PANK2 gene analysis confirms genetic heterogeneity in neurodegeneration with brain iron accumulation (NBIA) but mutations are rare in other types of adult neurodegenerative disease

Incidence of PKAN determined by bioinformatic and population-based analysis of ~140,000 humans

Panthothenate kinase-associated neurodegeneration (PKAN, OMIM 234200), is an inborn is an autosomal recessive inborn error of metabolism caused by pathogenic variants in PANK2. PANK2 encodes the enzyme pantothenate kinase 2 (EC 2.7.1.33), an essential regulatory enzyme in CoA biosynthesis. Clinical presentation includes dystonia, rigidity, bradykinesia, dysarthria, pigmentary retinopathy and dementia with variable age of onset ranging from childhood to adulthood. In order to provide an accurate incidence estimate of PKAN, we conducted a systematic review of the literature and databases for pathogenic mutations and constructed a bioinformatic profile for pathogenic missense variants in PANK2. We then studied the gnomAD cohort of ~140,000 unrelated adults from global populations to determine the allele frequency of the variants in PANK2 reported pathogenic for PKAN and for those additional variants identified in gnomAD that met bioinformatics criteria for being potentially pathogenic. Incidence was estimated based on three different models using the allele frequencies of pathogenic PKAN variants with or without those bioinformatically determined to be potentially pathogenic. Disease incidence calculations showed PKAN incidence ranging from 1:396,006 in Europeans, 1:1,526,982 in Africans, 1:480,826 in Latino, 1:523,551 in East Asians and 1:531,118 in South Asians. These results indicate PKAN is expected to occur in approximately 2 of every 1 million live births globally outside of Africa, and has a much lower incidence 1 in 1.5 million live births in the African population.

Neuropsychological functions and psychiatric symptoms in late-onset manifestation of pantothenate kinase-associated neurodegeneration: a clinical case report

Purpose of the study: Pantothenate Kinase-associated Neurodegeneration (PKAN) is a form of Neurodegeneration with brain iron accumulation (NBIA) due to gene mutations. Classical phenotype showed progressive neurological symptoms associated to a characteristic pattern of basal ganglia iron deposits. The atypical case, with adult-onset manifestation, could have neuropsychiatric symptoms with behavioral deficits. We described an adult-onset case of Pantothenate Kinase-associated Neurodegeneration.Materials and methods: The patient underwent neuropsychological and psychiatric evaluation and Magnetic Resonance Imaging, respectively for cognitive and behavioral assessment and to confirm the characteristic findings of this syndrome.Results: The patient showed atypical phenotype of Pantothenate Kinase-associated Neurodegeneration, characterized by language deficits, dixesecutive, and psychiatric manifestations, such as obsessive ideation, impulsivity, and disinhibition.Conclusions: This description could be helpful to a more correct diagnosis and clinical management.

Neurodegeneration with brain iron accumulation: Insights into the mitochondria dysregulation

NBIA (Neurodegeneration with brain iron accumulation) is a group of inherited neurologic disorders characterized by marked genetic heterogeneity, in which iron atypical accumulates in basal ganglia resulting in brain magnetic resonance imaging changes, histopathological abnormalities, and neuropsychiatric clinical symptoms. With the rapid development of high-throughput sequencing technologies, ten candidate genes have been identified, including PANK2, PLA2G6, C19orf12, WDR45, FA2H, ATP13A2, FTL, CP, C2orf37, and COASY. They are involved in seemingly unrelated cellular pathways, such as iron homeostasis (FTL, CP), lipid metabolism (PLA2G6, C19orf12, FA2H), Coenzyme A synthesis (PANK2, COASY), and autophagy (WDR45, ATP13A2). In particular, PANK2, COASY, PLA2G6, and C19orf12 are located on mitochondria, which associate with certain subtypes of NBIA showing mitochondria dysregulation. However, the relationships among those four genes are still unclear. Therefore, this review is specifically focused on dysregulation of mitochondria in NBIA and afore-mentioned four genes, with summaries of both pathological and clinical findings.

