Four-dimensional lipidomics profiling in X-linked adrenoleukodystrophy using trapped ion mobility mass spectrometry.

Lipids play pivotal roles in an extensive range of metabolic and physiological processes. In recent years, the convergence of trapped ion mobility spectrometry and MS has enabled 4D-lipidomics, a highly promising technology for comprehensive lipid analysis. 4D-lipidomics assesses lipid annotations across four distinct dimensions-retention time, collisional cross section, m/z (mass-to-charge ratio), and MS/MS spectra-providing a heightened level of confidence in lipid annotation. These advantages prove particularly valuable when investigating complex disorders involving lipid metabolism, such as adrenoleukodystrophy (ALD). ALD is characterized by the accumulation of very-long-chain fatty acids (VLCFAs) due to pathogenic variants in the ABCD1 gene. A comprehensive 4D-lipidomics strategy of ALD fibroblasts demonstrated significant elevations of various lipids from multiple classes. This indicates that the changes observed in ALD are not confined to a single lipid class and likely impacts a broad spectrum of lipid-mediated physiological processes. Our findings highlight the incorporation of mainly saturated and monounsaturated VLCFA variants into a range of lipid classes, encompassing phosphatidylcholines, triacylglycerols, and cholesterol esters. These include ultra-long-chain fatty acids with a length of up to thirty carbon atoms. Lipid species containing C26:0 and C26:1 were the most frequently detected VLCFA lipids in our study. Furthermore, we report a panel of 121 new candidate biomarkers in fibroblasts, exhibiting significant differentiation between controls and individuals with ALD. In summary, this study demonstrates the capabilities of a 4D-lipid profiling workflow in unraveling novel insights into the intricate lipid modifications associated with metabolic disorders like ALD.

Sex-specific newborn screening for X-linked adrenoleukodystrophy.

Males with X-linked adrenoleukodystrophy (ALD) are at high risk for developing adrenal insufficiency and/or progressive leukodystrophy (cerebral ALD) at an early age. Pathogenic variants in ABCD1 result in elevated levels of very long-chain fatty acids (VLCFA), including C26:0-lysophosphatidylcholine (C26:0-LPC). Newborn screening for ALD enables prospective monitoring and timely therapeutic intervention, thereby preventing irreversible damage and saving lives. The Dutch Health Council recommended to screen only male newborns for ALD without identifying untreatable conditions associated with elevated C26:0-LPC, like Zellweger spectrum disorders and single peroxisomal enzyme defects. Here, we present the results of the SCAN (Screening for ALD in the Netherlands) study which is the first sex-specific newborn screening program worldwide. Males with ALD are identified based on elevated C26:0-LPC levels, the presence of one X-chromosome and a variant in ABCD1, in heel prick dried bloodspots. Screening of 71 208 newborns resulted in the identification of four boys with ALD who, following referral to the pediatric neurologist and confirmation of the diagnosis, enrolled in a long-term follow-up program. The results of this pilot show the feasibility of employing a boys-only screening algorithm that identifies males with ALD without identifying untreatable conditions. This approach will be of interest to countries that are considering ALD newborn screening but are reluctant to identify girls with ALD because for girls there is no direct health benefit. We also analyzed whether gestational age, sex, birth weight and age at heel prick blood sampling affect C26:0-LPC concentrations and demonstrate that these covariates have a minimal effect.

Saturated very long-chain fatty acids regulate macrophage plasticity and invasiveness.

Saturated very long-chain fatty acids (VLCFA, ≥ C22), enriched in brain myelin and innate immune cells, accumulate in X-linked adrenoleukodystrophy (X-ALD) due to inherited dysfunction of the peroxisomal VLCFA transporter ABCD1. In its severest form, X-ALD causes cerebral myelin destruction with infiltration of pro-inflammatory skewed monocytes/macrophages. How VLCFA levels relate to macrophage activation is unclear. Here, whole transcriptome sequencing of X-ALD macrophages indicated that VLCFAs prime human macrophage membranes for inflammation and increased expression of factors involved in chemotaxis and invasion. When added externally to mimic lipid release in demyelinating X-ALD lesions, VLCFAs did not activate toll-like receptors in primary macrophages. In contrast, VLCFAs provoked pro-inflammatory responses through scavenger receptor CD36-mediated uptake, cumulating in JNK signalling and expression of matrix-degrading enzymes and chemokine release. Following pro-inflammatory LPS activation, VLCFA levels increased also in healthy macrophages. With the onset of the resolution, VLCFAs were rapidly cleared in control macrophages by increased peroxisomal VLCFA degradation through liver-X-receptor mediated upregulation of ABCD1. ABCD1 deficiency impaired VLCFA homeostasis and prolonged pro-inflammatory gene expression upon LPS treatment. Our study uncovers a pivotal role for ABCD1, a protein linked to neuroinflammation, and associated peroxisomal VLCFA degradation in regulating macrophage plasticity.

