PEX5 Research Articles

The Role of the Endoplasmic Reticulum in Peroxisome Biogenesis

Peroxisomes are essential cellular organelles involved in lipid metabolism. Patients affected by severe peroxisome biogenesis disorders rarely survive their first year. Genetic screens in several model organisms have identified more than 30 PEX genes that are required for the formation of functional peroxisomes. Despite significant work on the PEX genes, the biogenic origin of peroxisomes remains controversial. For at least two decades, the prevailing model postulated that peroxisomes propagate by growth and fission of preexisting peroxisomes. In this review, we focus on the recent evidence supporting a new, semiautonomous model of peroxisomal biogenesis. According to this model, peroxisomal membrane proteins (PMPs) traffic from the endoplasmic reticulum (ER) to the peroxisome by a vesicular budding, targeting, and fusion process while peroxisomal matrix proteins are imported into the organelle by an autonomous, posttranslational mechanism. We highlight the contradictory conclusions reached to answer the question of how PMPs are inserted into the ER. We then review what we know and what still remains to be elucidated about the mechanism of PMP exit from the ER and the contribution of preperoxisomal vesicles to mature peroxisomes. Finally, we discuss discrepancies in our understanding of de novo peroxisome biogenesis in wild-type cells. We anticipate that resolving these key issues will lead to a more complete picture of peroxisome biogenesis.

PTS1 Peroxisomal Import Pathway Plays Shared and Distinct Roles to PTS2 Pathway in Development and Pathogenicity of Magnaporthe oryzae

Peroxisomes participate in various important metabolisms and are required in pathogenicity of fungal plant pathogens. Peroxisomal matrix proteins are imported from cytoplasm into peroxisomes through peroxisomal targeting signal 1 (PTS1) or peroxisomal targeting signal 2 (PTS2) import pathway. PEX5 and PEX7 genes participate in the two pathways respectively. The involvement of PEX7 mediated PTS2 import pathway in fungal pathogenicity has been documented, while that of PTS1 remains unclear. Through null mutant analysis of MoPEX5, the PEX5 homolog in Magnaporthe oryzae, we report the crucial roles of PTS1 pathway in the development and host infection in the rice blast fungus, and compared with those of PTS2. We found that MoPEX5 disruption specifically blocked the PTS1 pathway. Δmopex5 was unable to use lipids as sole carbon source and lost pathogenicity completely. Similar as Δmopex7, Δmopex5 exhibited significant reduction in lipid utilization and mobilization, appressorial turgor genesis and H2O2 resistance. Additionally, Δmopex5 presented some distinct defects which were undetected in Δmopex7 in vegetative growth, conidial morphogenesis, appressorial morphogenesis and melanization. The results indicated that the PTS1 peroxisomal import pathway, in addition to PTS2, is required for fungal development and pathogenicity of the rice blast fungus, and also, as a main peroxisomal import pathway, played a more predominant role than PTS2.

Proteomic Analysis Reveals That the Rab GTPase RabE1c Is Involved in the Degradation of the Peroxisomal Protein Receptor PEX7 (Peroxin 7)

The biogenesis of peroxisomes is mediated by peroxins (PEXs). PEX7 is a cytosolic receptor that imports peroxisomal targeting signal type 2 (PTS2)-containing proteins. Although PEX7 is important for protein transport, the mechanisms that mediate its function are unknown. In this study, we performed proteomic analysis to identify PEX7-binding proteins using transgenic Arabidopsis expressing green fluorescent protein (GFP)-tagged PEX7. Our analysis identified RabE1c, a small GTPase, as a PEX7 binding partner. In vivo analysis revealed that GTP-bound RabE1c binds to PEX7 and that a subset of RabE1c localizes to peroxisomes and interacts with PEX7 on the peroxisome membrane. Unlike endogenous PEX7, which is predominantly localized to the cytosol, GFP-PEX7 accumulates abnormally on the peroxisomal membrane and induces degradation of endogenous PEX7, concomitant with a reduction in import of PTS2-containing proteins and decreased peroxisomal β-oxidation activity. Thus, GFP-PEX7 on the peroxisomal membrane exerts a dominant negative effect. Mutation of RabE1c restored endogenous PEX7 protein expression and import of PTS2-containing proteins as well as peroxisomal β-oxidation activity. Treatment with proteasome inhibitors also restored endogenous PEX7 protein levels in GFP-PEX7-expressing seedlings. Based on these findings, we conclude that RabE1c binds PEX7 and facilitates PEX7 degradation in the presence of immobile GFP-PEX7 accumulated at the membrane.

