Manganese transport disorder: novel SLC30A10 mutations and early phenotypes

Diagnosis of manganism and manganese neurotoxicity: A workshop report

With declining exposures to manganese (Mn) in occupational settings, there is a need for more sensitive exposure assessments and clinical diagnostic criteria for manganism and Mn neurotoxicity. To address this issue, a workshop was held on November 12-13, 2020, with international experts on Mn toxicity. The workshop discussions focused on the history of the diagnostic criteria for manganism, including those developed by the Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail (IRSST) in Quebec in 2005 and criteria developed by the Chinese government in 2002 and updated in 2006; the utility of biomarkers of exposure; recent developments in magnetic resonance imaging (MRI) for assessing Mn accumulation in the brain and diagnosing manganism; and potential future applications of metabolomics. The suggestions of the participants for updating manganism diagnostic criteria included the consideration of: i) A history of previous occupational and environmental exposure to Mn; ii) relevant clinical symptoms such as dystonia; iii) MRI imaging to document Mn accumulation in the neural tissues, including the basal ganglia; and iv) criteria for the differential diagnosis of manganism and other neurological conditions. Important research gaps include the characterization of Mn exposure and other co-exposures, exploration of the roles of different brain regions with MRI, understanding the complexity of metal ion transporters involved in Mn homeostasis, and a need for information on other neurotransmitter systems and brain regions underlying the pathophysiology of manganism.

Missing heritability of Wilson disease: a search for the uncharacterized mutations

Wilson disease (WD), a copper metabolism disorder caused by mutations in ATP7B, manifests heterogeneous clinical features. Interestingly, in a fraction of clinically diagnosed WD patients, mutations in ATP7B appears to be missing. In this review we discuss the plausible explanations of this missing heritability and propose a workflow that can identify the hidden mutations. Mutation analyses of WD generally includes targeted sequencing of ATP7B exons, exon-intron boundaries, and rarely, the proximal promoter region. We propose that variants in the distal cis-regulatory elements and/or deep intronic variants that impact splicing might well represent the hidden mutations. Heterozygous del/ins that remain refractory to conventional PCR-sequencing method may also represent such mutations. In this review, we also hypothesize that mutations in the key copper metabolism genes, like, ATOX1, COMMD1, and SLC31A1, could possibly lead to a WD-like phenotype. In fact, WD does present overlapping symptoms with other rare genetic disorders; hence, the possibility of a misdiagnosis and thus adding to missing heritability cannot be excluded. In this regard, it seems that whole-genome analysis will provide a comprehensive and rapid molecular diagnosis of WD. However, considering the associated cost for such a strategy, we propose an alternative customized screening schema of WD which include targeted sequencing of ATP7B locus as well as other key copper metabolism genes. Success of such a schema has been tested in a pilot study.

Hereditary Disorders of Manganese Metabolism: Pathophysiology of Childhood-Onset Dystonia-Parkinsonism in SLC39A14 Mutation Carriers and Genetic Animal Models

Over the last decade, several clinical reports have outlined cases of childhood-onset manganese (Mn)-induced dystonia-parkinsonism, resulting from loss-of-function mutations in the Mn influx transporter gene SLC39A14. These clinical cases have provided a wealth of knowledge on Mn toxicity and homeostasis. However, our current understanding of the underlying neuropathophysiology is severely lacking. The recent availability of Slc39a14 knockout (KO) murine and zebrafish animal models provide a powerful platform to investigate the neurological effects of elevated blood and brain Mn concentrations in vivo. As such, the objective of this review was to organize and summarize the current clinical literature and studies utilizing Slc39a14-KO animal models and assess the validity of the animal models based on the clinical presentation of the disease in human mutation carriers.

Clinical Profile and Treatment Outcomes of Hypermanganesemia with Dystonia 1 and 2 among 27 Indian Children

Background

Hypermanganesemia with dystonia 1 and 2 (HMNDYT1 and 2) are rare, inherited disorders of manganese transport.

Objectives

We aimed to describe clinical, laboratory features, and outcomes among children with HMNDYT.

Methods

We conducted a retrospective multicenter study involving tertiary centers across India. We enrolled children between 1 month to 18 years of age with genetically confirmed/clinically probable HMNDYT. Clinical, laboratory profile, genetic testing, treatment details, and outcomes scored by treating physicians on a Likert scale were recorded.

Results

We enrolled 27 children (19 girls). Fourteen harbored SLC30A10 mutations; nine had SLC39A14 mutations. The SLC39A14 cohort had lower median age at onset (1.3 [interquartile range (IQR), 0.7-5.5] years) versus SLC30A10 cohort (2.0 [IQR, 1.5-5.1] years). The most frequent neurological features were dystonia (100%; n = 27), gait abnormality (77.7%; n = 21), falls (66.7%; n = 18), and parkinsonism (59.3%; n = 16). Median serum manganese (Mn) levels among SLC39A14 (44.9 [IQR, 27.3-147.7] mcg/L) cohort were higher than SLC30A10 (29.4 [17.1-42.0] mcg/L); median hemoglobin was higher in SLC30A10 (16.3 [IQR, 15.2-17.5] g/dL) versus SLC39A14 cohort (12.5 [8.8-13.2] g/dL). Hepatic involvement and polycythaemia were observed exclusively in SLC30A10 variants. A total of 26/27 children underwent chelation with disodium calcium edetate. Nine demonstrated some improvement, three stabilized, two had marked improvement, and one had normalization. Children with SLC39A14 mutations had poorer response. Two children died and nine were lost to follow-up.

Conclusions

We found female predominance. Children with SLC39A14 mutations presented at younger age and responded less favorably to chelation compared to SLC30A10 mutations. There is emerging need to better define management strategies, especially in low resource settings.

