X-linked adrenoleukodystrophy: Very long-chain fatty acid metabolism, ABC half-transporters and the complicated route to treatment

Diagnosing X-Linked Adrenoleukodystrophy after Implementation of Newborn Screening: A Reference Laboratory Perspective

Adrenoleukodystrophy (ALD) is caused by pathogenic variants in the ABCD1 gene, encoding for the adrenoleukodystrophy protein (ALDP), leading to defective peroxisomal β-oxidation of very long-chain and branched-chain fatty acids (VLCFA). ALD manifests in both sexes with a spectrum of phenotypes, but approximately 35% of affected males develop childhood cerebral adrenoleukodystrophy (CCALD), which is lethal without hematopoietic stem cell transplant performed before symptoms start. Hence, ALD was added to the Recommended Uniform Screening Panel after the successful implementation in New York State (2013-2016). To date, thirty-five states have implemented newborn screening (NBS) for ALD, and a few programs have reported on the successes and challenges experienced. However, the overall impact of NBS on early detection of ALD has yet to be fully determined. Here, we conducted a retrospective analysis of VLCFA testing performed by our reference laboratory (ARUP Laboratories, Salt Lake City, UT, USA) over 10 years. Rate of detection, age at diagnosis, and male-to-female ratio were evaluated in patients with abnormal results before and after NBS implementation. After NBS inclusion, a significant increase in abnormal results was observed (471/6930, 6.8% vs. 384/11,670, 3.3%; p < 0.0001). Patients with ALDP deficiency identified via NBS were significantly younger (median age: 30 days vs. 21 years; p < 0.0001), and males and females were equally represented. ALD inclusion in NBS programs has increased pre-symptomatic detection of this disease, which is critical in preventing adrenal crisis as well as the severe cerebral form.

Role of 2-hydroxy acyl-CoA lyase HACL2 in odd-chain fatty acid production via α-oxidation in vivo

Although most fatty acids (FAs) are even chain, certain tissues, including brain, contain relatively large quantities of odd-chain FAs in their sphingolipids. One of the pathways producing odd-chain FAs is the α-oxidation of 2-hydroxy (2-OH) FAs, where 2-OH acyl-CoA lyases (HACL1 and HACL2) catalyze the key cleavage reaction. However, the contribution of each HACL to odd-chain FA production in vivo remains unknown. Here, we found that HACL2 and HACL1 play major roles in the α-oxidation of 2-OH FAs (especially very-long-chain types) and 3-methyl FAs (other α-oxidation substrates), respectively, using ectopic expression systems of human HACL2 and HACL1 in yeast and analyzing Hacl1 and/or Hacl2 knockout (KO) CHO-K1 cells. We then generated Hacl2 KO mice and measured the quantities of odd-chain and 2-OH lipids (free FAs and sphingolipids [ceramides, sphingomyelins, and monohexosylceramides]) in 17 tissues. We observed fewer odd-chain lipids and more 2-OH lipids in many tissues of Hacl2 KO mice than in wild-type mice, and of these differences the reductions were most prominent for odd-chain monohexosylceramides in the brain and ceramides in the stomach. These results indicate that HACL2-involved α-oxidation of 2-OH FAs is mainly responsible for odd-chain FA production in the brain and stomach.

Structure and Mechanism of Human ABC Transporters

ABC transporters are essential for cellular physiology. Humans have 48 ABC genes organized into seven distinct families. Of these genes, 44 (in five distinct families) encode for membrane transporters, of which several are involved in drug resistance and disease pathways resulting from transporter dysfunction. Over the last decade, advances in structural biology have vastly expanded our mechanistic understanding of human ABC transporter function, revealing details of their molecular arrangement, regulation, and interactions, facilitated in large part by advances in cryo-EM that have rendered hitherto inaccessible targets amenable to high-resolution structural analysis. As a result, experimentally determined structures of multiple members of each of the five families of ABC transporters in humans are now available. Here we review this recent progress, highlighting the physiological relevance of human ABC transporters and mechanistic insights gleaned from their direct structure determination. We also discuss the impact and limitations of model systems and structure prediction methods in understanding human ABC transporters and discuss current challenges and future research directions.

Newborn screening for X-linked adrenoleukodystrophy in Italy: Diagnostic algorithm and disease monitoring

Introduction

X-linked adrenoleukodystrophy (X-ALD) is the most common inherited peroxisomal disorder caused by variants in the ABCD1 gene. The main phenotypes observed in men with X-ALD are primary adrenal insufficiency, adrenomyeloneuropathy, and cerebral ALD (cALD). Cerebral ALD consists of a demyelinating progressive cerebral white matter (WM) disease associated with rapid clinical decline and is fatal if left untreated. Hematopoietic stem cell transplantation is the standard treatment for cALD as it stabilizes WM degeneration when performed early in the disease. For this reason, early diagnosis is crucial, and several countries have already implemented their newborn screening programs (NBS) with the assessment of C26:0-lysophosphatidylcholine (C26:0-LPC) values as screening for X-ALD.

Methods

In June 2021, an Italian group in Lombardy launched a pilot study for the implementation of X-ALD in the Italian NBS program. A three-tiered approach was adopted, and it involved quantifying the values of C26:0-LPC and other metabolites in dried blood spots with FIA-MS/MS first, followed by the more specific ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) technique and, finally, the genetic confirmation via focused NGS.

Discussion

Genetically confirmed patients are set to undergo a follow-up protocol and are periodically evaluated to promptly start a specific treatment if and when the first signs of brain damage appear, as suggested by international guidelines. A specific disease monitoring protocol has been created based on literature data and personal direct experience.

Conclusion

The primary aim of this study was to develop a model able to improve the early diagnosis and subsequent follow-up and timely treatment of X-ALD.

