Rapid stable isotope dilution analysis of very-long-chain fatty acids, pristanic acid and phytanic acid using gas chromatography-electron impact mass spectrometry

Phytanic acid: measurement of plasma concentrations by gas–liquid chromatography–mass spectrometry analysis and associations with diet and other plasma fatty acids

Epidemiological data suggest that a diet rich in animal foods may be associated with an increased risk of several cancers, including cancers of the prostate, colorectum and breast, but the possible mechanism is unclear. It is hypothesised that phytanic acid, a C20 branched-chain fatty acid found predominantly in foods from ruminant animals, may be involved in early cancer development because it has been shown to up regulate activity of α-methylacyl-coenzyme A racemase, an enzyme commonly found to be over-expressed in tumour cells compared with normal tissue. However, little is known about the distribution of plasma phytanic acid concentrations or its dietary determinants in the general population. The primary aim of the present cross-sectional study was to determine circulating phytanic acid concentrations among ninety-six meat-eating, lacto-ovo-vegetarian and vegan women, aged 20–69 years, recruited into the Oxford component of the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). Meat-eaters had, on average, a 6.7-fold higher geometric mean plasma phytanic acid concentration than the vegans (5·77v.0·86 μmol/l;P < 0·0001) and a 47 % higher mean concentration than the vegetarians (5·77v.3·93 μmol/l;P = 0·016). The strongest determinant of plasma phytanic acid concentration appeared to be dairy fat intake (r0·68;P < 0·0001); phytanic acid levels were not associated with age or other lifestyle factors. These data show that a diet high in fat from dairy products is associated with increased plasma phytanic acid concentration, which may play a role in cancer development.

Diagnosis of X-linked adrenoleukodystrophy in blood leukocytes

OBJECTIVES

Our aim was to replace cultured skin fibroblasts in the diagnosis of X-linked adrenoleukodystrophy (X-ALD) by peripheral blood cells.

DESIGN AND METHODS

Very long chain fatty acids (VLCFAs) were analyzed in leukocytes from X-ALD patients, heterozygotes, and controls using gas chromatography-mass spectrometry (GC-MS). Immunofluorescence for adrenoleukodystrophy protein (ALDP) was performed in mononuclear blood cell preparations of X-ALD patients known to be ALDP negative in fibroblasts, heterozygote relatives of these patients, and controls.

RESULTS

All X-ALD patients were distinguishable from controls by VLCFA analysis in leukocytes. 91.7% of heterozygotes were identified by combined VLCFA analysis in leukocytes and plasma. All patients investigated lacked ALDP immunoreactivity in mononuclear cells, while heterozygotes showed mosaic patterns of positive and negative cells.

CONCLUSION

Determination of VLCFAs by GC-MS in combination with ALDP immunofluorescence in peripheral blood cells provides a fast and minimally invasive diagnostic method for X-ALD, which, in contrast to plasma analysis, is independent of alimentary influences. Notably, joint evaluation of leukocytes and plasma considerably improves the identification of heterozygotes.

A lethal defect of mitochondrial and peroxisomal fission

We report on a newborn girl with microcephaly, abnormal brain development, optic atrophy and hypoplasia, persistent lactic acidemia, and a mildly elevated plasma concentration of very-long-chain fatty acids. We found a defect of the fission of both mitochondria and peroxisomes, as well as a heterozygous, dominant-negative mutation in the dynamin-like protein 1 gene (DLP1). The DLP1 protein has previously been implicated, in vitro, in the fission of both these organelles. Overexpression of the mutant DLP1 in control cells reproduced the fission defect. Our findings are representative of a class of disease characterized by defects in both mitochondria and peroxisomes.

Clinical, biochemical, and mutational spectrum of peroxisomal acyl–coenzyme A oxidase deficiency