Pathophysiological studies of aging Slc39a14 knockout mice to assess the progression of manganese-induced dystonia-parkinsonism

Over the last decade, several clinical reports have outlined cases of early-onset manganese (Mn)-induced dystonia-parkinsonism, resulting from loss of function mutations of the Mn transporter gene SLC39A14. Previously, we have performed characterization of the behavioral, neurochemical, and neuropathological changes in 60-day old (PN60) Slc39a14-knockout (KO) murine model of the human disease. Here, we extend our studies to aging Slc39a14-KO mice to assess the progression of the disease. Our results indicate that 365-day old (PN365) Slc39a14-KO mice present with markedly elevated blood and brain Mn levels, similar to those found in the PN60 mice and representative of the human cases of the disease. Furthermore, aging Slc39a14-KO mice consistently manifest a hypoactive and dystonic behavioral deficits, similar to the PN60 animals, suggesting that the behavioral changes are established early in life without further age-associated deterioration. Neurochemical, neuropathological, and functional assessment of the dopaminergic system of the basal ganglia revealed absence of neurodegenerative changes of dopamine (DA) neurons in the substantia nigra pars compacta (SNc), with no changes in DA or metabolite concentrations in the striatum of Slc39a14-KO mice relative to wildtype (WT). Similar to the PN60 animals, aging Slc39a14-KO mice expressed a marked inhibition of potassium-stimulated DA release in the striatum. Together our findings indicate that the pathophysiological changes observed in the basal ganglia of aging Slc39a14-KO animals are similar to those at PN60 and aging does not have a significant effect on these parameters.

Calcium and the Ca-ATPase SPCA1 modulate plasma membrane abundance of ZIP8 and ZIP14 to regulate Mn(II) uptake in brain microvascular endothelial cells

Manganese (II) accumulation in human brain microvascular endothelial cells is mediated by the metal-ion transporters ZRT IRT-like protein 8 (ZIP8) and ZRT IRT-like protein 14 (ZIP14). The plasma membrane occupancy of ZIP14, in particular, is increased in cells treated with Mn²⁺, lipopolysaccharide, or IL-6, but the mechanism of this regulation has not been elucidated. The calcium-transporting type 2C member 1 ATPase, SPCA1, is a Golgi-localized Ca²⁺-uptake transporter thought to support Golgi uptake of Mn²⁺ also. Here, we show using surface protein biotinylation, indirect immunofluorescence, and GFP-tagged proteins that cytoplasmic Ca²⁺ regulates ZIP8- and ZIP14-mediated manganese accumulation in human brain microvascular endothelial cells by increasing the plasma membrane localization of these transporters. We demonstrate that RNAi knockdown of SPCA1 expression results in an increase in cytoplasmic Ca²⁺ levels. In turn, we found increased cytoplasmic Ca²⁺ enhances membrane-localized ZIP8 and ZIP14 and a subsequent increase in ⁵⁴Mn²⁺ uptake. Furthermore, overexpression of WT SPCA1 or a gain-of-function mutant resulted in a decrease in cytoplasmic Ca²⁺ and ⁵⁴Mn²⁺ accumulation. While addition of Ca²⁺ positively regulated ZIP-mediated ⁵⁴Mn²⁺ uptake, we show chelation of Ca²⁺ diminished manganese transport. In conclusion, the modulation of ZIP8 and ZIP14 membrane cycling by cytoplasmic calcium is a novel finding and provides new insight into the regulation of the uptake of Mn²⁺ and other divalent metal ions–mediated ZIP metal transporters.

The role of manganese dysregulation in neurological disease: emerging evidence

Manganese is an essential trace metal. The dysregulation of manganese seen in a broad spectrum of neurological disorders reflects its importance in brain development and key neurophysiological processes. Historically, the observation of acquired manganism in miners and people who misuse drugs provided early evidence of brain toxicity related to manganese exposure. The identification of inherited manganese transportopathies, which cause neurodevelopmental and neurodegenerative syndromes, further corroborates the neurotoxic potential of this element. Moreover, manganese dyshomoeostasis is also implicated in Parkinson's disease and other neurodegenerative conditions, such as Alzheimer's disease and Huntington's disease. Ongoing and future research will facilitate the development of better targeted therapeutical strategies than are currently available for manganese-associated neurological disorders.

Unexpected (123I)FP-CIT SPECT findings: SWIDD, SWEDD and all DAT

Although the diagnosis of Parkinson's disease (PD) is essentially clinical, the implementation of imaging techniques can improve diagnostic accuracy. While some techniques (e.g. magnetic resonance imaging-MRI, computerized tomography-CT) are used to exclude secondary syndromes, presynaptic dopaminergic imaging including imaging of dopamine transporter (DAT)-can help the Neurologist in the differential diagnosis between neurodegenerative parkinsonian syndromes and parkinsonism without dopamine deficiency. DAT imaging can be useful in cases in which the clinical picture is not univocal, as in case of overlapping clinical features in patients with early disease, atypical syndromes or unsatisfying response to therapy. Currently, (¹²³I)FP-CIT ([123I]N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane) (trade name DaTSCAN) is the only agent approved by international regulatory agencies for this purpose. With the increasing use of this technique, some unexpected findings have been reported, including patients clinically diagnosed with PD with a normal SPECT scan [e.g. Scans Without Evidence of Dopaminergic Deficit (SWEDD)]; PD patients with a greater dopaminergic deficit in the striatum ipsilateral to the clinically more affected side [e.g. Scans With Ipsilateral Dopaminergic Deficit (SWIDD)]; as well as some artifacts. Moreover, the neurologist must remember that structural lesions and administration of some drugs might alter the result of DAT imaging. Unexpected findings, artifacts, and misinterpretation of imaging findings can lead to an erroneous diagnosis and inappropriate therapy, neglect of other medical conditions that might explain the clinical picture, and undermine the selection phase in clinical trials. The aim of the present review is to bring clarity on these controversial (and sometimes erroneous) results, in order to inform of these possibilities the clinicians requesting a DaTSCAN in clinical practice.

Copper, Iron, and Manganese Toxicity in Neuropsychiatric Conditions

Copper, manganese, and iron are vital elements required for the appropriate development and the general preservation of good health. Additionally, these essential metals play key roles in ensuring proper brain development and function. They also play vital roles in the central nervous system as significant cofactors for several enzymes, including the antioxidant enzyme superoxide dismutase (SOD) and other enzymes that take part in the creation and breakdown of neurotransmitters in the brain. An imbalance in the levels of these metals weakens the structural, regulatory, and catalytic roles of different enzymes, proteins, receptors, and transporters and is known to provoke the development of various neurological conditions through different mechanisms, such as via induction of oxidative stress, increased α-synuclein aggregation and fibril formation, and stimulation of microglial cells, thus resulting in inflammation and reduced production of metalloproteins. In the present review, the authors focus on neurological disorders with psychiatric signs associated with copper, iron, and manganese excess and the diagnosis and potential treatment of such disorders. In our review, we described diseases related to these metals, such as aceruloplasminaemia, neuroferritinopathy, pantothenate kinase-associated neurodegeneration (PKAN) and other very rare classical NBIA forms, manganism, attention-deficit/hyperactivity disorder (ADHD), ephedrone encephalopathy, HMNDYT1-SLC30A10 deficiency (HMNDYT1), HMNDYT2-SLC39A14 deficiency, CDG2N-SLC39A8 deficiency, hepatic encephalopathy, prion disease and “prion-like disease”, amyotrophic lateral sclerosis, Huntington’s disease, Friedreich’s ataxia, and depression.

