Iron in the Hallervorden-Spatz syndrome

Iron Dyshomeostasis in Neurodegeneration with Brain Iron Accumulation (NBIA): Is It the Cause or the Effect?

Iron is an essential metal ion implicated in several cellular processes. However, the reactive nature of iron renders this metal ion potentially dangerous for cells, and its levels need to be tightly controlled. Alterations in the intracellular concentration of iron are associated with different neuropathological conditions, including neurodegeneration with brain iron accumulation (NBIA). As the name suggests, NBIA encompasses a class of rare and still poorly investigated neurodegenerative disorders characterized by an abnormal accumulation of iron in the brain. NBIA is mostly a genetic pathology, and to date, 10 genes have been linked to familial forms of NBIA. In the present review, after the description of the principal mechanisms implicated in iron homeostasis, we summarize the research data concerning the pathological mechanisms underlying the genetic forms of NBIA and discuss the potential involvement of iron in such processes. The picture that emerges is that, while iron overload can contribute to the pathogenesis of NBIA, it does not seem to be the causal factor in most forms of the pathology. The onset of these pathologies is rather caused by a combination of processes involving the interplay between lipid metabolism, mitochondrial functions, and autophagic activity, eventually leading to iron dyshomeostasis.

Iron Load Toxicity in Medicine: From Molecular and Cellular Aspects to Clinical Implications

Iron is essential for all organisms and cells. Diseases of iron imbalance affect billions of patients, including those with iron overload and other forms of iron toxicity. Excess iron load is an adverse prognostic factor for all diseases and can cause serious organ damage and fatalities following chronic red blood cell transfusions in patients of many conditions, including hemoglobinopathies, myelodyspasia, and hematopoietic stem cell transplantation. Similar toxicity of excess body iron load but at a slower rate of disease progression is found in idiopathic haemochromatosis patients. Excess iron deposition in different regions of the brain with suspected toxicity has been identified by MRI T2* and similar methods in many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Based on its role as the major biological catalyst of free radical reactions and the Fenton reaction, iron has also been implicated in all diseases associated with free radical pathology and tissue damage. Furthermore, the recent discovery of ferroptosis, which is a cell death program based on free radical generation by iron and cell membrane lipid oxidation, sparked thousands of investigations and the association of iron with cardiac, kidney, liver, and many other diseases, including cancer and infections. The toxicity implications of iron in a labile, non-protein bound form and its complexes with dietary molecules such as vitamin C and drugs such as doxorubicin and other xenobiotic molecules in relation to carcinogenesis and other forms of toxicity are also discussed. In each case and form of iron toxicity, the mechanistic insights, diagnostic criteria, and molecular interactions are essential for the design of new and effective therapeutic interventions and of future targeted therapeutic strategies. In particular, this approach has been successful for the treatment of most iron loading conditions and especially for the transition of thalassemia from a fatal to a chronic disease due to new therapeutic protocols resulting in the complete elimination of iron overload and of iron toxicity.

Potential Treatment of Retinal Diseases with Iron Chelators

Iron is essential for life, while excess iron can be toxic. Iron generates hydroxyl radical, which is the most reactive free radical, causing oxidative stress. Since iron is absorbed through the diet but not excreted from the body, it accumulates with age in tissues, including the retina, consequently leading to age-related toxicity. This accumulation is further promoted by inflammation. Hereditary diseases such as aceruloplasminemia, Friedreich’s ataxia, pantothenate kinase-associated neurodegeneration, and posterior column ataxia with retinitis pigmentosa involve retinal degeneration associated with iron dysregulation. In addition to hereditary causes, dietary or parenteral iron supplementation has been recently reported to elevate iron levels in the retinal pigment epithelium (RPE) and promote retinal degeneration. Ocular siderosis from intraocular foreign bodies or subretinal hemorrhage can also lead to retinopathy. Evidence from mice and humans suggests that iron toxicity may contribute to age-related macular degeneration pathogenesis. Iron chelators can protect photoreceptors and RPE in various mouse models. The therapeutic potential for iron chelators is under investigation.

New Perspectives in Iron Chelation Therapy for the Treatment of Neurodegenerative Diseases

Iron chelation has been introduced as a new therapeutic concept for the treatment of neurodegenerative diseases with features of iron overload. At difference with iron chelators used in systemic diseases, effective chelators for the treatment of neurodegenerative diseases must cross the blood–brain barrier. Given the promissory but still inconclusive results obtained in clinical trials of iron chelation therapy, it is reasonable to postulate that new compounds with properties that extend beyond chelation should significantly improve these results. Desirable properties of a new generation of chelators include mitochondrial destination, the center of iron-reactive oxygen species interaction, and the ability to quench free radicals produced by the Fenton reaction. In addition, these chelators should have moderate iron binding affinity, sufficient to chelate excessive increments of the labile iron pool, estimated in the micromolar range, but not high enough to disrupt physiological iron homeostasis. Moreover, candidate chelators should have selectivity for the targeted neuronal type, to lessen unwanted secondary effects during long-term treatment. Here, on the basis of a number of clinical trials, we discuss critically the current situation of iron chelation therapy for the treatment of neurodegenerative diseases with an iron accumulation component. The list includes Parkinson’s disease, Friedreich’s ataxia, pantothenate kinase-associated neurodegeneration, Huntington disease and Alzheimer’s disease. We also review the upsurge of new multifunctional iron chelators that in the future may replace the conventional types as therapeutic agents for the treatment of neurodegenerative diseases.