Peroxisomal acyl-coenzyme A (acyl-CoA) oxidase deficiency is an autosomal recessive inborn error of peroxisomal fatty acid oxidation due to a deficiency of straight-chain acyl-CoA oxidase (SCOX). The biochemical hallmark of this disorder is the accumulation of very long-chain fatty acids. Although some case reports and small series of patients have been published, a comprehensive overview of the clinical, biochemical, and mutational spectrum of this disorder is still lacking. For this reason, we report clinical information for a cohort of 22 patients with peroxisomal acyl-CoA oxidase deficiency and the results from biochemical and mutation analyses in fibroblasts of the patients. No clear genotype-phenotype correlation was observed. An intriguing mutation in the alternatively-spliced transcript encoding the isoform SCOX-exon 3II in a patient with normal expression of the transcript encoding the isoform SCOX-exon 3I, prompted us to characterize these two isoforms of human SCOX. The recombinant SCOX-exon 3I displayed activity toward medium-chain fatty acyl-CoAs and was not active with very long-chain fatty acyl-CoAs. In contrast, recombinant SCOX-exon 3II was capable of oxidizing a broad range of substrates, including very long-chain fatty acyl-CoAs. These results explain why this patient with a mutation in exon 3II of the ACOX1 gene, but with normal expression of exon 3I, was indistinguishable from other patients with peroxisomal acyl-CoA oxidase deficiency with respect to his clinical presentation and the biochemical abnormalities in his fibroblasts.

Clinical and biochemical spectrum of D-bifunctional protein deficiency

OBJECTIVE

D-bifunctional protein deficiency is an autosomal recessive inborn error of peroxisomal fatty acid oxidation. Although case reports and small series of patients have been published, these do not give a complete and balanced picture of the clinical and biochemical spectrum associated with this disorder.

METHODS

To improve early recognition, diagnosis, prognosis, and management of this disorder and to provide markers for life expectancy, we performed extensive biochemical studies in a large cohort of D-bifunctional protein-deficient patients and sent out questionnaires about clinical signs and symptoms to the responsible physicians.

RESULTS

Virtually all children presented with neonatal hypotonia and seizures and died within the first 2 years of life without achieving any developmental milestones. However, within our cohort, 12 patients survived beyond the age of 2 years, and detailed information on 5 patients with prolonged survival (> or =7.5 years) is provided.

INTERPRETATION

Biochemical analyses showed that there is a clear correlation between several biochemical parameters and survival of the patient, with C26:0 beta-oxidation activity in cultured skin fibroblasts being the best predictive marker for life expectancy. Remarkably, three patients were identified without biochemical abnormalities in plasma, stressing that D-bifunctional protein deficiency cannot be excluded when all peroxisomal parameters in plasma are normal.

Mutational spectrum of D-bifunctional protein deficiency and structure-based genotype-phenotype analysis

D-bifunctional protein (DBP) deficiency is an autosomal recessive inborn error of peroxisomal fatty acid oxidation. The clinical presentation of DBP deficiency is usually very severe, but a few patients with a relatively mild presentation have been identified. In this article, we report the mutational spectrum of DBP deficiency on the basis of molecular analysis in 110 patients. We identified 61 different mutations by DBP cDNA analysis, 48 of which have not been reported previously. The predicted effects of the different disease-causing amino acid changes on protein structure were determined using the crystal structures of the (3R)-hydroxyacyl-coenzyme A (CoA) dehydrogenase unit of rat DBP and the 2-enoyl-CoA hydratase 2 unit and liganded sterol carrier protein 2-like unit of human DBP. The effects ranged from the replacement of catalytic amino acid residues or residues in direct contact with the substrate or cofactor to disturbances of protein folding or dimerization of the subunits. To study whether there is a genotype-phenotype correlation for DBP deficiency, these structure-based analyses were combined with extensive biochemical analyses of patient material (cultured skin fibroblasts and plasma) and available clinical information on the patients. We found that the effect of the mutations identified in patients with a relatively mild clinical and biochemical presentation was less detrimental to the protein structure than the effect of mutations identified in those with a very severe presentation. These results suggest that the amount of residual DBP activity correlates with the severity of the phenotype. From our data, we conclude that, on the basis of the predicted effect of the mutations on protein structure, a genotype-phenotype correlation exists for DBP deficiency.

Inactivation of the peroxisomal ABCD2 transporter in the mouse leads to late-onset ataxia involving mitochondria, Golgi and endoplasmic reticulum damage