Manganese and Movement Disorders: A Review

Scientific and technological advances achieved with industrial expansion have led to an ever-increasing demand for heavy metals. This demand has, in turn, led to increased contamination of soil, water and air with these metals. Chronic exposure to metals may be detrimental not only to occupational workers but also to the nonoccupational population exposed to these metals. Manganese (Mn), a commonly used heavy metal, is an essential cofactor for many enzymatic processes that drive biological functions. However, it is also a potential source of neurotoxicity, particularly in the field of movement disorders. The typical manifestation of Mn overexposure is parkinsonism, which may be difficult to differentiate from the more common idiopathic Parkinson's disease. In addition to environmental exposure to Mn, other potential etiologies causing hypermanganesemia include systemic health conditions, total parenteral nutrition and genetic mutations causing Mn dyshomeostasis. In this review, we critically analyze Mn and discuss its sources of exposure, pathophysiology and clinical manifestations. We have highlighted the global public health impact of Mn and emphasize that movement disorder specialists should record a detailed social and occupational history to ensure that a toxic etiology is not misdiagnosed as a neurodegenerative disease. In the absence of a definite therapeutic option, early diagnosis and timely institution of preventive measures are the keys to managing its toxic effects.

Clinico-radiological phenotyping and diagnostic pathways in childhood neurometabolic disorders-a practical introductory guide

Inborn errors of metabolism (IEM) although individually rare, together constitute a significant proportion of childhood neurological disorders. Majority of these disorders occur due to deficiency of an enzyme in a specific metabolic pathway, leading to damage by accumulation of a toxic substrate or deficiency of an essential metabolite. Early diagnosis is crucial in many of these conditions to prevent or minimise brain damage. Whilst many of the neuroimaging features are nonspecific, certain disorders demonstrate specific patterns due to selective vulnerability of different structures to different insults. Along with clinical and biochemical profile, neuroimaging thus plays a pivotal role in differentiating metabolic disorders from other causes, in providing a differential diagnosis or suggesting a metabolic pathway derangement, and on occasion also helps make a specific diagnosis. This allows initiation of targeted metabolic and genetic work up and treatment. Familiarity with the clinical features, relevant biochemical features and neuroimaging findings of common metabolic disorders to facilitate a prompt diagnosis cannot thus be overemphasized. In this article, we describe the latest classification scheme, the clinical and biochemical clues and common radiological patterns. The diagnostic algorithm followed in daily practice after clinico-radiological phenotyping is alluded to and illustrated by clinical vignettes. Focused sections on neonatal metabolic disorders and mitochondrial disorders are also provided. The purpose of this article is to provide a brief overview and serve as a practical primer to clinical and radiological phenotypes and diagnostic aspects of IEM.

Inherited Manganese Disorders and the Brain: What Neurologists Need to Know

Although acquired manganese neurotoxicity has been widely reported since its first description in 1837 and is popularly referred to as "manganism," inherited disorders of manganese homeostasis have received the first genetic signature as recently as 2012. These disorders, predominantly described in children and adolescents, involve mutations in three manganese transporter genes, i.e., SLC30A10 and SLC39A14 which lead to manganese overload, and SLC39A8, which leads to manganese deficiency. Both disorders of inherited hypermanganesemia typically exhibit dystonia and parkinsonism with relatively preserved cognition and are differentiated by the occurrence of polycythemia and liver involvement in the SLC30A10-associated condition. Mutations in SLC39A8 lead to a congenital disorder of glycosylation which presents with developmental delay, failure to thrive, intellectual impairment, and seizures due to manganese deficiency. Chelation with iron supplementation is the treatment of choice in inherited hypermanganesemia. In this review, we highlight the pathognomonic clinical, laboratory, imaging features and treatment modalities for these rare disorders.

Wilson disease

PURPOSE OF REVIEW

The aim of this article is to review recent developments in the areas of the disease features and treatment of Wilson disease, and survey disorders that share its pathophysiology or clinical symptoms.

RECENT FINDINGS

Knowledge of the clinical spectrum of Wilson disease has expanded with recognition of patients who present in atypical age groups - patients with very early onset (<5 years) and those in whom symptoms present in mid-to-late adulthood. A disease phenotype with dominant psychiatric features and increased risk of cardiac problems and various sleep disorders have been identified.In addition to a better understanding of the phenotype of Wilson disease itself, features of some related disorders ('Wilson disease-mimics') have been described leading to a better understanding of copper homeostasis in humans. These disorders include diseases of copper disposition, such as mental retardation, enteropathy, deafness, neuropathy, ichthyosis, keratoderma syndrome, Niemann-Pick type C, and certain congenital disorders of glycosylation, as well as analogous disorders of iron and manganese metabolism.Outcomes for existing treatments, including in certain patient subpopulations of interest, are better known. Novel treatment strategies being studied include testing of bis-choline tetrathiomolybdate in phase 2 clinical trial as well as various preclinical explorations of new copper chelators and ways to restore ATP7B function or repair the causative gene.

SUMMARY

Recent studies have expanded the phenotype of Wilson disease, identified rare inherited metal-related disorders that resemble Wilson disease, and studied long-term outcomes of existing treatments. These developments can be expected to have an immediate as well as a long-term impact on the clinical management of the disease, and point to promising avenues for future research.

