PEX5 Research Articles

Normal very long-chain fatty acids level in a patient with peroxisome biogenesis disorders: a case report

BackgroundZellweger spectrum disorders (ZSDs) are a group of peroxisome biogenesis disorders (PBDs) with different variants in the PEX genes. The main biochemical marker for screening peroxisomal disorders is very long-chain fatty acids (VLCFAs). The study reveals a rare case of PBD in the Zellweger spectrum in which she had normal plasma VLCFA levels.Case presentationHere, we report a 10-year-old girl with neurodevelopmental delay, facial dysmorphism, and hearing impairment. A brain magnetic resonance imaging scan was done to determine the reason for the seizures and neurodevelopmental delay. MRI images showed a mild widening in sulci especially in frontal lobes and sylvian fissures with pachygyria in the perisylvian regions. Biochemical analysis was done to detect ZSD. However, plasma VLCFA levels were normal. The diagnosis was made using whole-exome sequencing (WES). A homozygous variant of uncertain significance (VUS) in PEX6 NM_000287.4: c.1992G > C (p. Glu664Asp) was identified which has been confirmed through Sanger sequencing in probands and her parents.ConclusionsAccording to the case report, plasma VLCFA levels can be normal in patients with PBDs in the Zellweger spectrum. Furthermore, we could re-classify the c.1992G > C variant in the PEX6 gene from VUS to likely pathogenic based on clinical manifestations including facial dysmorphism, and hearing impairment.

Distinguishing PEX gene variant severity for mild, severe, and atypical peroxisome biogenesis disorders in Drosophila.

Peroxisomal biogenesis disorders (PBD) are autosomal recessive disorders caused by loss-of-function mutations of one of the PEX genes responsible for peroxisomal formation. Impaired peroxisome assembly causes severe multisystemic failure with patient phenotypes ranging from epilepsy, liver disease, feeding issues, biochemical abnormalities, and neurodegeneration. Variants in the same PEX gene can produce wide differences in severity, ranging from individuals with death in the first year of life to adults with milder complications. To study this strong genotype-phenotype correlation, we selected specific human PEX gene mutations and utilized Drosophila as a model organism. We generated flies replacing the coding sequence of our Pex gene of interest with a KozakGAL4 (KZ) promoter trap sequence. These cassettes simultaneously knock-out of the Pex gene and knock-in a GAL4 driver, ideal for making "humanized" flies in which the human PEX gene can replace the fly loss. We assessed Pex2 KZ and Pex16 KZ lines in lifespan, bang sensitivity, and climbing assays and confirmed that these are strong loss-of-function alleles. In parallel, we generated human reference and variant UAS-cDNA lines of PEX2 and PEX16 variants in Drosophila . We observed nearly complete phenotypic rescue of Drosophila Pex2 and Pex16 loss when human PEX2 Ref or PEX16 Ref , respectively, were expressed. We also provide evidence for an allele severity spectrum in PEX2 and PEX16 in which some missense alleles, such as PEX2 C247R , are equally severe as early truncations, such as PEX2 R119* . We also observed that alleles associated with mild PBD, such as PEX2 E55K , show variability depending on the assay but do not fully rescue. Finally, alleles associated with atypical ataxia phenotypes, such as PEX16 F332Del , can perform as well as PEX16 Ref , depending on the assay. Altogether, these Drosophila lines effectively model the range of severity of peroxisomal biogenesis disorders.

Positive Psychotic Symptoms after Escitalopram Treatment in a Female Adolescent with Peroxisome Spectrum Disorder Due to PEX-6 Gene Mutation

Introduction: In this case report, we present positive psychotic symptoms that developed after low-dose (5 mg/day) escitalopram treatment in a 16-year-old female adolescent with a peroxisome biogenesis disorder. Case presentation: Two weeks after starting escitalopram treatment for depression, the patient experienced vomiting attacks several times a day. About 2-3 days after the attacks began, the family stopped administering escitalopram. Five days after the onset of vomiting and 2-3 days after stopping escitalopram, the patient developed visual and auditory hallucinations and persecutory delusions. During the patient's follow-up period, the diversity of her hallucinations and delusions increased. When olanzapine treatment was gradually increased to 20 mg/day, the patient's psychotic symptoms disappeared. Conclusion: We discuss serotonin syndrome, drug-induced bipolar disorder, and psychotic disorder in the differential diagnosis. We believe that this case report is valuable as it is the first in the literature regarding the development of positive psychotic symptoms after SSRI use in a patient with a peroxisome biogenesis disorder.