Chemical chaperones improve peroxisomal biogenesis in fibroblasts of mild Zellweger syndrome spectrum patients

s ingediend voor het Amsterdam Kindersymposium 2013 21 Chemical chaperones improve peroxisomal biogenesis in fibroblasts of mild Zellweger syndrome spectrum patients Kevin Bere ndse (1,2), Merel S. Ebberink (1), Lodewijk IJlst (1), Bwee Tien Poll-The (2), Ronald J.A. Wanders(1), Hans R. Waterham (1) (1) Laboratory Genetic Metabolic Diseases, Academic Medical Center, Amsterdam, the Netherlands (2) Department of Paediatric Neurology, Emma Children’s Hospital, Academic Medical Center, Amsterdam, the Netherlands INTRODUCTION Zellweger syndrome spectrum (ZSS) disorders are multisystem genetic disorders which lack functional peroxisomes due to a defect in one of the PEX genes. The ZSS include three phenotypes, which represent a spectrum of disease severity with Zellweger syndrome (ZS) being the most severe. In contrast to patients with the ZS phenotype, mild patients can be characterized by very mildly abnormal peroxisomal parameters in cultured skin fi broblasts, including a mosaic catalase immunofl uorescence pattern. Such a mosaic pattern is described for specifi c missense mutations in various PEX genes. Possibly, these missense mutations cause an unstable and/or incorrect folded native state of the protein. We hypothesize that the functional activity of the mutant PEX1 can be enhanced by promoting protein folding with chemical chaperones (e.g. glycerol or arginine) and thereby stimulating peroxisome biogenesis. METHODS Fibroblasts from four patients with a defect in PEX1 and two controls were cultured for up to three weeks in DMEM medium with diff erent concentrations of arginine or glycerol. To determine the eff ect of diff erent chemicals on peroxisome biogenesis we studied the following parameters: (1) the levels of PEX1 protein, (2) the peroxisomal protein import capacity, (3) the levels of intra peroxisomal processed protein, and (4) the capacity to β-oxidize very long chain fatty acids. CONCLUSION The addition of arginine or glycerol to the medium improved both the peroxisomal biogenesis and the peroxisomal metabolic state of fi broblasts with a missense mutation in PEX1. We hypothesize that a signifi cant number of ZSS patients may benefi t from arginine treatment.

Identification of a novel missense mutation of PEX7 gene in an Iranian patient with rhizomelic chondrodysplasia punctata type 1

Deficiency in the PTS2 protein import pathway due to mutations in PEX7 gene results in the rhizomelic chondrodysplasia punctata (RCDP) type 1. In the present study, we have reported a novel missense mutation, W75R, in the PEX7 gene in an Iranian patient with the RCDP type 1. The inability of PEX7 protein to transport PTS2 containing proteins including peroxisomal 3-ketoacyl-CoA thiolase and PTS2-EGFP protein to the surface of the peroxisomes showed that the W75R mutation in PEX7 gene severely impaired the function of PEX7 protein and was responsible for RCDP type 1 in this patient.

Phenotypic Variability in Fraternal Twins with PEX1 Mutations: Zellweger Syndrome with Discordant Clinical Phenotype

Perioxisomal biogenesis disorders are a group of genetically and clinically variable disorders affect very-long chain fatty acid metabolism. Many PEX genes have been implicated in various disorders of the Zellweger syndrome spectrum (ZSS). Here we report the cases of fraternal twins who share the same PEX1 mutations and biochemical abnormalities classic ZSS, but who have a discordant clinical presentation. While twin A had classical clinical features of Zellweger Syndrome (ZS), twin B’s neonatal presentation was much milder and she may not have been initially identified as having ZSS had it not been for her brother’s presentation. The twins had nearly identical biochemical markers of peroxisome function. This report highlights the wide spectrum of ZSS and suggests that its variability cannot be accounted for by genetics, biochemistry, or even intrauterine environment.

Peroxisome deficient invertebrate and vertebrate animal models.