Brain manganese and the balance between essential roles and neurotoxicity

Manganese (Mn) is an essential micronutrient required for the normal development of many organs, including the brain. Although its roles as a cofactor in several enzymes and in maintaining optimal physiology are well-known, the overall biological functions of Mn are rather poorly understood. Alterations in body Mn status are associated with altered neuronal physiology and cognition in humans, and either overexposure or (more rarely) insufficiency can cause neurological dysfunction. The resultant balancing act can be viewed as a hormetic U-shaped relationship for biological Mn status and optimal brain health, with changes in the brain leading to physiological effects throughout the body and vice versa. This review discusses Mn homeostasis, biomarkers, molecular mechanisms of cellular transport, and neuropathological changes associated with disruptions of Mn homeostasis, especially in its excess, and identifies gaps in our understanding of the molecular and biochemical mechanisms underlying Mn homeostasis and neurotoxicity.

The Functions of ZIP8, ZIP14, and ZnT10 in the Regulation of Systemic Manganese Homeostasis

As an essential nutrient, manganese is required for the regulation of numerous cellular processes, including cell growth, neuronal health, immune cell function, and antioxidant defense. However, excess manganese in the body is toxic and produces symptoms of neurological and behavioral defects, clinically known as manganism. Therefore, manganese balance needs to be tightly controlled. In the past eight years, mutations of genes encoding metal transporters ZIP8 (SLC39A8), ZIP14 (SLC39A14), and ZnT10 (SLC30A10) have been identified to cause dysregulated manganese homeostasis in humans, highlighting the critical roles of these genes in manganese metabolism. This review focuses on the most recent advances in the understanding of physiological functions of these three identified manganese transporters and summarizes the molecular mechanisms underlying how the loss of functions in these genes leads to impaired manganese homeostasis and human diseases.

Treatable Inherited Movement Disorders in Children: Spotlight on Clinical and Biochemical Features

Background

About 80% of monogenic metabolic diseases causing movement disorders (MDs) emerges during the first 2 decades of life, and a number of these conditions offers the opportunity of a disease-modifying treatment. The implementation of enlarged neonatal screening programs and the impressive rapid increase of the identification of new conditions are enhancing our potential to recognize and treat several diseases causing MDs, changing their outcome and phenotypic spectrum.

Methods and Findings

A literature review of monogenic disorders causing MDs amenable to treatment was conducted focusing on early clinical signs and diagnostic biomarkers. A classification in 3 broad categories based on the therapeutic approach has been proposed. Some disorders result in irreversible neurotoxic lesions that can only be prevented if treated in a presymptomatic stage, and others present with a progressive neurological impairment that a timely diagnosis and treatment may reverse or improve. Some MDs are the result of the failure of intracellular energy supply or altered glucose transport. The treatment in these conditions includes vitamins or a metabolic shift from a carbohydrate to a fatty acid catabolism, respectively. Finally, a group of highly treatable MDs are the result of defects of neurotransmitter metabolism. In these disorders, the supplementation of precursors or mimetics of neurotransmitters can deeply change the disease natural history.

Conclusions

To prevent serious and irreversible neurological impairment, the diagnostic work-up of MDs in children should consider a number of clinical red flags and biomarkers denoting specifically treatable diseases.

Heavy Metals Exposure and Alzheimer's Disease and Related Dementias

Alzheimer's disease and related dementias lack effective treatment or cures and are major public health challenges. Risk for Alzheimer's disease and related dementias is partially attributable to environmental factors. The heavy metals lead, cadmium, and manganese are widespread and persistent in our environments. Once persons are exposed to these metals, they are adept at entering cells and reaching the brain. Lead and cadmium are associated with numerous health outcomes even at low levels of exposure. Although manganese is an essential metal, deficiency or environmental exposure or high levels of the metal can be toxic. In cell and animal model systems, lead, cadmium, and manganese are well documented neurotoxicants that contribute to canonical Alzheimer's disease pathologies. Adult human epidemiologic studies have consistently shown lead, cadmium, and manganese are associated with impaired cognitive function and cognitive decline. No longitudinal human epidemiology study has assessed lead or manganese exposure on Alzheimer's disease specifically though two studies have reported a link between cadmium and Alzheimer's disease mortality. More longitudinal epidemiologic studies with high-quality time course exposure data and incident cases of Alzheimer's disease and related dementias are warranted to confirm and estimate the proportion of risk attributable to these exposures. Given the widespread and global exposure to lead, cadmium, and manganese, even small increases in the risks of Alzheimer's disease and related dementias would have a major population impact on the burden on disease. This article reviews the experimental and epidemiologic literature of the associations between lead, cadmium, and manganese on Alzheimer's disease and related dementias and makes recommendations of critical areas of future investment.

ZIP14 is degraded in response to manganese exposure

Manganese (Mn) is an essential element necessary for proper development and brain function. Circulating Mn levels are regulated by hepatobiliary clearance to limit toxic levels and prevent tissue deposition. To characterize mechanisms involved in hepatocyte Mn uptake, polarized human HepaRG cells were used for this study. Western blot analysis and immunofluorescence microscopy showed the Mn transporter ZIP14 was expressed and localized to the basolateral surface of polarized HepaRG cells. HepaRG cells took up 54Mn in a time- and temperature-dependent manner but uptake was reduced after exposure to Mn. This loss in transport activity was associated with decreased ZIP14 protein levels in response to Mn exposure. Mn-induced degradation of ZIP14 was blocked by bafilomycin A1, which increased localization of the transporter in Lamp1-positive vesicles. Mn exposure also down-regulated the Golgi proteins TMEM165 and GPP130 while the ER stress marker BiP was induced. These results indicate that Mn exposure decreases ZIP14 protein levels to limit subsequent uptake of Mn as a cytoprotective response. Thus, high levels of Mn may compromise first-pass-hepatic clearance mechanisms.

Parkinsonism in diseases predominantly presenting with dystonia

If the presence of dystonia is a well-recognized phenomenon in disorders predominantly presenting with parkinsonism, including sporadic Parkinson Disease, the term dystonia-parkinsonism usually refers to rare conditions, often genetic, in which the severity of dystonia usually equates that of parkinsonism. At variance with parkinsonian syndromes with additional dystonia, the conditions reviewed in this chapter have usually their onset in childhood and their diagnostic work-up is different. In fact, the phenotype is not usually specific of the underlying defect and additional investigations are therefore required. Here, we review the diseases predominantly presenting with dystonia where parkinsonism can develop, according to their main pathophysiological mechanism including disorders of dopamine biosynthesis, neurotransmitter transporter disorders, disorder of metal metabolism (i.e., iron, copper and manganese) and other inherited dystonia-parkinsonism conditions.

