Zellweger Syndrome Research Articles

Zellweger syndrome: prenatal and postnatal growth failure with epiphyseal stippling

We present a 2-month-old male affected by Zellweger syndrome, a rare peroxisomal disorder. The diagnosis was supported by clinical and radiological findings and established by biochemical tests. The characteristic radiological features included anomalous ossification (epiphyseal stippling). We also discuss main differential diagnoses of epiphyseal stippling and a brief literature review.

Metabolic functions of peroxisomes in health and disease

Peroxisomes are subcellular organelles which are present in virtually every eukaryotic cell and catalyze a large number of metabolic functions. The importance of peroxisomes for humans is stressed by the existence of a large group of genetic diseases in which either the biogenesis of peroxisomes is impaired or one of its metabolic functions. Thanks to the work on Zellweger syndrome which is the prototype of the group of peroxisomal disorders, much has been learned about the metabolism and biogenesis of peroxisomes in humans. These metabolic functions include: (1.) fatty acid beta-oxidation; (2.) etherphospholipid biosynthesis; (3.) fatty acid alpha-oxidation, and (4.) glyoxylate detoxification. Since peroxisomes lack a citric acid cycle and a respiratory chain, peroxisomes are relatively helpless organelles which rely heavily on their cross-talk with other subcellular organelles in order to metabolize the end products of metabolism as generated in peroxisomes. The metabolic functions of peroxisomes in humans will be briefly described in this review with emphasis on the cross-talk with other subcellular organelles as well as the peroxisomal disorders in which one or more peroxisomal functions are impaired.

Altered phospholipid molecular species and glycolipid composition in brain, liver and fibroblasts of Zellweger syndrome

We studied the altered molecular species of lipids in brain and liver tissues, and fibroblasts from patients with Zellweger syndrome (ZS). ZS cerebellum samples contained a higher amount of sphingomyelin with shorter chain fatty acids compared to that in normal controls. The amount of phosphatidylethanolamine (PE) was less than half of that in controls, with the absence of the PE-type of plasmalogen. Gangliosides were accumulated in the brains and fibroblasts of ZS patients. To investigate whether or not impaired beta-oxidation of very long chain fatty acids and/or plasmalogen synthesis affects glycolipids metabolism, RNAi of peroxisomal acylCo-A oxidase (ACOX1) and glyceronephosphate O-acyltransferase (GNPAT) was performed using cultured neural cells. In neuronal F3-Ngn1 cells, ACOX1 and GNPAT silencing up-regulated ceramide galactosyltransferase (UGT8) mRNA expression, and down-regulated UDP-glucose ceramide glucosyltransferase (UGCG). These results suggest that both impaired beta-oxidation of very long chain fatty acids and plasmalogen synthesis affect glycolipid metabolism in neuronal cells.

14. EEG in Ohtahara syndrome and hereditary neurometabolic diseases

Ohtahara syndrome is classified among early infantile progressive epileptic encephalopathies. EEG is characterized by a suppression burst pattern, which appears with onset of seizures and disappears within the first 6 months of life. It is characterized by periods of low voltage basic rhythm (below 5, 10 or 15 microvolts) of different duration (2–10 s) discontinued with paroxysmal high voltage theta or delta waves intermixed with sharp waves. This pattern can be persistent in all sleep stages in severe cases, or present only in sleep in milder ones. Underlying causes are disturbances of brain development as hemimegalencephaly, porencephaly, Aicardy syndrome, focal cortical dysplasias and hypoxic–ischemic encephalopathy. Early myoclonic encephalopathy usually starts in the first day of life and frequently before 10th day. The EEG also shows burst suppression pattern, but types of seizures are different from those in epileptic enhcephalopathy. Causal factors are inherited metabolic disorders (nonketotic hypeglycinemia, propionic aciduria, methylmalonic acidaemia, D-glyceric acidemia, sulphite and xanthine oxidase deficiency, Zellweger syndrome, molybdenum co-factor deficiency). EEG in B6 dependent epilepsy, maple sirup urine disease, pyridoxal phosphate oxidase deficiency could show burst suppression pattern, but also other discharges. In de Vivo disease, GLUT1 transporter deficiency, EEG may show very different findings.