Biochemical Studies in Fibroblasts to Interpret Variants of Unknown Significance in the ABCD1 Gene.

Due to newborn screening for X-linked adrenoleukodystrophy (ALD), and the use of exome sequencing in clinical practice, the detection of variants of unknown significance (VUS) in the ABCD1 gene is increasing. In these cases, functional tests in fibroblasts may help to classify a variant as (likely) benign or pathogenic. We sought to establish reference ranges for these tests in ALD patients and control subjects with the aim of helping to determine the pathogenicity of VUS in ABCD1. Fibroblasts from 36 male patients with confirmed ALD, 26 healthy control subjects and 17 individuals without a family history of ALD, all with an uncertain clinical diagnosis and a VUS identified in ABCD1, were included. We performed a combination of tests: (i) a test for very-long-chain fatty acids (VLCFA) levels, (ii) a D3-C22:0 loading test to study the VLCFA metabolism and (iii) immunoblotting for ALD protein. All ALD patient fibroblasts had elevated VLCFA levels and a reduced peroxisomal ß-oxidation capacity (as measured by the D3-C16:0/D3-C22:0 ratio in the D3-C22:0 loading test) compared to the control subjects. Of the VUS cases, the VLCFA metabolism was not significantly impaired (most test results were within the reference range) in 6/17, the VLCFA metabolism was significantly impaired (most test results were within/near the ALD range) in 9/17 and a definite conclusion could not be drawn in 2/17 of the cases. Biochemical studies in fibroblasts provided clearly defined reference and disease ranges for the VLCFA metabolism. In 15/17 (88%) VUS we were able to classify the variant as being likely benign or pathogenic. This is of great clinical importance as new variants will be detected.

Corrigendum: Adrenoleukodystrophy Newborn Screening in the Netherlands (SCAN Study): The X-Factor.

[This corrects the article DOI: 10.3389/fcell.2020.00499.].

Comparison of the Diagnostic Performance of C26:0-Lysophosphatidylcholine and Very Long-Chain Fatty Acids Analysis for Peroxisomal Disorders.

Peroxisomes are subcellular organelles that are involved in various important physiological processes such as the oxidation of fatty acids and the biosynthesis of bile acids and plasmalogens. The gold standard in the diagnostic work-up for patients with peroxisomal disorders is the analysis of very long-chain fatty acid (VLCFA) levels in plasma. Alternatively, C26:0-lysophosphatidylcholine (C26:0-LPC) can be measured in dried blood spots (DBS) using liquid chromatography tandem mass spectrometry (LC-MS/MS); a fast and easy method but not yet widely used. Currently, little is known about the correlation of C26:0-LPC in DBS and C26:0-LPC in plasma, and how C26:0-LPC analysis compares to VLCFA analysis in diagnostic performance. We investigated the correlation between C26:0-LPC levels measured in DBS and plasma prepared from the same blood sample. For this analysis we included 43 controls and 38 adrenoleukodystrophy (ALD) (21 males and 17 females) and 33 Zellweger spectrum disorder (ZSD) patients. In combined control and patient samples there was a strong positive correlation between DBS C26:0-LPC and plasma C26:0-LPC, with a Spearman's rank correlation coefficient of r (114) = 0.962, p < 0.001. These data show that both plasma and DBS are suitable to determine blood C26:0-LPC levels and that there is a strong correlation between C26:0-LPC levels in both matrices. Following this, we investigated how VLCFA and C26:0-LPC analysis compare in diagnostic performance for 67 controls, 26 ALD males, 19 ALD females, and 35 ZSD patients. For C26:0-LPC, all ALD and ZSD samples had C26:0-LPC levels above the upper limit of the reference range. For C26:0, one out of 67 controls had C26:0 levels above the upper reference range. For 1 out of 26 (1/26) ALD males, 1/19 ALD females and 3/35 ZSD patients, the C26:0 concentration was within the reference range. The C26:0/C22:0 ratio was within the reference range for 0/26 ALD males, 1/19 ALD females and 2/35 ZSD patients. Overall, these data demonstrate that C26:0-LPC analysis has a superior diagnostic performance compared to VLCFA analysis (C26:0 and C26:0/C22:0 ratio) in all patient groups. Based on our results we recommend implementation of C26:0-LPC analysis in DBS and/or plasma in the diagnostic work-up for peroxisomal disorders.

