Fatty acids and TxA(2) generation, in the absence of platelet-COX-1 activity.

BACKGROUND AND AIMS: Omega-3 fatty acids suppress Thromboxane A(2) (TxA(2)) generation via mechanisms independent to that of aspirin therapy. We sought to evaluate whether baseline omega-3 fatty acid levels influence arachidonic acid proven platelet-cyclooxygenase-1 (COX-1) independent TxA(2) generation (TxA(2) generation despite adequate aspirin use). METHODS AND RESULTS: Subjects with acute myocardial infarction, stable CVD or at high risk for CVD, on adequate aspirin therapy were included in this study. Adequate aspirin action was defined as complete inhibition of platelet-COX-1 activity as assessed by <10% change in light transmission aggregometry to ≥1 mmol/L arachidonic acid. TxA(2) production was measured via liquid chromatography-tandem mass spectrometry for the stable TxA(2) metabolite 11-dehydro-thromboxane B2 (UTxB2) in urine. The relationship between baseline fatty acids, demographics and UTxB(2) were evaluated. Baseline omega-3 fatty acid levels were not associated with UTxB(2) concentration. However, smoking was associated with UTxB(2) in this study. CONCLUSION: Baseline omega-3 fatty acid levels do not influence TxA(2) generation in patients with or at high risk for CVD receiving adequate aspirin therapy. The association of smoking and TxA(2) generation, in the absence of platelet COX-1 activity, among aspirin treated patients warrants further study.

Docosahexaenoic acid therapy in peroxisomal diseases: results of a double-blind, randomized trial.

OBJECTIVES: Peroxisome assembly disorders are genetic disorders characterized by biochemical abnormalities, including low docosahexaenoic acid (DHA). The objective was to assess whether treatment with DHA supplementation would improve biochemical abnormalities, visual function, and growth in affected individuals. METHODS: This was a randomized, double-blind, placebo-controlled trial conducted at a single center. Treatment groups received supplements of DHA (100 mg/kg per day). The primary outcome measures were the change from baseline in the visual function and physical growth during the 1 year follow-up period. RESULTS: Fifty individuals were enrolled and randomized. Two were subsequently excluded from study analysis when it was determined that they had a single enzyme disorder of peroxisomal beta oxidation. Thirty-four returned for follow-up. Nine patients died during the trial of their disorder, and 5 others were lost to follow-up. DHA supplementation was well tolerated. There was no difference in the outcomes between the treated and untreated groups in biochemical function, electroretinogram, or growth. Improvements were seen in both groups in certain individuals. CONCLUSIONS: DHA supplementation did not improve the visual function or growth of treated individuals with peroxisome assembly disorders. CLASSIFICATION OF EVIDENCE: This interventional study provides Class II evidence that DHA supplementation did not improve the visual function or growth of treated individuals with peroxisome assembly disorders during an average of 1 year of follow-up in patients aged 1 to 144 months.

A PEX10 defect in a patient with no detectable defect in peroxisome assembly or metabolism in cultured fibroblasts.

Zellweger spectrum disorders (ZSD) are diagnosed by biochemical assay in blood, urine and cultured fibroblasts and PEX gene mutation identification. In most cases studies in fibroblasts corroborate results obtained in body fluids. In 1996 Clayton and colleagues described a 10-year old girl with evidence of a peroxisome disorder, based on elevated bile acid metabolites and phytanate. At the time it was not possible to distinguish whether she had a ZSD or a single peroxisomal protein defect. Studies in our laboratory showed that she also had elevated plasma pipecolate, supporting the former diagnosis. Despite the abnormal metabolites detected in blood (phytanate, bile acid intermediates and pipecolate), analysis of multiple peroxisomal pathways in fibroblasts yielded normal results. In addition, she had a milder clinical phenotype than usually associated with ZSD. Since complementation analysis to determine the gene defect was not possible, we screened this patient following the PEX Gene Screen algorithm (PGS). The PGS provides a template for sequencing PEX gene exons independent of complementation analysis. Two mutations in PEX10 were identified, a frameshift mutation inherited from her father and a de novo missense mutation in a conserved functional domain on the other allele. This case highlights that molecular analysis may be essential to the diagnosis of patients at the milder end of the ZSD spectrum. Furthermore, it supports the concept that some tissues are less affected by certain PEX gene defects than brain and liver.

