Genetic variants of methionine metabolism and X-ALD phenotype generation: results of a new study sample

Childhood Cerebral Adrenoleukodystrophy: Case Report and Literature Review Advocating for Newborn Screening

Background

X-linked adrenoleukodystrophy (ALD) is a rare genetic disorder caused by a pathogenic variant of the ABCD1 gene, leading to impaired peroxisomal function and the accumulation of very long-chain fatty acids (VLCFAs). ALD presents a wide range of neurological and adrenal symptoms, ranging from childhood cerebral adrenoleukodystrophy to adrenomyeloneuropathy and adrenal insufficiency. Newborn screening (NBS) for ALD is available in some regions but remains lacking in others, such as India.

Case Presentation

We present a case of a 10-year-old boy with ALD who presented with seizures, progressive weakness, visual impairment, and adrenal insufficiency. Despite symptomatic management and dietary adjustments, the disease progressed rapidly, leading to respiratory failure and eventual demise. The diagnosis was confirmed through molecular analysis and elevated VLCFA levels. Neuroimaging revealed characteristic white matter changes consistent with ALD.

Conclusion

ALD is a devastating disease with no cure, emphasizing the importance of early detection through newborn screening and genetic testing. Management strategies include adrenal hormone therapy, gene therapy, and allogenic stem cell transplantation, as well as investigational treatments such as VLCFA normalization. Our case advocates the need for worldwide NBS and pediatric neurologic follow-up to enable early intervention and improve patient outcomes. Additionally, the association between ALD, recurrent febrile seizures, and unexplained developmental delay warrants further investigation to better understand disease progression and potential therapeutic targets.

Edgetic Perturbations Contribute to Phenotypic Variability in PEX26 Deficiency

Peroxisomes share metabolic pathways with other organelles and peroxisomes are embedded into key cellular processes. However, the specific function of many peroxisomal proteins remains unclear and restricted knowledge of the peroxisomal protein interaction network limits a precise mapping of this network into the cellular metabolism. Inborn peroxisomal disorders are autosomal or X-linked recessive diseases that affect peroxisomal biogenesis (PBD) and/or peroxisomal metabolism. Pathogenic variants in the PEX26 gene lead to peroxisomal disorders of the full Zellweger spectrum continuum. To investigate the phenotypic complexity of PEX26 deficiency, we performed a combined organelle protein interaction screen and network medicine approach and 1) analyzed whether PEX26 establishes interactions with other peroxisomal proteins, 2) deciphered the PEX26 interaction network, 3) determined how PEX26 is involved in further processes of peroxisomal biogenesis and metabolism, and 4) showed how variant-specific disruption of protein-protein interactions (edgetic perturbations) may contribute to phenotypic variability in PEX26 deficient patients. The discovery of 14 novel protein-protein interactions for PEX26 revealed a hub position of PEX26 inside the peroxisomal interactome. Analysis of edgetic perturbations of PEX26 variants revealed a strong correlation between the number of affected protein-protein interactions and the molecular phenotype of matrix protein import. The role of PEX26 in peroxisomal biogenesis was expanded encompassing matrix protein import, division and proliferation, and membrane assembly. Moreover, the PEX26 interaction network intersects with cellular lipid metabolism at different steps. The results of this study expand the knowledge about the function of PEX26 and refine genotype-phenotype correlations, which may contribute to our understanding of the underlying disease mechanism of PEX26 deficiency.

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.

Natural history of a cohort of ABCD1 variant female carriers

BACKGROUND AND PURPOSE

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.

METHODS

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.

RESULTS

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 41 years being crucial for phenoconversion. VLCFA levels were not predictive and did not change over time. Symptomatic carriers were followed up for 3.45 ± 2.1 years. 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.

CONCLUSIONS

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.

Adrenoleukodystrophy - neuroendocrine pathogenesis and redefinition of natural history

X-Linked adrenoleukodystrophy (ALD) is a peroxisomal metabolic disorder with a highly complex clinical presentation. ALD is caused by mutations in the ABCD1 gene, which leads to the accumulation of very long-chain fatty acids in plasma and tissues. Virtually all men with ALD develop adrenal insufficiency and myelopathy. Approximately 60% of men develop progressive cerebral white matter lesions (known as cerebral ALD). However, one cannot identify these individuals until the early changes are seen using brain imaging. Women with ALD also develop myelopathy, but generally at a later age than men and adrenal insufficiency or cerebral ALD are very rare. Owing to the multisystem symptomatology of the disease, patients can be assessed by the paediatrician, general practitioner, endocrinologist or a neurologist. This Review describes current knowledge on the clinical presentation, diagnosis and treatment of ALD, and highlights gaps in our knowledge of the natural history of the disease owing to an absence of large-scale prospective cohort studies. Such studies are necessary for the identification of new prognostic biomarkers to improve care for patients with ALD, which is particularly relevant now that newborn screening for ALD is being introduced.

