Characterization of Severity in Zellweger Spectrum Disorder by Clinical Findings: A Scoping Review, Meta-Analysis and Medical Chart Review

Overexpression of PEX14 results in mistargeting to mitochondria, accompanied by organelle fragmentation and clustering in human embryonic kidney cells

Peroxisome biogenesis disorders are caused by pathogenic variants in genes involved in biogenesis and maintenance of peroxisomes. However, mitochondria are also often affected in these diseases. Peroxisomal membrane proteins, including PEX14, have been found to mislocalise to mitochondria in cells lacking peroxisomes. Recent studies indicated that this mislocalisation contributes to mitochondrial abnormalities in PEX3-deficient patient fibroblasts cells. Here, we studied whether mitochondrial morphology is also affected in PEX3-deficient HEK293 cells and whether PEX14 mislocalises to mitochondria in these cells. Using high-resolution imaging techniques, we show that although endogenous PEX14 mislocalises to mitochondria, mitochondrial morphology was normal in PEX3-KO HEK293 cells. However, we discovered that overexpression of tagged PEX14 in wild-type HEK293 cells resulted in its mitochondrial localisation, accompanied by altered mitochondrial morphology. Our data indicate that overexpression of tagged PEX14 alone directly or indirectly cause mitochondrial abnormalities in cells containing peroxisomes.

Identifying Metabolic Diseases That Precipitate Neonatal Seizures

Although a rare cause of neonatal seizures, inborn errors of metabolism (IEMs) remain an essential component of a comprehensive differential diagnosis for poorly controlled neonatal epilepsy. Diagnosing neonatal-onset metabolic conditions proves a difficult task for clinicians; however, routine state newborn screening panels now include many IEMs. Three in particular-pyridoxine-dependent epilepsy, maple syrup urine disease, and Zellweger spectrum disorders-are highly associated with neonatal epilepsy and neurocognitive injury yet are often misdiagnosed. As research surrounding biomarkers for these conditions is emerging and gene sequencing technologies are advancing, clinicians are beginning to better establish early identification strategies for these diseases. In this literature review, the authors aim to present clinicians with an innovative clinical guide highlighting IEMs associated with neonatal-onset seizures, with the goal of promoting quality care and safety.

Systematic study of ophthalmological findings in 10 patients with PEX1-mediated Zellweger spectrum disorder

PURPOSE

This cross-sectional study describes the ophthalmological and general phenotype of 10 patients from six different families with a comparatively mild form of Zellweger spectrum disorder (ZSD), a rare peroxisomal disorder.

METHODS

Ophthalmological assessment included best-corrected visual acuity (BCVA), perimetry, microperimetry, ophthalmoscopy, fundus photography, spectral-domain optical coherence tomography (SD-OCT), and fundus autofluorescence (FAF) imaging. Medical records were reviewed for medical history and systemic manifestations of ZSD.

RESULTS

Nine patients were homozygous for c.2528 G > A (p.Gly843Asp) variants in PEX1 and one patient was compound heterozygous for c.2528 G>A (p.Gly843Asp) and c.2097_2098insT (p.Ile700TyrfsTer42) in PEX1. Median age was 22.6 years (interquartile range (IQR): 15.9 - 29.9 years) at the most recent examination, with a median symptom duration of 22.1 years. Symptom onset was variable with presentations of hearing loss (n = 7) or nyctalopia/reduced visual acuity (n = 3) at a median age of 6 months (IQR: 1.9-8.3 months). BCVA (median of 0.8 logMAR; IQR: 0.6-0.9 logMAR) remained stable over 10.8 years and all patients were hyperopic. Fundus examination revealed a variable retinitis pigmentosa (RP)-like phenotype with rounded hyperpigmentations as most prominent feature in six out of nine patients. Electroretinography, visual field measurements, and microperimetry further established the RP-like phenotype. Multimodal imaging revealed significant intraretinal fluid cavities on SD-OCT and a remarkable pattern of hyperautofluorescent abnormalities on FAF in all patients.

CONCLUSION

This study highlights the ophthalmological phenotype resembling RP with moderate to severe visual impairment in patients with mild ZSD. These findings can aid ophthalmologists in diagnosing, counselling, and managing patients with mild ZSD.

Zellweger Syndrome: A Case Report

Zellweger syndrome is an autosomal recessive disease within the spectrum of peroxisome biogenesis disorder manifesting in the neonatal period with profound dysfunction of the central nervous system, liver and kidney. Common clinical presentations include hypotonia, seizure, hepatomegaly, craniofacial dysmorphism and early death. Mutation in one of the PEX genes coding for a peroxisome assembly protein creates a functionally incompetent organelle causing accumulation of very long chain fatty acids in various organs. Here we report the case of a 5-month-old male presented at birth with hypotonia, poor feeding, gross congenital anomalies and later during early infancy with failure to thrive, several episodes of seizures, aspiration due to feeding difficulties and recurrent severe pneumonia. A whole genomic sequencing brought us to the final diagnosis of Zellweger syndrome. Despite an absence of treatment options, prompt diagnosis of Zellweger syndrome is important for providing appropriate symptomatic care, definitive genetic testing and prenatal counselling.

