ATP Binding Cassette Subfamily D Member 1 Research Articles

Genetic analysis of the X-linked Adrenoleukodystrophy ABCD1 gene in Drosophila uncovers a role in Peroxisomal dynamics.

X-linked adrenoleukodystrophy (X-ALD) is a progressive neurodegenerative disorder caused by a loss-of-function (LOF) mutation in the ATP-binding cassette subfamily D member 1 (ABCD1) gene, leading to the accumulation of very long-chain fatty acids (VLCFAs). This disorder exhibits striking heterogeneity; some male patients develop an early childhood neuroinflammatory demyelination disorder, while other patients, including adult males and most affected female carriers, experience a chronic progressive myelopathy. Adrenocortical failure is observed in almost all male patients, with age of onset varying sometimes being the first diagnostic finding. The gene underlying this spectrum of disease encodes an ATP-binding cassette (ABC) transporter that localizes to peroxisomes and facilitates VLCFA transport. X-ALD is considered a single peroxisomal component defect and does not play a direct role in peroxisome assembly. Drosophila models of other peroxisomal genes have provided mechanistic insight into some of the neurodegenerative mechanisms with reduced lifespan, retinal degeneration, and VLCFA accumulation. Here, we perform a genetic analysis of the fly ABCD1 ortholog Abcd1 (CG2316). Knockdown or deficiency of Abcd1 leads to VLCFA accumulation, salivary gland defects, locomotor impairment and retinal lipid abnormalities. Interestingly, there is also evidence of reduced peroxisomal numbers. Flies overexpressing the human cDNA for ABCD1 display a wing crumpling phenotype characteristic of the pex2 loss-of-function. Surprisingly, overexpression of human ABCD1 appears to inhibit or overwhelm peroxisomal biogenesis to levels similar to null mutations in fly pex2, pex16 and pex3. Drosophila Abcd1 is therefore implicated in peroxisomal number, and overexpression of the human ABCD1 gene acts a potent inhibitor of peroxisomal biogenesis in flies.

Innovative tree-based method for sampling molecular conformations: exploring the ATP-binding cassette subfamily D member 1 (ABCD1) transporter as a case study.

We introduce a novel tree-based method for visualizing molecular conformation sampling. Our method offers enhanced precision in highlighting conformational differences and facilitates the observation of local minimas within proteins fold space. The projection of empirical laboratory data on the tree allows us to create a link between protein conformations and disease relevant data. To demonstrate the efficacy of our approach, we applied it to the ATP-binding cassette subfamily D member 1 (ABCD1) transporter responsible for very long-chain fatty acids (VLCFAs) import into peroxisomes. The genetic disorder called X-linked adrenoleukodystrophy (XALD) is characterized by the accumulation of VLCFA due to pathogenic variants in the ABCD1 gene. Using in silico molecular simulation, we examined the behavior of 16 prevalent mutations alongside the wild-type protein, exploring both inward and outward open forms of the transporter through molecular simulations. We evaluated from resulting trajectories the energy potential related to the ABCD1 interactions with ATP molecules. We categorized XALD patients based on the severity and progression of their disease, providing a unique clinical perspective. By integrating this data into our numerical framework, our study aimed to uncover the molecular underpinnings of XALD, offering new insights into disease progression. As we explored molecular trajectories and conformations resulting from our study, the tree-based method not only contributes valuable insights into XALD but also lays a solid foundation for forthcoming drug design studies. We advocate for the broader adoption of our innovative approach, proposing it as a valuable tool for researchers engaged in molecular simulation studies.

X‑linked adrenoleukodystrophy caused by maternal ABCD1 mutation and paternal X chromosome inactivation

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. It is caused by defects in the ATP-binding cassette subfamily D member 1 (ABCD1) gene, resulting in impaired peroxisomal β-oxidation of very-long-chain fatty acids (VLCFAs). As an X-linked recessive disease, female X-ALD carriers are typically asymptomatic. In the present study, a 7-year-old girl was diagnosed with cerebral ALD. Brain magnetic resonance imaging revealed asymmetric demyelination of bilateral white matter. Plasma VLCFAs level showed a substantial increase. Whole exome and Sanger sequencing revealed an ABCD1 c.919C>T (p.Q307X) heterozygous pathogenic mutation, which was inherited from the asymptomatic mother. X chromosome inactivation (XCI) analysis revealed that the normal paternal X chromosome was almost completely inactivated. Thus, the maternal ABCD1 mutation and paternal XCI were responsible for causing the disease in the patient. XCI may be one reason female X-ALD carriers can be symptomatic.