Although peroxisomes are ubiquitous organelles in all animal species, their importance for the functioning of tissues and organs remains largely unresolved. Because peroxins are essential for the biogenesis of peroxisomes, an obvious approach to investigate their physiological role is to inactivate a Pex gene or to suppress its translation. This has been performed in mice but also in more primitive organisms including D. melanogaster, C. elegans, and D. rerio, and the major findings and abnormalities in these models will be highlighted. Although peroxisomes are generally not essential for embryonic development and organogenesis, a generalized inactivity of peroxisomes affects lifespan and posthatching/postnatal growth, proving that peroxisomal metabolism is necessary for the normal maturation of these organisms. Strikingly, despite the wide variety of model organisms, corresponding tissues are affected including the central nervous system and the testis. By inactivating peroxisomes in a cell type selective way in the brain of mice, it was also demonstrated that peroxisomes are necessary to prevent neurodegeneration. As these peroxisome deficient model organisms recapitulate pathologies of patients affected with peroxisomal diseases, their further analysis will contribute to the elucidation of still elusive pathogenic mechanisms.

Newly identified milder phenotype of peroxisome biogenesis disorder caused by mutated PEX3 gene

We identified the first patient with infantile Refsum disease (IRD), a milder phenotype of peroxisome biogenesis disorder (PBD) caused by a mutated PEX3, and investigated the clinical, molecular and cellular characterization in this patient. The patient presented psychomotor regression, late-onset leukodystrophy, peripheral neuropathy, hearing impairment, a renal cyst, and renal hypertension and survived until the age of 36. Furthermore, fibroblasts from the patient indicated a mosaic pattern of catalase-positive particles (peroxisomes) and numerous peroxisomal membrane structures. Molecular analysis was homozygous for the D347Y mutation and reduced gene expression of PEX3 which encodes a peroxisomal membrane protein, pex3p, involved in peroxisome assembly at the early stage of peroxisomal membrane vesicle formation, therefore, patients with a mutated PEX3 gene have been reported to have only a severe phenotype of Zellweger syndrome and no or less peroxisomal remnant membrane structure. This is not only a newly identified milder PBD caused by a mutated PEX3 gene but also the first report of a Japanese patient with IRD who had not been diagnosed until over 30years of age, which suggests there must be more variant PBD in patients with degenerative neurologic disorder, and to bring them to light is necessary.

Analysis of a Chinese pedigree with Zellweger syndrome reveals a novel PEX1 mutation by next-generation sequencing

BackgroundAutosomal recessive Zellweger spectrum disorder (ZSD), the main subgroup of the peroxisome biogenesis disorders (PBDs), can be caused by mutations in any of the 13 PEX genes. Zellweger syndrome (ZS) is the most common and severe phenotype in the heterogeneous ZSD. For the large number genes involved, it is difficult to make a precise genetic diagnosis by traditional methods at a time. A combination of enrichment of targeted genes and next-generation sequencing (NGS) would result in both high efficiency and low cost for targeted sequencing of genes of interest. MethodsTo identify potential mutations in a Chinese family associated with Zellweger syndrome, 1930kb of all the targeted region of PEX genes were captured and sequenced using NGS. We also performed Sanger sequencing to validate the NGS results. ResultsHere, we reported a Chinese patient diagnosed as a severe classic type of PBD based on a clinical investigation. We then performed microarray-based NGS to detect the variants in PEX genes of the whole family. One reported heterozygosis mutation (c.782_783delAA) was identified in the patient's father and one novel heterozygosis missense mutation (c.475G>C) was found in the patient's mother, the patient inherited both mutations. ConclusionsThe results proved that the application of target sequence capture using chip and high-throughput NGS is a valuable tool for the molecular diagnosis of peroxisome biogenesis disorders. The accuracy, high-throughput and speed of the method make it suitable for clinical application.

A founder mutation in the PEX6 gene is responsible for increased incidence of Zellweger syndrome in a French Canadian population

BackgroundZellweger syndrome (ZS) is a peroxisome biogenesis disorder due to mutations in any one of 13 PEX genes. Increased incidence of ZS has been suspected in French-Canadians of the Saguenay-Lac-St-Jean region (SLSJ) of Quebec, but this remains unsolved.MethodsWe identified 5 ZS patients from SLSJ diagnosed by peroxisome dysfunction between 1990–2010 and sequenced all coding exons of known PEX genes in one patient using Next Generation Sequencing (NGS) for diagnostic confirmation.ResultsA homozygous mutation (c.802_815del, p.[Val207_Gln294del, Val76_Gln294del]) in PEX6 was identified and then shown in 4 other patients. Parental heterozygosity was confirmed in all. Incidence of ZS was estimated to 1 in 12,191 live births, with a carrier frequency of 1 in 55. In addition, we present data suggesting that this mutation abolishes a SF2/ASF splice enhancer binding site, resulting in the use of two alternative cryptic donor splice sites and predicted to encode an internally deleted in-frame protein.ConclusionWe report increased incidence of ZS in French-Canadians of SLSJ caused by a PEX6 founder mutation. To our knowledge, this is the highest reported incidence of ZS worldwide. These findings have implications for carrier screening and support the utility of NGS for molecular confirmation of peroxisomal disorders.