The solute carriers ZIP8 and ZIP14 regulate manganese accumulation in brain microvascular endothelial cells and control brain manganese levels

Manganese supports numerous neuronal functions but in excess is neurotoxic. Consequently, regulation of manganese flux at the blood-brain barrier (BBB) is critical to brain homeostasis. However, the molecular pathways supporting the transcellular trafficking of divalent manganese ions within the microvascular capillary endothelial cells (BMVECs) that constitute the BBB have not been examined. In this study, we have determined that ZIP8 and ZIP14 (Zrt- and Irt-like proteins 8 and 14) support Mn²⁺ uptake by BMVECs and that neither DMT1 nor an endocytosis-dependent pathway play any significant role in Mn²⁺ uptake. Specifically, siRNA-mediated knockdown of ZIP8 and ZIP14 coincided with a decrease in manganese uptake, and kinetic analyses revealed that manganese uptake depends on pH and bicarbonate and is up-regulated by lipopolysaccharide, all biochemical markers of ZIP8 or ZIP14 activity. Mn²⁺ uptake also was associated with cell-surface membrane presentation of ZIP8 and ZIP14, as indicated by membrane protein biotinylation. Importantly, surface ZIP8 and ZIP14 biotinylation and Mn²⁺-uptake experiments together revealed that these transporters support manganese uptake at both the apical, blood and basal, brain sides of BMVECs. This indicated that in the BMVECs of the BBB, these two transporters support a bidirectional Mn²⁺ flux. We conclude that BMVECs play a critical role in controlling manganese homeostasis in the brain.

A case of dystonia with polycythemia and hypermanganesemia caused by SLC30A10 mutation: a treatable inborn error of manganese metabolism

Background

Manganese is a critical trace element that not only has antioxidant properties, but also is essential for various metabolic pathways and neurotransmitters production. However, it can be toxic at high levels, particularly in the central nervous system. Manganese intoxication can be acquired, but an inherited form due to autosomal-recessive mutations in the SLC30A10 gene encoding a Mn transporter protein has also been reported recently. These mutations are associated with significant failure of manganese excretion and its storage in the liver, brain (especially basal ganglia), and other peripheral tissues, resulting in toxicity.

Case presentation

A 10-year-old boy from consanguineous parents presented with a history of progressive truncal instability, gait difficulty, and frequent falls for 2 months. He had dystonia, rigidity, ataxia, dysarthria, bradykinesia and a plethoric skin. Investigations showed polycythemia, low serum iron and ferritin levels, and increased total iron binding capacity. A brain MRI revealed symmetric hyperintensities in the basal ganglia and dentate nucleuses on TI images that were suggestive of brain metal deposition together with clinical manifestations. Serum calcium and copper levels were normal, while the manganese level was significantly higher than normal values. There was no history of environmental overexposure to manganese. Genetic testing showed a homozygous missense mutation in SLC30A10 (c.C1006T, p.His336Tyr) and Sanger sequencing confirmed a homozygous state in the proband and a heterozygous state in the parents. Regular treatment with monthly infusions of disodium calcium edetate and oral iron compounds resulted in decreased serum manganese and hemoglobin levels to normal values, significant resolution of MRI lesions, and partial improvement of neurological symptoms during 6 months of follow-up.

Conclusion

The syndrome of hepatic cirrhosis, dystonia, polycythemia, and hypermanganesemia caused by SLC30A10 mutation is a treatable inherited metal deposition syndrome. The patient may only have pure neurological without hepatic manifestations. Although this is a rare and potentially fatal inborn error of metabolism, early diagnosis and continuous chelation therapy might improve the symptoms and prevent disease progression.

Putative metal binding site in the transmembrane domain of the manganese transporter SLC30A10 is different from that of related zinc transporters

SLC30 proteins belong to the cation diffusion facilitator (CDF) superfamily of metal transporters. SLC30A10 mediates manganese efflux, while other SLC30 members transport zinc. Metal specificity of CDFs may be conferred by amino acids that form a transmembrane metal binding site (Site A). Site A of zinc-transporting CDFs, such as SLC30A1/ZnT1, have a HXXXD motif, but manganese transporters, such as SLC30A10, harbor a NXXXD motif. This critical histidine-to-asparagine substitution, at residue 43, was proposed to underlie manganese transport specificity of SLC30A10. However, we recently discovered that asparagine-43 was dispensable for manganese efflux in HeLa cells; instead, glutamate-25, aspartate-40, asparagine-127, and aspartate-248 were required. In contrast, another group reported that asparagine-43 was required in a chicken cell line. The goal of this study was to resolve the divergent results about the requirement of the crucial asparagine-43 residue. For this, we compared the manganese efflux activity of four cell types that stably over-expressed SLC30A10wild-type (WT), SLC30A10N43A or SLC30A10E25A: physiologically-relevant hepatic HepG2 and neuronal AF5 cells, HEK cells, and embryonic fibroblasts from Slc30a10-/- mice. In all cell types, manganese efflux activity of SLC30A10N43A was comparable to WT, while SLC30A10E25A lacked activity. Importantly, unlike SLC30A10, the histidine residue of the HXXXD motif of SLC30A1/ZnT1 was required for zinc transport. These results imply that the mechanisms of ion coordination within the transmembrane domain of SLC30A10 substantially differ from previously-studied CDFs, suggest that factors beyond Site A residues may confer metal specificity to CDFs, and improve understanding of the pathobiology of manganese toxicity due to mutations in SLC30A10.

Genetic Disorders of Manganese Metabolism

Purpose of Review

This article provides an overview of the pathogenesis, clinical presentation and treatment of inherited manganese transporter defects.

Recent Findings

Identification of a new group of manganese transportopathies has greatly advanced our understanding of how manganese homeostasis is regulated in vivo. While the manganese efflux transporter SLC30A10 and the uptake transporter SLC39A14 work synergistically to reduce the manganese load, SLC39A8 has an opposing function facilitating manganese uptake into the organism. Bi-allelic mutations in any of these transporter proteins disrupt the manganese equilibrium and lead to neurological disease: Hypermanganesaemia with dystonia 1 (SLC30A10 deficiency) and hypermanganesaemia with dystonia 2 (SLC39A14 deficiency) are characterised by manganese neurotoxicity while SLC39A8 mutations cause a congenital disorder of glycosylation type IIn due to Mn deficiency.