Adrenoleukodystrophy Newborn Screening in the Netherlands (SCAN Study): The X-Factor.

X-linked adrenoleukodystrophy (ALD) is a devastating metabolic disorder affecting the adrenal glands, brain and spinal cord. Males with ALD are at high risk for developing adrenal insufficiency or progressive cerebral white matter lesions (cerebral ALD) at an early age. If untreated, cerebral ALD is often fatal. Women with ALD are not at risk for adrenal insufficiency or cerebral ALD. Newborn screening for ALD in males enables prospective monitoring and timely therapeutic intervention, thereby preventing irreparable damage and saving lives. The Dutch Ministry of Health adopted the advice of the Dutch Health Council to add a boys-only screen for ALD to the newborn screening panel. The recommendation made by the Dutch Health Council to only screen boys, without gathering any unsolicited findings, posed a challenge. We were invited to set up a prospective pilot study that became known as the SCAN study (SCreening for ALD in the Netherlands). The objectives of the SCAN study are: (1) designing a boys-only screening algorithm that identifies males with ALD and without unsolicited findings; (2) integrating this algorithm into the structure of the Dutch newborn screening program without harming the current newborn screening; (3) assessing the practical and ethical implications of screening only boys for ALD; and (4) setting up a comprehensive follow-up that is both patient- and parent-friendly. We successfully developed and validated a screening algorithm that can be integrated into the Dutch newborn screening program. The core of this algorithm is the "X-counter." The X-counter determines the number of X chromosomes without assessing the presence of a Y chromosome. The X-counter is integrated as second tier in our 4-tier screening algorithm. Furthermore, we ensured that our screening algorithm does not result in unsolicited findings. Finally, we developed a patient- and parent-friendly, multidisciplinary, centralized follow-up protocol. Our boys-only ALD screening algorithm offers a solution for countries that encounter similar ethical considerations, for ALD as well as for other X-linked diseases. For ALD, this alternative boys-only screening algorithm may result in a more rapid inclusion of ALD in newborn screening programs worldwide.

Comparison of C26:0-carnitine and C26:0-lysophosphatidylcholine as diagnostic markers in dried blood spots from newborns and patients with adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is the most common leukodystrophy with a birth incidence of 1:14,700 live births. The disease is caused by mutations in ABCD1 and characterized by very long-chain fatty acids (VLCFA) accumulation. In childhood, male patients are at high-risk to develop adrenal insufficiency and/or cerebral demyelination. Timely diagnosis is essential. Untreated adrenal insufficiency can be life-threatening and hematopoietic stem cell transplantation is curative for cerebral ALD provided the procedure is performed in an early stage of the disease. For this reason, ALD is being added to an increasing number of newborn screening programs. ALD newborn screening involves the quantification of C26:0-lysoPC in dried blood spots which requires a dedicated method. C26:0-carnitine, that was recently identified as a potential new biomarker for ALD, has the advantage that it can be added as one more analyte to the routine analysis of amino acids and acylcarnitines already in use. The first objective of this study was a comparison of the sensitivity of C26:0-carnitine and C26:0-lysoPC in dried blood spots from control and ALD newborns both in a case-control study and in newborns included in the New York State screening program. While C26:0-lysoPC was elevated in all ALD newborns, C26:0-carnitine was elevated only in 83%. Therefore, C26:0-carnitine is not a suitable biomarker to use in ALD newborn screen. In women with ALD, plasma VLCFA analysis results in a false negative result in approximately 15-20% of cases. The second objective of this study was to compare plasma VLCFA analysis with C26:0-carnitine and C26:0-lysoPC in dried blood spots of women with ALD. Our results show that C26:0-lysoPC was elevated in dried blood spots from all women with ALD, including from those with normal plasma C26:0 levels. This shows that C26:0-lysoPC is a better and more accurate biomarker for ALD than plasma VLCFA levels. We recommend that C26:0-lysoPC be added to the routine biochemical array of diagnostic tests for peroxisomal disorders.