Bioinformaticresearch of the family of <I>PEX11</I>, peroxisomeproliferous factor in fungus

The family members of PEX11 are key factors involved in regulation of peroxisome proliferation. Sixty-six PEX11p candidates of PEX11 gene family from 26 representative fungal species were obtained and analyzed by bioinformatic strategies. In most filamentous fungi, 2 or 3 potential PEX11ps were found, in contrast with 1 or 2 in yeast species. Compared with other fungal species, the Ascomycetes tend to have more PEX11ps, and even 5 in several individuals. The data of phylogenetic analysis and protein structure indicated that all of the PEX11ps were divided into 3 groups: I, II, and III. The members of group I and group III existed in most species, while those in group II were found only in Pezizomycotina. By MEME analysis, 5-6 conserved motifs were found in each PEX11ps. Among them,motif 8 in C-terminal had the most conservation, indicating that this motif probably plays a key role in maintaining the proper function of PEX11p.

A novel defect of peroxisome division due to a homozygous non-sense mutation in the PEX11β gene

BackgroundPeroxisomes are organelles that proliferate continuously and play an indispensable role in human metabolism. Consequently, peroxisomal gene defects can cause multiple, often severe disorders, including the peroxisome biogenesis disorders. Currently,...

Peroxisome deficiency-induced ER stress and SREBP-2 pathway activation in the liver of newborn PEX2 knock-out mice

Disruption of the Pex2 gene leads to peroxisome deficiency and widespread metabolic dysfunction. We previously demonstrated that peroxisomes are critical for maintaining cholesterol homeostasis, using peroxisome-deficient Pex2−/− mice on a hybrid Swiss Webster×129S6/SvEv (SW/129) genetic background. Peroxisome deficiency activates hepatic endoplasmic reticulum (ER) stress pathways, leading to dysregulation of the endogenous sterol response mechanism. Herein, we demonstrate a more profound dysregulation of cholesterol homeostasis in newborn Pex2−/− mice congenic on a 129S6/SvEv (129) genetic background, and substantial differences between newborn versus postnatal Pex2−/− mice in factors that activate ER stress. These differences extend to relationships between activation of genes regulated by SREBP-2 versus PPARα. The SREBP-2 pathway is induced in neonatal Pex2−/− livers from 129 and SW/129 strains, despite normal hepatic cholesterol levels. ER stress markers are increased in newborn 129 Pex2−/− livers, which occurs in the absence of hepatic steatosis or accumulation of peroxins in the ER. Moreover, the induction of SREBP-2 and ER stress pathways is independent of PPARα activation in livers of newborn 129 and SW/129 Pex2−/− mice. Two-week-old wild-type mice treated with the peroxisome proliferator WY-14,643 show strong induction of PPARα-regulated genes and decreased expression of SREBP-2 and its target genes, further demonstrating that SREBP-2 pathway induction is not dependent on PPARα activation. Lastly, there is no activation of either SREBP-2 or ER stress pathways in kidney and lung of newborn Pex2−/− mice, suggesting a parallel induction of these pathways in peroxisome-deficient mice. These findings establish novel associations between SREBP-2, ER stress and PPARα pathway inductions.

Comparative profiling of the peroxisomal proteome of wildtype and Pex7 knockout mice by quantitative mass spectrometry

We present a label-free quantitative proteomic approach for the study of kidney peroxisomes of Pex7 knockout mice which is a bona-fide model for the human disease rhizomelic chondrodysplasia punctata (RCDP). RCDP is an autosomal recessive human disorder caused by mutations in the PEX7 gene encoding for Pex7, the cytosolic receptor protein that is essential for the import of proteins containing a functional peroxisomal targeting signal (PTS)-type 2. In this work, we quantitatively followed hundreds of proteins through high density gradient fractions of wildtype (WT) and Pex7 knockout (Pex7−/−) mice by high resolution mass spectrometry. A set of candidate proteins with altered abundance was defined via statistical and quantitative assessment of protein profiles obtained from WT and Pex7−/− mice. The results obtained demonstrate the feasibility of this approach to identify proteins specifically affected in abundance by the deletion of Pex7. All three known PTS2 proteins, including acetyl-Coenzyme A acyltransferase, alkylglycerone phosphate synthase and phytanoyl-CoA hydroxylase were determined to be virtually absent in these fractions whereas KIAA0564, a so far uncharacterized protein, was barely detectable in peroxisomal fractions of Pex7−/− mice. Furthermore, we report numerous PTS1 proteins with increased abundance levels in Pex7−/− mice that fulfill essential functions in the β-oxidation of very long-chain fatty acids or the biosynthesis of ether-phospholipids in peroxisomes.

