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The terms "neuroacanthocytosis" (NA) and "neurodegeneration with brain iron accumulation" (NBIA) both refer to groups of genetically heterogeneous disorders, classified together due to similarities of their phenotypic or pathological findings. Even collectively, the disorders that comprise these sets are exceedingly rare and challenging to study. The NBIA disorders are defined by their appearance on brain magnetic resonance imaging, with iron deposition in the basal ganglia. Clinical features vary, but most include a movement disorder. New causative genes are being rapidly identified; however, the mechanisms by which mutations cause iron accumulation and neurodegeneration are not well understood. NA syndromes are also characterized by a progressive movement disorder, accompanied by cognitive and psychiatric features, resulting from mutations in a number of genes whose roles are also basically unknown. An overlapping feature of the two groups, NBIA and NA, is the occurrence of acanthocytes, spiky red cells with a poorly-understood membrane dysfunction. In this review we summarise recent developments in this field, specifically insights into cellular mechanisms and from animal models. Cell membrane research may shed light upon the significance of the erythrocyte abnormality, and upon possible connections between the two sets of disorders. Shared pathophysiologic mechanisms may lead to progress in the understanding of other types of neurodegeneration. Published by Elsevier Inc.

Iron is an essential element necessary for energy production, DNA and neurotransmitter synthesis, myelination and phospholipid metabolism. Neurodegeneration with brain iron accumulation (NBIA) involves several genetic disorders, two of which, aceruloplasminemia and neuroferritinopathy, are caused by mutations in genes directly involved in iron metabolic pathway, and others, such as pantothenate-kinase 2, phospholipase-A2 and fatty acid 2-hydroxylase associated neurodegeneration, are caused by mutations in genes coding for proteins involved in phospholipid metabolism. Phospholipids are major constituents of myelin and iron accumulation has been linked to myelin derangements. Another group of NBIAs is caused by mutations in lysosomal enzymes or transporters such as ATP13A2, mucolipin-1 and possibly also β-galactosidase and α-fucosidase. Increased cellular iron uptake in these diseases may be caused by impaired recycling of iron which normally involves lysosomes. Abnormal iron utilization by mitochondria, as has been proposed in Friedreich's ataxia, is another possible mechanism of iron accumulation. Other, more common degenerative movement disorders, such as Parkinson's disease, Huntington's disease, multiple system atrophy and progressive supranuclear palsy also exhibit increased brain iron content. Finally, brain iron deficiency has been implicated in restless legs syndrome. This review provides an update on recent findings related to genetics, pathogenic mechanisms, diagnosis, and treatment of movement disorders associated with dysregulation of brain iron. We also propose a new classification of NBIAs.

Aberrant brain iron deposition is observed in both common and rare neurodegenerative disorders, including those categorized as Neurodegeneration with Brain Iron Accumulation (NBIA), which are characterized by focal iron accumulation in the basal ganglia. Two NBIA genes are directly involved in iron metabolism, but whether other NBIA-related genes also regulate iron homeostasis in the human brain, and whether aberrant iron deposition contributes to neurodegenerative processes remains largely unknown. This study aims to expand our understanding of these iron overload diseases and identify relationships between known NBIA genes and their main interacting partners by using a systems biology approach. We used whole-transcriptome gene expression data from human brain samples originating from 101 neuropathologically normal individuals (10 brain regions) to generate weighted gene co-expression networks and cluster the 10 known NBIA genes in an unsupervised manner. We investigated NBIA-enriched networks for relevant cell types and pathways, and whether they are disrupted by iron loading in NBIA diseased tissue and in an in vivo mouse model. We identified two basal ganglia gene co-expression modules significantly enriched for NBIA genes, which resemble neuronal and oligodendrocytic signatures. These NBIA gene networks are enriched for iron-related genes, and implicate synapse and lipid metabolism related pathways. Our data also indicates that these networks are disrupted by excessive brain iron loading. We identified multiple cell types in the origin of NBIA disorders. We also found unforeseen links between NBIA networks and iron-related processes, and demonstrate convergent pathways connecting NBIAs and phenotypically overlapping diseases. Our results are of further relevance for these diseases by providing candidates for new causative genes and possible points for therapeutic intervention.