Ethics

The study was approved by the local ethics committee. The research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest.

[X-Linked Adrenoleukodystrophy or the Management of Rare Diseases in the General Practice]

X-Linked Adrenoleukodystrophy or the Management of Rare Diseases in the General Practice Abstract. We report on a 48-year-old patient with X-linked adrenoleukodystrophy with slowly progressive leg-accentuated spastic paraparesis, vegetative dysfunction with bladder and sexual dysfunction, and primary adrenal insufficiency. The diagnosis of adrenomyeloneuropathy, the adult form of adrenoleukodystrophy, and Addison's disease was made at the age of 20 by evidence of an increased concentration of long-chain fatty acids in the plasma. The therapy is symptom-oriented.

The Mystery of Extramitochondrial Proteins Lysine Succinylation

Lysine succinylation is a post-translational modification which alters protein function in both physiological and pathological processes. Mindful that it requires succinyl-CoA, a metabolite formed within the mitochondrial matrix that cannot permeate the inner mitochondrial membrane, the question arises as to how there can be succinylation of proteins outside mitochondria. The present mini-review examines pathways participating in peroxisomal fatty acid oxidation that lead to succinyl-CoA production, potentially supporting succinylation of extramitochondrial proteins. Furthermore, the influence of the mitochondrial status on cytosolic NAD⁺ availability affecting the activity of cytosolic SIRT5 iso1 and iso4—in turn regulating cytosolic protein lysine succinylations—is presented. Finally, the discovery that glia in the adult human brain lack subunits of both alpha-ketoglutarate dehydrogenase complex and succinate-CoA ligase—thus being unable to produce succinyl-CoA in the matrix—and yet exhibit robust pancellular lysine succinylation, is highlighted.

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.

A defect in the peroxisomal biogenesis in germ cells induces a spermatogenic arrest at the round spermatid stage in mice

Peroxisomes are involved in the degradation of very long-chain fatty acids (VLCFAs) by β-oxidation. Besides neurological defects, peroxisomal dysfunction can also lead to testicular abnormalities. However, underlying alterations in the testes due to a peroxisomal defect are not well characterized yet. To maintain all metabolic functions, peroxisomes require an import machinery for the transport of matrix proteins. One component of this translocation machinery is PEX13. Its inactivation leads to a peroxisomal biogenesis defect. We have established a germ cell-specific KO of Pex13 to study the function of peroxisomes during spermatogenesis in mice. Exon 2 of floxed Pex13 was specifically excised in germ cells prior to meiosis by using a transgenic mouse strain carrying a STRA8 inducible Cre recombinase. Germ cell differentiation was interrupted at the round spermatid stage in Pex13 KO mice with formation of multinucleated giant cells (MNCs) and loss of mature spermatids. Due to a different cellular content in the germinal epithelium of Pex13 KO testes compared to control, whole testes biopsies were used for the analyses. Thus, differences in lipid composition and gene expression are only shown for whole testicular tissue but cannot be limited to single cells. Gas chromatography revealed an increase of shorter fatty acids and a decrease of n-6 docosapentaenoic acid (C22:5n-6) and n-3 docosahexaenoic acid (C22:6n-3), the main components of sperm plasma membranes. Representative genes of the metabolite transport and peroxisomal β-oxidation were strongly down-regulated. In addition, structural components of the blood-testis barrier (BTB) were altered. To conclude, defects in the peroxisomal compartment interfere with normal spermatogenesis.

Metabolic dysfunctions in multiple sclerosis: implications as to causation, early detection, and treatment, a case control study

Background

Biochemical changes associated with multiple sclerosis (MS), and its various clinical forms have not been characterized well. Therefore, we investigated the biochemistry of MS in relation to its natural history using targeted lipidomics platforms.

Methods

Cross-sectional serum samples from 24 secondary progressive (SPMS), 100 relapsing remitting (RRMS), 19 primary progressive MS (PPMS), and 55 age-matched control subjects were analyzed by flow injection tandem mass spectrometry for very long chain fatty acid (VLCFA) containing phosphatidyl ethanolamines (PtdEtn), plasmalogen ethanolamines (PlsEtn) and for novel anti-inflammatory gastrointestinal tract acids (GTAs). Changes in analyte levels relative to healthy controls were correlated with the disease stage and disease duration.

Results

RRMS subjects having <13 years disease duration had elevated levels (p < 0.05) of anti-inflammatory metabolites (GTAs) and normal levels (p > 0.05) of mitochondrial stress biomarkers (VLCFA-PtdEtn), compared to controls. SPMS subjects had statistically similar levels of anti-inflammatory metabolites (GTAs), elevated mitochondrial stress metabolites (VLCFA-PtdEtn) and elevated peroxisomal metabolites (PlsEtn) compared to controls (p < 0.05). RRMS subjects with > = 13 years disease duration exhibited metabolic profiles intermediate between short-duration RRMS and SPMS, based on statistical significance. Therefore, RRMS cohort appear to comprise of two metabolically distinct subpopulations. The key clinical discriminator of these two groups was disease duration. PPMS patients exhibited metabolic profiles distinct from RRMS and SPMS.

Conclusions

These data indicate that inflammation and mitochondrial stress are intricately involved in the etiology of MS and that progression in MS can potentially be monitored using serum metabolic biomarkers.