Characterization of two common 5' polymorphisms in PEX1 and correlation to survival in PEX1 peroxisome biogenesis disorder patients

BackgroundMutations in PEX1 are the most common primary cause of Zellweger syndrome. In addition to exonic mutations, deletions and splice site mutations two 5' polymorphisms at c.-137 and c.-53 with a potential influence on PEX1 protein levels have been described in the 5' untranslated region (UTR) of the PEX1 gene.MethodsWe used RACE and in silico promoter prediction analysis to study the 5' UTR of PEX1. We determined the distribution of PEX1 5' polymorphisms in a cohort of 30 Zellweger syndrome patients by standard DNA sequencing. 5' polymorphisms were analysed in relation to the two most common mutations in PEX1 and were incorporated into a novel genotype-phenotype analysis by correlation of three classes of PEX1 mutations with patient survival.ResultsWe provide evidence that the polymorphism 137 bp upstream of the ATG codon is not part of the UTR, rendering it a promoter polymorphism. We show that the first, but not the second most common PEX1 mutation arose independently of a specific upstream polymorphic constellation. By genotype-phenotype analysis we identified patients with identical exonic mutation and identical 5' polymorphisms, but strongly differing survival.ConclusionsOur study suggests that two different types of PEX1 5' polymorphisms have to be distinguished: a 5' UTR polymorphism at position c.-53 and a promoter polymorphism 137 bp upstream of the PEX1 start codon. Our results indicate that the exonic PEX1 mutation correlates with patient survival, but the two 5' polymorphisms analysed in this study do not have to be considered for diagnostic and/or prognostic purposes.

Drosophila Carrying Pex3 or Pex16 Mutations Are Models of Zellweger Syndrome That Reflect Its Symptoms Associated with the Absence of Peroxisomes

The peroxisome biogenesis disorders (PBDs) are currently difficult-to-treat multiple-organ dysfunction disorders that result from the defective biogenesis of peroxisomes. Genes encoding Peroxins, which are required for peroxisome biogenesis or functions, are known causative genes of PBDs. The human peroxin genes PEX3 or PEX16 are required for peroxisomal membrane protein targeting, and their mutations cause Zellweger syndrome, a class of PBDs. Lack of understanding about the pathogenesis of Zellweger syndrome has hindered the development of effective treatments. Here, we developed potential Drosophila models for Zellweger syndrome, in which the Drosophila pex3 or pex16 gene was disrupted. As found in Zellweger syndrome patients, peroxisomes were not observed in the homozygous Drosophila pex3 mutant, which was larval lethal. However, the pex16 homozygote lacking its maternal contribution was viable and still maintained a small number of peroxisome-like granules, even though PEX16 is essential for the biosynthesis of peroxisomes in humans. These results suggest that the requirements for pex3 and pex16 in peroxisome biosynthesis in Drosophila are different, and the role of PEX16 orthologs may have diverged between mammals and Drosophila. The phenotypes of our Zellweger syndrome model flies, such as larval lethality in pex3, and reduced size, shortened longevity, locomotion defects, and abnormal lipid metabolisms in pex16, were reminiscent of symptoms of this disorder, although the Drosophila pex16 mutant does not recapitulate the infant death of Zellweger syndrome. Furthermore, pex16 mutants showed male-specific sterility that resulted from the arrest of spermatocyte maturation. pex16 expressed in somatic cyst cells but not germline cells had an essential role in the maturation of male germline cells, suggesting that peroxisome-dependent signals in somatic cyst cells could contribute to the progression of male germ-cell maturation. These potential Drosophila models for Zellweger syndrome should contribute to our understanding of its pathology.