Orthotopic liver transplantation from a living-related donor in an infant with a peroxisome biogenesis defect of the infantile Refsum disease type.

Peroxisomal biogenesis defects include a number of severe neurodevelopmental disorders, among which infantile Refsum disease (IRD) occupies the mildest end of the spectrum. Although high docosahexaenoic acid (DHA) and low phytanic acid diets can correct some of the biochemical defects, they have not consistently altered the progressive course of the disease. We carried out orthotopic liver transplantation (OLT) in a mildly symptomatic 6-month-old infant who was a sibling of a severely neurologically impaired older sister. After transplantation the clinical course of this young child appeared much improved by comparison to her older sister. She walked alone at 4 years, had acceptable social interaction and had a noticeable recovery of audition. After transplantation her biochemical parameters were significantly improved: phytanic acid and very long-chain fatty acid (VLCFA) serum concentrations decreased. Abnormal bile acids disappeared from plasma. Although the OLT did not result in a cure of the disorder, the clinical and biochemical results suggest that OLT should be considered in mildly symptomatic patients.

MRI and proton MRSI in women heterozygous for X-linked adrenoleukodystrophy.

OBJECTIVE: To utilize neuroimaging procedures to assess the extent of cerebral involvement in female subjects heterozygous for X-linked adrenoleukodystrophy (X-ALD). METHODS: Brain MRI studies were performed in 76 female subjects heterozygous for X-ALD (mean age 43 years, range 8 to 75 years). Sixty-five had clinical evidence of spinal cord involvement resembling that in males with adrenomyeloneuropathy (AMN), two had clinical evidence of cerebral involvement, and nine showed no neurologic abnormality. Readers blinded to clinical findings further analyzed abnormal MRI studies. In eight women whose MRI results were normal, four-slice long echo time MRS imaging (MRSI) studies were performed and compared to those of eight age-matched controls. RESULTS: MRI results were normal in 65 subjects and abnormal in 11. In eight of the latter group, the MRI changes were judged to be due to causes other than X-ALD. Lesions were attributed to X-ALD in the remaining three. Two of these patients had lesions that resembled those in male patients with cerebral X-ALD. In one patient with a mild AMN-like syndrome, brain MRI abnormalities were confined to the corticospinal tract. When compared to those of controls, MRSI studies in eight female patients with normal results on brain MRI showed a significant reduction of N-acetylaspartate/creatine and N-acetylaspartate/choline ratios in the internal capsule and corticospinal projection fibers. The N-acetylaspartate/choline ratio was significantly reduced in the parieto-occipital white matter and the choline/creatine ratio was significantly increased in the frontal white matter. CONCLUSION: Brain involvement demonstrable by MRI is rare in female subjects heterozygous for X-ALD, including those who have clinical evidence of spinal cord involvement. Nevertheless, N-acetylaspartate levels are reduced in the corticospinal projection fibers in female subjects with normal results on MRI, suggesting axonal dysfunction.

Lipid status and long-chain polyunsaturated fatty acid concentrations in adults and adolescents with phenylketonuria on phenylalanine-restricted diet.

Blood lipid studies are reported in 25 adults and 2 adolescents with PKU who had been on phenylalanine-restricted diets for a mean period of 22.6 years (range 7-39 years). Measurements included plasma concentrations of phenylalanine, cholesterol, lipoproteins, triglycerides and fatty acid profiles, including the analysis of seven fatty acids in plasma and red blood cells. Lipid screening identified 7 subjects with significantly elevated cholesterol/HDL ratios ranging from 5.6 to 10.3. Triglyceridaemia was documented in 5 of these 7, with concentrations ranging between 0.24 and 4.5 mmol/L (219-402 mg/dl) with a mean of 3.5 mmol/L (310 mg/dl). The fatty acid analyses demonstrated slight but statistically significant reductions in the concentrations of long-chain polyunsaturated fatty acids (LCPUFA), including plasma docosahexaenoic (DHA) and arachidonic acid (AA), and red blood cell DHA concentrations. The pattern resembles that reported previously in children, but alterations in the mean levels are less severe. In six of the adult patients plasma DHA or AA concentrations were less than 50% of controls. Since DHA and AA have important physiological roles, including brain and retinal function, it is recommended that blood lipid concentrations be monitored in all patients with PKU, including adults, and that DHA and AA supplementation be provided, particularly in those patients in whom the blood concentrations of these substances are reduced significantly.