Novel insight into etiology, diagnosis and management of primary adrenal insufficiency

Primary adrenal insufficiency (PAI) is a rare condition in childhood which is either inherited (mostly) or acquired. It is characterized by glucocorticoid and maybe mineralocorticoid deficiency. The most common form in children is 21-hydroxylase deficiency, which belongs to the steroid biosynthetic defects causing PAI. Newer forms of complex defects of steroid biosynthesis are P450 oxidoreductase deficiency and (apparent) cortisone reductase deficiency. Other forms of PAI include metabolic disorders, autoimmune disorders and adrenal dysgenesis, e.g. the IMAGe syndrome, for which the underlying genetic defect has been recently identified. Newer work has also expanded the genetic causes underlying isolated, familial glucocorticoid deficiency (FGD). Mild mutations of CYP11A1 or StAR have been identified in patients with FGD. MCM4 mutations were found in a variant of FGD in an Irish travelling community manifesting with PAI, short stature, microcephaly and recurrent infections. Finally, mutations in genes involved in the detoxification of reactive oxygen species were identified in patients with unsolved FGD. Most mutations were found in the enzyme nicotinamide nucleotide transhydrogenase, which uses the mitochondrial proton pump gradient to produce NADPH. NADPH is essential in maintaining high levels of reduced forms of antioxidant enzymes for the reduction of hydrogen peroxide. Similarly, mutations in the gene for TXNRD2 involved in this system were found in FGD patients, suggesting that the adrenal cortex is particularly susceptible to oxidative stress.

Identification of reference genes in human myelomonocytic cells for gene expression studies in altered gravity

Gene expression studies are indispensable for investigation and elucidation of molecular mechanisms. For the process of normalization, reference genes (“housekeeping genes”) are essential to verify gene expression analysis. Thus, it is assumed that these reference genes demonstrate similar expression levels over all experimental conditions. However, common recommendations about reference genes were established during 1 g conditions and therefore their applicability in studies with altered gravity has not been demonstrated yet. The microarray technology is frequently used to generate expression profiles under defined conditions and to determine the relative difference in expression levels between two or more different states. In our study, we searched for potential reference genes with stable expression during different gravitational conditions (microgravity, normogravity, and hypergravity) which are additionally not altered in different hardware systems. We were able to identify eight genes (ALB, B4GALT6, GAPDH, HMBS, YWHAZ, ABCA5, ABCA9, and ABCC1) which demonstrated no altered gene expression levels in all tested conditions and therefore represent good candidates for the standardization of gene expression studies in altered gravity.

The genetically modified polysialylated form of neural cell adhesion molecule-positive cells for potential treatment of X-linked adrenoleukodystrophy

PURPOSE

Cell transplantation of myelin-producing exogenous cells is being extensively explored as a means of remyelinating axons in X-linked adrenoleukodystrophy. We determined whether 3,3',5-Triiodo-L-thyronine (T3) overexpresses the ABCD2 gene in the polysialylated (PSA) form of neural cell adhesion molecule (NCAM)-positive cells and promotes cell proliferation and favors oligodendrocyte lineage differentiation.

MATERIALS AND METHODS

PSA-NCAM+ cells from newborn Sprague-Dawley rats were grown for five days on uncoated dishes in defined medium with or without supplementation of basic fibroblast growth factor (bFGF) and/or T3. Then, PSA-NCAM+ spheres were prepared in single cells and transferred to polyornithine/fibronectin-coated glass coverslips for five days to determine the fate of the cells according to the supplementation of these molecules. T3 responsiveness of ABCD2 was analyzed using real-time quantitative polymerase chain reaction, the growth and fate of cells were determined using 5-bromo-2-deoxyuridine incorporation and immunocytochemistry, respectively.

RESULTS

Results demonstrated that T3 induces overexpression of the ABCD2 gene in PSA-NCAM+ cells, and can enhance PSA-NCAM+ cell growth in the presence of bFGF, favoring an oligodendrocyte fate.

CONCLUSION

These results may provide new insights into investigation of PSA-NCAM+ cells for therapeutic application to X-linked adrenoleukodystrophy.

Induced pluripotent stem cells to model and treat neurogenetic disorders

Remarkable advances in cellular reprogramming have made it possible to generate pluripotent stem cells from somatic cells, such as fibroblasts obtained from human skin biopsies. As a result, human diseases can now be investigated in relevant cell populations derived from induced pluripotent stem cells (iPSCs) of patients. The rapid growth of iPSC technology has turned these cells into multipurpose basic and clinical research tools. In this paper, we highlight the roles of iPSC technology that are helping us to understand and potentially treat neurological diseases. Recent studies using iPSCs to model various neurogenetic disorders are summarized, and we discuss the therapeutic implications of iPSCs, including drug screening and cell therapy for neurogenetic disorders. Although iPSCs have been used in animal models with promising results to treat neurogenetic disorders, there are still many issues associated with reprogramming that must be addressed before iPSC technology can be fully exploited with translation to the clinic.

Reproductive function in men affected by X-linked adrenoleukodystrophy/adrenomyeloneuropathy

BACKGROUND

X-linked adrenoleukodystrophy (X-ALD) is the most frequent, severely neurodegenerative, clinically heterogeneous peroxisomal disorder, the signs of which are a consequence of myelin, adrenal cortex, and testes impairment.

OBJECTIVE

We studied testosterone, LH, and FSH levels in X-ALD/adrenomyeloneuropathy (AMN) patients. We evaluate the ability to procreate of these patients by analysis of pedigree and family screening by detection of very long-chain fatty acid (VLCFA) levels.

SUBJECT AND METHODS

Seventeen patients with X-ALD/AMN (16 with AMN and one asymptomatic) aged 24-48 (mean±S.D., 34.7±5.9) years, were identified based on the clinical picture, magnetic resonance imaging, and the presence of increased serum VLCFA levels. Nine X-ALD/AMN patients' daughters, mean ages ±S.D.=7.7±3.8 years, were identified as heterozygote by elevated VLCFA levels. Serum VLCFA levels were determined as ester derivatives by a gas chromatography method. Serum testosterone, LH, and FSH levels in X-ALD/AMN patients were detected by IRMAs.