Summary

Inherited manganese transporter defects are an important differential diagnosis of paediatric movement disorders. Manganese blood levels and MRI brain are diagnostic and allow early diagnosis to avoid treatment delay.

Zinc transporter 10 (ZnT10)-dependent extrusion of cellular Mn2+ is driven by an active Ca2+-coupled exchange

Manganese (Mn²⁺) is extruded from the cell by the zinc transporter 10 (ZnT10). Loss of ZnT10 expression caused by autosomal mutations in the ZnT10 gene leads to hypermanganesemia in multiple organs. Here, combining fluorescent monitoring of cation influx in HEK293-T cells expressing human ZnT10 with molecular modeling of ZnT10 cation selectivity, we show that ZnT10 is exploiting the transmembrane Ca²⁺ inward gradient for active cellular exchange of Mn²⁺ In analyzing ZnT10 activity we used the ability of Fura-2 to spectrally distinguish between Mn²⁺ and Ca²⁺ fluxes. We found that (a) application of Mn²⁺-containing Ca²⁺-free solution to ZnT10-expressing cells triggers an influx of Mn²⁺, (b) reintroduction of Ca²⁺ leads to cellular Mn²⁺ extrusion against an inward Mn²⁺ gradient, and (c) the cellular transport of Mn²⁺ by ZnT10 is coupled to a reciprocal movement of Ca²⁺ Remarkably, replacing a single asparagine residue in ZnT10 (Asp-43) with threonine (ZnT10 N43T) converted the Mn²⁺/Ca²⁺ exchange to an uncoupled channel mode, permeable to both Ca²⁺ and Mn²⁺ The findings in our study identify the first ion transporter that uses the Ca²⁺ gradient for active counter-ion exchange. They highlight a remarkable versatility in metal selectivity and mode of transport controlled by the tetrahedral metal transport site of ZnT proteins.

SLC30A10 transporter in the digestive system regulates brain manganese under basal conditions while brain SLC30A10 protects against neurotoxicity

The essential metal manganese becomes neurotoxic at elevated levels. Yet, the mechanisms by which brain manganese homeostasis is regulated are unclear. Loss-of-function mutations in SLC30A10, a cell surface-localized manganese efflux transporter in the brain and liver, induce familial manganese neurotoxicity. To elucidate the role of SLC30A10 in regulating brain manganese, we compared the phenotypes of whole-body and tissue-specific Slc30a10 knockout mice. Surprisingly, unlike whole-body knockouts, brain manganese levels were unaltered in pan-neuronal/glial Slc30a10 knockouts under basal physiological conditions. Further, although transport into bile is a major route of manganese excretion, manganese levels in the brain, blood, and liver of liver-specific Slc30a10 knockouts were only minimally elevated, suggesting that another organ compensated for loss-of-function in the liver. Additional assays revealed that SLC30A10 was also expressed in the gastrointestinal tract. In differentiated enterocytes, SLC30A10 localized to the apical/luminal domain and transported intracellular manganese to the lumen. Importantly, endoderm-specific knockouts, lacking SLC30A10 in the liver and gastrointestinal tract, had markedly elevated manganese levels in the brain, blood, and liver. Thus, under basal physiological conditions, brain manganese is regulated by activity of SLC30A10 in the liver and gastrointestinal tract, and not the brain or just the liver. Notably, however, brain manganese levels of endoderm-specific knockouts were lower than whole-body knockouts, and only whole-body knockouts exhibited manganese-induced neurobehavioral defects. Moreover, after elevated exposure, pan-neuronal/glial knockouts had higher manganese levels in the basal ganglia and thalamus than controls. Therefore, when manganese levels increase, activity of SLC30A10 in the brain protects against neurotoxicity.

Manganese transport and toxicity in polarized WIF-B hepatocytes

Manganese (Mn) toxicity arises from nutritional problems, community and occupational exposures, and genetic risks. Mn blood levels are controlled by hepatobiliary clearance. The goals of this study were to determine the cellular distribution of Mn transporters in polarized hepatocytes, to establish an in vitro assay for hepatocyte Mn efflux, and to examine possible roles the Mn transporters would play in metal import and export. For these experiments, hepatocytoma WIF-B cells were grown for 12-14 days to achieve maximal polarity. Immunoblots showed that Mn transporters ZIP8, ZnT10, ferroportin (Fpn), and ZIP14 were present. Indirect immunofluorescence microscopy localized Fpn and ZIP14 to WIF-B cell basolateral domains whereas ZnT10 and ZIP8 associated with intracellular vesicular compartments. ZIP8-positive structures were distributed uniformly throughout the cytoplasm, but ZnT10-positive vesicles were adjacent to apical bile compartments. WIF-B cells were sensitive to Mn toxicity, showing decreased viability after 16 h exposure to >250 μM MnCl₂. However, the hepatocytes were resistant to 4-h exposures of up to 500 μM MnCl₂ despite 50-fold increased Mn content. Washout experiments showed time-dependent efflux with 80% Mn released after a 4 h chase period. Hepcidin reduced levels of Fpn in WIF-B cells, clearing Fpn from the cell surface, but Mn efflux was unaffected. The secretory inhibitor, brefeldin A, did block release of Mn from WIF-B cells, suggesting vesicle fusion may be involved in export. These results point to a possible role of ZnT10 to import Mn into vesicles that subsequently fuse with the apical membrane and empty their contents into bile. NEW & NOTEWORTHY Polarized WIF-B hepatocytes express manganese (Mn) transporters ZIP8, ZnT10, ferroportin (Fpn), and ZIP14. Fpn and ZIP14 localize to basolateral domains. ZnT10-positive vesicles were adjacent to apical bile compartments, and ZIP8-positive vesicles were distributed uniformly throughout the cytoplasm. WIF-B hepatocyte Mn export was resistant to hepcidin but inhibited by brefeldin A, pointing to an efflux mechanism involving ZnT10-mediated uptake of Mn into vesicles that subsequently fuse with and empty their contents across the apical bile canalicular membrane.