Disrupted iron regulation in the brain and periphery in cocaine addiction

Stimulant drugs acutely increase dopamine neurotransmission in the brain, and chronic use leads to neuroadaptive changes in the mesolimbic dopamine system and morphological changes in basal ganglia structures. Little is known about the mechanisms underlying these changes but preclinical evidence suggests that iron, a coenzyme in dopamine synthesis and storage, may be a candidate mediator. Iron is present in high concentrations in the basal ganglia and stimulant drugs may interfere with iron homeostasis. We hypothesised that morphological brain changes in cocaine addiction relate to abnormal iron regulation in the brain and periphery. We determined iron concentration in the brain, using quantitative susceptibility mapping, and in the periphery, using iron markers in circulating blood, in 44 patients with cocaine addiction and 44 healthy controls. Cocaine-addicted individuals showed excess iron accumulation in the globus pallidus, which strongly correlated with duration of cocaine use, and mild iron deficiency in the periphery, which was associated with low iron levels in the red nucleus. Our findings show that iron dysregulation occurs in cocaine addiction and suggest that it arises consequent to chronic cocaine use. Putamen enlargement in these individuals was unrelated to iron concentrations, suggesting that these are co-occurring morphological changes that may respectively reflect predisposition to, and consequences of cocaine addiction. Understanding the mechanisms by which cocaine affects iron metabolism may reveal novel therapeutic targets, and determine the value of iron levels in the brain and periphery as biomarkers of vulnerability to, as well as progression and response to treatment of cocaine addiction.

Lysosomal iron modulates NMDA receptor-mediated excitation via small GTPase, Dexras1

Background

Activation of NMDA receptors can induce iron movement into neurons by the small GTPase Dexras1 via the divalent metal transporter 1 (DMT1). This pathway under pathological conditions such as NMDA excitotoxicity contributes to metal-catalyzed reactive oxygen species (ROS) generation and neuronal cell death, and yet its physiological role is not well understood.

Results

We found that genetic and pharmacological ablation of this neuronal iron pathway in the mice increased glutamatergic transmission. Voltage sensitive dye imaging of hippocampal slices and whole-cell patch clamping of synaptic currents, indicated that the increase in excitability was due to synaptic modification of NMDA receptor activity via modulation of the PKC/Src/NR2A pathway. Moreover, we identified that lysosomal iron serves as a main source for intracellular iron signaling modulating glutamatergic excitability.

Conclusions

Our data indicates that intracellular iron is dynamically regulated in the neurons and robustly modulate synaptic excitability under physiological condition. Since NMDA receptors play a central role in synaptic neurophysiology, plasticity, neuronal homeostasis, neurodevelopment as well as in the neurobiology of many diseases, endogenous iron is therefore likely to have functional relevance to each of these areas.

Iron deposits in the chronically inflamed central nervous system and contributes to neurodegeneration

Neurodegenerative disorders are characterized by the presence of inflammation in areas with neuronal cell death and a regional increase in iron that exceeds what occurs during normal aging. The inflammatory process accompanying the neuronal degeneration involves glial cells of the central nervous system (CNS) and monocytes of the circulation that migrate into the CNS while transforming into phagocytic macrophages. This review outlines the possible mechanisms responsible for deposition of iron in neurodegenerative disorders with a main emphasis on how iron-containing monocytes may migrate into the CNS, transform into macrophages, and die out subsequently to their phagocytosis of damaged and dying neuronal cells. The dying macrophages may in turn release their iron, which enters the pool of labile iron to catalytically promote formation of free-radical-mediated stress and oxidative damage to adjacent cells, including neurons. Healthy neurons may also chronically acquire iron from the extracellular space as another principle mechanism for oxidative stress-mediated damage. Pharmacological handling of monocyte migration into the CNS combined with chelators that neutralize the effects of extracellular iron occurring due to the release from dying macrophages as well as intraneuronal chelation may denote good possibilities for reducing the deleterious consequences of iron deposition in the CNS.

A new in vivo model of pantothenate kinase-associated neurodegeneration reveals a surprising role for transcriptional regulation in pathogenesis

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is a neurodegenerative disorder with a poorly understood molecular mechanism. It is caused by mutations in Pantothenate Kinase, the first enzyme in the Coenzyme A (CoA) biosynthetic pathway. Here, we developed a Drosophila model of PKAN (tim-fbl flies) that allows us to continuously monitor the modeled disease in the brain. In tim-fbl flies, downregulation of fumble, the Drosophila PanK homologue in the cells containing a circadian clock results in characteristic features of PKAN such as developmental lethality, hypersensitivity to oxidative stress, and diminished life span. Despite quasi-normal circadian transcriptional rhythms, tim-fbl flies display brain-specific aberrant circadian locomotor rhythms, and a unique transcriptional signature. Comparison with expression data from flies exposed to paraquat demonstrates that, as previously suggested, pathways others than oxidative stress are affected by PANK downregulation. Surprisingly we found a significant decrease in the expression of key components of the photoreceptor recycling pathways, which could lead to retinal degeneration, a hallmark of PKAN. Importantly, these defects are not accompanied by changes in structural components in eye genes suggesting that changes in gene expression in the eye precede and may cause the retinal degeneration. Indeed tim-fbl flies have diminished response to light transitions, and their altered day/night patterns of activity demonstrates defects in light perception. This suggest that retinal lesions are not solely due to oxidative stress and demonstrates a role for the transcriptional response to CoA deficiency underlying the defects observed in dPanK deficient flies. Moreover, in the present study we developed a new fly model that can be applied to other diseases and that allows the assessment of neurodegeneration in the brains of living flies.

