Molecular analysis of peroxisomal beta-oxidation enzymes in infants with Zellweger syndrome and Zellweger-like syndrome: further heterogeneity of the peroxisomal disorder

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.

Restoration of biochemical function of the peroxisome in the temperature-sensitive mild forms of peroxisome biogenesis disorder in humans

We have found that peroxisome assembly is temperature-sensitive (ts) in mild forms of peroxisome biogenesis disorders (PBDs), that is all infantile Refsum disease (IRD) patients and a few neonatal adrenoleukodystrophy patients of several complementation groups. The number of peroxisomes increased daily in incubation at 30 degrees C in the ts cells. Oxidation of very long-chain fatty acids, processing of acyl-CoA oxidase and dihydroxyacetonephosphate acyltransferase activity also improved after 8 days incubation at 30 degrees C in the IRD fibroblasts. These biochemical functions of the peroxisome did not change at 30 degrees C in Zellweger fibroblasts. Number of peroxisomes gradually decreased after 4 days when the temperature shifted from 30 to 37 degrees C in the ts cells. These results indicate that the biochemical functions of peroxisome are also restored by incubation at 30 degrees C in the mild and ts phenotype of PBDs, and the results will aid to predict the severity and the prognosis of affected children.

Highly toxic coplanar PCB126 reduces liver peroxisomal enzyme activities in rats

The effect of the highly toxic coplanar PCB congener, 3,4,5,3',4'-pentachlorobiphenyl (PCB126) on hepatic peroxisomes was studied in rats. The aim of this study was to investigate whether a toxic dose of the dioxin-like coplanar PCB modifies enzyme activities in peroxisomes where plays an important role in lipid metabolism. Treatment with PCB126, at a single i.p. administration of 25 mg/kg which evokes clear suppression of body weight gain, resulted in marked reduction (to about 40-50%) of catalase activity and peroxisomal fatty acyl-CoA β-oxidizing system. Immunoblotting showed that expression of catalase was greatly reduced by the treatment in parallel with the activity. Light microscopy revealed a drastic reduction in granules possessing peroxidase activity, while electron microscopy demonstrated that no apparent morphological changes had taken place. Thus the reduction in catalase activity caused by PCB126 could be attributable to suppression of protein expression. The marked reduction of these peroxisomal enzyme activities might be related to hyperlipidemia caused by dioxin-related compounds in rats and humans.

Biochemical features of a patient with Zellweger-like syndrome with normal PTS-1 and PTS-2 peroxisomal protein import systems: a new peroxisomal disease

The peroxisomal disorders represent a group of inherited metabolic disorders that derive from defects of peroxisomal biogenesis and/or from dysfunction of single or multiple peroxisomal enzymes. We described earlier an 8 1/2 year-old with a history of progressive developmental delay, micronodular cirrhosis, and elevated very long chain fatty acids in plasma and skin fibroblasts. These findings were felt to be compatible with both neonatal adrenoleukodystrophy (nALD) and Zellweger syndrome (ZS). This patient is now 21 years old and his clinical course, inconsistent with either nALD or ZS, led us to examine his peroxisomal status in light of a possible new peroxisomal disease. The normal levels of bile acid precursors found in this patient suggest that peroxisomal beta-oxidation is functional. The activities of dihydroxyacetone phosphate acyltransferase and oxidation of lignoceric acid and phytanic acid were 14, 17, and 15% of the control, respectively. This partial activity for oxidation and the normal levels of bile acid precursors suggests that this patient has peroxisomes containing beta-oxidation enzymes. Western blot analysis of subcellular organelles showed that beta-oxidation enzyme proteins are present at normal levels in catalase-negative peroxisomes of density equivalent to normal peroxisomes. The presence of acyl-CoA oxidase and 3-ketoacyl-CoA thiolase in catalase-negative peroxisomes suggests that both peroxisomal targeting signal-1 (PTS-1), and peroxisomal targeting signal-2 (PTS-2)-mediated protein transport processes into peroxisomes are normal in this patient. These findings of catalase-negative peroxisomes of normal density and normal PTS-1 and PTS-2 import machinery with partial peroxisomal functions clearly demonstrate that this patient differs from those with known disorders of peroxisomal biogenesis.