Newborn Screening for X-Linked Adrenoleukodystrophy (X-ALD): Biochemical, Molecular, and Clinical Characteristics of Other Genetic Conditions.

The state of California (CA) added X-linked adrenoleukodystrophy (X-ALD) to newborn screening (NBS) in 2016 via the measurement of C26:0-lysophosphatidylcholine (C26:0-LPC) in a two-tier fashion, followed by sequencing of the ABCD1 gene. This has resulted in the identification of individuals with genetic conditions beyond X-ALD that can also result in elevated C26:0-LPC by NBS. We describe the biochemical, molecular, and clinical characteristics of nine patients from two metabolic centers in California who screened positive by NBS for elevated C26:0-LPC between 2016 and 2022 and were ultimately diagnosed with a genetic condition other than X-ALD. Seven individuals were diagnosed with Zellweger spectrum disorder (ZSD) due to biallelic variants in PEX genes. One male was diagnosed with Klinefelter syndrome and one female was found to have an X chromosome contiguous gene deletion syndrome after the identification of a heterozygous VUS and hemizygous VUS variant in ABCD1, respectively. Patients with ZSD had significantly higher first- and second-tier C26:0-LPC levels compared to the two non-ZSD cases. Identification of children with ZSD and atypical patterns of ABCD1 variants is a secondary benefit of NBS for X-ALD, leading to earlier diagnosis, prompt therapeutic initiation, and more accurate genetic counseling. As screening for X-ALD continues via the measurement of C26:0-LPC, our knowledge of additional genetic conditions associated with elevated C26:0-LPC will continue to advance, allowing for increased recognition of other genetic disorders for which early intervention is warranted.

PEX1 is essential for glycosome biogenesis and trypanosomatid parasite survival.

Trypanosomatid parasites are kinetoplastid protists that compartmentalize glycolytic enzymes in unique peroxisome-related organelles called glycosomes. The heterohexameric AAA-ATPase complex of PEX1-PEX6 is anchored to the peroxisomal membrane and functions in the export of matrix protein import receptor PEX5 from the peroxisomal membrane. Defects in PEX1, PEX6 or their membrane anchor causes dysfunction of peroxisomal matrix protein import cycle. In this study, we functionally characterized a putative Trypanosoma PEX1 orthologue by bioinformatic and experimental approaches and show that it is a true PEX1 orthologue. Using yeast two-hybrid analysis, we demonstrate that TbPEX1 can bind to TbPEX6. Endogenously tagged TbPEX1 localizes to glycosomes in the T. brucei parasites. Depletion of PEX1 gene expression by RNA interference causes lethality to the bloodstream form trypanosomes, due to a partial mislocalization of glycosomal enzymes to the cytosol and ATP depletion. TbPEX1 RNAi leads to a selective proteasomal degradation of both matrix protein import receptors TbPEX5 and TbPEX7. Unlike in yeast, PEX1 depletion did not result in an accumulation of ubiquitinated TbPEX5 in trypanosomes. As PEX1 turned out to be essential for trypanosomatid parasites, it could provide a suitable drug target for parasitic diseases. The results also suggest that these parasites possess a highly efficient quality control mechanism that exports the import receptors from glycosomes to the cytosol in the absence of a functional TbPEX1-TbPEX6 complex.

In Silico Characterization of Two Adjacent Novel Homozygous Nucleotide Variations in the PEX6 Gene Predict L898V Mutation to Enhance Infantile Refsum Disease and Heimler Syndrome