Retinal iron homeostasis in health and disease

Iron is essential for life, but excess iron can be toxic. As a potent free radical creator, iron generates hydroxyl radicals leading to significant oxidative stress. Since iron is not excreted from the body, it accumulates with age in tissues, including the retina, predisposing to age-related oxidative insult. Both hereditary and acquired retinal diseases are associated with increased iron levels. For example, retinal degenerations have been found in hereditary iron overload disorders, like aceruloplasminemia, Friedreich's ataxia, and pantothenate kinase-associated neurodegeneration. Similarly, mice with targeted mutation of the iron exporter ceruloplasmin and its homolog hephaestin showed age-related retinal iron accumulation and retinal degeneration with features resembling human age-related macular degeneration (AMD). Post mortem AMD eyes have increased levels of iron in retina compared to age-matched healthy donors. Iron accumulation in AMD is likely to result, in part, from inflammation, hypoxia, and oxidative stress, all of which can cause iron dysregulation. Fortunately, it has been demonstrated by in vitro and in vivo studies that iron in the retinal pigment epithelium (RPE) and retina is chelatable. Iron chelation protects photoreceptors and retinal pigment epithelial cells (RPE) in a variety of mouse models. This has therapeutic potential for diminishing iron-induced oxidative damage to prevent or treat AMD.

Late onset neurodegeneration with brain-iron accumulation presenting as parkinsonism

Neurodegeneration with brain-iron accumulation (NBIA) encompasses a family of neurodegenerative disorders connected by evidence of abnormal brain iron deposition. Advances in imaging and genetic testing expanded the clinical spectrum of these disorders. Here, a case of parkinsonism and dystonia with orofacial stereotypies is presented. While the patient was initially diagnosed with Parkinson's disease and placed on levodopa therapy, dopamine transporter imaging via (123)I-FP-CIT SPECT (DaTSCAN) was normal. MRI brain showed "eye of the tiger" sign on T2 weighted imaging. NBIA should be considered in the differential diagnosis of atypical parkinsonism.

Pantothenate kinase-associated neurodegeneration (PKAN) and PLA2G6-associated neurodegeneration (PLAN): review of two major neurodegeneration with brain iron accumulation (NBIA) phenotypes

Neurodegeneration with brain iron accumulation (NBIA) comprises a heterogeneous group of disorders characterized by the presence of radiologically discernible high brain iron, particularly within the basal ganglia. A number of childhood NBIA syndromes are described, of which two of the major subtypes are pantothenate kinase-associated neurodegeneration (PKAN) and PLA2G6-associated neurodegeneration (PLAN). PKAN and PLAN are autosomal recessive NBIA disorders due to mutations in PANK2 and PLA2G6, respectively. Presentation is usually in childhood, with features of neurological regression and motor dysfunction. In both PKAN and PLAN, a number of classical and atypical phenotypes are reported. In this chapter, we describe the clinical, radiological, and genetic features of these two disorders and also discuss the pathophysiological mechanisms postulated to play a role in disease pathogenesis.

Clinicopathological review of pallidonigroluysian atrophy

Pallidonigroluysian atrophy is a rare neurodegenerative disease characterized by degeneration of the globus pallidus, substantia nigra, and subthalamic nucleus. Few studies have comprehensively documented the clinical and pathological features of pallidonigroluysian atrophy. A systematic review of all published cases of pallidonigroluysian atrophy in English since 1970 was performed. We also report a new case of pallidonigroluysian atrophy. Twenty-five cases of pathologically proven pallidonigroluysian atrophy were reviewed, 24 from the literature and 1 of our own. Average age of onset was 54.3 ± 14.3 years, and average duration of disease was 7.9 ± 5.8 years. The most common first symptom was gait or balance disturbance. Patients had a diversity of movement disorders, including chorea in 5 cases (20%). Nine cases (36%) had coexistent motor neuron disease. Almost all cases had gliosis, and many cases had iron-positive pigments in the pallidonigroluysian system. Tauopathy was absent to rare in this region. Widespread tau-negative, p62-positive glial inclusions, described in 1 previous case, were also present in our patient. As pallidonigroluysian atrophy has a diversity of clinical presentations, it is best defined neuropathologically. The relative lack of tauopathy and the presence of p62-positive glial inclusions or iron-positive pigments in the pallidonigroluysian region may help to distinguish pallidonigroluysian atrophy from similar disease entities.