ATP-binding cassette (ABC) transporters facilitate unidirectional translocation of chemically diverse substances, ranging from peptides to lipids, across cell or organelle membranes. In peroxisomes, a subfamily of four ABC transporters (ABCD1 to ABCD4) has been related to fatty acid transport, because patients with mutations in ABCD1 (ALD gene) suffer from X-linked adrenoleukodystrophy (X-ALD), a disease characterized by an accumulation of very-long-chain fatty acids (VLCFAs). Inactivation in the mouse of the abcd1 gene leads to a late-onset neurodegenerative condition, comparable to the late-onset form of X-ALD [Pujol, A., Hindelang, C., Callizot, N., Bartsch, U., Schachner, M. and Mandel, J.L. (2002) Late onset neurological phenotype of the X-ALD gene inactivation in mice: a mouse model for adrenomyeloneuropathy. Hum. Mol. Genet., 11, 499-505.]. In the present work, we have generated and characterized a mouse deficient for abcd2, the closest paralog to abcd1. The main pathological feature in abcd2-/- mice is a late-onset cerebellar and sensory ataxia, with loss of cerebellar Purkinje cells and dorsal root ganglia cell degeneration, correlating with accumulation of VLCFAs in the latter cellular population. Axonal degeneration was present in dorsal and ventral columns in spinal cord. We have identified mitochondrial, Golgi and endoplasmic reticulum damage as the underlying pathological mechanism, thus providing evidence of a disturbed organelle cross-talk, which may be at the origin of the pathological cascade.

Mass spectrometry in metabolome analysis

In the post-genomic era, increasing efforts have been made to describe the relationship between the genome and the phenotype in cells and organisms. It has become clear that even a complete understanding of the state of the genes, messages, and proteins in a living system does not reveal its phenotype. Therefore, researchers have started to study the metabolome (or the metabolic complement of functional genomics). Within this context, mass spectrometry (MS) has increasingly occupied a central position in the methodologies developed for determination of the metabolic state. This review is mainly focused on the status of MS in the metabolome field, trying to direct the reader to the main approaches for analysis of metabolites, reviewing basic methodologies in sample preparation, and the most recent MS techniques introduced. Apart from the description of the different methods, this review will try to state a general comparison between the several different techniques that involve MS and metabolite analysis, and will highlight their limitations and preferred applicability.

Characterization of the final step in the conversion of phytol into phytanic acid

Phytol is a branched-chain fatty alcohol that is a naturally occurring precursor of phytanic acid, a fatty acid involved in the pathogenesis of Refsum disease. The conversion of phytol into phytanic acid is generally believed to take place via three enzymatic steps that involve 1) oxidation to its aldehyde, 2) further oxidation to phytenic acid, and 3) reduction of the double bond at the 2,3 position, yielding phytanic acid. Our recent investigations of this mechanism have elucidated the enzymatic steps leading to phytenic acid production, but the final step of the pathway has not been investigated so far. In this study, we describe the characterization of phytenic acid reduction in rat liver. NADPH-dependent conversion of phytenic acid into phytanic acid was detected, although at a slow rate. However, it was shown that phytenic acid can be activated to its CoA ester and that reduction of phytenoyl-CoA is much more efficient than that of phytenic acid. Furthermore, in rat hepatocytes cultured in the presence of phytol, phytenoyl-CoA could be detected, showing that it is a bona fide intermediate of phytol degradation. Subcellular fractionation experiments revealed that phytenoyl-CoA reductase activity is present in peroxisomes and mitochondria. With these findings, we have accomplished the full elucidation of the mechanism by which phytol is converted into phytanic acid.

An HPLC-MS approach for analysis of very long chain fatty acids and other apolar compounds on octadecyl-silica phase using partly miscible solvents

A novel approach for analyzing underivatized very long chain fatty acids (C16-C26) and other apolar compounds such as triacylglycerols is described. It is based on reversed-phase HPLC separation followed by mass spectrometric detection. Partly miscible solvents are used for stepwise gradient elution starting with a methanol/water and ending with a methanol/n-hexane binary mixture. The developed technique does not need derivatization, and analysis is fast (fatty acids were separated in 2-min-long chromatograms) and robust. The developed method is also very sensitive; a quantitation limit in the low-picogram range was achieved for fatty acids. The separation mechanism and advantages of the suggested technique are discussed and illustrated in the case of blood analysis and plant oil characterization.

A phytol-enriched diet induces changes in fatty acid metabolism in mice both via PPARalpha-dependent and -independent pathways