Potential environmental and host participants in the early white matter lesion of adreno-leukodystrophy: morphologic evidence for CD8 cytotoxic T cells, cytolysis of oligodendrocytes, and CD1-mediated lipid antigen presentation.

The 2 most common forms of X-linked adreno-leukodystrophy (ALD) are the juvenile or childhood cerebral form with inflammatory demyelination and the adult adrenomyeloneuropathy (AMN) involving spinal cord tracts without significant inflammation. Modifier genes or environmental factors may contribute to the phenotypic variability. We performed immunohistochemical, an in situ polymerase chain reaction, and TUNEL analyses to identify several viruses, lymphocyte subpopulations, apoptotic cells, and effector molecules, focusing on morphologically normal white matter, dysmyelinative and acute demyelinative lesions. No distinguishing viral antigens were detected. Most lymphocytes were CD8 cytotoxic T cells (CTLs) with the alpha/beta TCR, and they infiltrated morphologically unaffected white matter. Only a few oligodendrocytes were immunoreactive for caspase-3. MHC class II- and TGF-beta-positive microglia were present. CD44, which can mediate MHC-unrestricted target cell death, was seen on many lymphocytes and white matter elements. CD1 molecules, which play major roles in MHC-unrestricted lipid antigen presentation, were noted. Our data indicate that unconventional CD8 CTLs are operative in the early stages of dysmyelination/demyelination and that cytolysis of oligodendrocytes, rather than apoptosis, appears to be the major mode of oligodendrocytic death. The presentation of lipid antigens may be a key pathogenetic element in ALD and AMN-ALD.

Peroxisomal straight-chain Acyl-CoA oxidase and D-bifunctional protein are essential for the retroconversion step in docosahexaenoic acid synthesis.

Docosahexaenoic acid (DHA, C22:6n-3) is essential for normal brain and retinal development. The nature and subcellular location of the terminal steps in DHA biosynthesis have been controversial. Rather than direct Delta4-desaturation of C22:5n-3, it has been proposed that this intermediate is elongated to C24:5n-3, desaturated to C24:6n-3, and "retroconverted" to DHA via peroxisomal beta-oxidation. However, this hypothesis has recently been challenged. The goal of this study was to determine the mechanism and specific enzymes required for the retroconversion step in human skin fibroblasts. Cells from patients with deficiencies of either acyl-CoA oxidase or D-bifunctional protein, the first two enzymes of the peroxisomal straight-chain fatty acid beta-oxidation pathway, exhibited impaired (5-20% of control) conversion of either [1-14C]18:3n-3 or [1-14C]22:5n-3 to DHA as did cells from peroxisome biogenesis disorder patients comprising eight distinct genotypes. In contrast, normal DHA synthesis was observed in cells from patients with rhizomelic chondrodysplasia punctata, Refsum disease, X-linked adrenoleukodystrophy, and deficiency of mitochondrial medium- or very long-chain acyl-CoA dehydrogenase. Acyl-CoA oxidase-deficient cells accumulated 2-5 times more radiolabeled C24:6n-3 than did controls. Our data are consistent with the retroconversion hypothesis and demonstrate that peroxisomal beta-oxidation enzymes acyl-CoA oxidase and D-bifunctional protein are essential for this process in human skin fibroblasts.

The dorsal root ganglia in adrenomyeloneuropathy: neuronal atrophy and abnormal mitochondria.

Adrenomyeloneuropathy (AMN), a disease of spinal cord, brain, adrenal, and testis, mostly affects men with spastic paraparesis or ataxia beginning in their second or third decade. The spinal cord displays bilateral, usually symmetrical, long tract degeneration particularly of the gracile tract in a "dying-back" pattern. The available data strongly indicate that the fundamental lesion in AMN is an axonopathy or neuronopathy. We compared lumbar dorsal root ganglia (DRG) from 3 AMN patients to 6 age-matched controls histologically, morphometrically, immunohistochemically, and ultrastructurally. There was no apparent neuronal loss, necrosis or apoptosis, nor obvious atrophy; nodules of Nageotte were sparse in both groups. The morphometric studies, however, did reveal neuronal atrophy with a decrease in the number of large neurons and a corresponding increase in neurons less than 2,000 microm2, especially in the 1,500-1,999 microm2 range. No consistent immunohistochemical differences were observed, and no specific cell type appeared to be lost. Many mitochondria in the AMN neurons demonstrated lipidic inclusions; this raises the possibility that, in addition to the well-known peroxisomal defect, impaired mitochondrial function may lead to a failure of ATP-dependent axoplasmic transport in AMN spinal tracts with consequent "dying-back" axonal degeneration. The observation that the DRG parent neurons of the degenerate gracile tracts in AMN undergo atrophy and do not display appreciable evidence of cell death, even at autopsy, provides a wide window of opportunity for the development of therapeutic strategies to combat or prevent this myeloneuropathy.