Background: Zellweger spectrum disorders are autosomal recessive in origin due to defects in peroxisome biogenesis and with variable severity. The present work aims to characterize a South Asian Indian Zellweger spectrum disorder family with PEX6 mutation for a genotype-phenotype association. Method: The affected and unaffected individuals in the family were evaluated. A comprehensive examination of the ocular, auditory, dental, integumentary, neuronal, hepato-renal, endocrine, skeletal, cardiac, and other systems was conducted. Investigations deemed fit for diagnosis and management were done. Karyotyping and molecular genetic screening of the peripheral venous blood were performed for aneuploidy and mutation detection. Retinal fundus photograph, optical coherence tomography, bilateral audiogram, magnetic resonance imaging of the brain, ultrasonography of the abdomen, electrocardiography, and echocardiogram were performed. Any non-synonymous nucleotide variations detected were analyzed using in silico methods. Results: The proband was born of consanguinity and had retinitis pigmentosa in both eyes, bilateral sensorineural deafness, amelogenesis imperfecta, Beau's line, and punctate leukonychia corresponding to Heimler syndrome. In addition, the proband had developmental nuclear cataracts, ichthyosis, developmental delay, cerebellar ataxia, cognitive deficit, peripheral neuropathy, and muscle movement disorder corresponding to inherited Refsum disease. The proband did not have anosmia. The brain's magnetic resonance imaging, abdomen ultrasonography, electrocardiography, and echocardiogram were normal. The karyotyping revealed euploidy status. The molecular genetic screening detected two novel adjacent homozygous non-synonymous nucleotide variations c.2691C>A (p.Ser897Arg) and c.2692C>G (p.Leu898Val) in the PEX6 gene. The pathogenic effect, structural destabilization effect, and functional impact of the variants were analyzed through in silico methods. The L898V variant was highly pathogenic compared to the non-conserved S897R variant of PEX6, leading to structural instability and loss of functionality. The molecular dynamics simulation studies also revealed the L898V variant to cause structural instability of PEX6 with higher backbone deviations and residue-wise fluctuations. Conclusion: This study confirms the significance of L898V variant on the functionality of PEX6 that resulted in a severe disease phenotype. Genetic counseling, followed by multidisciplinary clinical evaluation was required to manage the patient with peroxisomal biogenesis disorder. A phytanic acid-restricted diet may be beneficial to control the infantile refsum disease severity.

Avidity sequencing of whole genomes from retinal degeneration pedigrees identifies causal variants.

Whole genome sequencing has been an effective tool in the discovery of variants that cause rare diseases. In this study, we determined the suitability of a novel avidity sequencing approach for rare disease applications. We built a sample to results workflow, combining this sequencing technology with standard library preparation kits, analysis workflows, and interpretation tools. We applied the workflow to ten pedigrees with inherited retinal degeneration (IRD) phenotype. Candidate variants of interest identified through whole genome sequencing were further evaluated using segregation analysis in the additional family members. Potentially causal variants in known IRD genes were detected in five of the ten cases. These high confidence variants were found in ABCA4, CERKL, MAK, PEX6 and RDH12 genes associated with retinal degeneration, that could be sufficient to cause pathology. Pending confirmatory clinical evaluation, we observed a 50% diagnostic yield, consistent with previously reported outcomes of IRD patient analysis. The study confirms that avidity sequencing is effective in detection of causal variants when used for whole genome sequencing in rare disease applications.

GENES FROM PEROXISOME AND INTEGRATED STRESS RESPONSE IN REGULATION OF HUMAN LONGEVITY

Abstract Dietary/caloric restriction shares pathways with peroxisome, a cellular organelle that regulates the synthesis and turnover of complex lipids. PEX3, a peroxisomal biogenesis factor involved in selective type of autophagy. EIF2AK4, a sensor of amino acid deprivation in the integrated stress response (ISR) involved in lifespan regulation. We hypothesize that interplay between EIF2AK4 and PEX3 is associated with human survival. We applied logistic regression model with the interaction term to the analysis of Health and Retirement Study (HRS) and UK Biobank (UKB) parents data to test whether interactions of SNPs from the EIF2AK4 and SNPs from the PEX3 are associated with the dichotomous survival trait (ST) with case group defined as: lifespan ≥ 85; and control as: 75 ≤ (lifespan or age at last follow-up) < 85. Analyses of HRS data showed that interactions between SNPs rs4924405, rs2250402, rs8031319, rs16970049, rs3816899, rs16970112, rs2412459 from the EIF2AK4 gene and SNP rs161070 from the PEX3 gene are significantly associated with ST. In the UKB data, interactions of rs161070 from the PEX3 gene and rs7176881 and rs117778159 SNPs from the EIF2AK4 gene showed nominally significant associations with ST. Analyses of linkage disequilibrium (LD) between the EIF2AK4 SNPs detected in HRS and UKB data showed that their LD are close to the highest values for SNPs with allele frequencies specific for detected variants. Our results confirm association of interplay between EIF2AK4 and PEX3 with human longevity. They also show how information from experimental studies could be transformed to the form useful for human applications.