Molecular basis of Zellweger syndrome, beta-ketothiolase deficiency and mucopolysaccharidoses

1. A human peroxisome assembly factor-1 (PAF-1) complementary DNA has been cloned that restores the morphological and biochemical abnormalities (including defective peroxisome assembly) in fibroblasts from a patient with group F Zellweger syndrome. The cause of the syndrome in this patient was a point mutation that resulted in the premature termination of PAF-1. The homozygous patient apparently inherited the mutation from her parents, each of whom was heterozygous for that mutation. Furthermore, we cloned and characterized the rat and human cDNAs for peroxisome-assembly factor-2 (PAF-2), which restores peroxisomes of the complementary group C Zellweger cells, by functional complementation, and identified two pathogenic mutations in the PAF-2 gene in two patients. 2. Seventeen mutations have been identified in 13 mitochondrial acetoacetyl-CoA thiolase-deficient patients. 3. We purified N-acetylgalactosamine-6-sulfate (GalNAc6S) sulfatase and cloned the full-length cDNA of human N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The gene encoding GalNAc6S sulfatase has been localized by fluorescence in situ hybridization to chromosome 16q24, and the entire genomic gene structure has been characterized. About 40 different GALNS gene mutations have been identified in the patients with mucopolysaccharidosis IV A.

Biochemistry of peroxisomes in health and disease

The ubiquitous distribution of peroxisomes and the identification of a number of inherited diseases associated with peroxisomal dysfunction indicate that peroxisomes play an essential part in cellular metabolism. Some of the most important metabolic functions of peroxisomes include the synthesis of plasmalogens, bile acids, cholesterol and dolichol, and the oxidation of fatty acids (very long chain fatty acids > C22, branched chain fatty acids (e.g. phytanic acid), dicarboxylic acids, unsaturated fatty acids, prostaglandins, pipecolic acid and glutaric acid). Peroxisomes are also responsible for the metabolism of purines, polyamines, amino acids, glyoxylate and reactive oxygen species (e.g. O-2 and H2O2). Peroxisomal diseases result from the dysfunction of one or more peroxisomal metabolic functions, the majority of which manifest as neurological abnormalities. The quantitation of peroxisomal metabolic functions (e.g. levels of specific metabolites and/or enzyme activity) has become the basis of clinical diagnosis of diseases associated with the organelle. The study of peroxisomal diseases has also contributed towards the further elucidation of a number of metabolic functions of peroxisomes.

Immunotitration analysis of cytosolic acetoacetyl-coenzyme A thiolase activity in human fibroblasts

There are five known thiolases in human fibroblasts, and all but mitochondrial trifunctional protein (TFP) have thiolase activity toward acetoacetyl-CoA (AACoA). We investigated the contribution of mitochondrial acetoacetyl-CoA thiolase (AACoAT) (T2), cytosolic AACoAT (CT), and mitochondrial 3-ketoacyl-CoA thiolase (T1) to the total AACoAT activity in control human fibroblasts. Immunotitration of AACoAT activity with antibodies against T2, CT, or T1 was carried out in control fibroblasts, with the following results. In the case of AACoAT activity in the absence of potassium ion, 26-38%, 40-47%, and 11-20% of the total activity derived from CT, T1, and T2, respectively. The residual 6-9% total activity was not immunotitrated when three antibodies were used in combination. Hence, the contribution of peroxisomal 3-ketoacyl-CoA thiolase to the total AACoAT activity in the absence of potassium ion was at least less than 6-9%. Because the normal range of total AACoAT activity is relatively wide, it is difficult to evaluate CT defects based on a decrease of total AACoAT activity. Immunotitration with anti-CT antibody in six control fibroblasts revealed that CT activity ranges between 1.3 and 2.4 nmol/min/mg of protein. Immunotitration proved to be an accurate method to evaluate CT activity. The two cell lines from patients with CT deficiency have become extinct.

