ABCD1 Mutation Research Articles

Phenotypes of female adrenoleukodystrophy

Adrenoleukodystrophy-adrenomyeloneuropathy (ALD-AMN) is an X-linked disorder of the peroxisomal beta oxidation characterized by the accumulation of saturated very long chain fatty acids (VLCFA) predominantly in adrenal cortex and central as well as peripheral myelin.1 ALD-AMN is caused by mutations of the ABCD1 gene, a member of the ATP-binding cassette (ABC) transporter superfamily, and more than 400 pathogenic ABCD1 mutations have been described (www.x-ald.nl).2 The incidence of ALD-AMN is estimated to be between 1:20,000 and 1:100,000. Affected men may present with childhood cerebral ALD, adult-onset AMN, or Addison disease only.1,3 Approximately 20% of heterozygous women develop mild AMN with a mean onset age around 40 years.1 Childhood onset, cognitive decline, visual disturbances, or adrenal dysfunction are exceptional.1,3,4 Herein, we describe two female ALD-AMN heterozygotes presenting with particular cerebral phenotypes, thereby expanding the clinical spectrum of female ALD-AMN and demonstrating a substantial intrafamilial variability. #### Case 1. This patient was diagnosed with manic-hebephrenic disorder at age 8 years, and had recurrent psychotic episodes thereafter. At age 25 years, neurologic examination revealed spastic paraparesis. Twenty years later, neurologic examination documented moderate cognitive deficits, severe spastic paraparesis, and a cerebellar syndrome with unsteady smooth pursuit gaze movements, dysarthria, and intention tremor. Cerebral MRI …

The role of peroxisomal ABC transporters in the mouse adrenal gland: the loss of Abcd2 (ALDR), Not Abcd1 (ALD), causes oxidative damage

X-linked adreno-leukodystrophy is a progressive, systemic peroxisomal disorder that primarily affects the adrenal cortex, as well as myelin and axons of the central nervous system. Marked phenotypic heterogeneity does not correlate with disease-causing mutations in ABCD1, which encodes a peroxisomal membrane protein that is a member of the ABC transmembrane transporter proteins. The precise physiological functions of ABCD1 and ABCD2, a closely related peroxisomal membrane half-transporter, are unknown. The abcd1 knockout mouse does not develop the inflammatory demyelination so typical and devastating in adreno-leukodystrophy, but it does display the same lamellae and lipid profiles in adrenocortical cells under the electron microscope as the human patients. The adrenocortical cells in the mouse also exhibit immunohistochemical evidence of oxidative stress at 12 weeks but no evidence of oxidative damage. To better understand the pathogenesis of this complex disease, we evaluate the adrenal lesion of the abcd1 knockout mouse as a function of normal aging, dietary or therapeutic manipulations, and abcd genotype. The loss of abcd2 causes oxidative stress in the adrenal at 12 weeks, as judged by increased immunoreactivity for the mitochondrial manganese superoxide dismutase, in both the inner cortex and medulla. The loss of abcd2 (n=20), but not abcd1 (n=27), results in the spontaneous and premature deposition of ceroid, a known end-product of oxidative damage, predominantly in adrenal medullary cells. These data indicate that the loss of abcd2 results in greater oxidative stress in murine adrenal cells than the loss of abcd1, providing a clue to its cellular function. We also find that the adrenocortical lesion of the abcd1 knockout mouse does not produce functional impairment at ten to nineteen months or overt hypocortisolism at any age, nor does it progress histologically; these and other data align this mouse model closer to human female heterozygotes than to male ALD or AMN hemizygotes.

Uptake and metabolism of plasma-derived erucic acid by rat brain

We examined the ability of erucic acid (22:1n-9) to cross the blood-brain barrier (BBB) by infusing [14-14C]22:1n-9 (170 microCi/kg, iv and icv) into awake, male rats. [1-14C]arachidonic acid (20:4n-6) [intravenous (i.v.)] was the positive control. After i.v. infusion, 0.011% of the plasma [14-14C]22:1n-9 was extracted by the brain, compared with 0.055% of the plasma [1-14C]20:4n-6. The [14-14C]22:1n-9 was extensively beta-oxidized (60%), compared with 30% for [1-14C]20:4n-6. Although 20:4n-6 was targeted primarily to phospholipid pools, 22:1n-9 was targeted to cholesteryl esters, triglycerides, and phospholipids. When [14-14C]22:1n-9 was infused directly into the fourth ventricle of the brain [intracerebroventricular (i.c.v.)] for 7 days, 60% of the tracer entered the phospholipid pools, similar to the distribution observed for [1-14C]20:4n-6. This demonstrates plasticity in the ability of the brain to esterify 22:1n-9 in an exposure-dependent manner. In i.v. and i.c.v. infused rats, a significant amount of tracer found in the phospholipid pools underwent sequential rounds of chain shortening and was found as [12-14C]20:1n-9 and [10-14C]oleic acid. These results demonstrate for the first time that intact 22:1n-9 crosses the BBB, is incorporated into specific lipid pools, and is chain-shortened.