Adrenoleukodystrophy: incidence, new mutation rate, and results of extended family screening.

Utilizing the plasma very long chain fatty acid assay, supplemented by mutation analysis and immunofluorescence assay, we determined the number of X-linked adrenoleukodystrophy (X-ALD) hemizygotes from the United States identified each year in the two laboratories that perform most of the assays in this country: the Kennedy Krieger Institute between 1981 and 1998 and the Mayo Clinic Rochester from 1996 to 1998. The minimum frequency of hemizygotes identified in the United States is estimated to be 1:42,000 and that of hemizygotes plus heterozygotes 1:16,800. Our studies involved 616 pedigrees with a total of 12,787 identified at-risk members. Diagnostic assays were performed in 4,169 at-risk persons (33%) and included members of the extended family. Only 5% of male probands and 1.7% of X-ALD hemizygotes were found to have new mutations. The extended family testing led to the identification of 594 hemizygotes and 1,270 heterozygotes. Two hundred fifty of the newly identified hemizygotes were asymptomatic and represent the group in which therapy has the greatest chance of success. Identification of heterozygotes provides the opportunity for disease prevention through genetic counseling. Diagnostic tests should be offered to all at-risk relatives of X-ALD patients and should include members of the extended family.

Neurological and neuropathologic heterogeneity in two brothers with cobalamin C deficiency.

Two adult brothers, one documented to have methylmalonic acidemia with homocystinuria, or cobalamin C deficiency, after autopsy, displayed severe but divergent neurological presentations. One exhibited a myelopathy and the other chronic endocrine problems (Schmidt's syndrome) followed by a neuropsychiatric and dementing disorder owing to cerebral perivascular demyelination. The recognition of cobalamin C deficiency has practical implications because it is one of the few inherited diseases of central white matter that is treatable.

Peroxisomal ghosts are intracellular structures distinct from lysosomal compartments in Zellweger syndrome: a confocal laser scanning microscopy study.

Peroxisome ghosts are aberrant peroxisomal structures found in cultured skin fibroblasts from patients affected by Zellweger Syndrome (ZS), a genetic disorder of peroxisomal assembly. They contain peroxisomal integral membrane proteins (PxIMPs) and they lack most of the matrix enzymes that should be inside the organelle (Santos et al., Science 239 (1988) 1536-1538). Considerable evidence indicates that these ghosts result from genetic defects in the cellular machinery for importing newly-synthesized peroxisomal proteins into the organelle. In contrast to these observations, (Heikoop et al., Eur. J. Cell Biol. 57 (1992) 165-171) report that in Zellweger Syndrome, peroxisomal membranes are located within lysosomes and/or contain lysosomal enzymes. We have undertaken a more detailed and systematic investigation of this matter, employing confocal laser scanning microscopy (CLSM). In fibroblasts derived from ZS patients belonging to different complementation groups, peroxisomes were labeled with antibodies against PxIMPs and lysosomes were labeled with an antibody against a lysosome associated membrane protein (LAMP-2) or with LysoTracker. The results unambiguously demonstrated no appreciable colocalization of PxIMPs and LAMPs (or LysoTracker), indicating that peroxisomal ghosts are distinct subcellular structures, occupying separate subcellular locations.

Adrenomyeloneuropathy: a neuropathologic review featuring its noninflammatory myelopathy.