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 β-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.

Peroxisome biogenesis in mammalian cells: The impact of genes and environment

The initiation and progression of many human diseases are mediated by a complex interplay of genetic, epigenetic, and environmental factors. As all diseases begin with an imbalance at the cellular level, it is essential to understand how various types of molecular aberrations, metabolic changes, and environmental stressors function as switching points in essential communication networks. In recent years, peroxisomes have emerged as important intracellular hubs for redox-, lipid-, inflammatory-, and nucleic acid-mediated signaling pathways. In this review, we focus on how nature and nurture modulate peroxisome biogenesis and function in mammalian cells. First, we review emerging evidence that changes in peroxisome activity can be linked to the epigenetic regulation of cell function. Next, we outline how defects in peroxisome biogenesis may directly impact cellular pathways involved in the development of disease. In addition, we discuss how changes in the cellular microenvironment can modulate peroxisome biogenesis and function. Finally, given the importance of peroxisome function in multiple aspects of health, disease, and aging, we highlight the need for more research in this still understudied field.

The genetic landscape of X-linked adrenoleukodystrophy: inheritance, mutations, modifier genes, and diagnosis

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene encoding a peroxisomal ABC transporter. In this review, we compare estimates of incidence derived from different populations in order to provide an overview of the worldwide incidence of X-ALD. X-ALD presents with heterogeneous phenotypes ranging from adrenomyeloneuropathy (AMN) to inflammatory demyelinating cerebral ALD (CALD). A large number of different mutations has been described, providing a unique opportunity for analysis of functional domains within ABC transporters. Yet the molecular basis for the heterogeneity of clinical symptoms is still largely unresolved, as no correlation between genotype and phenotype exists in X-ALD. Beyond ABCD1, environmental triggers and other genetic factors have been suggested as modifiers of the disease course. Here, we summarize the findings of numerous reports that aimed at identifying modifier genes in X-ALD and discuss potential problems and future approaches to address this issue. Different options for prenatal diagnosis are summarized, and potential pitfalls when applying next-generation sequencing approaches are discussed. Recently, the measurement of very long-chain fatty acids in lysophosphatidylcholine for the identification of peroxisomal disorders was included in newborn screening programs.

Association of transcobalamin c. 776C>G with overall survival in patients with primary central nervous system lymphoma

Background:

Chemotherapy for primary central nervous system lymphoma (PCNSL) is based on methotrexate (MTX), which interferes with both nucleic acid synthesis and methionine metabolism. We have reported previously that genetic variants with influence on methionine metabolism are associated with MTX side effects, that is, the occurrence of white matter lesions as a sign of MTX neurotoxicity. Here, we investigated whether such variants are associated with MTX efficacy in terms of overall survival in MTX-treated PCNSL patients.

Methods:

We analysed seven genetic variants influencing methionine metabolism in 68 PCNSL patients treated with systemic and facultative intraventricular MTX-based polychemotherapy (Bonn protocol).

Results:

Median age at diagnosis was 59 years (range: 28–77), 32 patients were female. Younger age (Wald=8.9; P=0.003) and the wild-type C (CC) allele of the genotype transcobalamin c (Tc2). 776C>G (Wald=6.7; P=0.010) were associated with longer overall survival in a multivariate COX regression analysis.

Conclusion:

This observation suggests that the missense variant Tc2. 776C>G influences both neurotoxicity and efficacy of MTX in the Bonn PCNSL protocol.

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.

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.

Leukodystrophies with late disease onset: an update

PURPOSE OF REVIEW

Knowledge of the metabolic and genetic basis of known and previously unknown leukodystrophies is constantly increasing, opening new treatment options such as enzyme replacement or cell-based therapies. This brief review highlights some recent work, particularly emphasizing results from studies in adulthood leukodystrophies.

RECENT FINDINGS

Evidence from recent studies suggests increasing importance of metabolic dysfunctions, for example, in peroxisomal lipid metabolism or energy homeostasis, influencing axonal integrity and oligodendrocyte function and leading to white matter demyelination. In addition, diagnostic and therapeutic progress in metachromatic leukodystrophy, X-linked adrenoleukodystrophy, Krabbe diseases and other rare leukodystrophies with late onset are summarized.

SUMMARY

Better understanding of leukodystrophies in neurological routine practice is of crucial importance for differentiating between other white matter diseases such as toxic, inflammatory or vascular leukoencephalopathies. Many leukodystrophies are particularly important to recognize because specific treatments already exist or are currently under investigation. The article also provides an overview of currently known leukodystrophies in adulthood.