Cognitive Evaluation of Neurologically Asymptomatic Boys With X-linked Adrenoleukodystrophy

Various studies have demonstrated abnormal neuropsychological function in boys with the childhood cerebral phenotype of X-linked adrenoleukodystrophy. Not much is known about the cognitive function of neurologically asymptomatic boys with X-linked adrenoleukodystrophy who have normal brain magnetic resonance imaging results. To describe the cognitive profile of 52 neurologically asymptomatic boys with X-linked adrenoleukodystrophy (mean +/- SD age, 6.7 +/- 3.6 years). Neuropsychological tests included evaluation of IQ (full-scale IQ, verbal IQ, and performance IQ), 5 major cognitive domains (language, visuospatial skills, perception, visuomotor or graphomotor skills, memory, and attention or executive function), adaptive skills, and academic achievement. Standardized z scores relative to age-appropriate published norms were generated. Association between age and cognitive performance was evaluated using nonparametric Spearman rank correlation and robust median regression adjusting for full-scale IQ and socioeconomic status. All but 4 patients had normal cognitive function. There was a negative correlation between age and visual perception as well as age and visuomotor skills after adjustment for full-scale IQ and socioeconomic status. This study provides, to our knowledge, the first evidence of overall normal cognitive function in neurologically and radiologically normal boys with X-linked adrenoleukodystrophy, indicating no evidence of neurodevelopmental abnormalities despite the inherent ABCD1 mutation. Subtle deterioration with age was observed in some functional domains. This suggests that prevention and timely institution of therapy can potentially preserve cognitive function seen in patients with the cerebral X-linked adrenoleukodystrophy phenotype. X-linked adrenoleukodystrophy should be considered a candidate disorder for neonatal screening.

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.

X-linked adrenoleukodystrophy mice demonstrate abnormalities in cholesterol metabolism

The neurodegenerative disorder X-linked adrenoleukodystrophy (X-ALD) is caused by ABCD1 mutations and characterized by very long-chain fatty acid (VLCFA) accumulation. Cholesterol-lowering normalized VLCFA in fibroblasts and plasma of X-ALD patients. We show that in cultured cells, cholesterol-loading induces ABCD1. In X-ALD mice, plasma cholesterol is elevated and not further increasable by cholesterol-feeding, whereas hepatic HMG-CoA reductase and Abcd2 are downregulated. Upon cholesterol modulation, brain VLCFA increased in X-ALD mice, but decreased in controls. In murine X-ALD fibroblasts, cholesterol-lowering did not normalize VLCFA. Thus, ALDP-deficiency and VLCFA are linked to cholesterol but species differences complicate evaluating cholesterol-lowering drugs in X-ALD mice.

ABCD1 Gene Mutations in Chinese Patients with ALD

Thirty-two different ABCD1 mutations were identified by direct sequencing of polymerase chain reaction products in 34 unrelated Chinese X-linked adrenoleukodystrophy (ALD) patients examined at Peking University First Hospital, Beijing, PRC.

Magnetic resonance spectroscopy

X-linked adrenoleukodystrophy (ALD) has two distinct neurologic phenotypes: the slowly progressive adrenomyeloneuropathy (AMN) and the rapidly progressive inflammatory cerebral phenotypes (CERALD).1 The main pathologic abnormality in AMN is a non-inflammatory distal axonopathy that affects the long tracts in the spinal cord most severely.2 A recent spectroscopy study demonstrated evidence of axonal pathology in the brain of pure AMN patients.3 In CERALD there is an inflammatory cerebral myelopathy associated with intense perivascular cuffing by cells, most of which are CD8 cytotoxic T-cells. The CD1 mediated presentation of lipid antigens that contain the saturated very long chain fatty acids that are characteristic of ALD may be a key pathogenetic element.4 More than 400 different mutations in ABCD1 , the gene that is deficient in ALD, have been identified. They do not correlate with the neurologic phenotype.1 AMN and CERALD often co-occur in the same family. The inability to predict whether a young asymptomatic boy with ALD is at risk for AMN or for CERALD is one of the most serious gaps in knowledge about ALD. While there is as yet no consistently effective therapy for AMN, hematopoietic stem cell transplantation (HSCT) can benefit patients with CERALD. This is documented in the recent study by Peters et al. …