A Drosophila model for the Zellweger spectrum of peroxisome biogenesis disorders

SUMMARYHuman peroxisome biogenesis disorders are lethal genetic diseases in which abnormal peroxisome assembly compromises overall peroxisome and cellular function. Peroxisomes are ubiquitous membrane-bound organelles involved in several important biochemical processes, notably lipid metabolism and the use of reactive oxygen species for detoxification. Using cultured cells, we systematically characterized the peroxisome assembly phenotypes associated with dsRNA-mediated knockdown of 14 predicted Drosophila homologs of PEX genes (encoding peroxins; required for peroxisome assembly and linked to peroxisome biogenesis disorders), and confirmed that at least 13 of them are required for normal peroxisome assembly. We also demonstrate the relevance of Drosophila as a genetic model for the early developmental defects associated with the human peroxisome biogenesis disorders. Mutation of the PEX1 gene is the most common cause of peroxisome biogenesis disorders and is one of the causes of the most severe form of the disease, Zellweger syndrome. Inherited mutations in Drosophila Pex1 correlate with reproducible defects during early development. Notably, Pex1 mutant larvae exhibit abnormalities that are analogous to those exhibited by Zellweger syndrome patients, including developmental delay, poor feeding, severe structural abnormalities in the peripheral and central nervous systems, and early death. Finally, microarray analysis defined several clusters of genes whose expression varied significantly between wild-type and mutant larvae, implicating peroxisomal function in neuronal development, innate immunity, lipid and protein metabolism, gamete formation, and meiosis.

The significance of peroxisomes in secondary metabolite biosynthesis in filamentous fungi

Peroxisomes are ubiquitous organelles characterized by a protein-rich matrix surrounded by a single membrane. In filamentous fungi, peroxisomes are crucial for the primary metabolism of several unusual carbon sources used for growth (e.g. fatty acids), but increasing evidence is presented that emphasize the crucial role of these organelles in the formation of a variety of secondary metabolites. In filamentous fungi, peroxisomes also play a role in development and differentiation whereas specialized peroxisomes, the Woronin bodies, play a structural role in plugging septal pores. The biogenesis of peroxisomes in filamentous fungi involves the function of conserved PEX genes, as well as genes that are unique for these organisms. Peroxisomes are also subject to autophagic degradation, a process that involves ATG genes. The interplay between organelle biogenesis and degradation may serve a quality control function, thereby allowing a continuous rejuvenation of the organelle population in the cells.

Nonsense suppressor therapies rescue peroxisome lipid metabolism and assembly in cells from patients with specific PEX gene mutations

Peroxisome biogenesis disorders (PBDs) are multisystemic autosomal recessive disorders resulting from mutations in PEX genes required for normal peroxisome assembly and metabolic activities. Here, we evaluated the potential effectiveness of aminoglycoside G418 (geneticin) and PTC124 (ataluren) nonsense suppression therapies for the treatment of PBD patients with disease-causing nonsense mutations. PBD patient skin fibroblasts producing stable PEX2 or PEX12 nonsense transcripts and Chinese hamster ovary (CHO) cells with a Pex2 nonsense allele all showed dramatic improvements in peroxisomal very long chain fatty acid catabolism and plasmalogen biosynthesis in response to G418 treatments. Cell imaging assays provided complementary confirmatory evidence of improved peroxisome assembly in G418-treated patient fibroblasts. In contrast, we observed no appreciable rescue of peroxisome lipid metabolism or assembly for any patient fibroblast or CHO cell culture treated with various doses of PTC124. Additionally, PTC124 did not show measurable nonsense suppression in immunoblot assays that directly evaluated the read-through of PEX7 nonsense alleles found in PBD patients with rhizomelic chondrodysplasia punctata type 1 (RCDP1). Overall, our results support the continued development of safe and effective nonsense suppressor therapies that could benefit a significant subset of individuals with PBDs. Furthermore, we suggest that the described cell culture assay systems could be useful for evaluating and screening for novel nonsense suppressor therapies.

Autosomal recessive cerebellar ataxia caused by mutations in the PEX2 gene

ObjectiveTo expand the spectrum of genetic causes of autosomal recessive cerebellar ataxia (ARCA).Case reportTwo brothers are described who developed progressive cerebellar ataxia at 3 1/2 and 18 years, respectively. After ruling out known common genetic causes of ARCA, analysis of blood peroxisomal markers strongly suggested a peroxisomal biogenesis disorder. Sequencing of candidate PEX genes revealed a homozygous c.865_866insA mutation in the PEX2 gene leading to a frameshift 17 codons upstream of the stop codon. PEX gene mutations usually result in a severe neurological phenotype (Zellweger spectrum disorders).ConclusionsGenetic screening of PEX2 and other PEX genes involved in peroxisomal biogenesis is warranted in children and adults with ARCA.