Peroxisome biogenesis disorders: Biological, clinical and pathophysiological perspectives

The peroxisome biogenesis disorders (PBD) are a heterogeneous group of autosomal recessive disorders in which peroxisome assembly is impaired, leading to multiple peroxisome enzyme deficiencies, complex developmental sequelae and progressive disabilities. Mammalian peroxisome assembly involves the protein products of 16 PEX genes; defects in 14 of these have been shown to cause PBD. Three broad phenotypic groups are described on a spectrum of severity: Zellweger syndrome is the most severe, neonatal adrenoleukodystrophy is intermediate and infantile Refsum disease is less severe. Another group is Rhizomelic chondrodysplasia punctata spectrum. Recently, atypical phenotypes have been described, indicating that the full spectrum of these disorders remains to be identified. For most patients, there is a correlation between clinical severity and effect of the mutation on PEX protein function. Diagnosis relies on biochemical measurements of peroxisome functions and PEX gene sequencing. There are no targeted therapies, although management protocols have been suggested and research endeavors continue. In this review we will discuss peroxisome biology and PBD, and research contributions to pathophysiology and treatment.

Impaired Very Long-chain Acyl-CoA β-Oxidation in Human X-linked Adrenoleukodystrophy Fibroblasts Is a Direct Consequence of ABCD1 Transporter Dysfunction

X-linked adrenoleukodystrophy (X-ALD), an inherited peroxisomal disorder, is caused by mutations in the ABCD1 gene encoding the peroxisomal ATP-binding cassette (ABC) transporter ABCD1 (adrenoleukodystrophy protein, ALDP). Biochemically, X-ALD is characterized by an accumulation of very long-chain fatty acids and partially impaired peroxisomal β-oxidation. In this study, we used primary human fibroblasts from X-ALD and Zellweger syndrome patients to investigate the peroxisomal β-oxidation defect. Our results show that the degradation of C26:0-CoA esters is as severely impaired as degradation of unesterified very long-chain fatty acids in X-ALD and is abolished in Zellweger syndrome. Interestingly, the β-oxidation rates for both C26:0-CoA and C22:0-CoA were similarly affected, although C22:0 does not accumulate in patient fibroblasts. Furthermore, we show that the β-oxidation defect in X-ALD is directly caused by ABCD1 dysfunction as blocking ABCD1 function with a specific antibody reduced β-oxidation to levels observed in X-ALD fibroblasts. By quantification of mRNA and protein levels of the peroxisomal ABC transporters and by blocking with specific antibodies, we found that residual β-oxidation activity toward C26:0-CoA in X-ALD fibroblasts is mediated by ABCD3, although the efficacy of ABCD3 appeared to be much lower than that of ABCD1. Finally, using isolated peroxisomes, we show that β-oxidation of C26:0-CoA is independent of additional CoA but requires a cytosolic factor of >10-kDa molecular mass that is resistant to N-ethylmaleimide and heat inactivation. In conclusion, our findings in human cells suggest that, in contrast to yeast cells, very long-chain acyl-CoA esters are transported into peroxisomes by ABCD1 independently of additional synthetase activity.