Overexpression and characterization of the human peroxisomal acyl-CoA oxidase in insect cells

Human liver peroxisomes contain two acyl-CoA oxidases, namely, palmitoyl-CoA oxidase and a branched chain acyl-CoA oxidase. The palmitoyl-CoA oxidase (ACOX) oxidizes the CoA esters of straight chain fatty acids and prostaglandins and donates electrons directly to molecular oxygen, thereby producing H2O2. The inducibility of this H2O2-generating ACOX in rat and mouse liver by peroxisome proliferators and the postulated role of the resulting oxidative stress in hepatocarcinogenesis generated interest in characterizing the structure and function of human ACOX. We have constructed a full-length cDNA encoding a 660-amino acid residue human ACOX and produced a catalytically active human ACOX protein at high levels in Spodoptera frugiperda (Sf9) insect cells using the baculovirus vector. Immunoblot analysis demonstrated that the full-length 72-kDa polypeptide (component A) was partially processed into its constituent 51-kDa (component B) and 21-kDa (component C) products, respectively. Recombinant protein (approximately 20 mg/l x 10(9) cells) was purified to homogeneity by a single-step procedure on a nickel-nitrilo-triacetic acid affinity column. Using the purified enzyme, Km and Vmax values for palmitoyl-CoA were found to be 10 microM and 1.4 units/mg of protein, respectively. The maximal activities for saturated fatty acids were observed with C12-18 substrates. The overexpressed human ACOX protein was identified in the cytoplasm of the insect cells by immunocytochemical staining. Individual expression of either the truncated ACOX 51-kDa (component B) or the 21-kDa (component C) revealed lack of enzyme activity, but co-infection of the insect cells with recombinant viruses expressing components B and C resulted in the formation of an enzymatically active heterodimeric B+C complex which could subsequently be inactivated by dissociating with detergent.

Differential protein import deficiencies in human peroxisome assembly disorders

Two peroxisome targeting signals (PTSs) for matrix proteins have been well defined to date. PTS1 comprises a COOH-terminal tripeptide, SKL, and has been found in several matrix proteins, whereas PTS2 has been found only in peroxisomal thiolase and is contained within an NH2-terminal cleavable presequence. We have investigated the functional integrity of the import routes for PTS1 and PTS2 in fibroblasts from patients suffering from peroxisome assembly disorders. Three of the five complementation groups tested showed a general loss of PTS1 and PTS2 import. Two complementation groups showed a differential loss of peroxisomal protein import: group I cells were able to import a PTS1- but not a PTS2- containing reporter protein into their peroxisomes, and group IV cells were able to import the PTS2 but not the PTS1 reporter into aberrant, peroxisomal ghostlike structures. The observation that the PTS2 import pathway is intact only in group IV cells is supported by the protection of endogenous thiolase from protease degradation in group IV cells and its sensitivity in the remaining complementation groups, including the partialized disorder of group I. The functionality of the PTS2 import pathway and colocalization of endogenous thiolase with the peroxisomal membranes in group IV cells was substantiated further using immunofluorescence, subcellular fractionation, and immunoelectron microscopy. The phenotypes of group I and IV cells provide the first evidence for differential import deficiencies in higher eukaryotes. These phenotypes are analogous to those found in Saccharomyces cerevisiae peroxisome assembly mutants.

Prenatal diagnosis of peroxisomal disorders. Biochemical and immunocytochemical studies on peroxisomes in human amniocytes

Prenatal diagnoses of peroxisomal disorders, including peroxisome-deficient Zellweger syndrome, isolated deficiency of peroxisomal beta-oxidation enzyme and rhizomelic type chondrodysplasia punctata were investigated by means of the lignoceric acid oxidation assay, indirect immunofluorescence staining and pulse-chase experiments, using cultured amniocytes. Assessment of peroxisomal beta-oxidation activity by means of [1-14C]lignoceric acid oxidation is essential for the diagnosis of a single enzyme deficiency of peroxisomal beta-oxidation with detectable enzyme protein. For the diagnosis of Zellweger syndrome, the absence of peroxisomes was readily determined by immunofluorescence staining of only a few amniocytes. Evidence for abnormal processing of 3-ketoacyl-CoA thiolase leads to the diagnosis of rhizomelic chondrodysplasia punctata. All the fetuses were considered to be normal and the neonates were normal. Use of these methods requires only a small number of amniocytes and will facilitate the prenatal diagnosis of peroxisomal disorders.