Increased levels of hexacosanoic acid in the brain of Wistar rats: a behavioral study

Introduction: X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal metabolic disorder associated with mutations in the ATP-binding cassette sub-family D member1 ( ABCD1 ) gene. Practically all male patients with X-ALD develop adrenocortical insufficiency during childhood and progressive myelopathy and peripheral neuropathy in adulthood. However, some male patients develop a fatal cerebral demyelinating disease named cerebral adrenoleukodystrophy. Although the exact mechanisms underlying brain damage in X-ALD are still poorly elucidated, it is known that hexacosanoic acid (C26:0) accumulation represents a hallmark in the pathogenesis of this disease. In this study, we examined whether an overload of C26:0 injected in Wistar rats was capable of causing behavioral changes in these animals. Methods: Egg lecithin in ethanol was dried under a nitrogen stream and mixed with C26:0 methyl ester. Male Wistar rats at 2–3 weeks of age were obtained from Universidade Federal do Rio Grande do Sul (UFRGS), divided into 8 groups, and submitted to an open field test. We then analyzed line crossings (locomotion and exploration), rearing (orienting and investigatory responses), grooming (anxiety manifestation), and latency to move for each animal. Results: Animals subjected to C26:0 administration presented fewer crossings and rearing episodes and a higher latency to move 45 minutes after C26:0 injection. The present work yields experimental evidence that C26:0, the main accumulated metabolite in X-ALD, can cause behavioral alterations in rats such as the impairment of locomotion and exploratory capabilities, as well as a reduction in orienting and investigatory responses. Conclusion: Although our results are preliminary, they are extremely important for future studies that investigate C26:0 accumulation and locomotor impairment in patients with X-ALD.

Deciphering the modifiers for phenotypic variability of X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD), an inborn error of peroxisomal β-oxidation, is caused by defects in the ATP Binding Cassette Subfamily D Member 1 (ABCD1) gene. X-ALD patients may be asymptomatic or present with several clinical phenotypes varying from severe to mild, severe cerebral adrenoleuko-dystrophy to mild adrenomyeloneuropathy (AMN). Although most female heterozygotes present with AMN-like symptoms after 60 years of age, occasional cases of females with the cerebral form have been reported. Phenotypic variability has been described within the same kindreds and even among monozygotic twins. There is no association between the nature of ABCD1 mutation and the clinical phenotypes, and the molecular basis of phenotypic variability in X-ALD is yet to be resolved. Various genetic, epigenetic, and environmental influences are speculated to modify the disease onset and severity. In this review, we summarize the observations made in various studies investigating the potential modifying factors regulating the clinical manifestation of X-ALD, which could help understand the pathogenesis of the disease and develop suitable therapeutic strategies.

The Clinical Impact of CLIR Tools toward Rapid Resolution of Post-Newborn Screening Confirmatory Testing for X-Linked Adrenoleukodystrophy in California.

Since the start of X-linked adrenoleukodystrophy (ALD) newborn screening in California, more than half of the diagnosed cases were found to have an ATP binding cassette subfamily D member 1 (ABCD1) gene variant of uncertain significance (VUS). To determine retrospectively the likelihood that these were true positive cases, we used a web-based post-analytical tool in Collaborative Laboratory Integrated Reports (CLIR). Confirmatory plasma very long-chain fatty-acids (VLCFA) profiles for ALD screen positive infant boys were run through the CLIR ALD tool. We compared the distribution by ABCD1 variant classification (pathogenic, likely pathogenic, VUS, and no variant) with the CLIR tool score interpretation (non-informative, possibly ALD, likely ALD, and very likely ALD) and the current case diagnosis. The study showed that CLIR tool positive interpretations were consistent with 100% of the pathogenic and likely pathogenic variants on the ABCD1 gene if a more conservative guideline was used. The tool interpretations were also consistent with screened cases that were determined to not have disease (our no-disorder group). The CLIR tool identified 19 diagnosed ALD cases with VUS to be potential false positives, representing a 40% reduction among all diagnosed ALD cases with VUS. The reduction could be extended to 65% if a more aggressive threshold was used. Identifying such preventable false positives could alleviate the follow-up burden for patients, their families, and California Special Care Centers.