RESULTS

Serum testosterone levels were at the lowest levels of normal range but serum LH and FSH concentrations were increased in 57.1 and in 42.9% of X-ALD/AMN patients respectively. Among the 11 investigated of X-ALD/AMN married adult men, nine had produced offspring, a total of 13 children. All patients' daughters showed elevated serum VLCFA at heterozygote levels.

CONCLUSION

In this study, we report that in a group of X-ALD/AMN married adult men, we did not find a significant decrease in fertility compared with the Polish population (18.2 vs 15%).

Identification of a new fatty acid synthesis-transport machinery at the peroxisomal membrane

The neurodegenerative disease X-linked adrenoleukodystrophy (X-ALD) is characterized by the abnormal accumulation of very long chain fatty acids. Mutations in the gene encoding the peroxisomal ATP-binding cassette half-transporter, adrenoleukodystrophy protein (ALDP), are the primary cause of X-ALD. To gain a better understanding of ALDP dysfunction, we searched for interaction partners of ALDP and identified binary interactions to proteins with functions in fatty acid synthesis (ACLY, FASN, and ACC) and activation (FATP4), constituting a thus far unknown fatty acid synthesis-transport machinery at the cytoplasmic side of the peroxisomal membrane. This machinery adds to the knowledge of the complex mechanisms of peroxisomal fatty acid metabolism at a molecular level and elucidates potential epigenetic mechanisms as regulatory processes in the pathogenesis and thus the clinical course of X-ALD.

Germ cells of male mice express genes for peroxisomal metabolic pathways implicated in the regulation of spermatogenesis and the protection against oxidative stress

Peroxisomes are organelles with main functions in the metabolism of lipids and of reactive oxygen species. Within the testis, they have different functional profiles depending on the cell types. A dysfunction of peroxisomes interferes with regular spermatogenesis and can lead to infertility due to spermatogenic arrest. However, so far only very little is known about the functions of peroxisomes in germ cells. We have therefore analyzed the peroxisomal compartment in germ cells and its alterations during spermatogenesis by fluorescence and electron microscopy as well as by expression profiling of peroxisome-related genes in purified cell populations isolated from mouse testis. We could show that peroxisomes are present in all germ cells of the germinal epithelium. During late spermiogenesis, the peroxisomes form large clusters that are segregated from the spermatozoa into the residual bodies upon release from the germinal epithelium. Germ cells express genes for proteins involved in numerous metabolic pathways of peroxisomes. Based on the expression profile, we conclude that newly identified functions of germ cell peroxisomes are the synthesis of plasmalogens as well as the metabolism of retinoids, polyunsaturated fatty acids and polyamines. Thus, germ cell peroxisomes are involved in the regulation of the homeostasis of signaling molecules regulating spermatogenesis and they contribute to the protection of germ cells against oxidative stress.

HDAC inhibitor SAHA normalizes the levels of VLCFAs in human skin fibroblasts from X-ALD patients and downregulates the expression of proinflammatory cytokines in Abcd1/2-silenced mouse astrocytes

X-adrenoleukodystrophy (X-ALD) is a peroxisomal metabolic disorder caused by mutations in the ABCD1 gene encoding the peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). The consistent metabolic abnormality in all forms of X-ALD is an inherited defect in the peroxisomal β-oxidation of very long chain FAs (VLCFAs >C22:0) and the resultant pathognomic accumulation of VLCFA. The accumulation of VLCFA leads to a neuroinflammatory disease process associated with demyelination of the cerebral white matter. The present study underlines the importance of a potent histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA) in inducing the expression of ABCD2 [adrenoleukodystrophy-related protein (ALDRP)], and normalizing the peroxisomal β-oxidation, as well as the saturated and monounsaturated VLCFAs in cultured human skin fibroblasts of X-ALD patients. The expression of ELOVL1, the single elongase catalyzing the synthesis of both saturated VLCFA (C26:0) and monounsaturated VLCFA (C26:1), was also reduced by SAHA treatment. In addition, using Abcd1/Abcd2-silenced mouse primary astrocytes, we also examined the effects of SAHA in VLCFA-induced inflammatory response. SAHA treatment decreased the inflammatory response as expression of inducible nitric oxide synthase, inflammatory cytokine, and activation of NF-κB in Abcd1/Abcd2-silenced mouse primary astrocytes was reduced. These observations indicate that SAHA corrects both the metabolic disease of VLCFA as well as secondary inflammatory disease; therefore, it may be an ideal drug candidate to be tested for X-ALD therapy in humans.

Conservation of targeting but divergence in function and quality control of peroxisomal ABC transporters: an analysis using cross-kingdom expression

ABC (ATP-binding cassette) subfamily D transporters are found in all eukaryotic kingdoms and are known to play essential roles in mammals and plants; however, their number, organization and physiological contexts differ. Via cross-kingdom expression experiments, we have explored the conservation of targeting, protein stability and function between mammalian and plant ABCD transporters. When expressed in tobacco epidermal cells, the mammalian ABCD proteins ALDP (adrenoleukodystrophy protein), ALDR (adrenoleukodystrophy-related protein) and PMP70 (70 kDa peroxisomal membrane protein) targeted faithfully to peroxisomes and P70R (PMP70-related protein) targeted to the ER (endoplasmic reticulum), as in the native host. The Arabidopsis thaliana peroxin AtPex19_1 interacted with human peroxisomal ABC transporters both in vivo and in vitro, providing an explanation for the fidelity of targeting. The fate of X-linked adrenoleukodystrophy disease-related mutants differed between fibroblasts and plant cells. In fibroblasts, levels of ALDP in some 'protein-absent' mutants were increased by low-temperature culture, in some cases restoring function. In contrast, all mutant ALDP proteins examined were stable and correctly targeted in plant cells, regardless of their fate in fibroblasts. ALDR complemented the seed germination defect of the Arabidopsis cts-1 mutant which lacks the peroxisomal ABCD transporter CTS (Comatose), but neither ALDR nor ALDP was able to rescue the defect in fatty acid β-oxidation in establishing seedlings. Taken together, our results indicate that the mechanism for trafficking of peroxisomal membrane proteins is shared between plants and mammals, but suggest differences in the sensing and turnover of mutant ABC transporter proteins and differences in substrate specificity and/or function.