Inborn Errors of Metabolism with Movement Disorders: Defects in Metal Transport and Neurotransmitter Metabolism

Movement disorders in the pediatric age group are largely of the hyperkinetic type. Metal ion accumulation in the central nervous system presents predominantly with movement disorders and over time leads to psychomotor decline. Abnormalities in monoamine and amino acidergic neurotransmitter metabolism present in individuals with a combination of abnormal movements, epilepsy, and cognitive and motor delay. Detailed clinical history, careful examination, appropriate diagnostic work-up with metabolic screening, cerebrospinal fluid neurotransmitters, and targeted genetic testing help with accurate diagnosis and appropriate treatment. This article provides an overview on movement disorders present in childhood secondary to inborn errors of metal transport and neurotransmitter metabolism.

Hypermanganesemia with dystonia, polycythemia and cirrhosis in 10 patients: Six novel SLC30A10 mutations and further phenotype delineation

Biallelic mutations in the SLC30A10 gene cause an inborn error of Mn metabolism characterized by hypermanganesemia, polycythemia, early-onset dystonia, and liver cirrhosis (HMDPC). To date, only 14 families from various ethnic groups have been reported. Here, we describe 10 patients from 7 unrelated Egyptian families with HMDPC. Markedly elevated blood Mn levels, the characteristic basal ganglia hyperintensity on T1-weighted images, and variable degrees of extrapyramidal manifestations with or without liver disease were cardinal features in all patients. Eight patients presented with striking early diseased onset (≤2 years). Unexpectedly, early hepatic involvement before the neurological regression was noted in 3 patients. Mutational analysis of SLC30A10 gene revealed 6 novel homozygous mutations (c.77T > C (p.Leu26Pro), c.90C > G (p.Tyr30*), c.119A > C (p.Asp40Ala), c.122_124delCCT (p.Ser41del), c.780_782delCAT (p.Iso260del) and c.957 + 1G > C). Treatment using 2,3 dimercaptosuccinic acid as a manganese chelating agent showed satisfactory results with improvement of biochemical markers, hepatic manifestations and relative amelioration of the neurological symptoms. Our findings present a large cohort of patients with HMDPC from same ethnic group. The majority of our patients showed severe and early presentation with clear phenotypic variability among sibship. Moreover, we extend the phenotypic and mutational spectrum and emphasize the importance of early diagnosis and treatment of this potentially fatal disorder.

SLC39A14 deficiency alters manganese homeostasis and excretion resulting in brain manganese accumulation and motor deficits in mice

Solute carrier family 39, member 14 (SLC39A14) is a transmembrane transporter that can mediate the cellular uptake of zinc, iron, and manganese (Mn). Studies of Slc39a14 knockout (Slc39a14^-/-) mice have documented that SLC39A14 is required for systemic growth, hepatic zinc uptake during inflammation, and iron loading of the liver in iron overload. The normal physiological roles of SLC39A14, however, remain incompletely characterized. Here, we report that Slc39a14^-/- mice spontaneously display dramatic alterations in tissue Mn concentrations, suggesting that Mn is a main physiological substrate for SLC39A14. Specifically, Slc39a14^-/- mice have abnormally low Mn levels in the liver coupled with markedly elevated Mn concentrations in blood and most other organs, especially the brain and bone. Radiotracer studies using ⁵⁴Mn reveal that Slc39a14^-/- mice have impaired Mn uptake by the liver and pancreas and reduced gastrointestinal Mn excretion. In the brain of Slc39a14^-/- mice, Mn accumulated in the pons and basal ganglia, including the globus pallidus, a region susceptible to Mn-related neurotoxicity. Brain Mn accumulation in Slc39a14^-/- mice was associated with locomotor impairments, as assessed by various behavioral tests. Although a low-Mn diet started at weaning was able to reverse brain Mn accumulation in Slc39a14^-/- mice, it did not correct their motor deficits. We conclude that SLC39A14 is essential for efficient Mn uptake by the liver and pancreas, and its deficiency results in impaired Mn excretion and accumulation of the metal in other tissues. The inability of Mn depletion to correct the motor deficits in Slc39a14^-/- mice suggests that the motor impairments represent lasting effects of early-life Mn exposure.

Hypermanganesemia due to mutations in SLC39A14: further insights into Mn deposition in the central nervous system

Background

The SLC39A14, SLC30A10 and SLC39A8 are considered to be key genes involved in manganese (Mn) homeostasis in humans. Mn levels in plasma and urine are useful tools for early recognition of these disorders. We aimed to explore further biomarkers of Mn deposition in the central nervous system in two siblings presenting with acute dystonia and hypermanganesemia due to mutations in SLC39A14. These biomarkers may help clinicians to establish faster and accurate diagnosis and to monitor disease progression after chelation therapy is administered.

Results

A customized gene panel for movement disorders revealed a novel missense variant (c.311G > T; p.Ser104Ile) in SLC39A14 gene in two siblings presenting at the age of 10 months with acute dystonia and motor regression. Mn concentrations were analyzed using inductively coupled mass spectrometry in plasma and cerebrospinal fluid, disclosing elevated Mn levels in the index case compared to control patients. Surprisingly, Mn values were 3-fold higher in CSF than in plasma. We quantified the pallidal index, defined as the ratio between the signal intensity in the globus pallidus and the subcortical frontal white matter in axial T1-weighted MRI, and found significantly higher values in the SLC39A14 patient than in controls. These values increased over a period of 10 years, suggesting the relentless pallidal accumulation of Mn. Following genetic confirmation, a trial with the Mn chelator Na₂CaEDTA led to a reduction in plasma Mn, zinc and selenium levels. However, parents reported worsening of cervical dystonia, irritability and sleep difficulties and chelation therapy was discontinued.

Conclusions

Our study expands the very few descriptions of patients with SLC39A14 mutations. We report for the first time the elevation of Mn in CSF of SLC39A14 mutated patients, supporting the hypothesis that brain is an important organ of Mn deposition in SLC39A14-related disease. The pallidal index is an indirect and non-invasive method that can be used to rate disease progression on follow-up MRIs. Finally, we propose that patients with inherited defects of manganese transport should be initially treated with low doses of Na₂CaEDTA followed by gradual dose escalation, together with a close monitoring of blood trace elements in order to avoid side effects.