A novel compound heterozygous PEX1 variant in Heimler syndrome

Heimler syndrome (HS) is a rare autosomal recessive hereditary disease that is caused by biallelic variants in peroxisomal biogenic factor 1 gene (PEX1), peroxisomal biogenic factor 6 gene (PEX6) or peroxisomal biogenic factor 26 gene (PEX26), resulting in intracellular peroxisomal dysfunction (PBDs). We report a patient with HS with a new compound heterozygous PEX1 variant. Exon sequencing was used to screen pathologic variants in the patient. Retinal characteristics and serum metabolome alterations were evaluated. Scanning laser ophthalmoscope showed a large area of retinal choroidal atrophy at the posterior pole of the retina, with scattered patchy subretinal pigmentation. Optical coherence tomography showed fovea atrophy accompanied by retinal retinoschisis in the right eye and macular retinoschisis and edema in the left eye. The electroretinogram showed obviously reduced amplitudes of a-waves and b-waves under photopic and scotopic conditions in both eyes. Visual field tests showed a reduced central visual field in both eyes. Exon sequencing identified the compound heterozygous variant including c.2966T > C and c.1670+1G > T of the PEX1 gene, with the latter being novel. Nontargeted determination of total lipid metabolites and targeted determination of medium- and long-chain fatty acids in the serum of the patient and his healthy sibling were tested. This study identified a new compound heterozygous PEX1 variant, expanding our understanding of phenotypes in HS.

Autosomal dominant Zellweger spectrum disorder caused by de novo variants in PEX14 gene

PurposeZellweger spectrum disorders (ZSDs) are known as autosomal recessive disorders caused by defective peroxisome biogenesis due to bi-allelic pathogenic variants in any of at least 13 different PEX genes. Here, we report 2 unrelated patients who present with an autosomal dominant ZSD. MethodsWe performed biochemical and genetic studies in blood and skin fibroblasts of the patients and demonstrated the pathogenicity of the identified PEX14 variants by functional cell studies. ResultsWe identified 2 different single heterozygous de novo variants in the PEX14 genes of 2 patients diagnosed with ZSD. Both variants cause messenger RNA mis-splicing, leading to stable expression of similar C-terminally truncated PEX14 proteins. Functional studies indicated that the truncated PEX14 proteins lost their function in peroxisomal matrix protein import and cause increased degradation of peroxisomes, ie, pexophagy, thus exerting a dominant-negative effect on peroxisome functioning. Inhibition of pexophagy by different autophagy inhibitors or genetic knockdown of the peroxisomal autophagy receptor NBR1 resulted in restoration of peroxisomal functions in the patients’ fibroblasts. ConclusionOur finding of an autosomal dominant ZSD expands the genetic repertoire of ZSDs. Our study underscores that single heterozygous variants should not be ignored as possible genetic cause of diseases with an established autosomal recessive mode of inheritance.

295-LB: Pancreatic Peroxisomes Are Required for Physiological Regulation of Insulin Secretion and Maintenance of Normal Glucose Tolerance in Male Mice

The regulation of glucose-stimulated insulin secretion (GSIS) is central to maintenance of glucose disposal. The role of lipid storage and lipid oxidation to regulate pancreatic islet β-cell insulin secretion is not completely understood. Peroxisomes are enriched in insulin-producing β-cells, but their contribution to β-cell function and maturity is lacking. Therefore, we generated a novel model of peroxisomal dysfunction to test the hypothesis that peroxisomal lipid metabolism is required to prevent a hyperlipidemic environment that interferes with β-cell function and maturity. Pex5 plays a critical role in importing the majority of peroxisomal proteins into the peroxisomal matrix; thus, deletion of the Pex5 gene creates a cellular environment with reductions in function of this organelle. In this study, we bred Pex5 mice on a C57BL/6J background containing ‘floxed’ alleles to Pdx1-cre mice to generate offspring with a pancreas-wide deficiency in Pex5 expression and abundance. Glucose tolerance was impaired by 12 weeks in male mice (n=20; AUC p<0.05). Surprisingly, GSIS was elevated in Pex5Pdx1-/- mice compared to littermate controls both in vivo (n=15; AUC p<0.05) and ex vivo in isolated islets as measured by perifusion analysis (n=12; AUC p<0.01). We further found that a subset of β-cells from Pex5Pdx1-/- mice expressed the de-differentiation marker Aldh1a3, while a subset of β-cells showed reductions in MafA and Nkx6.1 staining compared to controls. Perilipin-1 staining showed increased presence of lipid droplets in pancreatic tissue of Pex5Pdx1-/- mice versus controls. Thus, pancreatic deletion of peroxisomal function results in increased lipid storage in pancreatic tissue that is correlated with exaggerated insulin secretion. Collectively, these data are in support of a model whereby peroxisomal function supports β-cell insulin secretion and maintenance of the fully differentiated state. Disclosure S. Burke: None. S. Ghosh: None. D. Burk: None. R. Noland: None. J. Collier: None.