A splice-site variant in FLVCR1 produces retinitis pigmentosa without posterior column ataxia

FLVCR1 (feline leukemia virus subgroup c receptor 1) is a transmembrane protein involved in the trafficking of intracellular heme. Homozygous variants in FLVCR1 have been described in association with a clinical syndrome of posterior column ataxia with retinitis pigmentosa (PCARP). Here, we describe a patient with non-syndromic retinitis pigmentosa homozygous for a splice-site variant in FLVCR1 (c.1092 + 5G>A) without evidence of posterior column ataxia or cerebellar degeneration. We suggest an association between intronic splice-site variants in FLVCR1 and the absence of posterior column degeneration and suggest a hypothesis to explain this observation. Should this association be proven, it would provide valuable prognostic information for patients. Retinal degeneration appears to be the sole clinical manifestation of this FLVCR1 variant; gene therapy approaches using an adeno-associated viral vector with sub-retinal delivery may therefore represent a therapeutic approach to halting retinal degeneration in this patient group.

Parkinson's disease-related DJ-1 functions in thiol quality control against aldehyde attack in vitro

DJ-1 (also known as PARK7) has been identified as a causal gene for hereditary recessive Parkinson’s disease (PD). Consequently, the full elucidation of DJ-1 function will help decipher the molecular mechanisms underlying PD pathogenesis. However, because various, and sometimes inconsistent, roles for DJ-1 have been reported, the molecular function of DJ-1 remains controversial. Recently, a number of papers have suggested that DJ-1 family proteins are involved in aldehyde detoxification. We found that DJ-1 indeed converts methylglyoxal (pyruvaldehyde)-adducted glutathione (GSH) to intact GSH and lactate. Based on evidence that DJ-1 functions in mitochondrial homeostasis, we focused on the possibility that DJ-1 protects co-enzyme A (CoA) and its precursor in the CoA synthetic pathway from aldehyde attack. Here, we show that intact CoA and β-alanine, an intermediate in CoA synthesis, are recovered from methylglyoxal-adducts by recombinant DJ-1 purified from E. coli. In this process, methylglyoxal is converted to L-lactate rather than the D-lactate produced by a conventional glyoxalase. PD-related pathogenic mutations of DJ-1 (L10P, M26I, A104T, D149A, and L166P) impair or abolish detoxification activity, suggesting a pathological significance. We infer that a key to understanding the biological function of DJ-1 resides in its methylglyoxal-adduct hydrolase activity, which protects low-molecular thiols, including CoA, from aldehydes.

Dystonic opisthotonus: a "red flag" for neurodegeneration with brain iron accumulation syndromes?

Back arching was reported in one of the very first patients with neurodegeneration with brain iron accumulation syndrome (NBIAs) published in 1936. However, recent reports have mainly focused on the genetic and imaging aspects of these disorders, and the phenotypic characterization of the dystonia has been lost. In evaluating patients with NBIAs in our centers, we have observed that action-induced dystonic opisthotonus is a common and characteristic feature of NBIAs. Here, we present a case series of patients with NBIAs presenting this feature demonstrated by videos. We suggest that dystonic opisthotonus could be a useful “red flag” for clinicians to suspect NBIAs, and we discuss the differential diagnosis of this feature. This would be particularly useful in identifying patients with NBIAs and no iron accumulation as yet on brain imaging (for example, as in phospholipase A2, group IV (cytosolic, calcium-independent) [PLA2G6]-related disorders), and it has management implications. © 2013 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

MRI Findings in Patients with Clinical Onset Consistent with Infantile Neuroaxonal Dystrophy (INAD), Literature Review, Clinical and MRI Follow-up