Branched-chain fatty acids (such as phytanic and pristanic acid) are ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha) in vitro. To investigate the effects of these physiological compounds in vivo, wild-type and PPARalpha-deficient (PPARalpha-/-) mice were fed a phytol-enriched diet. This resulted in increased plasma and liver levels of the phytol metabolites phytanic and pristanic acid. In wild-type mice, plasma fatty acid levels decreased after phytol feeding, whereas in PPARalpha-/- mice, the already elevated fatty acid levels increased. In addition, PPARalpha-/- mice were found to be carnitine deficient in both plasma and liver. Dietary phytol increased liver free carnitine in wild-type animals but not in PPARalpha-/- mice. Investigation of carnitine biosynthesis revealed that PPARalpha is likely involved in the regulation of carnitine homeostasis. Furthermore, phytol feeding resulted in a PPARalpha-dependent induction of various peroxisomal and mitochondrial beta-oxidation enzymes. In addition, a PPARalpha-independent induction of catalase, phytanoyl-CoA hydroxylase, carnitine octanoyltransferase, peroxisomal 3-ketoacyl-CoA thiolase, and straight-chain acyl-CoA oxidase was observed. In conclusion, branched-chain fatty acids are physiologically relevant ligands of PPARalpha in mice. These findings are especially relevant for disorders in which branched-chain fatty acids accumulate, such as Refsum disease and peroxisome biogenesis disorders.

Identification of the molecular defect in patients with peroxisomal mosaicism using a novel method involving culturing of cells at 40°C: Implications for other inborn errors of metabolism

The peroxisome biogenesis disorders (PBDs), which comprise Zellweger syndrome (ZS), neonatal adrenoleukodystrophy, and infantile Refsum disease (IRD), represent a spectrum of disease severity, with ZS being the most severe, and IRD the least severe disorder. The PBDs are caused by mutations in one of the at least 12 different PEX genes encoding proteins involved in the biogenesis of peroxisomes. We report the biochemical characteristics and molecular basis of a subset of atypical PBD patients. These patients were characterized by abnormal peroxisomal plasma metabolites, but otherwise normal to very mildly abnormal peroxisomal parameters in cultured skin fibroblasts, including a mosaic catalase immunofluorescence pattern in fibroblasts. Since this latter feature made standard complementation analysis impossible, we developed a novel complementation technique in which fibroblasts were cultured at 40 degrees C, which exacerbates the defect in peroxisome biogenesis. Using this method, we were able to assign eight patients to complementation group 3 (CG3), followed by the identification of a single homozygous c.959C>T (p.S320F) mutation in their PEX12 gene. We also investigated various peroxisomal biochemical parameters in fibroblasts at 30 degrees C, 37 degrees C, and 40 degrees C, and found that all parameters showed a temperature-dependent behavior. The principle of culturing cells at elevated temperatures to exacerbate the defect in peroxisome biogenesis, and thereby preventing certain mutations from being missed, may well have a much wider applicability for a range of different inborn errors of metabolism.

Simultaneous determination of fatty, dicarboxylic and amino acids based on derivatization with isobutyl chloroformate followed by gas chromatography—positive ion chemical ionization mass spectrometry

Gas chromatography-mass spectrometry (GC-MS) with positive ion chemical ionization (PICI) using isobutane as reagent gas was applied for analysis of isobutoxycarbonyl/isobutyl derivatives of 13 fatty, 6 dicarboxylic and 13 amino acids in a single run. For all investigated compounds (except several amino acids) the quasimolecular ions [MH](+) were registered. Asparagine underwent fragmentation via decarboxylation followed by elimination of OC(4)H(9) ([M-117](+)), whereas serine and tyrosine produced the cluster ions [M+C(4)H(9)OCO](+). Estimated detection limits were 6-250 pg in the total ion current (TIC) mode and 3-10 times lower using the selected-ion monitoring (SIM) mode.

Peroxisome biogenesis disorders with prolonged survival: Phenotypic expression in a cohort of 31 patients

The peroxisome biogenesis disorders (PBDs) with generalized peroxisomal dysfunction include Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD). There is clinical, biochemical, and genetic overlap among the three phenotypes, also known as Zellweger spectrum disorders. Clinical distinctions between the phenotypes are not sharply defined. Only limited sources are available to serve as a background for prognosis in PBD, especially in case of prolonged survival. We delineated the natural history of 31 PBD patients (age 1.2-24 years) through systematic clinical and biochemical investigations. We excluded classical ZS from our study, and included all patients with a biochemically confirmed generalized peroxisomal disorder over 1 year of age, irrespective of the previously diagnosed phenotype. The initial clinical suspicion, age at diagnosis, growth, development, neurological symptoms, organ involvements, and survival are summarized. Common to all patients were cognitive and motor dysfunction, retinopathy, sensorineural hearing impairment, and hepatic involvement. Many patients showed postnatal growth failure, 10 patients displayed hyperoxaluria of whom 4 had renal stones. Motor skills ranged from sitting with support to normal gait. Speech development ranged from non-verbal expression to grammatical speech and comprehensive reading. The neurodevelopmental course was variable with stable course, rapid decline with leukodystrophy, spinocerebellar syndrome, and slow decline over a wide range of faculties as outcome profiles. At the molecular level, 21 patients had mutations in the PEX1 gene. The two most common PEX1 mutations were the G843D (c.2528G-->A) missense and the c.2097insT frameshift mutation. Patients having the G843D/G843D or the G843D/c.2097insT genotypes were compared. Patients homozygous for G843D generally had a better developmental outcome. However, one patient who was homozygous for the "mild" G843D mutation had an early lethal disease, whereas two other patients had a phenotype overlapping with the G843D/c.2097insT group. This indicates that next to the PEX1 genotype other yet unknown factors determine the ultimate phenotype.

