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.

Magnetization transfer MRI demonstrates spinal cord abnormalities in adrenomyeloneuropathy.

BACKGROUND: In adrenomyeloneuropathy (AMN) conventional MRI detects only spinal cord atrophy in the late stages. OBJECTIVE: To apply a magnetization transfer-weighted (MTw) imaging to patients with AMN and AMN-like syndrome in order to visualize and quantitatively assess the pathology of white matter tracts in the cervical spinal cord. METHODS: MTw studies were conducted in nine men with AMN, eight symptomatic heterozygous women, and 10 age- and sex-matched controls and compared to the Expanded Disability Status Scale (EDSS) and quantitative tests of vibratory sense and postural sway. MTw data sets were obtained at the level of C1 to C3 using a three-dimensional gradient echo acquisition technique, these images were then standardized between subjects by using the in-slice CSF signal as a normalization reference, allowing a quantitative assessment of the MTw signal. RESULTS: In contrast to conventional MRI, MTw images showed signal hyperintensities in the lateral and dorsal columns of all patients. The MT signal quantified in the dorsal column showed significant differences between patients with AMN, X-linked adrenoleukodystrophy heterozygotes, and controls. MT hyperintensity in the dorsal column correlated with EDSS, vibratory sense, and postural sway. CONCLUSION: Magnetization transfer-weighted imaging is a sensitive modality for the visual and quantitative assessment of spinal cord pathology in adrenomyeloneuropathy, and is a potential tool for evaluation of new therapies.

Spectroscopic evidence of cerebral axonopathy in patients with "pure" adrenomyeloneuropathy.

BACKGROUND: Adrenomyeloneuropathy (AMN) is the adult variant of X-linked adrenoleukodystrophy. The disease pathology is usually limited to spinal cord and peripheral nerves, and when this is the case, it is referred to as "pure" AMN. Histopathology shows cerebral involvement even in pure AMN; however, not much is known about the nature, extent, and clinical relevance of these findings. OBJECTIVE: To investigate brain involvement in AMN patients with normal MRI, employing multislice MR spectroscopic imaging. METHODS: Twelve men with pure AMN were compared with 19 age-matched healthy volunteers. Metabolite ratios (N-acetylaspartate [NAA]/choline [Cho], NAA/creatine [Cr], and Cho/Cr) were measured from seven brain regions. Global metabolite ratios were generated as an average of these seven regional ratios. The Expanded Disability Status Scale (EDSS) was used for neurologic evaluation. RESULTS: The patients with AMN showed reduced global NAA/Cho (AMN 1.40 +/- 0.16 vs controls 1.75 +/- 0.34; p = 0.003)) and global NAA/Cr (AMN 2.32 +/- 0.13 vs controls 2.62 +/- 0.43; p = 0.03). Regionally, NAA/Cho was lowered in the internal capsule (AMN 1.30 +/- 0.20 vs controls 1.69 +/- 0.37; p = 0.002) and in parieto-occipital white matter (AMN 1.45 +/- 0.19 vs controls 1.78 +/- 0.55; p = 0.04). NAA/Cr was lowered in parieto-occipital white matter (AMN 2.34 +/- 0.31 vs controls 2.83 +/- 0.71; p = 0.04). EDSS demonstrated an inverse association with global NAA/Cr (r = -0.65, p = 0.02) and NAA/Cr in centrum semiovale (r = -0.73, p = 0.006) and in parieto-occipital white matter (r = -0.64, p = 0.02). Cho/Cr was not significantly elevated. CONCLUSIONS: (1)H-MR spectroscopic imaging is able to detect biochemical abnormalities suggestive of axonal damage even in the brains of patients with pure adrenomyeloneuropathy. The axonopathy is most prominent in internal capsule and parieto-occipital white matter and may contribute to clinical disability.

Analysis of MRI patterns aids prediction of progression in X-linked adrenoleukodystrophy.