Skin fibroblasts from pantothenate kinase-associated neurodegeneration patients show altered cellular oxidative status and have defective iron-handling properties

Pantothenate kinase-associated neurodegeneration (PKAN) is a neurodegenerative disease belonging to the group of neurodegeneration with brain iron accumulation disorders. It is characterized by progressive impairments in movement, speech and cognition. The disease is inherited in a recessive manner due to mutations in the Pantothenate Kinase-2 (PANK2) gene that encodes a mitochondrial protein involved in Coenzyme A synthesis. To investigate the link between a PANK2 gene defect and iron accumulation, we analyzed primary skin fibroblasts from three PKAN patients and three unaffected subjects. The oxidative status of the cells and their ability to respond to iron were analyzed in both basal and iron supplementation conditions. In basal conditions, PKAN fibroblasts show an increase in carbonylated proteins and altered expression of antioxidant enzymes with respect to the controls. After iron supplementation, the PKAN fibroblasts had a defective response to the additional iron. Under these conditions, ferritins were up-regulated and Transferrin Receptor 1 (TfR1) was down-regulated to a minor extent in patients compared with the controls. Analysis of iron regulatory proteins (IRPs) reveals that, with respect to the controls, PKAN fibroblasts have a reduced amount of membrane-associated mRNA-bound IRP1, which responds imperfectly to iron. This accounts for the defective expression of ferritin and TfR1 in patients' cells. The inaccurate quantity of these proteins produced a higher bioactive labile iron pool and consequently increased iron-dependent reactive oxygen species formation. Our results suggest that Pank2 deficiency promotes an increased oxidative status that is further enhanced by the addition of iron, potentially causing damage in cells.

Transcranial ultrasound in neurodegeneration with brain iron accumulation (NBIA)

NBIA/HSS is a neurodegenerative disorder associated with iron accumulation in specific brain regions. To date, the diagnosis is obtained by typical MRI changes followed by genetic mutation analysis. This procedure is laborious and limited to a few specially equipped medical centres. Since transcranial sonography (TCS) is widely used for the early diagnosis of PD in adults displaying parenchymal metal deposits, it is likely to be a reliable diagnostic tool for the early diagnosis of NBIA. In 7 patients with proven NBIA and 13 age-matched controls without record of neurological disease TCS was performed by an experienced ultrasound examiner. Data were analysed by two blinded investigators regarding hyperechogenicity and size of the substantia nigra (SN). SN size and hyperechogenicity was significantly increased in patients with NBIA compared to controls (students t-test: p < 0.001). TCS appears to be a non-invasive and inexpensive screening technique in patients with suspected NBIA. Performed by an experienced physician, it could enable an earlier diagnosis and pre-selection of patients for the MRI scan and genetic testing, which are still the diagnostic gold standard.

Case report: MR spectroscopy in pantothenate kinase-2 associated neurodegeneration

We report a case of a 13-year-old girl with Hallervorden-Spatz disease (HSD) or pantothenate kinase-2 associated neurodegeneration (PKAN). HSD is a rare neurodegenerative disorder, which is characterized by a rapidly progressive extrapyramidal syndrome, dementia with optic atrophy, and retinal degeneration. It is associated with accumulation of cysteine-iron complex in the globus pallidi and substantia nigra. The MRI “eye of the tiger” sign is the characteristic. MRI spectroscopy is also characteristic. It shows markedly decreased NAA/Cr values in the globus pallidi and substantia nigra with increased mI/Cr values that suggest of gliosis.

Pantothenate kinase-2 (Pank2) silencing causes cell growth reduction, cell-specific ferroportin upregulation and iron deregulation

Pantothenate kinase 2 (Pank2) is a mitochondrial enzyme that catalyses the first regulatory step of Coenzyme A synthesis and that is responsible for a genetic movement disorder named Pank-associated neurodegeneration (PKAN). This is characterized by abnormal iron accumulation in the brain, particularly in the globus pallidus. We downregulated Pank2 in some cell lines by using specific siRNAs to study its effect on iron homeostasis. In HeLa cells this caused a reduction of cell proliferation and of aconitase activity, signs of cytosolic iron deficiency without mitochondrial iron deposition, and a 12-fold induction of ferroportin mRNA. Pank2 silencing caused a strong induction of ferroportin mRNA also in hepatoma HepG2, a modest one in neuroblastoma SH-SY5Y and none in glioma U373 cells. A reduction of cell growth was observed in all these cell types. The strong Pank2-mediated alteration of ferroportin expression in some cell types might alter iron transfer to the brain and be connected with brain iron accumulation.

[Adult-onset case of idiopathic neurodegeneration with brain iron accumulation without mutations in the PANK2 and PLA2G6 genes]

A 47-year-old man with a 15-year history of bipolar disorder treated with anti-depressants, lithium carbonate or neuroleptics was admitted because of marked difficulty in gait and speech. At the age 45, he was unable to walk without bilateral assists and became a wheel-chair state. There was no family history and his mother, father and younger sister were neurologically free. General physical examinations revealed no abnormalities. Neurologically, he was moderately demented (mini mental state examination: 18/30) and showed bilateral horizontal gaze nystagmus, parkinsonism, cerebellar ataxia, dysarthria and moderate spastic paraparesis. No involuntary movements were noted. Wet blood smear showed acanthocytes, while blood chemistries revealed no abnormalities including levels of serum creatine kinase, hepatic enzymes and blood beta-lipoprotein. Kell antigen expressions of the red blood cells were within normal limit. Western blot analysis with anti-chorein antibody detected normal chorein expression levels of the red blood cells. Cranial MRI showed severe symmetric atrophy of the frontotemporal lobes, caudate nuclei, putamen, and brainstem. Also, MRI-gradient echo showed symmetric iron accumulation in the medial portion of the globus pallidus without surrounding high intensity areas, so called "eye-of-the-tiger sign". Genetic analyses revealed no mutations in the PANK2 and PLA2G6 genes. Therefore, he was diagnosed as idiopathic neurodegeneration with brain iron accumulation (NBIA). These findings suggest that NBIA is heterogeneous and other additional genes remain to be found.