Unusual orthochromatic leukodystrophy with epitheloid cells (Norman-Gullotta): increase of very long chain fatty acids in brain discloses a peroxisomal disorder

Very long chain fatty acids (VLCFA) were found to be markedly increased and phytanic acid was borderline above normal in formalin-fixed brain white matter of case with an unusual type of familial leukodystrophy with epitheloid cells as described previously by Gullotta et al. [Neuropädiatrie (1970) 2: 173-186]. Increased VLCFA in brain clearly demonstrate that the patient had suffered from a peroxisomal disease. This diagnosis is corroborated by ultrastructural findings in brain showing typical lamellar inclusions. The particular type of peroxisomal disorder present in case (heterozygote of X-linked adrenoleukodystrophy?) remains speculative.

Human liver pathology in peroxisomal diseases: a review including novel data

Results from electron microscopic morphometry, enzyme cytochemistry and immunolocalization in liver biopsies are reviewed. Emphasis is put on the following aspects: 1) relationship between peroxisomal size and enzyme concentration; 2) abnormal enlargement of peroxisomes in many congenital disorders with peroxisomal dysfunction; 3) normal localization of matrix enzymes in several patients with peroxisomal dysfunction, with the exception of catalase, which is mainly cytoplasmic; 4) ghost-like peroxisomes in the liver of several syndromes but not in nine cases labelled as Zellweger; 5) discrepancies between liver and cultured fibroblasts; 6) trilamellar, regularly spaced inclusions, large stacks of which are birefringent, indicate a peroxisomal dysfunction; their absence does not exclude it. The same rule holds for lipid in macrophages which is insoluble in acetone and n-hexane (after fixation). The chemical nature of these two storage materials remains unclear; and 7) proliferation of human peroxisomes is frequent in acquired liver diseases and drug toxicity, but is never accompanied by an increase in size, in contrast to the effect of the fibrates and phthalates in rat and mouse. Novel data from seven peroxisomal patients are included.

Transformation and characterization of mutant human fibroblasts defective in peroxisome assembly

Human skin fibroblasts deficient in peroxisome biogenesis were transformed by transfecting SV40 ori- DNA with the use of an electroporator, and the biochemical, immunocytochemical, and cytogenetic properties of the transformants were analyzed. Cells (1 x 10(6)) from a patient with Zellweger syndrome and one with neonatal adrenoleukodystrophy were suspended with 2 micrograms of SV40 ori- DNA in PBS; then a high-voltage pulse (2000 V, 30 microseconds) was generated two times. Several colonies expressing large T-antigen were picked up 4 weeks after transfection. Doubling time of the transformants was about half of that and the saturation density was 5 to 10 times greater than that of the parental cells. Biochemical abnormalities including defective lignoceric acid oxidation, dihydroxyacetone phosphate acyltransferase deficiency, and disturbed biosynthesis of peroxisomal beta-oxidation enzymes were preserved in the transformants. Peroxisomes were defective in all colonies, as determined by immunofluorescence staining using anti-catalase IgG. Cell fusion studies confirmed that the transformants belong to the same complementation groups as those of the parental cells. These transformed mutant cell lines are expected to be useful tools for investigating the pathogenesis of inherited diseases related to defects in peroxisome biogenesis.