BACKGROUND: X-linked adrenoleukodystrophy (X-ALD) has variants with widely different outcomes, hampering clinical counseling and evaluation of therapies. OBJECTIVE: To evaluate the degree to which MRI patterns can predict lesion progression. METHODS: Two hundred six boys and men with cerebral X-ALD (median age 12.2 years, mean age 18.5 years, age range 1.7 to 73.8 years) were studied. In 140 individuals, follow-up MRI were available. Data after bone marrow transplantation (BMT) were excluded. The patterns of MRI abnormalities were subdivided into five groups based on the anatomic location of the initial T2 signal hyperintensity (pattern 1: parieto-occipital white matter, pattern 2: frontal white matter, pattern 3: corticospinal tract, pattern 4: cerebellar white matter, pattern 5: concomitant parieto-occipital and frontal white matter). The X-ALD MRI Severity Scale, a 34-point scale previously described, was used in the analysis. RESULTS: Pattern 1 patients had rapid progression if contrast enhancement was present and if the MRI abnormality manifested at an early age. The latter was also true for pattern 2 patients. Based on these variables, predictive formulas were constructed for these two patterns using multiple regressions. MRI progression was much slower in pattern 3 and 4 patients, whereas in the few pattern 5 patients, it was more rapid than in any other of the patterns. Patterns 1 and 5 occurred mainly in childhood, patterns 2 and 4 in adolescence, and pattern 3 in adults. CONCLUSIONS: MRI progression in X-ALD depends on patient age, initial MRI Severity Scale score, and anatomic location of the lesion. When used in combination, these data aid the prediction of disease course and the selection of patients for BMT.

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.

Proton MR spectroscopic imaging predicts lesion progression on MRI in X-linked adrenoleukodystrophy.

BACKGROUND: The phenotypic expression of X-linked adrenoleukodystrophy (X-ALD) ranges from the rapidly progressive childhood cerebral form to the milder adrenomyeloneuropathy in adults. It is not possible to predict phenotype by mutation analysis or biochemical assays. Multislice proton MRS imaging (MRSI) has previously detected more extensive brain abnormalities in X-ALD than conventional MRI, which has been suggested to predict impending demyelination. However, the significance of these changes is unclear. OBJECTIVE: The purpose of this study was to determine the long-term sensitivity and specificity of MRSI for disease progression in X-ALD. METHODS: Twenty-five patients with X-ALD were investigated (average age, 15 years; range, 2-43 years) with MRI and proton MRSI at baseline and follow-up MRI over a mean period of 3.5 years. Eight patients had normal MRI findings at baseline and on follow-up (noncerebral group), 11 had abnormal MRI at baseline and no change on follow-up (cerebral nonprogressive group), and 6 had progressive MRI abnormalities (cerebral progressive group). On MRSI, voxels were analyzed in the normal MRI-appearing perilesional white matter, or in the corresponding area in the noncerebral group. RESULTS: The concentration ratio of N-acetylaspartate (NAA) to choline was the most sensitive indicator of disease progression. The average NAA/choline ratio was 5.99 for the noncerebral group, 5.75 for the cerebral nonprogressive group, and 3.74 for the cerebral progressive group (p = 0.002). At a cut-off point of 5.0, the NAA/choline ratio predicted disease progression in all patients with six cerebral progressive disease (sensitivity 100%). The specificity was 83%, the positive predictive value was 66%, and the negative predictive value was 100%. CONCLUSIONS: Multislice proton MRS imaging is able to identify impending or beginning degeneration in white matter that still appears normal on conventional MRI. Multislice proton MRSI may be a suitable technique for the prediction of lesion progression on MRI in X-linked adrenoleukodystrophy.

Neuroimaging studies in Rett syndrome.

Neuroimaging is a key instrument for determining structural and in vivo functional status of the brain, non-invasively. Multiple approaches can now determine aspects of anatomic and neurochemical changes in brain, and have been utilized effectively in Rett Syndrome patients to understand the biological basis of this neurodevelopmental disorder. Studies performed at our institute include volumetric analyses of MRI, magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), cerebral blood flow measurements with MRI, and positron emission tomography scans (PET). These studies have provided considerable insight into mechanisms underlying the clinical features of this disease. Volumetric analyses suggest that decreased brain volume in RS results from global reductions in both gray and white matter of the brain. A selective vulnerability of the frontal lobes is evidenced by the preferential reduction of blood flow, increased choline and reduced n-acetyl aspartate (NAA) by MRS, and increased glucose uptake in these same regions as shown by ((18)F)-fluorodeoxyglucose (FDG) PET scans. We hypothesize that the increased glucose uptake relates to increased glutamate cycling in synapses. The resulting neuroexcitotoxic injury to the developing brain contributes to the seizures, behavioral disturbance and respiratory irregularities commonly seen in phases 1 and 2 of this disorder.

ABCD1 mutations and the X-linked adrenoleukodystrophy mutation database: role in diagnosis and clinical correlations.