Clinical characteristics and phenotype distribution in 10 Chinese patients with X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD) is the most frequent type of inherited demyelinating peroxisomal disease caused by mutations in the ATP binding cassette subfamily D member 1 (ABCD1) gene. The rate of early recognition and genetic diagnosis of X-ALD remains low due to its variable clinical manifestations. The present study summarized the clinical features Chinese X-ALD patients and performed a follow-up study to further precisely characterize this disease. A total of 10 patients diagnosed with X-ALD between 1994 and 2016 at Shandong Provincial Hospital Affiliated to Shandong University (Jinan, China) were included in the present study. Through reviewing their medical records and performing telephone follow-ups, the clinical features, biochemical laboratory data, brain images, treatments and long-term outcomes were retrospectively summarized. Mutation analysis of the ABCD1 gene was performed in certain patients. Most of the patients (8/10) had the childhood cerebral form of X-ALD. One patient presented with the olivo-ponto-cerebellar form, the rarest form of X-ALD. In all patients, brain magnetic resonance images revealed abnormalities with typical T2-weighted hyperintensity. Analysis of very long chain fatty acid revealed high plasma levels of hexacosanoic acid in all patients. Increased adrenocorticotropic hormone, decreased cortisol and neurophysiological manifestations were also observed. Three different mutations of the ABCD1 gene were identified in the 3 patients subjected to genotyping. During the follow-ups, most patients took neurotrophic drugs and received hydrocortisone replacement when required. One patient received a hematopoietic stem cell transplantation, but died 1 year following the transplantation. Chronic myelopathy and peripheral neuropathy progressed with time, gradually leading to a vegetative state or paralysis within several years of clinical symptom onset. In conclusion, male patients with adrenocortical insufficiency should be further investigated for X-ALD. Early detection is critical to prevent the progression of X-ALD with mutation analysis of ABCD1 the most accurate method to confirm diagnosis.

The experience of allogeneic hematopoietic stem cell transplantation in a patient with X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD), a progressive neurometabolic disorder that is caused by a defect in the gene ABCD1 (ATP-binding cassette, subfamily D, member 1), which encodes the peroxisomal ABC half-transporter ALD protein. Recently, allogeneic hematopoietic stem cell transplantation (alloHSCT) is the only therapy known to prevent disease progression. In this study, we would like to present our experience of alloHSCT for X-ALD from a HLA matched related sibling by the use of reduced intensity conditioning regimen composed of fludarabine, busulfan and ATG which allows us to reduce procedure-related toxicity and prevent mortality while achieving a curative effect.

SIRT1 activation alleviates brain microvascularendothelial dysfunction in peroxisomal disorders.

Peroxisomal disorders are genetically heterogeneous metabolic disorders associated with a deficit of very long chain fatty acid β-oxidation that commonly manifest as early-onset neurodegeneration. Brain microvascular endothelial dysfunction with increased permeability to monocytes has been described in X-linked adrenoleukodystrophy, one of the most common peroxisomal disorders caused by mutations of the ATP binding cassette subfamily D member 1 (ABCD1) gene. The present study demonstrated that dysregulation of sirtuin 1 (SIRT1) in human brain microvascular endothelial cells (HBMECs) mediates changes in adhesion molecules and tight-junction protein expression, as well as increased adhesion to monocytes associated with peroxisomal dysfunction due to ABCD1 or hydroxysteroid 17-β dehydrogenase 4 silencing. Furthermore, enhancement of the function of SIRT1 by resve-ratrol attenuated this molecular and functional dysregulation of HBMECs via modulation of the nuclear factor-κB and Krüppel-like factor 4 signaling pathways.

