is usually prelingual. The vestibular functions may also be disturbed in Usher type 1 and sometimes in type 3. Vestibular areflexia is helpful in making a proper diagnosis of the syndrome, but, often, the syndrome is misdiagnosed as a nonsyndromic hearing loss. Here, we present a Polish family with hearing loss, which was clinically classified as nonsyndromic. After excluding mutations in the DFNB1 locus, we implemented the next-generation sequencing method and revealed that hearing loss was syndromic and mutations in the USH2A gene indicate Usher syndrome. This research highlights the importance of molecular analysis in establishing a clinical diagnosis of congenital hearing loss.

Clinical Auditory Phenotypes Associated with GATA3 Gene Mutations in Familial Hypoparathyroidism-deafness-renal Dysplasia Syndrome

Background:

Hypoparathyroidism-deafness-renal dysplasia (HDR) syndrome is an autosomal dominant disorder primarily caused by haploinsufficiency of GATA binding protein 3 (GATA3) gene mutations, and hearing loss is the most frequent phenotypic feature. This study aimed at identifying the causative gene mutation for a three-generation Chinese family with HDR syndrome and analyzing auditory phenotypes in all familial HDR syndrome cases.

Methods:

Three affected family members underwent otologic examinations, biochemistry tests, and other clinical evaluations. Targeted genes capture combining next-generation sequencing was performed within the family. Sanger sequencing was used to confirm the causative mutation. The auditory phenotypes of all reported familial HDR syndrome cases analyzed were provided.

Results:

In Chinese family 7121, a heterozygous nonsense mutation c.826C>T (p.R276*) was identified in GATA3. All the three affected members suffered from sensorineural deafness and hypocalcemia; however, renal dysplasia only appeared in the youngest patient. Furthermore, an overview of thirty HDR syndrome families with corresponding GATA3 mutations revealed that hearing impairment occurred earlier in the younger generation in at least nine familial cases (30%) and two thirds of them were found to carry premature stop mutations.

Conclusions:

This study highlights the phenotypic heterogeneity of HDR and points to a possible genetic anticipation in patients with HDR, which needs to be further investigated.

ZO-2, a tight junction protein involved in gene expression, proliferation, apoptosis, and cell size regulation

ZO-2 is a peripheral tight junction protein that belongs to the membrane-associated guanylate kinase protein family. Here, we explain the modular and supramodular organization of ZO-2 that allows it to interact with a wide variety of molecules, including cell-cell adhesion proteins, cytoskeletal components, and nuclear factors. We also describe how ZO proteins evolved through metazoan evolution and analyze the intracellular traffic of ZO-2, as well as the roles played by ZO-2 at the plasma membrane and nucleus that translate into the regulation of proliferation, cell size, and apoptosis. In addition, we focus on the impact of ZO-2 expression on male fertility and on maladies like cancer, cholestasis, and hearing loss.

A novel dominant GJB2 (DFNA3) mutation in a Chinese family

To decipher the phenotype and genotype of a Chinese family with autosomal dominant non-syndromic hearing loss (ADNSHL) and a novel dominant missense mutation in the GJB2 gene (DFNA3), mutation screening of GJB2 was performed on the propositus from a five-generation ADNSHL family through polymerase chain reaction amplification and Sanger sequencing. The candidate variation and the co-segregation of the phenotype were verified in all ascertained family members. Targeted genes capture and next-generation sequencing (NGS) were performed to explore additional genetic variations. We identified the novel GJB2 mutation c.524C > A (p.P175H), which segregated with high frequency and was involved in progressive sensorineural hearing loss. One subject with an additional c.235delC mutation showed a more severe phenotype than did the other members with single GJB2 dominant variations. Four patients diagnosed with noise-induced hearing loss did not carry this mutation. No other pathogenic variations or modifier genes were identified by NGS. In conclusion, a novel missense mutation in GJB2 (DFNA3), affecting the second extracellular domain of the protein, was identified in a family with ADNSHL.