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene, which encodes a peroxisomal ABC half-transporter (ALDP) involved in the import of very long-chain fatty acids (VLCFA) into the peroxisome. The disease is characterized by a striking and unpredictable variation in phenotypic expression. Phenotypes include the rapidly progressive childhood cerebral form (CCALD), the milder adult form, adrenomyeloneuropathy (AMN), and variants without neurologic involvement. There is no apparent correlation between genotype and phenotype. In males, unambiguous diagnosis can be achieved by demonstration of elevated levels of VLCFA in plasma. In 15 to 20% of obligate heterozygotes, however, test results are false-negative. Therefore, mutation analysis is the only reliable method for the identification of heterozygotes. Since most X-ALD kindreds have a unique mutation, a great number of mutations have been identified in the ABCD1 gene in the last seven years. In order to catalog and facilitate the analysis of these mutations, we have established a mutation database for X-ALD ( http://www.x-ald.nl). In this review we report a detailed analysis of all 406 X-ALD mutations currently included in the database. Also, we present 47 novel mutations. In addition, we review the various X-ALD phenotypes, the different diagnostic tools, and the need for extended family screening for the identification of new patients.

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.

Brain uptake and utilization of fatty acids: recommendations for future research.

A primary goal of the international workshop "Brain Uptake and Utilization of Fatty Acids" was to identify research areas that would benefit from further investigation. The major themes for future research are presented below: (1) Elucidating the role of the developing and mature cerebrovascular endothelium (CVE) in the uptake of fatty acids (FA) into the brain. (2) Clarifying the role of diffusion and receptor-mediated uptake of FAs by various brain cell membranes and protein-mediated shuttling of FAs between the CVE and various brain cells and tissues. (3) Illuminating the mechanisms of intermediate metabolism and the roles of polyunsaturated fatty acids (PUFA) in astrocytes, neurons and oligodendrocytes. Of special interest are the long-chain omega-3 PUFA and their derivatives, such as lipoproteins, phospholipids and plasmalogens, that have been associated with various disease states (such as those listed in [5], below). (4) Elucidating the role of gene expression on long-chain omega-3 PUFA incorporation in membranes and the regulatory role these and other PUFA have on gene expression in the brain. (5) Elucidating the recently identified roles of long-chain omega-3 PUFA in mood disorders, schizophrenia, stroke, peroxisomal biogenesis disorders, Huntington's disease, other neurodegenerative disorders and disorders of oxidative stress. (6) Undertaking placebo-controlled clinical trials to assess the therapeutic potential of omega-3 PUFA in the above disorders. (7) Developing new, and utilizing existing animal models in the above studies. (8) Developing noninvasive imaging and tagging methods for quantifying the migration and distribution of PUFA and their derivatives in the brain. (9) Applying multi-disciplinary collaborations among biophysicists, physiologists and molecular biologists to the resolution of the above.

The peroxisome deficient PEX2 Zellweger mouse: pathologic and biochemical correlates of lipid dysfunction.

Zellweger syndrome is the prototypic human peroxisomal biogenesis disorder that results in abnormal neuronal migration in the central nervous system and severe neurologic dysfunction. A murine model for this disorder was previously developed by targeted deletion of the PEX2 peroxisomal gene. By labeling neuronal precursor cells in vivo with a mitotic marker, we can demonstrate a delay in neuronal migration in the cerebral cortex of homozygous PEX2 mutant mice. Postnatal PEX2 Zellweger mice develop severe cerebellar defects with abnormal Purkinje cell development and an altered folial pattern. When the PEX2 mutation is placed on an inbred murine genetic background, there is significant embryonic lethality and widespread neuronal lipidosis throughout the brain. Biochemical analysis of PEX2 mutant mice shows the characteristic accumulation of very long chain fatty acids and deficient plasmalogens in a wide variety of tissues. Docosahexaenoic acid levels (DHA; 22:6n-3) were found to be reduced in the brain of mutant mice but were normal in visceral organs at birth. All tissues examined in postnatal mutant mice had reduced DHA. The combined use of morphologic and biochemical analyses in these mice will be essential to elucidate the pathogenesis of this complex peroxisomal disease.

Brain uptake and utilization of fatty acids: applications to peroxisomal biogenesis diseases.

The brain is rich in diverse fatty acids saturated, monounsaturated and polyunsaturated fatty acids with chain lengths ranging from less than 16 to more than 24 carbons that make up the complex lipids present in this organ. While some fatty acids are derived from endogenous synthesis, others must come from exogenous sources. The mechanism(s) by which fatty acids enter cells has been the subject of much debate. While some investigators argue for a protein-mediated process, others suggest that simple diffusion is sufficient. In the brain, uptake is further complicated by the presence of the blood-brain barrier. Brain fatty acid homeostasis is disturbed in many human disorders, as typified by the peroxisomal biogenesis diseases. A workshop designed to bring together researchers from varied backgrounds to discuss these issues in an open forum was held in March, 2000. In addition to assessing the current state of knowledge, areas requiring additional investigation were identified and recommendations for future research were made. A brief overview of the invited talks is presented here.