Iron localization in superficial siderosis of the central nervous system

Originally conceived as an uncommon disorder, with the advent of MRI, CNS superficial siderosis has been observed more frequently. We present histologic, histochemical, immunohistochemical, immunofluorescent and ultrastructural evaluation of a 56-year-old woman with superficial siderosis. Iron was concentrated in macrophages, superficial astrocytes and gray matter oligodendroglia deep within the cord. While spatially associated with dystrophic glial and neuronal spheroids, iron did not colocalize with mitochondria. Neurotoxic effects were observed despite selective iron localization only within a variety of non-neuronal cell types.

Immunohistochemical Features of Dystrophic Axons in Papillon Dogs with Neuroaxonal Dystrophy

The immunohistochemical features of dystrophic axons in brain tissues of Papillon dogs with neuroaxonal dystrophy (NAD) were examined in comparison with 1 dog with cerebellar cortical abiotrophy (CCA) and a dog without neurologic signs. Histologically, many dystrophic axons were observed throughout the central nervous system of all dogs with NAD. These axonal changes were absent in the dog with CCA and in the control dog. Severe Purkinje cell loss was found in the dog with CCA, whereas the lesions were milder in all dogs with NAD. Immunohistochemically, the many dystrophic axons were positive for neurofilaments, tau, α/β-synuclein, HSP70, ubiquitin, synaptophysin, syntaxin-1, and synaptosomal-associated protein-25 (SNAP-25). A few dystrophic axons were positive for α-synuclein. In addition, these dystrophic axons, especially in the nucleus gracilis, cuneatus, olivaris, and spinal tract of the trigeminal nerve, were intensely immunopositive for the 3 calcium-binding proteins calretinin, calbindin, and parvalbumin. The accumulation of synapse-associated proteins in the dystrophic axons may indicate dysfunction of the synapse at the presynaptic portion. The accumulation of α-synuclein in the dystrophic axon and region-specific appearance of calcium-binding protein-positive spheroids are considered as unique features in NAD of Papillon dogs, providing the key to elucidate the pathogenesis.

Clinical and genetic delineation of neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) describes a group of progressive neurodegenerative disorders characterised by high brain iron and the presence of axonal spheroids, usually limited to the central nervous system. Mutations in the PANK2 gene account for the majority of NBIA cases and cause an autosomal recessive inborn error of coenzyme A metabolism called pantothenate kinase associated neurodegeneration (PKAN). More recently, it was found that mutations in the PLA2G6 gene cause both infantile neuroaxonal dystrophy (INAD) and, more rarely, an atypical neuroaxonal dystrophy that overlaps clinically with other forms of NBIA. High brain iron is also present in a portion of these cases. Clinical assessment, neuroimaging, and molecular genetic testing all play a role in guiding the diagnostic evaluation and treatment of NBIA.

Pallidal stimulation for dystonia in pantothenate kinase-associated neurodegeneration

Patients with generalized dystonia secondary to pantothenate kinase-associated neurodegeneration are traditionally treated palliatively with medical therapy. Therapeutic advances include stereotactic basal ganglia ablative techniques and, more recently, pallidal deep-brain stimulation. We report the course of dystonia in a teenage male. Bilateral microelectrode-guided pallidal deep-brain stimulators were placed while the patient was awake. Three parasagittal microelectrodes were inserted simultaneously. Two anterior microelectrodes were relatively quiet. The posterior electrode demonstrated a pattern of frequent bursts with high-frequency activity. The stimulator was therefore placed in the posterior location, which resulted in symptomatic improvement. Pallidal deep-brain stimulation appears to create a functional correction that may alter globus pallidus internus inhibitory output to the motor thalamus. The prominent, noisy bursting patterns observed in the globus pallidus internus suggests that high-frequency stimulation may improve signs of dystonia by normalizing thalamic discharge patterns.

Novel mutation in the PANK2 gene leads to pantothenate kinase-associated neurodegeneration in a Pakistani family

Pantothenate kinase-associated neurodegeneration is an autosomal-recessive disorder associated with the accumulation of iron in the basal ganglia. The disease presents with dystonia, rigidity, and gait impairment, leading to restriction of activities and loss of ambulation. The disorder is caused by defective iron metabolism associated with mutations in the PANK2 gene, which codes for the pantothenate kinase enzyme. We report on a mutation screen conducted in two siblings to establish a molecular diagnosis of the disease and a genetic test for the family.