Retracted : Identification of seven novel mutations in ABCD1 by a DHPLC‐based assay in Italian patients with X‐linked adrenoleukodystrophy

We report the molecular findings in 14 patients (12 families) with X-linked adrenoleukodystrophy (X-ALD, MIM# 300100), a well-defined peroxisomal disorder attributed to mutations in the ABCD1 gene on chromosome Xq28. With the aims of determining the spectrum of mutations and developing an efficient molecular genetic test for analysis of at-risk women whose carrier status is unknown, and to offer molecular confirmation of their status to obligate heterozygotes, regardless of their clinical status, we carried out molecular screening by setting up a denaturing high-performance liquid chromatography (DHPLC)-based protocol. We identified eleven hemizygous base changes in ABCD1, including seven new mutations (c.145underscore;146ins4, c.264C>G, c.919C>T, c.994C>T, c.1027G>A, c.1508T>C, and c.1540A>C, resulting in the p.Pro193fs, p.Cys88Trp, p.Gln307X, p.Gln332X, p.Gly343Ser, p.Leu503Pro, and p.Ser514Arg changes, respectively). Adding new variants to the repertoire of ABCD1 mutations in X-ALD, our data provide an efficient, cost-effective, and reliable DHPLC detection protocol for mutation screening of X-ALD families.

A very long-chain acyl-CoA synthetase-deficient mouse and its relevance to X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative and endocrine disorder resulting from mutations in ABCD1 which encodes a peroxisomal membrane protein in the ATP binding cassette superfamily. The biochemical signature of X-ALD is increased levels of saturated very long-chain fatty acids (VLCFA; carbon chains of 22 or more) in tissues and plasma that has been associated with decreased peroxisomal very long-chain acyl-CoA synthetase (VLCS) activity and decreased peroxisomal VLCFA beta-oxidation. It has been hypothesized that ABCD1, which has no demonstrable VLCS activity itself, has an indirect effect on peroxisomal VLCS activity and VLCFA beta-oxidation by transporting fatty acid substrates, VLCS protein or some required co-factor into peroxisomes. Here we report the characterization of a Vlcs knockout mouse that exhibits decreased peroxisomal VLCS activity and VLCFA beta-oxidation but does not accumulate VLCFA. The XALD/Vlcs double knockout mouse has the biochemical abnormalities observed in the individual knockout mice but does not display a more severe X-ALD phenotype. These data lead us to conclude that (1) VLCFA levels are independent of peroxisomal fatty acid beta-oxidation, (2) there is no ABCD1/VLCS interaction and (3) the common severe forms of X-ALD cannot be modeled by decreasing peroxisomal VLCS activity in the XALD mouse.

Contiguous Deletion of the X-Linked Adrenoleukodystrophy Gene ( ABCD1) and D XS1357E: A Novel Neonatal Phenotype Similar to Peroxisomal Biogenesis Disorders

X-linked adrenoleukodystrophy (X-ALD) results from mutations in ABCD1. ABCD1 resides on Xq28 and encodes an integral peroxisomal membrane protein (ALD protein [ALDP]) that is of unknown function and that belongs to the ATP-binding cassette-transporter superfamily. Individuals with ABCD1 mutations accumulate very-long-chain fatty acids (VLCFA) (carbon length >22). Childhood cerebral X-ALD is the most devastating form of the disease. These children have the earliest onset (age 7.2 +/- 1.7 years) among the clinical phenotypes for ABCD1 mutations, but onset does not occur at <3 years of age. Individuals with either peroxisomal biogenesis disorders (PBD) or single-enzyme deficiencies (SED) in the peroxisomal beta-oxidation pathway--disorders such as acyl CoA oxidase deficiency and bifunctional protein deficiency--also accumulate VLCFA, but they present during the neonatal period. Until now, it has been possible to distinguish unequivocally between individuals with these autosomal recessively inherited syndromes and individuals with ABCD1 mutations, on the basis of the clinical presentation and measurement of other biochemical markers. We have identified three newborn boys who had clinical symptoms and initial biochemical results consistent with PBD or SED. In further study, however, we showed that they lacked ALDP, and we identified deletions that extended into the promoter region of ABCD1 and the neighboring gene, DXS1357E. Mutations in DXS1357E and the ABCD1 promoter region have not been described previously. We propose that the term "contiguous ABCD1 DXS1357E deletion syndrome" (CADDS) be used to identify this new contiguous-gene syndrome. The three patients with CADDS who are described here have important implications for genetic counseling, because individuals with CADDS may previously have been misdiagnosed as having an autosomal recessive PBD or SED

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.