Endocrine, metabolic, nutritional, and toxic disorders leading to dementia

One of the first steps toward the correct diagnosis of dementia is to segregate out the nondegenerative dementias from possible degenerative dementias. Nondegenerative dementias could be due to traumatic, endocrine, metabolic, nutritional, toxic, infective, and immunological causes. They could also be caused by tumors, subdural hematomas, and normal pressure hydrocephalus. Many of the nondegenerative dementias occur at an earlier age and often progress quickly compared to Alzheimer’s disease and other degenerative dementias. Many are treatable or preventable with simple measures. This review aims to give an overview of some of the more important endocrine, metabolic, nutritional, and toxic disorders that may lead to dementia.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Myelin lesions associated with lysosomal and peroxisomal disorders

Abnormalities of myelin are common in lysosomal and peroxisomal disorders. Most display a primary loss of myelin in which the myelin sheath and/or oligodendrocytes are selectively targeted by diverse pathogenetic processes. The most severe and, hence, clinically relevant are heritable diseases predominantly of infants and children, the leukodystrophies: metachromatic, globoid cell (Krabbe disease) and adreno-leukodystrophy. Our still limited understanding of these diseases has derived from multiple sources: originally, neurological-neuropathologic-neurochemical correlative studies of the natural disease in humans or other mammals, which has been enhanced by more sophisticated and contemporary techniques of cell and molecular biology. Transgenic mouse models seem to be the most promising methodology, allowing the examination of the cellular role of lysosomes and peroxisomes for formation and maintenance of both myelin and axons, and providing initial platforms to evaluate therapies. Treatment options are woefully inadequate and in their nascent stages, but still inspire some hope for the future.

Biochemical aspects of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. The disease is characterized by the accumulation of very long-chain fatty acids (VLCFA; >C22) in plasma and tissues. X-ALD is caused by mutations in the ABCD1 gene encoding ALDP, an adenosine triphosphate (ATP)-binding-cassette (ABC) transporter located in the peroxisomal membrane. In this paper, we describe the current knowledge on the function of ALDP, its role in peroxisomal VLCFA beta-oxidation and the consequences of a defect in ALDP on VLCFA metabolism. Furthermore, we pay special attention to the role of the VLCFA elongation system in VLCFA homeostasis, with elongation of very long-chain fatty acids like-1 (ELOVL1) as key player, and its relevance to X-ALD.

General aspects and neuropathology of X-linked adrenoleukodystrophy

X-adrenoleukodystrophy (X-ALD) is a metabolic, peroxisomal disease affecting the nervous system, adrenal cortex and testis resulting from inactivating mutations in ABCD1 gene which encodes a peroxisomal membrane half-adenosine triphosphate (ATP)-binding cassette transporter, ABCD1 (or ALDP), whose defect is associated with impaired peroxisomal beta-oxidation and accumulation of saturated very long-chain fatty acids (VLCFA) in tissues and body fluids. Several phenotypes are recognized in male patients including cerebral ALD in childhood, adolescence or adulthood, adrenomyeloneuropathy (AMN), Addison's disease and, eventually, gonadal insufficiency. Female carriers might present with mild to severe myeloneuropathy that resembles AMN. There is a lack of phenotype-genotype correlations, as the same ABCD1 gene mutation may be associated with different phenotypes in the same family, suggesting that genetic, epigenetic, environmental and stochastic factors are probably contributory to the development and course of the disease. Degenerative changes, like those seen in pure AMN without cerebral demyelination, are characterized by loss of axons and secondary myelin in the long tracts of the spinal cord, possibly related to the impaired lipid metabolism of VLCFAs and the associated alterations (ie, oxidative damage). Similar lesions are encountered following inactivation of ABCD1 in mice (ABCD1(-)). A different and more aggressive phenotype is secondary to cerebral demyelination, very often accompanied by inflammatory changes in the white matter of the brain and associated with activation of T lymphocytes, CD1 presentation and increased levels of cytokines, gamma-interferon, interleukin (IL)-1alpha, IL-2 and IL-6, Granulocyte macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor-alpha, chemokines and chemokine receptors.

Lipid biochemists salute the genome

The biochemistry of plant metabolic pathways has been studied for many generations; nevertheless, numerous new enzymes and metabolic products have been discovered in the last 5-10 years. More importantly, many intriguing questions remain in all areas of metabolism. In this review, we consider these issues with respect to several pathways of lipid metabolism and the contributions made by the Arabidopsis genome sequence and the tools that it has spawned. These tools have allowed identification of enzymes and transporters required for the mobilization of seed storage lipids, as well as transporters that facilitate movement of lipids from the endoplasmic reticulum to the chloroplast in green leaf cells. Genomic tools were important in recognition of novel components of the cutin and suberin polymers that form water-impermeable barriers in plants. The waxes that also contribute to these barriers are exported from cells of the epidermis by transporters that are now being identified. Biochemical and genetic knowledge from yeast and animals has permitted successful homology-based searches of the Arabidopsis genome for genes encoding enzymes involved in the elongation of fatty acids and the synthesis of sphingolipids. Knowledge of the genome has identified novel enzymes for the biosynthesis of the seed storage lipid, triacylglycerol, and provided a refined understanding of how the pathways of fatty acid and triacylglycerol synthesis are integrated into overall carbon metabolism in developing seeds.