Complementation study of peroxisome-deficient disorders by immunofluorescence staining and characterization of fused cells

Genetic heterogeneity in peroxisome-deficient disorders, including Zellweger's cerebrohepatorenal syndrome, neonatal adrenoleukodystrophy and infantile Refsum disease, was investigated. Fibroblasts from 17 patients were fused using polyethylene glycol, cultivated on cover slips, and the formation of peroxisomes in the fused cells was visualized by immunofluorescence staining, using anti-human catalase IgG. Two distinct staining patterns were observed: (1) peroxisomes appeared in the majority of multinucleated cells, and (2) practically no peroxisomes were identified. Single step 12-(1'-pyrene) dodecanoic acid/ultraviolet (P12/UV)-selection confirmed that the former groups were resistant to this selection, most of the surviving cells contained abundant peroxisomes, and the latter cells died. In the complementary matching, [1-14C]lignoceric acid oxidation and the biosynthesis of peroxisomal proteins were also normalized. Five complementation groups were identified. Group A: Zellweger syndrome and infantile Refsum disease; Groups B, C and D: Zellweger syndrome; Group E: Zellweger syndrome, neonatal adrenoleukodystrophy and infantile Refsum disease. We compared these groupings with those of Roscher and identified eight complementation groups. There was no obvious relation between complementation groups and clinical phenotypes. These results indicate that the transport, intracellular processing and function of peroxisomal proteins were normalized in the complementary matching and that at least eight different genes are involved in the formation of normal peroxisomes and in the transport of peroxisomal enzymes.

Immunochemical and biochemical studies of fatty acid oxidation in fibroblasts of Zellweger and X-linked adrenoleukodystrophy patients

Immunoblot analyses of peroxisomal beta-oxidation enzymes showed that subunit A of acyl-CoA oxidase gave a stronger immunoreaction in fibroblasts of Zellweger and X-linked adrenoleukodystrophy patients than in those of controls. Subunits B and C and 3-ketoacyl-CoA thiolase were detected in fibroblasts of controls and X-linked adrenoleukodystrophy patients, but not of Zellweger patients. Total oxidation of palmitic and lignoceric acid was normal in homogenates of fibroblasts from Zellweger and X-linked adrenoleukodystrophy patients. The peroxisomal oxidation of both acids was only deficient in Zellweger patients. These data may not reflect the situation in vivo, as is evident from the accumulation of very-long-chain fatty acids in Zellweger and X-linked adrenoleukodystrophy patients.

Effects of sodium 2-[5-(4-chlorophenyl)pentyl]-oxirane-2-carboxylate (POCA) on fatty acid oxidation in fibroblasts from patients with peroxisomal diseases

The effects of sodium 2-[5-(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA), a potent inhibitor of carnitine palmitoyltransferase I, on fatty acid oxidation were investigated using fibroblasts from control subjects and from patients with peroxisomal disorders. [1-14C]Palmitate oxidation was inhibited by 8% of the control value when 15 microM POCA was added to the medium. The inhibition by POCA was significantly (P less than 0.05) stronger in fibroblasts from patients with Zellweger syndrome or with neonatal adrenoleukodystrophy, in which peroxisomes and peroxisomal beta-oxidation enzymes were absent. However, the inhibition in fibroblasts from patients with X-linked adrenoleukodystrophy, in which a specific defect of peroxisomal lignoceroyl-CoA synthetase was speculated, was similar to that in the controls. [1-14C]Lignocerate oxidation was not influenced by the addition of POCA, in samples from the controls and from the patients. These results indicate that peroxisomes account for a small but demonstrable proportion of palmitate oxidation, and add new evidence to the concept that lignocerate is oxidized exclusively in the peroxisomes. Our findings also support the hypotheses that the activity of palmitoyl-CoA synthetase and the enzymes of beta-oxidation cycle in peroxisomes are normal in patients with X-linked adrenoleukodystrophy and that a specific defect of lignoceroyl-CoA synthetase is responsible for the accumulation of very long chain fatty acids in these patients.