Functional analysis of PEX13 mutation in a Zellweger syndrome spectrum patient reveals novel homooligomerization of PEX13 and its role in human peroxisome biogenesis

In humans, the concerted action of at least 13 different peroxisomal PEX proteins is needed for proper peroxisome biogenesis. Mutations in any of these PEX genes can lead to lethal neurometabolic disorders of the Zellweger syndrome spectrum (ZSS). Previously, we identified the W313G mutation located within the SH3 domain of the peroxisomal protein, PEX13. As this tryptophan residue is highly conserved in almost all known SH3 proteins, we investigated the pathogenic mechanism of the W313G mutation and its role in PEX13 interactions and functions in peroxisome biogenesis. Here, we report for the first time that human PEX13 interacts with itself in peroxisomes in living cells. We demonstrate that the import of PTS1 (peroxisomal targeting signal 1) proteins is specifically disrupted when homooligomerization of PEX13 is interrupted. Live cell FRET microscopy in living cells as well as co-immunoprecipitation experiments reveal that the highly conserved W313 residue is important for self-association of PEX13 but is not required for interaction with PEX14, a well-established interaction partner at the peroxisomal membrane. Experiments with truncated constructs indicate that although the W313G mutation resides in the C-terminal SH3 domain, the N-terminal half is necessary for peroxisomal localization, which in turn appears to be crucial for homooligomerization. Furthermore, rescue of homooligomerization in the W313G mutant cells through complementation with truncation constructs restores import of peroxisomal matrix proteins. Taken together, the thorough analyses of a ZSS patient mutation unraveled the general cell biological function of PEX13 and its mechanism in the import of peroxisomal matrix PTS1 proteins.

Child Neurology: Zellweger syndrome

Zellweger syndrome (ZS) is a severe manifestation of disease within the spectrum of peroxisome biogenesis disorders that includes neonatal adrenoleukodystrophy, infantile Refsum disease, and rhizomelic chondroplasia punctata. Patients with ZS present in the neonatal period with a characteristic phenotype of distinctive facial stigmata, pronounced hypotonia, poor feeding, hepatic dysfunction, and often seizures and boney abnormalities. In patients with ZS, a mutation in one of the PEX genes coding for a peroxin (a peroxisome assembly protein) creates functionally incompetent organelles causing an accumulation of very long chain fatty acids (VLCFA), among other complications. Despite an absence of treatment options, prompt diagnosis of ZS is important for providing appropriate symptomatic care, definitive genetic testing, and counseling regarding family planning.

A deleterious mutation in thePEX2gene causes Zellweger syndrome in individuals of Ashkenazi Jewish descent

Zellweger syndrome is known to be caused by numerous mutations that occur in at least 12 of the PEX genes. While phenotypes vary, many are severely debilitating, and death can result in affected newborns. Since the disease follows an autosomal recessive pattern of inheritance, carrier screening can be done for at-risk couples, but the number of potential mutations sites to screen can be daunting. Ethnicity-specific studies can help narrow this range by highlighting mutations that are present at higher percentages in certain populations. In this article, the carrier frequencies for two mutations causative of the severe Zellweger syndrome spectrum phenotype that occur in the PEX2 gene, c.355C>T and c.550del, were studied in individuals of Ashkenazi Jewish descent in order to advise on inclusion in existing carrier screening mutation panels for this population. The screening was performed for 2093 individuals through the use of TaqMan genotyping assays, real-time PCR, and allelic discrimination. Results indicated a carrier frequency of 0.813% (±0.385%) for the c.355C>T mutation and a carrier frequency of 0.00% (±0.00%) for the c.550del mutation. On the basis of these frequencies, we believe that the c.355C>T mutation should be considered for inclusion in carrier screening panels for the Ashkenazi population.

Tysnd1 deficiency in mice interferes with the peroxisomal localization of PTS2 enzymes, causing lipid metabolic abnormalities and male infertility.