X-linked adrenoleukodystrophy: clinical course and minimal incidence in South Brazil

X-linked adenoleukodystrophy is a genetic disease that affects the degradation of very long-chain fatty acids. In male patients, common pictures are the cerebral form (CALD), myeloneuropathy (AMN), and Addison-only.

OBJECTIVE

To describe the clinical course of affected male patients from South Brazil between 1993 and 2007.

METHODS

Affected male patients and their maternal lineages were studied from a clinical, neurological and biochemical standpoint.

RESULTS

Eighty-three male patients from 30 families were biochemically evaluated: 51 were affected. 27/51 (54%) presented the cerebral form; 11/51 had AMN (22%); 5 had Addison-only (10%), and 8 (16%) were asymptomatic. Between 2002 and 2006, the minimal incidence was 1:35,000 males in our State (South Brazil). Forty-three affected individuals were followed for 5.4+/-3.7 years. Of 10 boys detected at early stages, three developed CALD. These three boys and another five CALD at baseline were referred to hematopoietic stem cell transplantation. Seven transplants were carried out, 5 with good clinical evolution after 2.2 years post-transplant. The non-transplanted case was later defined as a stable cerebral form.

DISCUSSION

Among the present families, the observed cases were comparable to the 50% expected by Mendelian segregation. Based on the natural history, the number of cases that developed CALD was similar to the expected. Transplants were successful in 70% of cases. The occurrence of a stable cerebral form pointed to an urgent need for better markers of active cerebral disease.

Valproic acid induces antioxidant effects in X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a fatal, axonal demyelinating, neurometabolic disease. It results from the functional loss of a member of the peroxisomal ATP-binding cassette transporter subfamily D (ABCD1), which is involved in the metabolism of very long-chain fatty acids (VLCFA). Oxidative damage of proteins caused by excess of the hexacosanoic acid, the most prevalent VLCFA accumulating in X-ALD, is an early event in the neurodegenerative cascade. We demonstrate here that valproic acid (VPA), a widely used anti-epileptic drug with histone deacetylase inhibitor properties, induced the expression of the functionally overlapping ABCD2 peroxisomal transporter. VPA corrected the oxidative damage and decreased the levels of monounsaturated VLCFA (C26:1 n-9), but not saturated VLCFA. Overexpression of ABCD2 alone prevented oxidative lesions to proteins in a mouse model of X-ALD. A 6-month pilot trial of VPA in X-ALD patients resulted in reversion of the oxidative damage of proteins in peripheral blood mononuclear cells. Thus, we propose VPA as a promising novel therapeutic approach that warrants further clinical investigation in X-ALD.

Very long chain fatty acid levels in patients diagnosed with multiple sclerosis

In clinical practice it is not uncommon for patients with adrenomyeloneuropathy or female carriers of adrenoleucodystrophy to have a presenting history and examination compatible with multiple sclerosis. This suggests that there may be an under-diagnosis of adrenoleucodystrophy and its variants in the multiple sclerosis population. We measured levels of very long chain fatty acids, which are typically elevated in the plasma of patients with adrenoleucodystrophy, in a large cohort of patients diagnosed clinically with multiple sclerosis. We tested serum samples from patients with either a first degree relative with multiple sclerosis or those with a primary progressive phenotype. No elevations in very long chain fatty acids were found in the cohort. This study suggests that the number of cases of adrenomyeloneuropathy or adrenoleucodystrophy amongst patients diagnosed clinically with multiple sclerosis is likely to be extremely low. This has important diagnostic implications.

Therapy of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD; OMIM #300100) is caused by defects of the ABCD1 gene on chromosome Xq28, resulting in an impairment of peroxisomal beta-oxidation and the accumulation of saturated very long chain fatty acids (VLCFAs). Primary manifestations occur in the CNS, the adrenal cortex and the testes' Leydig cells. The clinical presentation shows a marked variability which is not explained by the different X-ALD genotypes. Phenotypes range from rapidly progressive cerebral disease with childhood (childhood cerebral ALD [CCALD]) or adulthood (adult cerebral ALD [ACALD]) onset leading to death within a few years, over adult-onset adrenomyeloneuropathy (AMN) with or without focal CNS demyelination, AMN converting into a rapidly progressive, cerebral demyelinating phenotype resembling CCALD, to slow disease progression over decades, or adrenal insufficiency only. Approximately 50% of female heterozygotes develop moderate spastic paresis resembling the AMN phenotype. This review focuses on current experiences with different therapeutic approaches. Lorenzo's oil did not prove to be effective in cerebral inflammatory disease variants, but asymptomatic patients, and speculatively AMN variants without cerebral involvement, as well as female carriers may benefit from early intake of oleic and erucic acids in addition to VLCFA restriction. Hormone-replacement therapy is necessary in all patients with adrenal insufficiency. Hematopoietic stem cell transplantation has been reported to be effective in presymptomatic or early symptomatic CCALD, and may well also be a final therapeutic option in early ACALD patients. Early detection of mutation carriers and timely initiation of therapy is important for the effectiveness of all therapeutic efforts. Gene therapy of endogenous hematopoietic stem cells, pharmacological upregulation of other genes encoding proteins involved in peroxisomal beta-oxidation, reduction of oxidative stress, and possibly lovastatin are candidates for future X-ALD therapies.