Influence of iron metabolism on manganese transport and toxicity

Although manganese (Mn) is critical for the proper functioning of various metabolic enzymes and cofactors, excess Mn in the brain causes neurotoxicity. While the exact transport mechanism of Mn has not been fully understood, several importers and exporters for Mn have been identified over the past decade. In addition to Mn-specific transporters, it has been demonstrated that iron transporters can mediate Mn transport in the brain and peripheral tissues. However, while the expression of iron transporters is regulated by body iron stores, whether or not disorders of iron metabolism modify Mn homeostasis has not been systematically discussed. The present review will provide an update on the role of altered iron status in the transport and toxicity of Mn.

Zebrafish slc30a10 deficiency revealed a novel compensatory mechanism of Atp2c1 in maintaining manganese homeostasis

Recent studies found that mutations in the human SLC30A10 gene, which encodes a manganese (Mn) efflux transporter, are associated with hypermanganesemia with dystonia, polycythemia, and cirrhosis (HMDPC). However, the relationship between Mn metabolism and HMDPC is poorly understood, and no specific treatments are available for this disorder. Here, we generated two zebrafish slc30a10 mutant lines using the CRISPR/Cas9 system. Compared to wild-type animals, mutant adult animals developed significantly higher systemic Mn levels, and Mn accumulated in the brain and liver of mutant embryos in response to exogenous Mn. Interestingly, slc30a10 mutants developed neurological deficits in adulthood, as well as environmental Mn-induced manganism in the embryonic stage; moreover, mutant animals had impaired dopaminergic and GABAergic signaling. Finally, mutant animals developed steatosis, liver fibrosis, and polycythemia accompanied by increased epo expression. This phenotype was rescued partially by EDTA- CaNa₂ chelation therapy and iron supplementation. Interestingly, prior to the onset of slc30a10 expression, expressing ATP2C1 (ATPase secretory pathway Ca²⁺ transporting 1) protected mutant embryos from Mn exposure, suggesting a compensatory role for Atp2c1 in the absence of Slc30a10. Notably, expressing either wild-type or mutant forms of SLC30A10 was sufficient to inhibit the effect of ATP2C1 in response to Mn challenge in both zebrafish embryos and HeLa cells. These findings suggest that either activating ATP2C1 or restoring the Mn-induced trafficking of ATP2C1 can reduce Mn accumulation, providing a possible target for treating HMDPC.

Impaired function of the manganese transporter SLC30A10 has been implicated in HMDPC (hypermanganesemia with dystonia, polycythemia, and cirrhosis), an early-onset metabolic disorder clinically characterized by increased systemic Mn levels, neurological impairment, polycythemia, and hepatic injury. No specific treatment is currently available for HMDPC. Moreover, the mechanisms that underlie Mn metabolism are poorly understood, thereby hindering the development of effective treatments. To investigate the physiological processes underlying Mn metabolism and to develop new disease models of HMDPC, we generated two zebrafish slc30a10 mutant lines using the CRISPR/Cas9 system and found that these mutants develop clinical deficits typically associated with HMDPC. Furthermore, we identified a putative compensatory role for ATP2C1 in the absence of SLC30A10 with respect to modulating Mn metabolism. These findings provide a valuable tool for investigating the role of manganese dysregulation in neurological degenerative diseases and which can be used to develop new pharmacological approaches for managing Mn accumulation.

Hypermanganesemia with Dystonia, Polycythemia and Cirrhosis (HMDPC) due to mutation in the SLC30A10 gene

Manganese (Mn) is an essential element for metabolic pathways but it can be toxic when present in excessive amounts in the body. Hypermanganesemia along with dystonia, polycythemia, characteristic MRI brain findings in the basal ganglia, and chronic liver disease are the hallmarks of an inherited Mn transporter defect due to mutations in the SLC30A10 gene. We are reporting three siblings who presented with features of dystonia, polycythemia, MRI brain showing basal ganglia hyperintensity on T1 weighted images and chronic liver disease. Blood Mn levels were markedly elevated in the affected patients. Mutation analysis of DNA samples of the affected children confirmed a homozygous missense mutation in SLC30A10. Chelation therapy with intravenous disodium calcium edetate was started in two siblings and led to a marked decrease in whole blood Mn. Oral Penicillamine was later added to the therapy which further improved blood Mn levels. This is a rare disorder and is one of the potentially treatable inherited metal storage disorders. It can be fatal if left untreated. Penicillamine may be an effective alternative to disodium calcium edetate.

Common Polymorphisms in the Solute Carrier SLC30A10 are Associated With Blood Manganese and Neurological Function

Manganese (Mn) is an essential nutrient in humans, but excessive exposure to Mn may cause neurotoxicity. Despite homeostatic regulation, Mn concentrations in blood vary considerably among individuals. We evaluated if common single-nucleotide polymorphisms (SNPs) in SLC30A10, which likely encodes an Mn transporter, influence blood Mn concentrations and neurological function. We measured blood Mn concentrations by ICP-MS or atomic absorption spectroscopy and genotyped 2 SLC30A10 non-coding SNPs (rs2275707 and rs12064812) by TaqMan PCR in cohorts from Bangladesh (N = 406), the Argentinean Andes (N = 198), and Italy (N = 238). We also measured SLC30A10 expression in whole blood by TaqMan PCR in a sub-group (N = 101) from the Andean cohort, and neurological parameters (sway velocity and finger-tapping speed) in the Italian cohort. The rs2275707 variant allele was associated with increased Mn concentrations in the Andes (8%, P = .027) and Italy (10.6%, P = .012), but not as clear in Bangladesh (3.4%, P = .21; linear regression analysis adjusted for age, gender, and plasma ferritin). This allele was also associated with increased sway velocity (15%, P = .033; adjusted for age and sex) and reduced SLC30A10 expression (−24.6%, P = .029). In contrast, the rs12064812 variant homozygous genotype was associated with reduced Mn concentrations, particularly in the Italian cohort (−18.4%, P = .04), and increased finger-tapping speed (8.7%, P = .025). We show that common SNPs in SLC30A10 are associated with blood Mn concentrations in 3 unrelated cohorts and that their influence may be mediated by altered SLC30A10 expression. Moreover, the SNPs appeared to influence neurological functions independent of blood Mn concentrations, suggesting that SLC30A10 could regulate brain Mn levels.