Developing AAV-based gene therapy for adrenoleukodystrophy (X-ALD)

Background & Aim Adrenoleukodystrophy (X-ALD) is an X-linked disease. ALD is caused by mutations of the gene encoding ATP-Binding cassette subfamily D member 1 (ABCD1), a peroxisomal transmembrane protein. Dysfunctional ABCD1 protein results in excessive accumulation of very long chain fatty acid (VLCFA) in neural system and leads to demyelination and neural death. Currently, no effective treatments are available to cure X-ALD except BMT at very early stage of disease. Gene therapy using virus as a vehicle is an efficient method to transfer a target gene to human cells. Adeno-associated virus (AAV)-based gene therapy is of high interest for current research. The mechanism of AAV gene transfer does not cause any insertions of target gene into the human genome, which highly enhance the safety of the therapy. There are different serotypes of AAV, each targets different cell types. Therefore, AAV would be a promising vector to cure different diseases in the future. Methods, Results & Conclusion Here in this project, AAV vector with functional ABCD1 gene is constructed and its effectiveness is being tested in vitro for treating X-ALD. Meanwhile, a new animal model – ABCD1 gene mutated rabbit is used to mimic condition of X-ALD patients. Compared to the same age wild type rabbits, the diseased model shows a 5-10 folds increase in plasma VLCFA level before the treatment, and magnetic resonance imaging (MRI) scan is performed to determine demyelination inside the CNS. After AAV injection, rabbits' blood VLCFA level is monitored regularly, MRI scan and brain tissue sectioning are examined to determine the effectiveness of the AAV-based gene therapy targeting X-ALD.

Natural history of a cohort of ABCD1 variant female carriers.

The therapeutic scenario of X-linked adrenoleukodystrophy (X-ALD) is rapidly changing. Whereas the disease is well characterized in men, the condition remains to be fully clarified in women carrying ATP binding cassette subfamily D member 1 (ABCD1) variants. Specifically, data on clinical progression are needed, in order to recommend any appropriate management. The objective of this study was to outline the natural history of a cohort of untreated ABCD1 heterozygous female carriers. Longitudinal data from a single-center population of 60 carriers were retrospectively reviewed. Demographics, anthropometrics, serum very long chain fatty acid (VLCFA) levels, clinical parameters and the Adult ALD Clinical Score (AACS) were collected from every recorded visit in a 7-year period and analyzed to define the phenotype modifications, to determine factors associated with clinical features, and to estimate the annual progression rate and the subsequent sample size for interventional trials. Thirty-two patients were eligible for the study, and 59.4% were symptomatic at baseline. Clinical severity worsens with age which increases risk of symptom onset, the cut-off of 41years being crucial for phenoconversion. VLCFA levels were not predictive and did not change over time. Symptomatic carriers were followed up for 3.45±2.1years. The AACS increased at an annual rate of 0.24 points. The estimated sample size for 30% reduction in annual progression at 80% power was 272. This study provides data on the natural disease progression of untreated ABCD1 heterozygous female carriers, demonstrating the relevance of aging. The estimated annual increase of the AACS will be useful for future interventional studies.

Exome sequencing identifies mutations in ABCD1 and DACH2in two brothers with a distinct phenotype

BackgroundWe report on two brothers with a distinct syndromic phenotype and explore the potential pathogenic cause.MethodsCytogenetic tests and exome sequencing were performed on the two brothers and their parents. Variants detected by exome sequencing were validated by Sanger sequencing.ResultsThe main phenotype of the two brothers included congenital language disorder, growth retardation, intellectual disability, difficulty in standing and walking, and urinary and fecal incontinence. To the best of our knowledge, no similar phenotype has been reported previously. No abnormalities were detected by G-banding chromosome analysis or array comparative genomic hybridization. However, exome sequencing revealed novel mutations in the ATP-binding cassette, sub-family D member 1 (ABCD1) and Dachshund homolog 2 (DACH2) genes in both brothers. The ABCD1 mutation was a missense mutation c.1126G > C in exon 3 leading to a p.E376Q substitution. The DACH2 mutation was also a missense mutation c.1069A > T in exon 6, leading to a p.S357C substitution. The mother was an asymptomatic heterozygous carrier. Plasma levels of very-long-chain fatty acids were increased in both brothers, suggesting a diagnosis of adrenoleukodystrophy (ALD); however, their phenotype was not compatible with any reported forms of ALD. DACH2 plays an important role in the regulation of brain and limb development, suggesting that this mutation may be involved in the phenotype of the two brothers.ConclusionThe distinct phenotype demonstrated by these two brothers might represent a new form of ALD or a new syndrome. The combination of mutations in ABCD1 and DACH2 provides a plausible mechanism for this phenotype.