The neuropathologic features of adrenomyeloneuropathy (AMN) are reviewed by supplementing those few previously published cases with 5 additional cases collected over the years. The endocrine involvement in AMN is briefly presented to serve as a pathogenetic backdrop and to emphasize that most of the lesions in AMN, as in adreno-leukodystrophy (ALD), are noninflammatory in the traditional sense of the word. The myeloneuropathy is emphasized, but the dysmyelinative/inflammatory demyelinative lesions also are presented. The preponderance of available data indicates that the myeloneuropathy of AMN is a central-peripheral distal (dying-back) axonopathy, as was originally proposed. The severity of the myeloneuropathy does not appear to correlate with the duration or severity of endocrine dysfunction. Microglia are the dominant participating cells in the noninflammatory myelopathy. Abnormalities in the ALD gene, which encodes a peroxisomal ABC half-transporter, do not correlate with clinical phenotypes. The relationship of the gene product, ALDP, to the peroxisomal very long chain fatty acid (VLCFA) synthetase, the activity of which is deficient in ALD/AMN, is unclear. An ALD-knockout mouse model has developed axonal degeneration, particularly in spinal cord, and is therefore more reminiscent of AMN than ALD. We continue to postulate that the fundamental defect in the myeloneuropathy of AMN is an axonal or neuronal membrane abnormality perhaps due to the incorporation of VLCFA-gangliosides, which perturbs the membrane's microenvironment and leads to dysfunction and atrophy.

Determination of 30 X-linked adrenoleukodystrophy mutations, including 15 not previously described.

X-linked Adrenoleukodystrophy (X-ALD) is the most frequent peroxisomal disease. It mainly involves the nervous system white matter, adrenal cortex and testes. Several distinct clinical phenotypes are known. The principal biochemical abnormality is the accumulation of saturated very-long-chain fatty acids (VLCFAs : > C22:0, mainly C26:0), which is due to impaired capacity for beta-oxidation in peroxisomes. Diagnosis is usually based on the VLCFA levels in plasma or cultured skin fibroblasts in both patients and carriers. In 0.1% of affected males, however, the plasma C26:0 level is borderline normal, and 15% of obligate female carriers have normal results. Effective mutation detection in these families is therefore fundamental to unambiguously determine the genetic status of each individual at risk. Of particular concern are female members of kindreds segregating X-ALD mutations, because normal VLCFA levels do not guarantee lack of carrier status. We describe a fast method for detection of X-ALD mutations. The method is based on SSCP analysis of nested PCR fragments followed by sequence-determination reactions. Using this methodology we have found X-ALD mutations in 30 kindreds, including 15 not previously reported.

Pharmacological induction of peroxisomes in peroxisome biogenesis disorders.

Inherited aberrant peroxisome assembly results in a group of neurological diseases termed peroxisome biogenesis disorders (PBDs). PBDs include three major clinical phenotypes that represent a continuum of clinical features from the most severe form, Zellweger syndrome (ZS), through neonatal adrenoleukodystrophy (NALD) to the least severe form, infantile Refsum's disease (IRD). Somatic cell complementation studies have identified 13 PBD complementation groups, each representing a defect in a peroxisomal protein (peroxin) involved in peroxisome biogenesis. Most complementation groups include a range of clinical phenotypes. In this study, peroxisome numbers were determined in fibroblasts from 29 PBD (ZS, NALD, and IRD) patients, with various phenotypes from nine complementation groups, using antibodies against either a peroxisomal membrane protein (anti-Pex14p) or peroxisomal matrix proteins (anti-SKL). A correlation between the number of peroxisomes, determined with either antibody, and PBD phenotype was found, suggesting that induction of peroxisome number might have a favorable effect on PBD. After treatment of PBD fibroblasts with sodium 4-phenylbutyrate, a human peroxisome proliferator, there was an approximate twofold increase in peroxisome number. After 4-phenylbutyrate treatment, an increase in transcription of the adrenoleukodystrophy-related gene and the peroxin gene, PEX11alpha, was found in PBD fibroblasts. In NALD and IRD, but not ZS, fibroblasts there was an increase in very-long-chain fatty acid beta-oxidation and plasmalogen concentrations, and a decrease in very-long-chain fatty acid concentrations. These data suggest that pharmacological agents that induce peroxisome proliferation, such as 4-phenylbutyrate, may have therapeutic potential in the treatment of PBD patients with milder phenotypes (NALD and IRD).

Cerebellar atrophy in chronic rhizomelic chondrodysplasia punctata: a potential role for phytanic acid and calcium in the death of its Purkinje cells.