Peroxisomes are subcellular organelles involved in lipid metabolic processes, including those of very-long-chain fatty acids and branched-chain fatty acids, among others. Peroxisome matrix proteins are synthesized in the cytoplasm. Targeting signals (PTS or peroxisomal targeting signal) at the C-terminus (PTS1) or N-terminus (PTS2) of peroxisomal matrix proteins mediate their import into the organelle. In the case of PTS2-containing proteins, the PTS2 signal is cleaved from the protein when transported into peroxisomes. The functional mechanism of PTS2 processing, however, is poorly understood. Previously we identified Tysnd1 (Trypsin domain containing 1) and biochemically characterized it as a peroxisomal cysteine endopeptidase that directly processes PTS2-containing prethiolase Acaa1 and PTS1-containing Acox1, Hsd17b4, and ScpX. The latter three enzymes are crucial components of the very-long-chain fatty acids β-oxidation pathway. To clarify the in vivo functions and physiological role of Tysnd1, we analyzed the phenotype of Tysnd1−/− mice. Male Tysnd1−/− mice are infertile, and the epididymal sperms lack the acrosomal cap. These phenotypic features are most likely the result of changes in the molecular species composition of choline and ethanolamine plasmalogens. Tysnd1−/− mice also developed liver dysfunctions when the phytanic acid precursor phytol was orally administered. Phyh and Agps are known PTS2-containing proteins, but were identified as novel Tysnd1 substrates. Loss of Tysnd1 interferes with the peroxisomal localization of Acaa1, Phyh, and Agps, which might cause the mild Zellweger syndrome spectrum-resembling phenotypes. Our data established that peroxisomal processing protease Tysnd1 is necessary to mediate the physiological functions of PTS2-containing substrates.

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.

Rapid prenatal diagnosis of fetal Zellweger syndrome by biochemical tests, complementation studies, and molecular analyses

What's already known about this topic? Neuronal migration disorders are caused by many genetic conditions. Zellweger syndrome is a rare autosomal recessive cause. Prenatal diagnosis can be performed in further pregnancies.What does this study add? We show that early prenatal diagnosis can be reached by biochemical testing in pregnancies at risk for ZSS, even when no definite diagnosis has been established in a previous pregnancy. ZSS should be considered in fetus presenting with lissencephaly and other specific congenital anomalies.

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.

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.

Oral manifestations and dental management of a child with Zellweger syndrome

Zellweger syndrome (ZS) is a rare autosomal recessive disorder, resulting from an impairment in peroxisome function. It is characterized by craniofacial dysmorphism and neurological abnormalities, and involves several systems, which may complicate dental and anesthesia management. The case of a 7-year-old girl diagnosed with ZS is described with emphasis on oral manifestations, oral rehabilitation under general anesthesia (GA), and home oral care. Apart from the unique features of ZS, she presented with clinodactyly, distinctive palatal vault, Class III malocclusion, missing teeth, microdontia, and delayed dental formation. Dental treatment under GA was conducted with concerns of risk of respiratory insufficiency. Oral home care by the parent and regular recall visits were essential to maintain good oral health. Children with ZS may survive into late childhood. They, however, present multiple health problems that are of special concern for not only the pediatric dentist but also the anesthesiologist. Collaboration with the medical team is essential for optimal care of these patients.

Neonatal Adrenoleukodystrophy: A Clinical, Pathologic, and Biochemical Study

Neonatal adrenoleukodystrophy constitutes a distinct genetic disorder of autosomal recessive inheritance, and is distinguishable from the cerebro-hepato-renal syndrome of Zellweger and X-linked juvenile adrenoleukodystrophy, although all three conditions store very long chain fatty acids. Abnormal clinical features in neonatal adrenoleukodystrophy are generally present at birth, and include muscle hypotonia, severe psychomotor retardation, and failure to thrive. These infants are generally blind and deaf, with seizures developing during their first few weeks. A retinopathic "leopard spot" is common, and should help identify this disorder. The brains of four infants who died of neonatal adrenoleukodystrophy were biochemically analyzed for complex lipids, including cholesterol, cholesterol esters, total phospholipids, total galactolipids, and gangliosides. Additional analyses included the separation and identification of very long chain fatty acids and various forms of brain plasmalogen. Analyses of brains with neonatal adrenoleukodystrophy revealed the chemical identification of at least two stored lipid products. Very long chain fatty acids are present, especially in cholesterol esters, and vinyl ether ethanolamine plasmalogens are markedly elevated. The storage of vinyl ether plasmalogen in brains of infants dying of neonatal adrenoleukodystrophy clearly distinguishes them from those with cerebro-hepato-renal syndrome of Zellweger, which fail to synthesize plasmalogens.