Keywords

case reports; mutation; neonate; Zellweger syndrome.

Exercise-induced expression of genes associated with aging in the hippocampus of rats

Recent research has underscored the influence of aging and exercise on brain function. In this study, we aimed to explore alterations in the expression of novel molecular factors and gain insight into underlying molecular mechanisms in the hippocampus of rats engaged in voluntary wheel running. We assessed the expression of aging-related genes in the hippocampus using a high-throughput whole genome DNA microarray approach in rats engaged in voluntary running for four weeks. The results indicated that compared to the control group, wheel running significantly altered the expressions of aging-related genes in the hippocampus. Functional categorization, utilizing pathway-focused gene classifications and disease state-focused gene classifications, along with Ingenuity Pathway Analysis (IPA), revealed changes in expression pattern in major categories of cell death and survival, renal necrosis/cell death, and cardiovascular disease genes. These findings suggest that exercise may mitigate the risk of age-related cognitive decline by regulating of aging-related genes in the hippocampus. Further research is warranted to elucidate the mechanisms driving changes in gene expression and to determine the long-term effects of exercise on brain function.

The peroxisome: an update on mysteries 3.0

Peroxisomes are highly dynamic, oxidative organelles with key metabolic functions in cellular lipid metabolism, such as the β-oxidation of fatty acids and the synthesis of myelin sheath lipids, as well as the regulation of cellular redox balance. Loss of peroxisomal functions causes severe metabolic disorders in humans. Furthermore, peroxisomes also fulfil protective roles in pathogen and viral defence and immunity, highlighting their wider significance in human health and disease. This has sparked increasing interest in peroxisome biology and their physiological functions. This review presents an update and a continuation of three previous review articles addressing the unsolved mysteries of this remarkable organelle. We continue to highlight recent discoveries, advancements, and trends in peroxisome research, and address novel findings on the metabolic functions of peroxisomes, their biogenesis, protein import, membrane dynamics and division, as well as on peroxisome-organelle membrane contact sites and organelle cooperation. Furthermore, recent insights into peroxisome organisation through super-resolution microscopy are discussed. Finally, we address new roles for peroxisomes in immune and defence mechanisms and in human disorders, and for peroxisomal functions in different cell/tissue types, in particular their contribution to organ-specific pathologies.

The psychosocial impact of childhood dementia on children and their parents: a systematic review

BACKGROUND

Childhood dementias are a group of rare and ultra-rare paediatric conditions clinically characterised by enduring global decline in central nervous system function, associated with a progressive loss of developmentally acquired skills, quality of life and shortened life expectancy. Traditional research, service development and advocacy efforts have been fragmented due to a focus on individual disorders, or groups classified by specific mechanisms or molecular pathogenesis. There are significant knowledge and clinician skill gaps regarding the shared psychosocial impacts of childhood dementia conditions. This systematic review integrates the existing international evidence of the collective psychosocial experiences of parents of children living with dementia.

METHODS

We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We systematically searched four databases to identify original, peer-reviewed research reporting on the psychosocial impacts of childhood dementia, from the parent perspective. We synthesised the data into three thematic categories: parents' healthcare experiences, psychosocial impacts, and information and support needs.

RESULTS

Nineteen articles met review criteria, representing 1856 parents. Parents highlighted extensive difficulties connecting with an engaged clinical team and navigating their child's rare, life-limiting, and progressive condition. Psychosocial challenges were manifold and encompassed physical, economic, social, emotional and psychological implications. Access to coordinated healthcare and community-based psychosocial supports was associated with improved parent coping, psychological resilience and reduced psychological isolation. Analysis identified a critical need to prioritize access to integrated family-centred psychosocial supports throughout distinct stages of their child's condition trajectory.

CONCLUSION

This review will encourage and guide the development of evidence-based and integrated psychosocial resources to optimise quality of life outcomes for of children with dementia and their families.

Zellweger's Syndrome With PEX6 Gene Mutation in Mixteco Neonates Due to Possible Founder Effect

Zellweger spectrum disorder (ZSD) is a group of autosomal recessive peroxisomal disorders caused by PEX gene mutations that commonly present with symptoms of severe hypotonia, epileptic seizures, failure to thrive, hepatomegaly, craniofacial dysmorphisms, and sensorineural hearing loss. This article highlights three patients born with ZSD in Central California. All three patients were born to Mixteco mothers. Patients were genetically analyzed, which revealed mutations that correspond to ZSD. They presented with hypotonia at birth, abnormal hepatic panels, and increased fatty acid levels, findings consistent with Zellweger syndrome (ZS). However, only two of three patients displayed sensorineural hearing loss. Two of the patients failed to survive more than one year of age, which reflects the average life expectancy of an infant presenting with ZS. Observed and recorded cases of ZS in the Mixteco population have been postulated to be related to consanguinity and/or a founder effect. Studies have shown that autosomal recessive diseases are more prevalent in consanguineous populations. Consanguinity has been denied by patient 1 and is unknown for patients 2 and 3. Founder mutations have been implicated in areas with high rates of autosomal recessive diseases. All three of our Mixteco patients share a distinct lineage as well as a mutation at PEX6, leading us to believe that they suffered from an inherited founder mutation. The Mixteco population is not studied well enough to come to a definitive conclusion; however, the recognition of the relationship between ZS and Mixteco background is important, as it allows parents to plan accordingly and increases awareness in the community.