Cerebellar atrophy, consequent to the postdevelopmental degeneration and loss of Purkinje cells and granular neurons, has been identified in three patients with rhizomelic chondrodysplasia punctata (RCDP). Cerebellar atrophy in our two chronic patients was symmetrical, but the vermis and medial portions of both hemispheres, particularly the dorsal lobules, displayed more severe atrophy than the lateral hemispheres. The distal tips of folia showed the greatest neuronal loss. Residual Purkinje cells showed progressive degenerative changes that appeared to be due, in part, to their topography. The precise mode of death of Purkinje cells in RCDP has not been established, but it does not appear to be mediated by entrance into the cell cycle or by ubiquitination; however, alterations in intracellular calcium levels and mitochondria may be involved. Elevated serum/CSF phytanic acid, decreased levels of tissue plasmalogens and increased chronological age are believed to play synergistic pathogenetic roles in this lesion.

Prenatal diagnosis of rhizomelic chondrodysplasia punctata due to isolated alkyldihydroacetonephosphate acyltransferase synthase deficiency.

Current practices in prenatal diagnosis of rhizomelic chondrodysplasia punctata (RCDP) are reviewed. A case is presented with a family having one daughter affected with RCDP due to alkyldihydroacetonephosphate acyltransferase synthase (DHAPAT synthase) deficiency, and three subsequent pregnancies. Biochemical test values are presented for the pregnancies and daughter. Post-mortem tests of one fetus of a terminated pregnancy showed that radiologic examination could not make the diagnosis of RCDP. We conclude that biochemical or molecular testing is necessary to accurately diagnose this type of RCDP prenatally.

Metabolic control of peroxisome abundance.

Zellweger syndrome and related disorders represent a group of lethal, genetically heterogeneous diseases. These peroxisome biogenesis disorders (PBDs) are characterized by defective peroxisomal matrix protein import and comprise at least 10 complementation groups. The genes defective in seven of these groups and more than 90% of PBD patients are now known. Here we examine the distribution of peroxisomal membrane proteins in fibroblasts from PBD patients representing the seven complementation groups for which the mutant gene is known. Peroxisomes were detected in all PBD cells, indicating that the ability to form a minimal peroxisomal structure is not blocked in these mutants. We also observed that peroxisome abundance was reduced fivefold in PBD cells that are defective in the PEX1, PEX5, PEX12, PEX6, PEX10, and PEX2 genes. These cell lines all display a defect in the import of proteins with the type-1 peroxisomal targeting signal (PTS1). In contrast, peroxisome abundance was unaffected in cells that are mutated in PEX7 and are defective only in the import of proteins with the type-2 peroxisomal targeting signal. Interestingly, a fivefold reduction in peroxisome abundance was also observed for cells lacking either of two PTS1-targeted peroxisomal beta-oxidation enzymes, acyl-CoA oxidase and 2-enoyl-CoA hydratase/D-3-hydroxyacyl-CoA dehydrogenase. These results indicate that reduced peroxisome abundance in PBD cells may be caused by their inability to import these PTS1-containing enzymes. Furthermore, the fact that peroxisome abundance is influenced by peroxisomal 105-oxidation activities suggests that there may be metabolic control of peroxisome abundance.

Peroxisomal very long chain fatty acid beta-oxidation activity is determined by the level of adrenodeukodystrophy protein (ALDP) expression.

Impaired peroxisomal beta-oxidation of saturated very long chain fatty acids (VLCFA, >/=C22:0) results in increased VLCFA levels in the tissues and body fluids of patients with disorders of peroxisomal biogenesis (i.e., Zellweger syndrome and neonatal adrenoleukodystrophy) and single peroxisomal protein defects (i.e., X-linked adrenoleukodystrophy (X-ALD) and acyl-CoA oxidase deficiency). We show that SV40T transformation also results in impaired peroxisomal beta-oxidation and VLCFA accumulation despite the presence of abundant peroxisomes. To explore the mechanism responsible for this observation, we have examined expression of key components of peroxisomal VLCFA beta-oxidation. We found that expression of both acyl-CoA oxidase, the rate limiting enzyme of peroxisomal VLCFA beta-oxidation and the adrenoleukodystrophy protein (ALDP), the defective gene product in X-ALD, are reduced after SV40T transformation. Surprisingly, ALDP overexpression by itself restores peroxisomal VLCFA beta-oxidation in SV40T-transformed control and X-ALD cells. These results demonstrate that ALDP is a fundamental component in VLCFA peroxisomal beta-oxidation and may serve as a "gatekeeper" for VLCFA homeostasis.