Iron homeostasis and toxicity in retinal degeneration

Iron is essential for many metabolic processes but can also cause damage. As a potent generator of hydroxyl radical, the most reactive of the free radicals, iron can cause considerable oxidative stress. Since iron is absorbed through diet but not excreted except through menstruation, total body iron levels buildup with age. Macular iron levels increase with age, in both men and women. This iron has the potential to contribute to retinal degeneration. Here we present an overview of the evidence suggesting that iron may contribute to retinal degenerations. Intraocular iron foreign bodies cause retinal degeneration. Retinal iron buildup resulting from hereditary iron homeostasis disorders aceruloplasminemia, Friedreich's ataxia, and panthothenate kinase-associated neurodegeneration cause retinal degeneration. Mice with targeted mutation of the iron exporter ceruloplasmin have age-dependent retinal iron overload and a resulting retinal degeneration with features of age-related macular degeneration (AMD). Post mortem retinas from patients with AMD have more iron and the iron carrier transferrin than age-matched controls. Over the past 10 years much has been learned about the intricate network of proteins involved in iron handling. Many of these, including transferrin, transferrin receptor, divalent metal transporter-1, ferritin, ferroportin, ceruloplasmin, hephaestin, iron-regulatory protein, and histocompatibility leukocyte antigen class I-like protein involved in iron homeostasis (HFE) have been found in the retina. Some of these proteins have been found in the cornea and lens as well. Levels of the iron carrier transferrin are high in the aqueous and vitreous humors. The functions of these proteins in other tissues, combined with studies on cultured ocular tissues, genetically engineered mice, and eye exams on patients with hereditary iron diseases provide clues regarding their ocular functions. Iron may play a role in a broad range of ocular diseases, including glaucoma, cataract, AMD, and conditions causing intraocular hemorrhage. While iron deficiency must be prevented, the therapeutic potential of limiting iron-induced ocular oxidative damage is high. Systemic, local, or topical iron chelation with an expanding repertoire of drugs has clinical potential.

Psychosis as presenting symptom in adult-onset Hallervorden-Spatz syndrome

BACKGROUND

Hallervorden-Spatz syndrome is characterized by pyramidal and extrapyramidal signs, and dysarthria and dementia. Psychiatric symptomatology can emerge in the course of the disorder. Mutations in the pantothenate kinase 2 gene have been found in many cases. We report a case with psychosis as sole presenting symptom.

CASE

A 41-year-old man presented with change in behavior and paranoid delusional ideation. Six months later, spasticity, extrapyramidal rigidity and dysarthria were added to the picture. Eventually, the patient became mute and wheel-chair bound. The brain magnetic resonance imaging (MRI) was consistent with iron depositions in the globus pallidus and substantia nigra.

CONCLUSIONS

In this case, the combination of clinical and MRI findings was consistent with Hallervorden-Spatz syndrome. The combination of psychiatric and MRI findings should lead to further neurological investigation.

Iron metabolism in Parkinsonian syndromes

Growing evidence suggests an involvement of iron in the pathophysiology of neurodegenerative diseases. Several of the diseases are associated with parkinsonian syndromes, induced by degeneration of basal ganglia regions that contain the highest amount of iron within the brain. The group of neurodegenerative disorders associated with parkinsonian syndromes with increased brain iron content can be devided into two groups: (1) parkinsonian syndromes associated with brain iron accumulation, including Parkinson's disease, diffuse Lewy body disease, parkinsonian type of multiple system atrophy, progressive supranuclear palsy, corticobasal ganglionic degeneration, and Westphal variant of Huntington's disease; and (2) monogenetically caused disturbances of brain iron metabolism associated with parkinsonian syndromes, including aceruloplasminemia, hereditary ferritinopathies affecting the basal ganglia, and panthotenate kinase associated neurodegeneration type 2. Although it is still a matter of debate whether iron accumulation is a primary cause or secondary event in the first group, there is no doubt that iron-induced oxidative stress contributes to neurodegeneration. Parallels concerning pathophysiological as well as clinical aspects can be drawn between disorders of both groups. Results from animal models and reduction of iron overload combined with at least partial relief of symptoms by application of iron chelators in patients of the second group give hope that targeting the iron overload might be one possibility to slow down the neurodegenerative cascade also in the first group of inevitably progressive neurodegenerative disorders.

Role of iron in neurodegenerative disorders

Although the pathophysiology underlying a number of neurodegenerative diseases is complex and, in many aspects, only partly understood, increased iron levels in pathologically relevant brain areas and iron-mediated oxidative stress seem to play a central role in many of them. Much has been learned from monogenetically caused disturbances of brain iron metabolism including pantothenate kinase-associated neurodegeneration type 2, hereditary ferritinopathies affecting the basal ganglia, and aceruloplasminemia that may well be applied to the most common neurodegenerative disorders associated with brain iron accumulation including Parkinson disease and Alzheimer disease. Iron-mediated oxidative stress in neurodegenerative diseases caused by other genetic pathways like Huntington disease and Friedreich ataxia underscore the complex interaction of this trace metal and genetic variations. Therapeutical strategies derived from application of iron chelators in monogenetically caused disturbances of brain iron metabolism and new iron and oxidative stress diminishing substances in animal models of Parkinson disease are promising and warrant further investigational effort.