Contiguous ABCD1 DXS1357E deletion syndrome: Report of an autopsy case

Contiguous ABCD1 DXS1357E deletion syndrome (CADDS) is a contiguous deletion syndrome involving the ABCD1 and DXS1357E/BAP31 genes on Xq28. Although ABCD1 is responsible for X-linked adrenoleukodystrophy (X-ALD), its phenotype differs from that of CADDS, which manifests with many features of Zellweger syndrome (ZS), including severe growth and developmental retardation, liver dysfunction, cholestasis and early infantile death. We report here the fourth case of CADDS, in which a boy had dysmorphic features, including a flat orbital edge, hypoplastic nose, micrognathia, inguinal hernia, micropenis, cryptorchidism and club feet, all of which are shared by ZS. The patient achieved no developmental milestones and died of pneumonia at 8 months. Biochemical studies demonstrated abnormal metabolism of very long chain fatty acids, which was higher than that seen in X-ALD. Immunocytochemistry and Western blot showed the absence of ALD protein (ALDP) despite the presence of other peroxisomal proteins. Pathological studies disclosed a small brain with hypomyelination and secondary hypoxic-ischemic changes. Neuronal heterotopia in the white matter and leptomeningeal glioneuronal heterotopia indicated a neuronal migration disorder. The liver showed fibrosis and cholestasis. The thymus and adrenal glands were hypoplastic. Array comparative genomic hybridization (CGH) analysis suggested that the deletion was a genomic rearrangement in the 90-kb span starting in DXS1357E/BACP31 exon 4 and included ABCD1, PLXNB3, SRPK3, IDH3G and SSR4, ending in PDZD4 exon 8. Thus, the absence of ALDP, when combined with defects in the B-cell antigen receptor associated protein 31 (BAP31) and other factors, severely affects VLCFA metabolism on peroxisomal functions and produces ZS-like pathology.

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.

Defective lipid remodeling of GPI anchors in peroxisomal disorders, Zellweger syndrome, and rhizomelic chondrodysplasia punctata

Many cell surface proteins in mammalian cells are anchored to the plasma membrane via glycosylphosphatidylinositol (GPI). The predominant form of mammalian GPI contains 1-alkyl-2-acyl phosphatidylinositol (PI), which is generated by lipid remodeling from diacyl PI. The conversion of diacyl PI to 1-alkyl-2-acyl PI occurs in the ER at the third intermediate in the GPI biosynthetic pathway. This lipid remodeling requires the alkyl-phospholipid biosynthetic pathway in peroxisome. Indeed, cells defective in dihydroxyacetone phosphate acyltransferase (DHAP-AT) or alkyl-DHAP synthase express only the diacyl form of GPI-anchored proteins. A defect in the alkyl-phospholipid biosynthetic pathway causes a peroxisomal disorder, rhizomelic chondrodysplasia punctata (RCDP), and defective biogenesis of peroxisomes causes Zellweger syndrome, both of which are lethal genetic diseases with multiple clinical phenotypes such as psychomotor defects, mental retardation, and skeletal abnormalities. Here, we report that GPI lipid remodeling is defective in cells from patients with Zellweger syndrome having mutations in the peroxisomal biogenesis factors PEX5, PEX16, and PEX19 and in cells from patients with RCDP types 1, 2, and 3 caused by mutations in PEX7, DHAP-AT, and alkyl-DHAP synthase, respectively. Absence of the 1-alkyl-2-acyl form of GPI-anchored proteins might account for some of the complex phenotypes of these two major peroxisomal disorders.