Inborn errors of bile acid metabolism

Cholesterol is converted to cholic acid and chenodeoxycholic acid by a series of reactions involving modifications to the steroid nucleus and oxidation of the side chain. These reactions can be affected by a number of inborn errors of metabolism. When this happens unusual bile acids or bile alcohols are synthesized; these can be identified using gas chromatography-mass spectrometry and fast atom bombardment mass spectrometry techniques. Two defects affecting the modifications to the steroid nucleus have been described; both present with cholestatic liver disease of neonatal onset. The better characterized of the two--3 beta-hydroxy-delta 5-C27-steroid dehydrogenase deficiency--leads to excretion of 3 beta-7 alpha-dihydroxy-5-cholenoic acid and 3 beta,7 alpha,12 alpha-trihydroxy-5-cholenoic acid in the urine. The liver disease improves dramatically on treatment with chenodeoxycholic acid. Deficient activity of 3-oxo-delta 4-steroid 5 beta-reductase is thought to be the cause of familial liver disease in some infants who excrete 7 alpha-hydroxy-3-oxo-4-cholenoic acid and 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acid in the urine. However, diagnosis of this disorder is problematical; a similar pattern of metabolite excretion can occur as a result of liver damage caused by viruses or inborn errors of pathways unrelated to bile acid synthesis. Defective side chain oxidation in patients with cerebrotendinous xanthomatosis (CTX) leads to synthesis of bile alcohols such as 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,25-pentol. Patients with CTX do not have cholestatic liver disease. Their major problems (neurological disease, atherosclerosis and xanthomata) are caused by accumulation of cholestanol and cholesterol in the tissues. Bile acid precursors are probably diverted into synthesis of cholestanol. Chenodeoxycholic acid suppresses the production of abnormal metabolites from cholesterol (by inhibition of cholesterol 7 alpha-hydroxylase) and leads to improvement in the neurological disease. Defective side chain oxidation also occurs in peroxisomal disorders but this time it leads to accumulation of C27 bile acids such as 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (trihydroxycoprostanic acid, THCA). This compound is readily detected in the bile and plasma of patients with defects of peroxisome biogenesis. In patients with defects of a single peroxisomal beta-oxidation enzyme (the 3-hydroxyacyl-CoA component of the bifunctional protein or the thiolase), the major C27 bile acid in bile may be 3 alpha,7 alpha,12 alpha,24-tetrahydroxy-5 beta-cholestanoic acid (varanic acid).(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular species of phosphatidylcholine containing very long chain fatty acids in human brain: enrichment in X-linked adrenoleukodystrophy brain and diseases of peroxisome biogenesis brain

Molecular species of phosphatidylcholine containing unsaturated (i.e., monoenoic and polyenoic) 32- to 40-carbon (very long chain) fatty acids (VLCFA-PC) are present in normal human brain, the fatty acid composition changing significantly with development. There is a marked increase in the concentration and a change in the polyenoic VLCFA composition of these molecular species in brains of patients with inherited defects in peroxisomal biogenesis [Zellweger's syndrome, neonatal adrenoleukodystrophy (ALD), and infantile Refsum's disease]. In contrast, there is a marked increase in monoenoic VLCFA-PC in X-linked ALD whereas molecular species containing polyenoic VLCFA are minor components.

Liver pathology and immunocytochemistry in congenital peroxisomal diseases: a review

Diagnostic and pathogenetic investigations of peroxisomal disorders should include the study of the macroscopic and microscopic pathology of the liver, in addition to careful clinical observations, skeletal X-ray and brain CT scan, assays of very long-chain fatty acids and bile acid intermediates, and selected enzyme activities. This review of the literature also contains novel observations about the following syndromes: cerebro-hepato-renal (Zellweger) syndrome, X-linked and neonatal adrenoleukodystrophies (ALD, NALD), NALD-like syndromes, infantile phytanic acid storage, classical Refsum disease, rhizomelic and other forms of chondrodysplasia punctata (XD, XR, AR), hyperpipecolic acidaemia, primary hyperoxaluria I, pseudo-Zellweger and Zellweger-like syndromes, and single enzyme deficiencies. Microscopic data include catalase staining and morphometry of peroxisomes, immunolocalization of beta-oxidation enzymes, detection of trilamellar, polarizing inclusions in PAS-positive macrophages, fibrosis and iron storage. Peroxisomal enlargement appears to be related to functional deficit in beta-oxidation disorders as well as in rhizomelic chondrodysplasia punctata. Because normal peroxisomal localization of active beta-oxidation enzymes can accompany a C26 beta-oxidation deficit, other mechanisms such as impaired transport of metabolites should be investigated. 'Ghost'-like organelles are shown in the liver of an infantile Refsum patient and in an NALD-like case; immuno-gold labelling of membrane proteins did not reveal ghosts in Zellweger livers.