Mutations in the Arabidopsis peroxisomal ABC transporter COMATOSE allow differentiation between multiple functions in planta: insights from an allelic series

COMATOSE (CTS), the Arabidopsis homologue of human Adrenoleukodystrophy protein (ALDP), is required for import of substrates for peroxisomal beta-oxidation. A new allelic series and a homology model based on the bacterial ABC transporter, Sav1866, provide novel insights into structure-function relations of ABC subfamily D proteins. In contrast to ALDP, where the majority of mutations result in protein absence from the peroxisomal membrane, all CTS mutants produced stable protein. Mutation of conserved residues in the Walker A and B motifs in CTS nucleotide-binding domain (NBD) 1 resulted in a null phenotype but had little effect in NBD2, indicating that the NBDs are functionally distinct in vivo. Two alleles containing mutations in NBD1 outside the Walker motifs (E617K and C631Y) exhibited resistance to auxin precursors 2,4-dichlorophenoxybutyric acid (2,4-DB) and indole butyric acid (IBA) but were wild type in all other tests. The homology model predicted that the transmission interfaces are domain-swapped in CTS, and the differential effects of mutations in the conserved "EAA motif" of coupling helix 2 supported this prediction, consistent with distinct roles for each NBD. Our findings demonstrate that CTS functions can be separated by mutagenesis and the structural model provides a framework for interpretation of phenotypic data.

Steroid hormones control circadian Elovl3 expression in mouse liver

The Elovl3 gene belongs to the Elovl gene family, which encodes for enzymes involved in the elongation of very long chain fatty acids. The recognized role for the enzyme is to control the elongation of saturated and monounsaturated fatty acids up to 24 carbons in length. Elovl3 was originally identified as a highly expressed gene in brown adipose tissue on cold exposure. Here we show that hepatic Elovl3 mRNA expression follows a distinct diurnal rhythm exclusively in mature male mice, with a sharp increase early in the morning Zeitgeber time (ZT) 20, peaks around ZT2, and is back to basal level at the end of the light period at ZT10. In female mice and sexually immature male mice, the Elovl3 expression was constantly low. Fasting and refeeding mice with chow or high-fat diet did not alter the Elovl3 mRNA levels. However, animals that were exclusively fed during the day for 9 d displayed an inverted expression profile. In addition, we show that Elovl3 expression is transcriptionally controlled and significantly induced by the exposure of the synthetic glucocorticoid dexamethasone. Taken together, these data suggest that Elovl3 expression in mouse liver is under strict diurnal control by circulating steroid hormones such as glucocorticoids and androgens. Finally, Elovl3 expression was found to be elevated in peroxisomal transporter ATP-binding cassette, subfamily D(ALD), member 2 ablated mice and suppressed in ATP-binding cassette subfamily D(ALD) member 2 overexpressing mice, implying a tight cross talk between very long chain fatty acid synthesis and peroxisomal fatty acid oxidation.

Pregnancy outcome after preimplantation genetic diagnosis in an affected couple with X-linked adrenoleukodystrophy

OBJECTIVE

To achieve a pregnancy free of X-linked adrenoleukodystrophy (X-ALD) by intracytoplasmic sperm injection (ICSI) and preimplantation genetic diagnosis (PGD).

DESIGN

Case report.

SETTING

Clínica FIV Recoletos, a private IVF center.

PATIENT(S)

A couple in which the man had X-ALD.

INTERVENTION(S)

The ICSI protocol and PGD of the obtained embryos.

MAIN OUTCOME MEASURE(S)

Blastomeres were analyzed by fluorescence in situ hybridization using sex selection techniques. Embryos were transferred and pregnancy was diagnosed by hCG analysis and ultrasonographic examination.

RESULT(S)

Ten embryos were obtained by ICSI. A biopsy was taken from eight embryos to perform PGD and two male embryos were transferred resulting in a twin pregnancy.

CONCLUSION(S)

This is the first registered gestation in which PGD has been used to prevent X-ALD transmission.

Adrénoleucodystrophie liée à l'X☆☆Cet article est publié en partenariat avec Orphanet et disponible sur le site www.orpha.net. © 2007 Orphanet. Publié par Elsevier Masson SAS. Tous droits réservés

X-linked adrenoleukodystrophy (ALD) is a severe neurodegenerative disorder. ALD is characterized by progressive demyelination within the central and peripheral nervous system, adrenal insufficiency (Addison's disease) and accumulation of very-long-chain fatty acids (VLCFA) in plasma, fibroblasts and tissues. The overall incidence of ALD is 1:17,000 including hemizygotes and heterozygotes who are frequently symptomatic. There are two main ALD phenotypes: 1) a cerebral demyelinating form which affects boys between 5-12 years, but also 35% of adult males; 2) a form that mainly involves the spinal cord (adrenomyeloneuropathy, AMN) in adult males between 20-50 years and 50% of heterozygous women after the age of 40 years. AMN presents with progressive spastic paraparesis. Addison's disease may be the first symptom of ALD in boys and adult males. These patients are at risk to develop cerebral ALD or AMN for life. ALD results from mutations in the ABCD1 gene without correlation between genotype and phenotype. The diagnosis of ALD relies upon the measurement of plasma VLCFA levels that allows the identification of 100% affected males and of 80-95% heterozygous women. Because of these false-negative, it is therefore mandatory to search for a mutation in the ABCD1 gene in all women at risk to be heterozygous for ALD. The ABCD1 gene encodes a peroxisomal transmembrane protein (ALD protein) with the structure of an half ATP-binding cassette transporter. It is possible that ALD protein imports VLCFA or VLCFA-CoA into peroxisomes in which they are degraded by a peroxisomal beta-oxidation system. Elongation of VLCFAs is enhanced in fibroblasts from ALD patients and likely contributes to the load of VLCFA in tissues. The underlying mechanisms that lead to cerebral demyelination, axonal degeneration in spinal cord and adrenal insufficiency are unknown. The "toxic" role of VLCFA accumulation remains to be demonstrated. The mechanisms that lead to the inflammatory reaction in cerebral ALD might involve abnormal acylation of gangliosides and phospholipids by VLCFA that would result in immune reaction of brain macrophages and astrocytes bearing CD1 molecules that recognize lipid antigens. De novo mutation of ABCD1 occurs in less than 8% of ALD patients. The genetic counseling aims to identify: 1) women who are at risk to be heterozygous; 2) neurologically asymptomatic boys. It is only at this stage that allogeneic bone marrow transplantation has clinical benefit; 3) ALD patients who have Addison's disease that can lead to sudden death. Prenatal diagnosis (chorionic villus samples, cultured amniotic fluid cells) relies upon DNA based mutation detection techniques, expression of ALD protein and measurement of VLCFA levels. Allogeneic bone marrow transplantation is the only treatment that provides a permanent cure when the procedure is performed at an early stage of cerebral demyelination, i.e when the patients are asymptomatic despite abnormal brain MRI. Treatment of Addison's disease is mandatory but does not modify the course of neurological symptoms. Dietary therapy failed to halt the neurologic progression in cerebral ALD and AMN. It might have a partial preventive effect in boys treated before 6 years of age.