Identification of axonal involvement in Hallervorden-Spatz disease with magnetic resonance spectroscopy

Hallervorden-Spatz disease is a neurodegenerative disorder associated with cysteine-iron complex accumulation typically seen as bilateral symmetrical hypointense signal changes in the medial globus pallidus on magnetic resonance imaging. We used magnetic resonance spectroscopy to identify and quantify neuronal damage in two siblings with Hallervorden-Spatz disease. The first patient presenting with a rapidly progressive extrapyramidal syndrome had markedly decreased N-acetylaspartate (NAA) to creatinine (Cr) ratios in the globus pallidi and the periatrial white matter. He also had increased myoinositol (mI) to creatinine (Cr) ratios implying glial proliferation in the affected regions. However the second patient who had the initial presentation of disease had normal NAA/Cr and mI/Cr ratios. These findings indicate that the quantification of NAA:Cr and mI:Cr ratios might be used to predict the extent of neuronal axonal loss and glial proliferation in patients with Hallervorden-Spatz disease respectively.

Neuro-ophthalmologic and electroretinographic findings in pantothenate kinase-associated neurodegeneration (formerly Hallervorden-Spatz syndrome)

PURPOSE

The onset of pantothenate kinase-associated neurodegeneration (PKAN) occurs in the first and second decade of life and a pigmentary retinal degeneration is a feature of the disorder. Since the neuro-ophthalmologic and electroretinographic (ERG) features have never been well delineated, we describe them in 16 patients with PKAN.

DESIGN

Observational case series.

METHODS

Sixteen patients with genetic and neuroimaging-confirmed PKAN were examined. Ten underwent neuro-ophthalmologic examination and all had ERGs.

RESULTS

Of the 10 who underwent neuro-ophthalmologic examination, all showed saccadic pursuits and eight showed hypometric or slowed vertical saccades. Seven of eight had inability to suppress the vestibulo-ocular reflex; two patients could not cooperate. Two had square wave jerks and four had poor convergence. Vertical optokinetic responses were abnormal in five, and two patients had blepharospasm. Eight patients had sectoral iris paralysis and partial loss of the pupillary ruff consistent with Adie's pupils in both eyes. Only four of 10 examined patients showed a pigmentary retinopathy, but 11 of 16 had abnormal ERGs ranging from mild cone abnormalities to severe rod-cone dysfunction. No patient had optic atrophy. The PANK2 mutations of all of the patients were heterogeneous.

CONCLUSIONS

Adie's-like pupils, abnormal vertical saccades, and saccadic pursuits were very common. These findings suggest that mid-brain degeneration occurs in PKAN more frequently than previously thought. ERG abnormalities were present in approximately 70% and no patient had optic atrophy. Although genotype-ocular phenotype correlations could not be established, allelic differences probably contributed to the variable clinical expression of retinopathy and other clinical characteristics in these patients.

Atypical Hallervorden-Spatz disease with preserved cognition and obtrusive obsessions and compulsions

We describe the case of an adult female with Hallervorden-Spatz disease (HSD), "eye-of-the-tiger" sign on cranial magnetic resonance imaging scan, and two mutations in the pantothenate kinase 2 (PANK2) gene. Symptomatic presentation included stuttering dysarthria, dystonic posturing, increased limb and axial muscle tone, choreoathetosis, stereotyped motor behaviors, and obsessive-compulsive symptomatology since adolescence. Extensive neuropsychological testing at 40 and 44 years of age revealed a relatively normal IQ and stable cognitive pattern overall. This case demonstrates that HSD patients who survive into middle age should not be assumed to have a progressive dementia. In such cases, atypical behavioral problems such as persistent obsessions and compulsions may be present instead.

Clinical heterogeneity of neurodegeneration with brain iron accumulation (Hallervorden-Spatz syndrome) and pantothenate kinase-associated neurodegeneration

Hallervorden Spatz syndrome (HSS), also referred to as neurodegeneration with brain iron accumulation (NBIA), is a rare inherited neurodegenerative disorder with childhood, adolescent, or adult onset. Patients with HSS/NBIA have a combination of motor symptoms in the form of dystonia, parkinsonism, choreoathetosis, corticospinal tract involvement, optic atrophy, pigmentary retinopathy, and cognitive impairment. After the recent identification of mutations in the PANK2 gene on chromosome 20p12.3-p13 in some patients with the HSS/NBIA phenotype, the term pantothenate kinase-associated neurodegeneration (PKAN) has been proposed for this group of disorders. To characterize clinically and genetically HSS/NBIA, we reviewed 34 affected individuals from 10 different families, who satisfied the inclusion criteria for NBIA. Relatives of patients who had clinical, magnetic resonance imaging (MRI), or pathological findings of NBIA were included in the study. Four patients were found to have mutations in the pantothenate kinase 2 (PANK2) gene. We compared the clinical features and MRI findings of those with and without PANK2 mutations. The presence of mutation in the PANK2 gene is associated with younger age at onset and a higher frequency of dystonia, dysarthria, intellectual impairment, and gait disturbance. Parkinsonism is seen predominantly in adult-onset patients whereas dystonia seems more frequent in the earlier-onset cases. The phenotypic heterogeneity observed in our patients supports the notion of genetic heterogeneity in the HSS/NBIA syndrome.