Gas chromatography/mass spectrometry analysis of very long chain fatty acids, docosahexaenoic acid, phytanic acid and plasmalogen for the screening of peroxisomal disorders

Very long chain fatty acids (VLCFAs) and docosahexaenoic acid (DHA), phytanic acid, and plasmalogens are usually measured individually. A novel method for the screening of peroxisomal disorders, using gas chromatography/mass spectrometry (GC/MS), was developed. Saturated and unsaturated fatty acids, including VLCFAs and DHA, phytanic acid, and plasmalogen were detected by a selected ion monitoring-electron impact method, using 100 microl of serum or plasma. Methyl-esterification and extraction could be done in one tube, and data were obtained within 4 h. All patients with Zellweger syndrome (ZS), X-linked adrenoleukodystrophy (ALD), isolated deficiency of peroxisomal beta-oxidation enzyme, and most ALD carriers showed increased VLCFA ratios, including C24:0/C22:0, C25:0/C22:0 and C26:0/C22:0. The ratio of DHA to palmitic acid (C16:0) and plasmalogen (measured as hexadecanal dimethyl acetal) to C16:0 in ZS patients was significantly lower than for the controls (P<0.001 for healthy high school students, P<0.05 for infants with other disorders). Plasmalogen was also decreased in patients with isolated deficiency of plasmalogen biosynthesis. Two of eight patients with ZS, two of four with RCDP, and all of three classical Refsum patients showed increased levels of phytanic acid. This method will simplify the screening for peroxisomal disorders.

Analysis of very long-chain fatty acids using electrospray ionization mass spectrometry

Elevated levels of very long-chain fatty acids (VLCFA) in plasma and tissues are the biochemical hallmark for patients with X-linked adrenoleukodystrophy (X-ALD). Current methods for the determination of VLCFA levels are laborious and time-consuming. We describe a rapid and easy method using electrospray ionization mass spectrometry (ESI-MS) with deuterated internal standards. VLCFA are hydrolyzed, extracted, and quantified in less than 4h. This includes 2h of hydrolysis and 4min of quantification. We validated the method by analyzing 60 plasma samples from controls and patients with X-ALD or Zellweger syndrome using both the ESI-MS protocol and an established method for VLCFA analysis using gas chromatography (GC). The C26:0 concentrations determined with ESI-MS in plasma and fibroblasts of X-ALD patients are in good agreement with those reported previously for GC and GC-MS. Besides saturated straight chain VLCFA, we also determined the concentrations of the mono-unsaturated VLCFA C24:1 and C26:1 and established that while C24:1 levels are not elevated, C26:1 levels are elevated in both plasma and fibroblasts from X-ALD patients.

The neuronal migration defect in mice with Zellweger syndrome (Pex5 knockout) is not caused by the inactivity of peroxisomal beta-oxidation

The purpose of this study was to investigate whether deficient peroxisomal beta-oxidation is causally involved in the neuronal migration defect observed in Pex5 knockout mice. These mice are models for Zellweger syndrome, a peroxisome biogenesis disorder. Neocortical development was evaluated in mice carrying a partial or complete defect of peroxisomal beta-oxidation at the level of the second enzyme of the pathway, namely, the hydratase-dehydrogenase multifunctional/bifunctional enzymes MFP1/L-PBE and MFP2/D-PBE. In contrast to patients with multifunctional protein 2 deficiency who present with neocortical dysgenesis, impairment of neuronal migration was not observed in the single MFP2 or in the double MFP1/MFP2 knockout mice. At birth, the double knockout pups displayed variable growth retardation and about one half of them were severely hypotonic, whereas the single MFP2 knockout animals were all normal in the perinatal period. These results indicate that in the mouse, defective peroxisomal beta-oxidation does not cause neuronal migration defects by itself. This does not exclude that the inactivity of this metabolic pathway contributes to the brain pathology in mice and patients with complete absence of functional peroxisomes.