Peroxisomes in human and mouse testis: differential expression of peroxisomal proteins in germ cells and distinct somatic cell types of the testis

The vital importance of peroxisomal metabolism for regular function of the testis is stressed by the severe spermatogenesis defects induced by peroxisomal dysfunction. However, only sparse information is available on the role and enzyme composition of this organelle in distinct cell types of the testis. In the present study, we characterized the peroxisomal compartment in human and mouse testis in primary cultures of murine somatic cells (Sertoli, peritubular myoid, and Leydig cells) and in GFP-PTS1 transgenic mice with a variety of morphological and biochemical techniques. Formerly, peroxisomes were thought to be absent in late stages of spermatogenesis. However, our results obtained by detection of different peroxisomal marker proteins show the presence of these organelles in most cell types in the testis, except for mature spermatozoa. Furthermore, we demonstrate a strong heterogeneity of peroxisomal protein content in various cell types of the human and mouse testis and show marked differences in structure, abundance, and localization of these organelles in spermatids, depending on their maturation. Highest and selective enrichment of the peroxisomal lipid transporters (ABCD1 and ABCD3) as well as ACOX2, the key regulatory enzyme of the beta-oxidation pathway 2 for side chain oxidation of cholesterol, were found in Sertoli cells, whereas Leydig cells were enriched in catalase and ABCD2. Our results suggest a cell type-specific metabolic function of peroxisomes in the testis and point to an important role for peroxisomes in spermiogenesis and in the lipid metabolism of Sertoli cells.

Proteomics characterization of mouse kidney peroxisomes by tandem mass spectrometry and protein correlation profiling

The peroxisome represents a ubiquitous single membrane-bound key organelle that executes various metabolic pathways such as fatty acid degradation by alpha- and beta-oxidation, ether-phospholipid biosynthesis, metabolism of reactive oxygen species, and detoxification of glyoxylate in mammals. To fulfil this vast array of metabolic functions, peroxisomes accommodate approximately 50 different enzymes at least as identified until now. Interest in peroxisomes has been fueled by the discovery of a group of genetic diseases in humans, which are caused by either a defect in peroxisome biogenesis or the deficient activity of a distinct peroxisomal enzyme or transporter. Although this research has greatly improved our understanding of peroxisomes and their role in mammalian metabolism, deeper insight into biochemistry and functions of peroxisomes is required to expand our knowledge of this low abundance but vital organelle. In this work, we used classical subcellular fractionation in combination with MS-based proteomics methodologies to characterize the proteome of mouse kidney peroxisomes. We could identify virtually all known components involved in peroxisomal metabolism and biogenesis. Moreover through protein localization studies by using a quantitative MS screen combined with statistical analyses, we identified 15 new peroxisomal candidates. Of these, we further investigated five candidates by immunocytochemistry, which confirmed their localization in peroxisomes. As a result of this joint effort, we believe to have compiled the so far most comprehensive protein catalogue of mammalian peroxisomes.

[Adrenoleukodystrophy: molecular pathogenesis and development of therapeutic agents]

Adrenoleukodystrophy (ALD) is an inherited disorder characterized by progressive demyelination of the central nervous system and adrenal dysfunction. The biochemical characterization is made based on the accumulation of pathognomonic amounts of saturated very long chain fatty acid (VLCFA, >22) in all tissues, including brain white matter and adrenal glands. The accumulation of VLCFA is linked to a mutation in the ABCD1 gene that encodes ABCD1/ALDP, a peroxisomal ABC protein. ABCD1/ALDP is thought to be involved in the active ATP-driven transport of VLCFA-CoA from the cytoplasm into the peroxisomes. However, the precise function of ABCD1/ALDP is still unclear. The accumulation of VLCFA is caused by reducing peroxisomal VLCFA beta-oxidation and/or increasing fatty acid elongation. Since the reduction of accumulated VLCFA in the brain is thought to be crucial for preventing the progression of neurologic symptoms in X-ALD, compounds that can cross the blood-brain barrier and decrease the VLCFA levels in the brain would be a highly attractive candidate for effective treatment of ALD patients. We found that baicalein 5,6,7-trimethyl ether, a flavonoid derivative, decreased the VLCFA level in X-ALD fibroblasts, possibly by activating peroxisomal fatty acid beta-oxidation. Continued pharmacologic studies of flavonoids and chemically modified derivatives may lead to major advances in the pharmacologic therapy for X-ALD.