Benefits and risks of deferiprone in iron overload in Thalassaemia and other conditions: comparison of epidemiological and therapeutic aspects with deferoxamine

Deferiprone is the only orally active iron-chelating drug to be used therapeutically in conditions of transfusional iron overload. It is an orphan drug designed and developed primarily by academic initiatives for the treatment of iron overload in thalassaemia, which is endemic in the Mediterranean, Middle East and South East Asia and is considered an orphan disease in the European Union and North America. Deferiprone has been used in several other iron or other metal imbalance conditions and has prospects of wider clinical applications. Deferiprone has high affinity for iron and interacts with almost all the iron pools at the molecular, cellular, tissue and organ levels. Doses of 50-120 mg/kg/day appear to be effective in bringing patients to negative iron balance. It increases urinary iron excretion, which mainly depends on the iron load of patients and the dose of the drug. It decreases serum ferritin levels and reduces the liver and heart iron content in the majority of chronically transfused iron loaded patients at doses >80 mg/kg/day. It is metabolised to a glucuronide conjugate and cleared through the urine in the metabolised and a non-metabolised form, usually of a 3 deferiprone: 1 iron complex, which gives the characteristic red colour urine. Peak serum levels of deferiprone are observed within 1 hour of its oral administration and clearance from blood is within 6 hours. There is variation among patients in iron excretion, the metabolism and pharmacokinetics of deferiprone. Deferiprone has been used in more than 7500 patients aged from 2-85 years in >50 countries, in some cases daily for >14 years. All the adverse effects of deferiprone are considered reversible, controllable and manageable. These include agranulocytosis with frequency of about 0.6%, neutropenia 6%, musculoskeletal and joint pains 15%, gastrointestinal complains 6% and zinc deficiency 1%. Discontinuation of the drug is recommended for patients developing agranulocytosis. Deferiprone is of similar therapeutic index to subcutaneous deferoxamine but is more effective in iron removal from the heart, which is the target organ of iron toxicity and mortality in iron-loaded thalassaemia patients. Deferiprone is much less expensive to produce than deferoxamine. Combination therapy of deferoxamine and deferiprone has been used in patients not complying with subcutaneous deferoxamine or experiencing toxicity or not excreting sufficient amounts of iron with use of either drug alone. New oral iron-chelating drugs are being developed, but even if successful these are likely to be more expensive than deferiprone and are not likely to become available in the next 5-8 years. About 25% of treated thalassaemia patients in Europe and more than 50% in India are using deferiprone. For most thalassaemia patients worldwide who are not at present receiving any form of chelation therapy the choice is between deferiprone and fatal iron toxicity.

Progressive dystonia in a 12-year-old boy

Pantothenate kinase-associated neurodegeneration (PKAN) (MIM 234200; Hallervorden-Spatz syndrome) is a degenerative, autosomal recessive disorder in childhood, currently without specific treatment. In contrast to variable clinical features, T2-weighted magnetic resonance images show a characteristic 'eye-of-the-tiger sign' in the globus pallidus due to excess iron deposition. Recently a defect in pantothenate kinase, the key regulatory enzyme in the synthesis of coenzyme A from pantothenate, has been identified as the cause of the disease. We report a 12-year-old boy with progressive rigidity, dystonia, impaired voluntary movement, dysarthria, and mental deterioration. Over 10 years the boy had been misdiagnosed with clumsiness, emotional and behavioural deficits, and attention deficit disorder, before neuroimaging was performed showing the characteristic 'eye-of-the-tiger sign'. Molecular analyses confirmed two mutations in the PANK2 gene [coding sequence of a gene that has homology to murine pantothenate kinase-1]. We conclude that in progressive childhood dystonia, PKAN should be considered and magnetic resonance imaging performed early. The newly described defect of the pantothenate kinase enzyme enables a novel therapeutic approach to be considered, based on the mutation analyses of the PANK2 gene, as well as the prenatal diagnosis of this disorder.

Iron in neurodegenerative disorders

Increasing evidence implicates a role of iron in the pathogenesis of numerous neurodegenerative diseases due to its capacity to enhance production of toxic reactive radicals and to induce protein aggregation. The underlying mechanism of iron accumulation in areas of the brain specific for the respective disease, however, is still unknown. Recent molecular and biochemical studies provide new insights into the consequences of impairment of brain iron metabolism. This review summarizes our understanding of the regulation of iron in the brain and defines the current knowledge on the involvement of iron metabolism in neurodegenerative diseases with genetically determined iron accumulation in the brain.

Neurologic manifestations of iron deficiency in childhood

Iron deficiency is a common disorder in pediatric patients. Although the most common manifestation is that of anemia, iron deficiency is frequently the source of a host of neurologic disorders presenting to general pediatric neurologic practices. These disorders include developmental delay, stroke, breath-holding episodes, pseudotumor cerebri, and cranial nerve palsies. Although frequent, the identification of iron deficiency as part of the differential diagnosis in these disorders is uncommon and frequently goes untreated. The purpose of the current review is to highlight what is understood regarding iron deficiency and it's underlying pathophysiology as it relates to the brain, and the association of iron deficiency with common neurologic pediatric disease.