Determination of l-Pipecolic Acid in Plasma Using Chiral Liquid Chromatography-Electrospray Tandem Mass Spectrometry

Background: l-Pipecolic acid (L-PA), an important biochemical marker for the diagnosis of peroxisomal disorders, is usually determined as the racemate. We developed a chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of L-PA in plasma.

Methods: We used a narrow bore chiral macrocyclic glycopeptide teicoplanin column for the enantioseparation of d-pipecolic acid (D-PA) and L-PA and interfaced the column directly to the electrospray source of a tandem mass spectrometer. We used phenylalanine-d5 as internal standard added to 50 μL of plasma followed by deproteinization, evaporation, and injection. The analysis was performed in the selected-reaction monitoring mode using two transitions: m/z 130→m/z 84 for PA, and m/z 171→m/z 125 for phenylalanine-d5. L-PA eluted at 7 min, and D-PA eluted at 11.7 min, whereas phenylalanine-d5 eluted at 6 min. The turnaround time for the assay was 20 min.

Results: Linear calibration curves were obtained in the range of 0.5–80 μmol/L. At a plasma concentration of 1.0 μmol/L, the signal-to-noise ratio was 50:1. The intra- and interassay variations were 3.1–7.9% and 5.7–13%, respectively, at concentrations of 1–50 μmol/L. Mean recoveries of L-PA added to plasma were 95% (5 μmol/L) and 102% (50 μmol/L). The method clearly distinguished between healthy individuals and peroxisomal disease patients.

Conclusions: The novel LC-MS/MS method is simple, rapid, and stereoselective, and uses only 50 μL of plasma, no derivatizing reagents, and a commercially available internal standard. Sample preparation is not complex and is faster than for all other methods.

Disorders of peroxisome biogenesis due to mutations in PEX1: phenotypes and PEX1 protein levels

Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD) are clinically overlapping syndromes, collectively called "peroxisome biogenesis disorders" (PBDs), with clinical features being most severe in ZS and least pronounced in IRD. Inheritance of these disorders is autosomal recessive. The peroxisome biogenesis disorders are genetically heterogeneous, having at least 12 different complementation groups (CGs). The gene affected in CG1 is PEX1. Approximately 65% of the patients with PBD harbor mutations in PEX1. In the present study, we used SSCP analysis to evaluate a series of patients belonging to CG1 for mutations in PEX1 and studied phenotype-genotype correlations. A complete lack of PEX1 protein was found to be associated with severe ZS; however, residual amounts of PEX1 protein were found in patients with the milder phenotypes, NALD and IRD. The majority of these latter patients carried at least one copy of the common G843D allele. When patient fibroblasts harboring this allele were grown at 30 degrees C, a two- to threefold increase in PEX1 protein levels was observed, associated with a recovery of peroxisomal function. This suggests that the G843D missense mutation results in a misfolded protein, which is more stable at lower temperatures. We conclude that the search for the factors and/or mechanisms that determine the stability of mutant PEX1 protein by high-throughput procedures will be a first step in the development of therapeutic strategies for patients with mild PBDs.

Mutations in the gene encoding peroxisomal alpha-methylacyl-CoA racemase cause adult-onset sensory motor neuropathy

Sensory motor neuropathy is associated with various inherited disorders including Charcot-Marie-Tooth disease, X-linked adrenoleukodystrophy/adrenomyeloneuropathy and Refsum disease. In the latter two, the neuropathy is thought to result from the accumulation of specific fatty acids. We describe here three patients with elevated plasma concentrations of pristanic acid (a branched-chain fatty acid) and C27-bile-acid intermediates. Two of the patients suffered from adult-onset sensory motor neuropathy. One patient also had pigmentary retinopathy, suggesting Refsum disease, whereas the other patient had upper motor neuron signs in the legs, suggesting adrenomyeloneuropathy. The third patient was a child without neuropathy. In all three patients we discovered a deficiency of alpha-methylacyl-CoA racemase (AMACR). This enzyme is responsible for the conversion of pristanoyl-CoA and C27-bile acyl-CoAs to their (S)-stereoisomers, which are the only stereoisomers that can be degraded via peroxisomal beta-oxidation. Sequence analysis of AMACR cDNA from the patients identified two different mutations that are likely to cause disease, based on analysis in Escherichia coli. Our findings have implications for the diagnosis of adult-onset neuropathies of unknown aetiology.