The peroxin Pex6p gene is impaired in peroxisomal biogenesis disorders of complementation group 6.

Human genetic peroxisomal biogenesis disorders (PBDs), such as Zellweger syndrome, comprise 13 different complementation groups (CGs). Eleven peroxin genes, termed PEXs, responsible for PBDs have been identified, whereas pathogenic genes for PBDs of 2CGs, CG-A (the same CG as CG8 in the United States and Europe) and CG6, remained unidentified. We herein provide several lines of novel evidence indicating that PEX6, the pathogenic gene for CG4, is impaired in PBD of CG6. Expression of PEX6 restored peroxisome assembly in fibroblasts from a CG6 PBD patient. This patient was a compound heterozygote for PEX6 gene alleles. Accordingly, by merging CG6 with CG4, human PBDs are now classified into 12CGs.

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.

Leukodystrophies: recent developments in genetics, molecular biology, pathogenesis and treatment.

The combined application of recently developed techniques for genetic and biochemical analysis, neuroimaging and the ability to create animal models has led to remarkable advances in the field of leukodystrophy research. The present review focuses on recent developments in X-linked adrenoleukodystrophy, Alexanders disease, Canavans disease, metachromatic leukodystrophy, globoid cell leukodystrophy (Krabbes disease) and Pelizaeus-Merzbacher disease, and briefly discusses new data on six other rare inherited leukodystrophies. Of the leukodystrophies, 12 can now be diagnosed precisely using noninvasive techniques, and the molecular defect has been identified in nine of these. Disease incidence can be reduced through genetic counselling. Presymptomatic diagnosis provides an opportunity for therapeutic intervention. Study of animal models facilitates elucidation of pathogenic mechanisms and identifies pathways that could be targeted by future therapies.

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.

T2 relaxation measurements in X-linked adrenoleukodystrophy performed using dual-echo fast fluid-attenuated inversion recovery MR imaging.

SUMMARY: The purpose of this study was to determine whether dual-echo fast fluid-attenuated inversion recovery MR imaging and corresponding T2 brain maps can show different zones in the affected white matter of patients with cerebral X-linked adrenoleukodystrophy. Ten male patients with cerebral X-linked adrenoleukodystrophy underwent imaging performed using dual-echo fast fluid-attenuated inversion recovery and dual-echo conventional spin-echo MR sequences. Corresponding T2 relaxation maps of the brain were generated. On the basis of dual-echo fast fluid-attenuated inversion recovery images and T2 maps, the affected white matter could be divided into two distinct zones in four patients with cerebral X-linked adrenoleukodystrophy.

Identification of a fatty acid delta6-desaturase deficiency in human skin fibroblasts.

Polyunsaturated fatty acid (PUFA) utilization was investigated in skin fibroblasts cultured from a female patient with an inherited abnormality in lipid metabolism. These deficient human skin fibroblasts (DF) converted 85;-95% less [1-14C]linoleic acid (18:2n-6) to arachidonic acid (20:4n-6), 95% less [3-14C]tetracosatetraenoic acid (24:4n-6) to docosapentaenoic acid (22:5n-6), and 95% less [1-14C]-linolenic acid (18:3n-3) and [3-14C]tetracosapentaenoic acid (24:5n-3) to docosahexaenoic acid (22:6n-3) than did normal human skin fibroblasts (NF). The only product formed by the DF cultures from [1-14C]tetradecadienoic acid (14:2n-6) was 18:2n-6. However, they produced 50;-90% as much 20:4n-6 as the NF cultures from [1-14C]hexadecatrienoic acid (16:3n-6), [1-14C]gamma-linolenic acid (18:3n-6), and [1-14C]dihomo-gamma-linolenic acid (20:3n-6), PUFA substrates that contain Delta6 double bonds. DF also contained 80% more 18:2n-6 and 25% less 20:4n-6. These results suggested that DF are deficient in Delta6 desaturation. This was confirmed by Northern blots demonstrating an 81;-94% decrease in Delta6-desaturase mRNA content in the DF cultures, whereas the Delta5-desaturase mRNA content was reduced by only 14%. This is the first inherited abnormality in human PUFA metabolism shown to be associated with a Delta6-desaturase deficiency. Furthermore, the finding that the 18- and 24-carbon substrates are equally affected suggests that a single enzyme carries out both Delta6 desaturation reactions in human PUFA metabolism.