A homozygous Gly470Ala variant in PEX6 causes severe Zellweger spectrum disorder.

Zellweger spectrum disorder (ZSD) is a group of autosomal recessive disorders caused by biallelic pathogenic variants in any one of the 13 PEX genes essential for peroxisomal biogenesis. We report a cohort of nine infants who presented at birth with severe neonatal features suggestive of ZSD and found to be homozygous for a variant in PEX6 (NM_000287.4:c.1409G > C[p.Gly470Ala]). All were of Mixtec ancestry and identified by the California Newborn Screening (NBS) Program to have elevated C26:0-lysophosphatidylcholine but no reportable variants in ABCD1. The clinical and biochemical features of this cohort are described within. Gly470Ala may represent a founder variant in the Mixtec population of Central California. ZSD should be considered in patients who present at birth with severe hypotonia and enlarged fontanelles, especially in the setting of an abnormal NBS, Mixtec ancestry, or family history of infant death. There is a need to further characterize the natural history of ZSD, the Gly470Ala variant, and expand upon possible genotype-phenotype correlations.

OsPEX1, an extensin-like protein, negatively regulates root growth in a gibberellin-mediated manner in rice

Leucine-rich repeat extensins (LRXs) are required for plant growth and development through affecting cell growth and cell wall formation. LRX gene family can be classified into two categories: predominantly vegetative-expressed LRX and reproductive-expressed PEX. In contrast to the tissue specificity of Arabidopsis PEX genes in reproductive organs, rice OsPEX1 is also highly expressed in roots in addition to reproductive tissue. However, whether and how OsPEX1 affects root growth is unclear. Here, we found that overexpression of OsPEX1 retarded root growth by reducing cell elongation likely caused by an increase of lignin deposition, whereas knockdown of OsPEX1 had an opposite effect on root growth, indicating that OsPEX1 negatively regulated root growth in rice. Further investigation uncovered the existence of a feedback loop between OsPEX1 expression level and GA biosynthesis for proper root growth. This was supported by the facts that exogenous GA3 application downregulated transcript levels of OsPEX1 and lignin-related genes and rescued the root developmental defects of the OsPEX1 overexpression mutant, whereas OsPEX1 overexpression reduced GA level and the expression of GA biosynthesis genes. Moreover, OsPEX1 and GA showed antagonistic action on the lignin biosynthesis in root. OsPEX1 overexpression upregulated transcript levels of lignin-related genes, whereas exogenous GA3 application downregulated their expression. Taken together, this study reveals a possible molecular pathway of OsPEX1mediated regulation of root growth through coordinate modulation of lignin deposition via a negative feedback regulation between OsPEX1 expression and GA biosynthesis.

Peroxin Pex14/17 Is Required for Trap Formation, and Plays Pleiotropic Roles in Mycelial Development, Stress Response, and Secondary Metabolism in Arthrobotrys oligospora.