Method for Measurement of Peroxisomal Very Long-Chain Fatty Acid Beta-Oxidation and De Novo C26:0 Synthesis Activity in Living Cells Using Stable-Isotope Labeled Docosanoic Acid.

Peroxisomes are present in virtually every eukaryotic cell type with the exception of the mature erythrocyte. In higher eukaryotes, one of the main functions of peroxisomes is lipid metabolism by means of beta-oxidation of very long-chain fatty acids (VLCFA; ≥22 carbon atoms). A dysfunction in peroxisomal VLCFA beta-oxidation results in elevated VLCFA levels in cells, tissue, and plasma. Here, we describe a straightforward and sensitive method to measure peroxisomal beta-oxidation capacity in living cells using stable-isotope labeled docosanoic acid (D3-C22:0).

CYP4F2 affects phenotypic outcome in adrenoleukodystrophy by modulating the clearance of very long-chain fatty acids.

X-linked adrenoleukodystrophy (ALD) is a severe neurodegenerative disorder caused by the accumulation of very long-chain fatty acids (VLCFA) due to mutations in the ABCD1 gene. The phenotypic spectrum ranges from a fatal cerebral demyelinating disease in childhood (cerebral ALD) to a progressive myelopathy without cerebral involvement in adulthood (adrenomyeloneuropathy). Because ABCD1 mutations have no predictive value with respect to clinical outcome a role for modifier genes was postulated. We report that the CYP4F2 polymorphism rs2108622 increases the risk of developing cerebral ALD in Caucasian patients. The rs2108622 polymorphism (c.1297G>A) results in an amino acid substitution valine for methionine at position 433 (p.V433M). Using cellular models of VLCFA accumulation, we show that p.V433M decreases the conversion of VLCFA into very long-chain dicarboxylic acids by ω-oxidation, a potential escape route for the deficient peroxisomal ß-oxidation of VLCFA in ALD. Although p.V433M does not affect the catalytic activity of CYP4F2 it reduces CYP4F2 protein levels markedly. These findings open perspectives for therapeutic interventions in a disease with currently limited treatment options.

Pathogenicity of novel ABCD1 variants: The need for biochemical testing in the era of advanced genetics.

X-linked adrenoleukodystrophy (ALD), a progressive neurodegenerative disease, is caused by mutations in ABCD1 and characterized by very-long-chain fatty acids (VLCFA) accumulation. In male patients, an increased plasma VLCFA levels in combination with a pathogenic mutation in ABCD1 confirms the diagnosis. Recent studies have shown that many women with ALD also develop myelopathy. Correct diagnosis is important for management including genetic counseling. Diagnosis in women can only be confirmed when VLCFA levels are elevated or when a known pathogenic ABCD1 mutation is identified. However, in 15-20% of women with ALD VLCFA plasma levels are not elevated. Demonstration that a novel sequence variant is pathogenic can be a challenge when VLCFA levels are in the normal range. Here we report two women with a clinical presentation compatible with ALD, an ABCD1 variation (p.Arg17His and p.Ser358Pro) of unknown significance, but with normal VLCFA levels. We developed a diagnostic test that is based on generating clonal cell lines that express only one of the two alleles. Subsequent biochemical studies enabled us to show that the two sequence variants were not pathogenic, thereby excluding the diagnosis ALD in these women. We conclude that the clonal approach is an important addition to the existing diagnostic array.

C26:0-Carnitine Is a New Biomarker for X-Linked Adrenoleukodystrophy in Mice and Man.