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.

Peroxisomes during postnatal development of mouse endocrine and exocrine pancreas display cell-type- and stage-specific protein composition

Peroxisomal dysfunction unhinges cellular metabolism by causing the accumulation of toxic metabolic intermediates (e.g. reactive oxygen species, very -chain fatty acids, phytanic acid or eicosanoids) and the depletion of important lipid products (e.g. plasmalogens, polyunsaturated fatty acids), leading to various proinflammatory and devastating pathophysiological conditions like metabolic syndrome and age-related diseases including diabetes. Because the peroxisomal antioxidative marker enzyme catalase is low abundant in Langerhans islet cells, peroxisomes were considered scarcely present in the endocrine pancreas. Recently, studies demonstrated that the peroxisomal metabolism is relevant for pancreatic cell functionality. During the postnatal period, significant changes occur in the cell structure and the metabolism to trigger the final maturation of the pancreas, including cell proliferation, regulation of energy metabolism, and activation of signalling pathways. Our aim in this study was to (i) morphometrically analyse the density of peroxisomes in mouse endocrine versus exocrine pancreas and (ii) investigate how the distribution and the abundance of peroxisomal proteins involved in biogenesis, antioxidative defence and fatty acid metabolism change during pancreatic maturation in the postnatal period. Our results prove that endocrine and exocrine pancreatic cells contain high amounts of peroxisomes with heterogeneous protein content indicating that distinct endocrine and exocrine cell types require a specific set of peroxisomal proteins depending on their individual physiological functions. We further show that significant postnatal changes occur in the peroxisomal compartment of different pancreatic cells that are most probably relevant for the metabolic maturation and differentiation of the pancreas during the development from birth to adulthood.

Transcriptional regulation of proximal tubular metabolism in acute kidney injury

The kidney, and in particular the proximal tubule (PT), has a high demand for ATP, due to its function in bulk reabsorption of solutes. In normal PT, ATP levels are predominantly maintained by fatty acid β-oxidation (FAO), the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. The normal PT also undertakes gluconeogenesis and metabolism of amino acids. Acute kidney injury (AKI) results in profound PT metabolic alterations, including suppression of FAO, gluconeogenesis, and metabolism of some amino acids, and upregulation of glycolytic enzymes. Recent studies have elucidated new transcriptional mechanisms regulating metabolic pathways in normal PT, as well as the metabolic switch in AKI. A number of transcription factors have been shown to play important roles in FAO, which are themselves downregulated in AKI, while hypoxia-inducible factor 1α, which is upregulated in ischemia-reperfusion injury, is a likely driver of the upregulation of glycolytic enzymes. Transcriptional regulation of amino acid metabolic pathways is less well understood, except for catabolism of branched-chain amino acids, which is likely suppressed in AKI by upregulation of Krüppel-like factor 6. This review will focus on the transcriptional regulation of specific metabolic pathways in normal PT and in AKI, as well as highlighting some of the gaps in knowledge and challenges that remain to be addressed.

Genetics behind Cerebral Disease with Ocular Comorbidity: Finding Parallels between the Brain and Eye Molecular Pathology

Cerebral visual impairments (CVIs) is an umbrella term that categorizes miscellaneous visual defects with parallel genetic brain disorders. While the manifestations of CVIs are diverse and ambiguous, molecular diagnostics stand out as a powerful approach for understanding pathomechanisms in CVIs. Nevertheless, the characterization of CVI disease cohorts has been fragmented and lacks integration. By revisiting the genome-wide and phenome-wide association studies (GWAS and PheWAS), we clustered a handful of renowned CVIs into five ontology groups, namely ciliopathies (Joubert syndrome, Bardet–Biedl syndrome, Alstrom syndrome), demyelination diseases (multiple sclerosis, Alexander disease, Pelizaeus–Merzbacher disease), transcriptional deregulation diseases (Mowat–Wilson disease, Pitt–Hopkins disease, Rett syndrome, Cockayne syndrome, X-linked alpha-thalassaemia mental retardation), compromised peroxisome disorders (Zellweger spectrum disorder, Refsum disease), and channelopathies (neuromyelitis optica spectrum disorder), and reviewed several mutation hotspots currently found to be associated with the CVIs. Moreover, we discussed the common manifestations in the brain and the eye, and collated animal study findings to discuss plausible gene editing strategies for future CVI correction.