The peroxins encoded by PEX genes involved in peroxisome biogenesis play a crucial role in cellular metabolism and pathogenicity in fungi. Herein, we characterized a filamentous fungus-specific peroxin Pex14/17 in the Arthrobotrys oligospora, a representative species of nematode-trapping fungi. The deletion of AoPEX14/17 resulted in a remarkable reduction in mycelial growth, conidia yield, trap formation, and pathogenicity. Compared with the wild-type strain, the ΔAopex14/17 mutant exhibited more lipid droplet and reactive oxygen species accumulation accompanied with a significant decrease in fatty acid utilization and tolerance to oxidative stress. Transcriptomic analysis indicated that AoPEX14/17 was involved in the regulation of metabolism, genetic information processing, environmental information processing, and cellular processes. In subcellular morphology, the deletion of AoPEX14/17 resulted in a decrease in the number of cell nuclei, autophagosomes, and Woronin bodies. Metabolic profile analysis showed that AoPex14/17 affects the biosynthesis of secondary metabolites. Yeast two-hybrid assay revealed that AoPex14/17 interacted with AoPex14 but not with AoPex13. Taken together, our results suggest that Pex14/17 is the main factor for modulating growth, development, and pathogenicity in A. oligospora. IMPORTANCE Peroxisome biogenesis genes (PEX) play an important role in growth, development, and pathogenicity in pathogenic fungi. However, the roles of PEX genes remain largely unknown in nematode-trapping (NT) fungi. Here, we provide direct evidence that AoPex14/17 regulates mycelial growth, conidiation, trap formation, autophagy, endocytosis, catalase activity, stress response to oxidants, lipid metabolism, and reactive oxygen species production. Transcriptome analysis and metabolic profile suggested that AoPex14/17 is involved in multiple cellular processes and the regulation of secondary metabolism. Therefore, our study extends the functions of PEX genes, which helps to elucidate the mechanism of organelle development and trap formation in NT fungi and lays the foundation for the development of efficient nematode biocontrol agents.

Comparison of human PEX knockout cell lines suggests a dual role of PEX1 in peroxisome biogenesis.

For the biogenesis and maintenance of peroxisomes several proteins, called peroxins, are essential. Malfunctions of these proteins lead to severe diseases summarized as peroxisome biogenesis disorders. The different genetic background of patient-derived cell lines and the residual expression of mutated PEX genes impede analysis ofthe whole spectrum of cellular functions of affected peroxins. To overcome these difficulties, we have generated a selected PEX knockout resource of HEK T-REx293 cells using the CRISPR/Cas9 technique. Comparative analyses of whole cell lysates revealed PEX-KO specific alterations in the steady-state level of peroxins and variations in the import efficacy of matrix proteins with a Type 2 peroxisomal targeting signal. One of the observed differences concerned PEX1 as in the complete absence of the protein, the number of peroxisomal ghosts is significantly increased. Upon expression of PEX1, import competence and abundance of peroxisomes was adjusted to the level of normal HEK cells. In contrast, expression of an alternatively spliced PEX1 isoform lacking 321 amino acids of the N-terminal region failed to rescue the peroxisomal import defects but reduced the number of peroxisomal vesicles. All in all, the data suggest a novel 'moonlighting' function of human PEX1 in the regulation of pre-peroxisomal vesicles.

Transforming Growth Factor-β1 Regulates Peroxisomal Genes/Proteins via Smad Signaling in Idiopathic Pulmonary Fibrosis Fibroblasts and Transgenic Mouse Models

Idiopathic pulmonary fibrosis (IPF) is a chronic human disease with persistent destruction of lung parenchyma. Transforming growth factor-β1 (TGF-β1) signaling plays a pivotal role in the initiation and pathogenesis of IPF. As shown herein, TGF-β1 signaling down-regulated not only peroxisome biogenesis but also the metabolism of these organelles in human IPF fibroblasts. Invitro cell culture observations in human fibroblasts and human lung tissue indicated that peroxisomal biogenesis and metabolic proteins were significantly down-regulated in the lung of 1-month-old transgenic mice expressing a constitutively active TGF-β type I receptor kinase (ALK5). The peroxisome biogenesis protein peroxisomal membrane protein Pex13p (PEX13p) as well as the peroxisomal lipid metabolic enzyme peroxisomal acyl-coenzyme A oxidase 1 (ACOX1) and antioxidative enzyme catalase were highly up-regulated in TGF-β type II receptor and Smad3 knockout mice. This study reports a novel mechanism of peroxisome biogenesis and metabolic regulation via TGF-β1-Smad signaling: interaction of the Smad3 transcription factor with the PEX13 gene in chromatin immunoprecipitation-on-chip assay as well as in a bleomycin-induced pulmonary fibrosis model applied to TGF-β type II receptor knockout mice. Taken together, data from this study suggest that TGF-β1 participates in regulation of peroxisomal biogenesis and metabolism via Smad-dependent signaling, opening up novel strategies for the development of therapeutic approaches to inhibit progression of pulmonary fibrosis patients with IPF.

Loss of Pex1 in Inner Ear Hair Cells Contributes to Cochlear Synaptopathy and Hearing Loss.