Exome sequencing identifies mutations in ABCD1 and DACH2 in two brothers with a distinct phenotype

BackgroundWe report on two brothers with a distinct syndromic phenotype and explore the potential pathogenic cause.MethodsCytogenetic tests and exome sequencing were performed on the two brothers and their parents. Variants detected by exome sequencing were validated by Sanger sequencing.ResultsThe main phenotype of the two brothers included congenital language disorder, growth retardation, intellectual disability, difficulty in standing and walking, and urinary and fecal incontinence. To the best of our knowledge, no similar phenotype has been reported previously. No abnormalities were detected by G-banding chromosome analysis or array comparative genomic hybridization. However, exome sequencing revealed novel mutations in the ATP-binding cassette, sub-family D member 1 (ABCD1) and Dachshund homolog 2 (DACH2) genes in both brothers. The ABCD1 mutation was a missense mutation c.1126G > C in exon 3 leading to a p.E376Q substitution. The DACH2 mutation was also a missense mutation c.1069A > T in exon 6, leading to a p.S357C substitution. The mother was an asymptomatic heterozygous carrier. Plasma levels of very-long-chain fatty acids were increased in both brothers, suggesting a diagnosis of adrenoleukodystrophy (ALD); however, their phenotype was not compatible with any reported forms of ALD. DACH2 plays an important role in the regulation of brain and limb development, suggesting that this mutation may be involved in the phenotype of the two brothers. ConclusionThe distinct phenotype demonstrated by these two brothers might represent a new form of ALD or a new syndrome. The combination of mutations in ABCD1 and DACH2 provides a plausible mechanism for this phenotype.

Heterozygous X-linked adrenoleukodystrophy-associated myelopathy mimicking primary progressive multiple sclerosis

We describe the case of a 73-year-old woman who was referred to our clinic because of a 10-year history of slowly progressive spastic paraparesis. The patient underwent a brain and spinal cord MRI that showed the presence of bihemispheral white matter hyperintensities and of a spinal cord lesion (Fig. 1). She was referred to our clinic because of suspected late-onset primary progressive multiple sclerosis. On admission, a neurologic examination showed the presence of paraparesis, increased leg tone and a spastic gait. All reflexes were brisk and a bilateral Babinski sign was elicited. Diminished sensation of vibration in both legs and bilateral hypoesthesia below the T5 level were present. Results of routine hematologic tests were normal, as were the screenings for autoimmune and infectious conditions (including testing for ANA, LAC, ACA, ANCA and antiborrelia, VDRL, and TPHA serologies). Cerebrospinal fluid isoelectric focusing showed no oligoclonal IgG bands. There was no family history of multiple sclerosis. However, the patient reported that several women (her mother, two sisters and two first-degree nieces) in her family were affected by a slowly progressive form of spastic paraparesis and that two of her brothers died when they were children after having developed motor and cognitive symptoms (Fig. 2). The differential diagnosis of primary progressive multiple sclerosis presenting as progressive spastic paraparesis includes different genetic conditions such as leucodystrophies and hereditary spastic paraplegia [1]. In particular, X-linked adrenoleukodystrophy (X-ALD) is a genetic disorder secondary to alterations in the ABCD1 (ATP-binding cassette, sub-family D, member 1) gene that shows a wide range of phenotypic expression, from a severe cerebral progressive form in childhood to a mild adult myelopathy [2]. For this reason, the molecular analysis of the ABCD1 gene was performed on DNA extracted from peripheral blood of the patient and her relatives, and revealed a heterozygous two base pair deletion at position 1415–1416 in exon 5 (c.1415_1416delAG; p.Gln472ArgfsX83), the most common mutation in X-ALD families [3]. In females heterozygous for X-ALD, neurologic symptoms are frequent [4]. In particular, it is estimated that up to 50% of women who are heterozygous for X-ALD may develop a slowly progressive myelopathy [2]. In contrast to multiple sclerosis, spinal cord involvement in X-ALD is not characterized by an overt inflammatory component [5] and conventional spinal cord MRI usually does not show significant abnormalities other than cord atrophy late in the disease [6]. Similarly, brain MRI abnormalities attributable to ALD are seen on conventional T2-weighted images only in a small number of XALD heterozygotes [6, 7]. In our patient, a hyperintense lesion with more pronounced involvement of the dorsal M. Di Filippo (&) E. Luchetti M. Di Gregorio N. Tambasco P. Sarchielli P. Calabresi Section of Neurology, S. Maria della Misericordia Hospital, University of Perugia, Perugia, Italy e-mail: difilippo@unipg.it