The MR spectrum of peroxisomal disorders

In the last decade an increasing number of peroxisomal disorders has been recognized. Almost all peroxisomal disorders affect the central nervous system. Many of them lead to demyelination, some of them lead to migrational disturbances. The MR pattern of X-linked adrenoleukodystrophy is well known, but the pattern of the other peroxisomal disorders is less well known. We evaluated the gray and white matter abnormalities of 20 patients on 32 occasions. We compared the results with histological data and in this way came to the description of a number of characteristic MR patterns occurring in peroxisomal disorders: (1) Neuronal migrational disturbances in combination with hypomyelination, dysmyelination or demyelination. (2) Symmetrical demyelination of posterior limb of the internal capsule, cerebellar white matter and brain stem tracts with a variable affection of cerebral hemispheres. (3) Symmetrical demyelination, exhibiting two zones, starting in the occipital area and spreading outwards and forwards; affection of brain stem tracts. (4) Less characteristic patterns of demyelination. The patterns are illustrated and differentiation from other disorders is discussed.

Peroxisomal beta-oxidation defect with detectable peroxisomes: a case with neonatal onset and progressive course

A progressive demyelinating cerebral disorder is described in a normally-appearing female infant with neonatal seizures, progressive psychomotor deterioration, deafness, retinopathy, peripheral neuropathy and loss of myelin observed on magnetic resonance imaging (MRI) scanning. MRI also showed the absence of macroscopic neocortical dysplasia which is usually found in Zellweger syndrome (ZS). Adrenal cortical function was normal. The patient died at the age of 37 months. Extensive biochemical investigations of peroxisomal functions in the patient revealed an impairment of peroxisomal beta-oxidation resulting in elevated levels of very long (greater than C22) chain fatty acids in plasma and fibroblasts. Moreover, elevated plasma levels of intermediates of bile acid biosynthesis such as tri- and dihydroxycholestanoic acid were found. Other peroxisomal functions were normal. Immunoblotting of the peroxisomal beta-oxidation enzyme proteins in liver from the patient revealed normal responses with antisera against acyl-CoA oxidase, bifunctional protein and thiolase respectively. From these data we conclude that the patient had a deficiency of a single peroxisomal beta-oxidation enzyme at the level of either the bifunctional protein or peroxisomal thiolase with retained immunoreactivity against these enzymes.

The inborn errors of peroxisomal beta-oxidation: a review

In recent years a growing number of inherited diseases in man have been recognized in which there is an impairment in peroxisomal beta-oxidation. In some diseases this is due to the (virtual) absence of peroxisomes leading to a generalized loss of peroxisomal functions including peroxisomal beta-oxidation. In most inborn errors of peroxisomal beta-oxidation, however, peroxisomes are normally present and the impairment in peroxisomal beta-oxidation is due to the single or multiple loss of peroxisomal beta-oxidation enzyme activities. In all these disorders there is accumulation of very-long-chain fatty acids in plasma, which allows biochemical diagnosis of patients affected by an inborn error of peroxisomal beta-oxidation to be done via gas-chromatographic analysis of plasma very-long-chain fatty acids. Subsequent enzymic and immunological investigations are required to identify the precise enzymic defects in these patients. In all inborn errors of peroxisomal beta-oxidation known today there are multiple abnormalities, especially neurological with death usually occurring in the first decade of life. Prenatal diagnosis of these disorders has recently become possible.

Molecular analysis of peroxisomal beta-oxidation enzymes in infants with peroxisomal disorders indicates heterogeneity of the primary defect