Peroxisome Biogenesis Disorders (PBD) and Zellweger syndrome spectrum disorders (ZSD) are rare genetic multisystem disorders that include hearing impairment and are associated with defects in peroxisome assembly, function, or both. Mutations in 13 peroxin (PEX) genes have been found to cause PBD-ZSD with ~70% of patients harboring mutations in PEX1. Limited research has focused on the impact of peroxisomal disorders on auditory function. As sensory hair cells are particularly vulnerable to metabolic changes, we hypothesize that mutations in PEX1 lead to oxidative stress affecting hair cells of the inner ear, subsequently resulting in hair cell degeneration and hearing loss. Global deletion of the Pex1 gene is neonatal lethal in mice, impairing any postnatal studies. To overcome this limitation, we created conditional knockout mice (cKO) using Gfi1Creor VGlut3Cre expressing mice crossed to floxed Pex1 mice to allow for selective deletion of Pex1 in the hair cells of the inner ear. We find that Pex1 excision in inner hair cells (IHCs) leads to progressive hearing loss associated with significant decrease in auditory brainstem responses (ABR), specifically ABR wave I amplitude, indicative of synaptic defects. Analysis of IHC synapses in cKO mice reveals a decrease in ribbon synapse volume and functional alterations in exocytosis. Concomitantly, we observe a decrease in peroxisomal number, indicative of oxidative stress imbalance. Taken together, these results suggest a critical function of Pex1 in development and maturation of IHC-spiral ganglion synapses and auditory function.

Novel phenotype–genotype correlation with PEX6 gene in Saudi patients with Heimler syndrome

AbstractPurpose: Peroxisome biogenesis disorders (PBDs; MIM# 601539) are heterogeneous disorders caused by defects in genes encoding proteins that are essential for peroxisomal matrix and membrane proteins. Heimler syndrome is one of PBDs that is caused by mutations in PEX1 and PEX6 genes. In this study, we aimed to fully characterize the clinical and molecular aspects of two Saudi probands who were diagnosed early as Usher syndrome.Methods: We set up a comprehensive clinical and molecular genetic workflow including detailed ophthalmological, audiological and systemic assessments followed by genome‐wide SNP microarrays analysis and targeted PEX6 gene screening by Sanger sequencing.Results: Clinically: both patients appeared dysmorphic with long faces, high forehead, short nose, small low set ears, and full lips. The ophthalmological assessment revealed advanced inherited retinal dysfunction represented by waxy pallor optic disc, attenuated vessels, RPE mottling with intraretinal bony spicules pigmentations and central foveal atrophic changes in both eyes. Both Indexes exhibited bilateral sensory neural hearing loss and amelogenesis imperfecta. Genetically: an autozygous block was identified on chromosome 6p21.1 encompassing PEX6 gene using SNP microarrays. Novel PEX6 (NM_000287.3) c.290 T > G (p.Val97Gly) was found by Sanger sequencing. The identified variant co‐segregated with the phenotype in both families and found to be “likely pathogenic” according to ACMG guidelines.Conclusions: Our study represents the first report of PEX6 associated Heimler syndrome in the middle east and considered to be the third in the literature so far. It highlights the importance of combining molecular diagnosis with the clinical findings to expand our knowledge of PEX6‐related PBDs phenotype and the allelic spectrum for this gene.

Increased Nuchal Translucency Without Aneuploidy in a Fetus: Abnormal Postnatal Radiograph and a Novel Mutation.

Increased Nuchal Translucency Without Aneuploidy in a Fetus: Abnormal Postnatal Radiograph and a Novel Mutation.

The Effect of a Pex3 Mutation on Hearing and Lipid Content of the Inner Ear.

Peroxisome biogenesis disorders (due to PEX gene mutations) are associated with symptoms that range in severity and can lead to early childhood death, but a common feature is hearing impairment. In this study, mice carrying Pex3 mutations were found to show normal auditory development followed by an early-onset progressive increase in auditory response thresholds. The only structural defect detected in the cochlea at four weeks old was the disruption of synapses below inner hair cells. A conditional approach was used to establish that Pex3 expression is required locally within the cochlea for normal hearing, rather than hearing loss being due to systemic effects. A lipidomics analysis of the inner ear revealed a local reduction in plasmalogens in the Pex3 mouse mutants, comparable to the systemic plasmalogen reduction reported in human peroxisome biogenesis disorders. Thus, mice with Pex3 mutations may be a useful tool to understand the physiological basis of peroxisome biogenesis disorders.