Infantile neuroaxonal dystrophy (INAD) is a rare autosomal recessive neurodegenerative disorder characterized by infantile onset and rapid progression of psychomotor regression and hypotonia evolving into spasticity. The neuroradiologic hallmark of the disease is represented by progressive cerebellar atrophy. Prior to the discovery of mutations in the PLA2G6 gene in family with INAD, the clinical diagnosis of the disease had been confirmed by the presence of spheroid bodies (SB) in a peripheral nerve biopsy. Various studies have found that some patients with mutations lacked SB and some without mutations had SB, indicating incomplete detection using either pathologic or molecular methods 7. This, together with the observation that the spectrum of clinical features associated with mutations in PLA2G6 is broader than previously described, has increased the usefulness of Magnetic Resonance (MR) in INAD diagnosis, particularly in the frequent occurrence of atypical cases, especially in the early stages of the disease. We retrospectively reviewed the MR studies of eight patients in whom clinical and imaging onset met the typical criteria for INAD. Their clinical and MR imaging (MRI) onset and follow-up were evaluated together with the neuroradiological findings reported in the literature in order to identify MRI features useful in differentiating INAD from other diseases with similar clinical onset and to discuss which of them are the most important, thus suggesting INAD diagnosis. Our contribution included the use of Proton Spectroscopy (1H-MR), diffusion weighted MR imaging (DWI) and diffusion tensor imaging (DTI) in the follow-up of seven of the eight patients. The literature reviewed included attempts to correlate clinical and MR data with the genotype in the group of patients carrying PLA2G6 mutations. From the limited and inhomogeneous cohort of patients included in our study, a correlation between the MR features, phenotype and genotype was not exhaustive.

Novel compound heterozygous mutations in the pantothenate kinase 2 gene in a korean patient with atypical pantothenate kinase associated neurodegeneration

Pantothenate kinase-associated neurodegeneration (PKAN) is an autosomal recessive disorder that is characterized by mutations in the pantothenate kinase 2 gene (PANK2) and typical magnetic resonance imaging findings. We report a case of atypical PKAN presenting with generalized dystonia. Our patient had compound heterozygous mutations in the PANK2 gene, including mutation in exon 3 (p.D268G) and exon 4 (p.R330P). To our knowledge, this patient is the first to have the p.R330P mutation and the second to have the p.D268G mutation.

Neuropathologic Findings in an Aged Albino Gorilla

Pallido-nigral spheroids associated with iron deposition have been observed in some aged clinically normal nonhuman primates. In humans, similar findings are observed in neurodegeneration with brain iron accumulation diseases, which, in some cases, show associated mutations in pantothenate kinase 2 gene (PANK2). Here we present an aged gorilla, 40 years old, suffering during the last 2 years of life from progressive tetraparesis, nystagmus, and dyskinesia of the arms, hands, and neck, with accompanying abnormal behavior. The postmortem neuropathologic examination revealed, in addition to aging-associated changes in the brain, numerous corpora amylacea in some brain areas, especially the substantia nigra, and large numbers of axonal spheroids associated with iron accumulation in the internal globus pallidus. Sequencing of the gorilla PANK2 gene failed to detect any mutation. The clinical, neuropathologic, and genetic findings in this gorilla point to an age-related pallido-nigral degeneration that presented PKAN-like neurologic deficits.

Non-transferrin-bound iron reaches mitochondria by a chelator-inaccessible mechanism: biological and clinical implications

Non-transferrin-bound iron, commonly found in the plasma of iron-overloaded individuals, permeates into cells via pathways independent of the transferrin receptor. This may lead to excessive cellular accumulation of labile iron followed by oxidative damage and eventually organ failure. Mitochondria are the principal destination of iron in cells and a primary site of prooxidant generation, yet their mode of acquisition of iron is poorly understood. Using fluorescent probes sensitive to iron or to reactive oxygen species, targeted to cytosol and/or to mitochondria, we traced the ingress of labile iron into these compartments by fluorescence microscopy and quantitative fluorimetry. We observed that 1) penetration of non-transferrin-bound iron into the cytosol and subsequently into mitochondria occurs with barely detectable delay and 2) loading of the cytosol with high-affinity iron-binding chelators does not abrogate iron uptake into mitochondria. Therefore, a fraction of non-transferrin-bound iron acquired by cells reaches the mitochondria in a nonlabile form. The physiological role of occluded iron transfer might be to confer cells with a “safe and efficient cytosolic iron corridor” to mitochondria. However, such a mechanism might be deleterious in iron-overload conditions, because it could lead to surplus accumulation of iron in these critical organelles.

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.