Immunoblot analysis of peroxisomal beta-oxidation enzymes proteins was carried on liver samples from 15 patients with peroxisomal disorders in which accumulation of very long chain fatty acids was always observed in plasma. In 11 cases including 4 cerebro-hepatorenal syndrome (CHRS), 4 neonatal adrenoleukodystrophy (NALD) and 3 infantile Refsum's disease, the liver peroxisomes could not be detected by electron microscopy. Immunoblot analysis revealed the absence, or presence in weak amounts, of the 72-kDa subunit of acyl-CoA oxidase, and the complete absence of the 52-kDa and 21-kDa subunits which are processed from the 72-kDa. The bifunctional protein (78-kDa) was absent or very reduced, as was the mature form of peroxisomal 3-ketoacyl-CoA thiolase (41-kDa). Multiple defects of peroxisomal beta-oxidation enzymes may be caused by an absence of synthesis or an inability to import proteins into peroxisomes in these patients. One patient, diagnosed as NALD, had no detectable liver peroxisomes but the presence, in normal amounts, of the three peroxisomal beta-oxidation enzyme proteins suggests that the transport of these enzymes into "peroxisomal ghosts" was still intact. The last 3 patients, clinically diagnosed as NALD, had normal liver peroxisomes. One patient had an isolated deficiency of the bifunctional protein and the 2 others had normal amounts of the 3 peroxisomal beta-oxidation enzymes, as shown by immunoblotting. This suggests that import and translocation of some peroxisomal proteins had occurred and that a mechanism is therefore required to explain the defect in these patients.

Peroxisomal disorders in neurology

Although peroxisomes were initially believed to play only a minor role in mammalian metabolism, it is now clear that they catalyse essential reactions in a number of different metabolic pathways and thus play an indispensable role in intermediary metabolism. The metabolic pathways in which peroxisomes are involved include the biosynthesis of ether phospholipids and bile acids, the oxidation of very long chain fatty acids, prostaglandins and unsaturated long chain fatty acids and the catabolism of phytanate and (in man) pipecolate and glyoxylate. The importance of peroxisomes in cellular metabolism is stressed by the existence of a group of inherited diseases, the peroxisomal disorders, caused by an impairment in one or more peroxisomal functions. In the last decade our knowledge about peroxisomes and peroxisomal disorders has progressed enormously and has been the subject of several reviews. New developments include the identification of several additional peroxisomal disorders, the discovery of the primary defect in several of these peroxisomal disorders, the recognition of novel peroxisomal functions and the application of complementation analysis to obtain information on the genetic relationship between the different peroxisomal disorders. The peroxisomal disorders recognized at present comprise 12 different diseases, with neurological involvement in 10 of them. These diseases include: (1) those in which peroxisomes are virtually absent leading to a generalized impairment of peroxisomal functions (the cerebro-hepato-renal syndrome of Zellweger, neonatal adrenoleukodystrophy, infantile Refsum disease and hyperpipecolic acidaemia); (2) those in which peroxisomes are present and several peroxisomal functions are impaired (the rhizomelic form of chondrodysplasia punctata, combined peroxisomal beta-oxidation enzyme protein deficiency); and (3) those in which peroxisomes are present and only a single peroxisomal function is impaired (X-linked adrenoleukodystrophy, peroxisomal thiolase deficiency (pseudo-Zellweger syndrome), acyl-CoA oxidase deficiency (pseudo-neonatal adrenoleukodystrophy) and probably, the classic form of Refsum disease.

Zellweger-like syndrome with detectable hepatic peroxisomes: a variant form of peroxisomal disorder

A male infant with typical clinical and biochemical findings of Zellweger syndrome, but in whom hepatic peroxisomes were detected by electron microscopy, had profound hypotonia, hepatomegaly, typical facial appearance including large fontanelle and frontal bossing, convulsions, panaminoaciduria, and hyperammonemia. He died of liver failure at age 5 months. There were increased levels of very long chain fatty acids and trihydroxycoprostanic acid in serum, and increased excretion of dicarboxylic acids and tyrosine metabolites in the urine. Levels of peroxisomal enzymes, acyl coenzyme A oxidase, bifunctional protein, 3-ketoacyl coenzyme A thiolase, and dihydroxyacetone phosphate acyltransferase in the liver tissue from the patient were all deficient, findings consistent with Zellweger syndrome. However, immunocytochemical study and electron microscopic examination of the liver at autopsy revealed that hepatic peroxisomes were present at a level similar to that in a control subject. These observations suggest further heterogeneity in Zellweger syndrome and a different pathogenesis in this variant case.