X-linked adrenoleukodystrophy (ALD), a progressive neurodegenerative disease, is caused by mutations in ABCD1 and characterized by very-long-chain fatty acids (VLCFA) accumulation. Virtually all males develop progressive myelopathy (AMN). A subset of patients, however, develops a fatal cerebral demyelinating disease (cerebral ALD). Hematopoietic stem cell transplantation is curative for cerebral ALD provided the procedure is performed in an early stage of the disease. Unfortunately, this narrow therapeutic window is often missed. Therefore, an increasing number of newborn screening programs are including ALD. To identify new biomarkers for ALD, we developed an Abcd1 knockout mouse with enhanced VLCFA synthesis either ubiquitous or restricted to oligodendrocytes. Biochemical analysis revealed VLCFA accumulation in different lipid classes and acylcarnitines. Both C26:0-lysoPC and C26:0-carnitine were highly elevated in brain, spinal cord, but also in bloodspots. We extended the analysis to patients and confirmed that C26:0-carnitine is also elevated in bloodspots from ALD patients. We anticipate that validation of C26:0-carnitine for the diagnosis of ALD in newborn bloodspots may lead to a faster inclusion of ALD in newborn screening programs in countries that already screen for other inborn errors of metabolism.

Enzymatic characterization of ELOVL1, a key enzyme in very long-chain fatty acid synthesis.

X-linked adrenoleukodystrophy (X-ALD) is a neurometabolic disease that is caused by mutations in the ABCD1 gene. ABCD1 protein deficiency impairs peroxisomal very long-chain fatty acid (VLCFA) degradation resulting in increased cytosolic VLCFA-CoA levels, which are further elongated by the VLCFA-specific elongase, ELOVL1. In adulthood, X-ALD most commonly manifests as a gradually progressive myelopathy (adrenomyeloneuropathy; AMN) without any curative or disease modifying treatments. We recently showed that bezafibrate reduces VLCFA accumulation in X-ALD fibroblasts by inhibiting ELOVL1. Although, in a clinical trial, bezafibrate was unable to lower VLCFA levels in plasma or lymphocytes in X-ALD patients, inhibition of ELOVL1 remains an attractive therapeutic option. In this study, we investigated the kinetic characteristics of ELOVL1 using X-ALD fibroblasts and microsomal fractions from ELOVL1 over-expressing HEK293 cell lines and analyzed the inhibition kinetics of a series of fibrates. Our data show that the CoA esters of bezafibrate and gemfibrozil reduce chain elongation by specifically inhibiting ELOVL1. These fibrates can therefore serve as lead compounds for the development of more potent and more specific inhibitors for ELOVL1.

X-linked adrenoleukodystrophy in women: a cross-sectional cohort study.

X-linked adrenoleukodystrophy is the most common peroxisomal disorder. The disease is caused by mutations in the ABCD1 gene that encodes the peroxisomal transporter of very long-chain fatty acids. A defect in the ABCD1 protein results in elevated levels of very long-chain fatty acids in plasma and tissues. The clinical spectrum in males with X-linked adrenoleukodystrophy has been well described and ranges from isolated adrenocortical insufficiency and slowly progressive myelopathy to devastating cerebral demyelination. As in many X-linked diseases, it was assumed that female carriers remain asymptomatic and only a few studies addressed the phenotype of X-linked adrenoleukodystrophy carriers. These studies, however, provided no information on the prevalence of neurological symptoms in the entire population of X-linked adrenoleukodystrophy carriers, since data were acquired in small groups and may be biased towards women with symptoms. Our primary goal was to investigate the symptoms and their frequency in X-linked adrenoleukodystrophy carriers. The secondary goal was to determine if the X-inactivation pattern of the ABCD1 gene was associated with symptomatic status. We included 46 X-linked adrenoleukodystrophy carriers in a prospective cross-sectional cohort study. Our data show that X-linked adrenoleukodystrophy carriers develop signs and symptoms of myelopathy (29/46, 63%) and/or peripheral neuropathy (26/46, 57%). Especially striking was the occurrence of faecal incontinence (13/46, 28%). The frequency of symptomatic women increased sharply with age (from 18% in women <40 years to 88% in women >60 years of age). Virtually all (44/45, 98%) X-linked adrenoleukodystrophy carriers had increased very long-chain fatty acids in plasma and/or fibroblasts, and/or decreased very long-chain fatty acids beta-oxidation in fibroblasts. We did not find an association between the X-inactivation pattern and symptomatic status. We conclude that X-linked adrenoleukodystrophy carriers develop an adrenomyeloneuropathy-like phenotype and there is a strong association between symptomatic status and age. X-linked adrenoleukodystrophy should be considered in the differential diagnosis in women with chronic myelopathy and/or peripheral neuropathy (especially with early faecal incontinence). ABCD1 mutation analysis deserves a place in diagnostic protocols for chronic non-compressive myelopathy.

Bezafibrate for X-linked adrenoleukodystrophy.

UNLABELLED: X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene and is characterized by impaired beta-oxidation of very-long-chain fatty acids (VLCFA) and subsequent VLCFA accumulation in tissues. In adulthood X-ALD most commonly manifests as a gradually progressive myelopathy, (adrenomyeloneuropathy; AMN) without any curative or disease modifying treatments. We recently showed that bezafibrate (BF), a drug used for the treatment of hyperlipidaemia, reduces VLCFA accumulation in X-ALD fibroblasts by inhibiting ELOVL1, an enzyme involved in the VLCFA synthesis. We therefore designed a proof-of-principal clinical trial to determine whether BF reduces VLCFA levels in plasma and lymphocytes of X-ALD patients. Ten males with AMN were treated with BF for 12 weeks at a dose of 400 mg daily, followed by 12 weeks of 800 mg daily. Every 4 weeks patients were evaluated for side effects and blood samples were taken for analysis. Adherence was good as indicated by a clear reduction in triglycerides. There was no reduction in VLCFA in either plasma or lymphocytes. Plasma levels of BF did not exceed 25 µmol/L. We concluded that BF, at least in the dose given, is unable to lower VLCFA levels in plasma or lymphocytes in X-ALD patients. It is unclear whether this is due to the low levels of BF reached in plasma. Our future work is aimed at the identification of highly-specific inhibitors of ELOVL1 that act at much lower concentrations than BF and are well tolerated. BF appears to have no therapeutic utility in X-ALD. TRIAL REGISTRATION: ClinicalTrials.gov NCT01165060.

Bezafibrate lowers very long-chain fatty acids in X-linked adrenoleukodystrophy fibroblasts by inhibiting fatty acid elongation.

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene encoding ALDP, an ATP-binding-cassette (ABC) transporter located in the peroxisomal membrane. ALDP deficiency results in impaired peroxisomal ß-oxidation and the subsequent accumulation of very long-chain fatty acids (VLCFA; > C22:0) in plasma and tissues. VLCFA are primarily derived from endogenous synthesis by ELOVL1. Therefore inhibiting this enzyme might constitute a feasible therapeutic approach. In this paper we demonstrate that bezafibrate, a PPAR pan agonist used for the treatment of patients with hyperlipidaemia reduces VLCFA levels in X-ALD fibroblasts. Surprisingly, the VLCFA-lowering effect was independent of PPAR activation and not caused by the increase in either mitochondrial or peroxisomal fatty acid ß-oxidation capacity. In fact, our results show that bezafibrate reduces VLCFA synthesis by decreasing the synthesis of C26:0 through a direct inhibition of fatty acid elongation activity. Taken together, our data indicate bezafibrate as a potential pharmacotherapeutic treatment for X-ALD. A clinical trial is currently ongoing to evaluate the effect in patients with X-ALD.

The role of ELOVL1 in very long-chain fatty acid homeostasis and X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene encoding the peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). X-ALD is characterized by the accumulation of very long-chain fatty acids (VLCFA; > or =C24) in plasma and tissues. In this manuscript we provide insight into the pathway underlying the elevated levels of C26:0 in X-ALD. ALDP transports VLCFacyl-CoA across the peroxisomal membrane. A deficiency in ALDP impairs peroxisomal beta-oxidation of VLCFA but also raises cytosolic levels of VLCFacyl-CoA which are substrate for further elongation. We identify ELOVL1 (elongation of very-long-chain-fatty acids) as the single elongase catalysing the synthesis of both saturated VLCFA (C26:0) and mono-unsaturated VLCFA (C26:1). ELOVL1 expression is not increased in X-ALD fibroblasts suggesting that increased levels of C26:0 result from increased substrate availability due to the primary deficiency in ALDP. Importantly, ELOVL1 knockdown reduces elongation of C22:0 to C26:0 and lowers C26:0 levels in X-ALD fibroblasts. Given the likely pathogenic effects of high C26:0 levels, our findings highlight the potential of modulating ELOVL1 activity in the treatment of X-ALD.