Correction of a genetic deficiency in pantothenate kinase 1 using phosphopantothenate replacement therapy

Coenzyme A (CoA) is a ubiquitous cofactor involved in numerous essential biochemical transformations, and along with its thioesters is a key regulator of intermediary metabolism. Pantothenate (vitamin B5) phosphorylation by pantothenate kinase (PanK) is thought to control the rate of CoA production. Pantothenate kinase associated neurodegeneration is a hereditary disease that arises from mutations that inactivate the human PANK2 gene. Aryl phosphoramidate phosphopantothenate derivatives were prepared to test the feasibility of using phosphopantothenate replacement therapy to bypass the genetic deficiency in the Pank1(-/-) mouse model. The efficacies of candidate compounds were first compared by measuring the ability to increase CoA levels in Pank1(-/-) mouse embryo fibroblasts. Administration of selected candidate compounds to Pank1(-/-) mice corrected their deficiency in hepatic CoA. The PanK bypass was confirmed by the incorporation of intact phosphopantothenate into CoA using triple-isotopically labeled compound. These results provide strong support for PanK as a master regulator of intracellular CoA and illustrate the feasibility of employing PanK bypass therapy to restore CoA levels in genetically deficient mice.

Metabolic consequences of mitochondrial coenzyme A deficiency in patients with PANK2 mutations

Pantothenate kinase-associated neurodegeneration (PKAN) is a rare, inborn error of metabolism characterized by iron accumulation in the basal ganglia and by the presence of dystonia, dysarthria, and retinal degeneration. Mutations in pantothenate kinase 2 (PANK2), the rate-limiting enzyme in mitochondrial coenzyme A biosynthesis, represent the most common genetic cause of this disorder. How mutations in this core metabolic enzyme give rise to such a broad clinical spectrum of pathology remains a mystery. To systematically explore its pathogenesis, we performed global metabolic profiling on plasma from a cohort of 14 genetically defined patients and 18 controls. Notably, lactate is elevated in PKAN patients, suggesting dysfunctional mitochondrial metabolism. As predicted, but never previously reported, pantothenate levels are higher in patients with premature stop mutations in PANK2. Global metabolic profiling and follow-up studies in patient-derived fibroblasts also reveal defects in bile acid conjugation and lipid metabolism, pathways that require coenzyme A. These findings raise a novel therapeutic hypothesis, namely, that dietary fats and bile acid supplements may hold potential as disease-modifying interventions. Our study illustrates the value of metabolic profiling as a tool for systematically exploring the biochemical basis of inherited metabolic diseases.

Intellectual and adaptive behaviour functioning in pantothenate kinase-associated neurodegeneration

BACKGROUND

Pantothenate kinase-associated neurodegeneration (PKAN), an extremely rare autosomal recessive disorder resulting in iron accumulation in the brain, has a diverse phenotypic expression. Based on limited case studies of one or two patients, intellectual impairment is considered part of PKAN. Investigations of cognitive functioning have utilized specific neuropsychological tests, without attention to general intellectual skills or adaptive behaviour.

METHODS

Sixteen individuals with PKAN completed measures of global intellectual functioning, and participants or care providers completed measures of adaptive behaviour skills and day-to-day functional limitations. Clinicians provided global ratings of condition severity.

RESULTS

Testing with standardized measures documented varied phenotypic expression, with general cognitive skills and adaptive behaviour ranging from high average to well below average. Age of disease onset correlated with measures of intellectual functioning, adaptive functioning and disease severity.

CONCLUSIONS

Findings support previously described clinical impressions of varied cognitive impairment and the association between age of onset and impairment. Further, they add important information regarding the natural history of the disease and suggest assessment strategies for use in treatment trials.

The diverse phenotype and genotype of pantothenate kinase-associated neurodegeneration

Pantothenate kinase-associated neurodegeneration (PKAN) is a rare autosomal-recessive disorder caused by mutations in the PANK2 gene. The authors report clinical and genetic findings of 16 patients with PKAN. The authors identified 12 mutations in the PANK2 gene, five of which were new. Only nine patients could be classified as classic or atypical PKAN, and intermediate phenotypes are described. Two patients presented with motor tics and obsessive-compulsive behavior suggestive of Tourette syndrome.

Altered neuronal mitochondrial coenzyme A synthesis in neurodegeneration with brain iron accumulation caused by abnormal processing, stability, and catalytic activity of mutant pantothenate kinase 2

Mutations in the pantothenate kinase 2 (PANK2) gene have been identified in patients with neurodegeneration with brain iron accumulation (NBIA; formerly Hallervorden-Spatz disease). However, the mechanisms by which these mutations cause neurodegeneration are unclear, especially given the existence of multiple pantothenate kinase genes in humans and multiple PanK2 transcripts with potentially different subcellular localizations. We demonstrate that PanK2 protein is localized to mitochondria of neurons in human brain, distinguishing it from other pantothenate kinases that do not possess mitochondrial-targeting sequences. PanK2 protein translated from the most 5' start site is sequentially cleaved at two sites by the mitochondrial processing peptidase, generating a long-lived 48 kDa mature protein identical to that found in human brain extracts. The mature protein catalyzes the initial step in coenzyme A (CoA) synthesis but displays feedback inhibition in response to species of acyl CoA rather than CoA itself. Some, but not all disease-associated point mutations result in significantly reduced catalytic activity. The most common mutation, G521R, results in marked instability of the intermediate PanK2 isoform and reduced production of the mature isoform. These results suggest that NBIA is caused by altered neuronal mitochondrial lipid metabolism caused by mutations disrupting PanK2 protein levels and catalytic activity.

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.

[Tourettism, hemiballism and juvenile Parkinsonism: expanding the clinical spectrum of the neurodegeneration associated to pantothenate kinase deficiency (Hallervorden Spatz syndrome)]

INTRODUCTION

Pantothenate kinase deficiency (Hallervorden-Spatz syndrome, HSS) triggers cerebral neurodegeneration with iron deposition in the basal ganglia. The classical form has an early onset in infancy, a progressive course, the presence of extrapyramidal symptoms (dystonia, chorea, rigidity) and pigmentary retinitis. There are atypical late onset forms with predominance of symptoms of Parkinsonism and dementia, which progress slowly and course somewhat less progressively.

CASE REPORT

We describe three patients with HSS and an atypical presentation, with onset during the second decade of life. In all cases magnetic resonance imaging showed areas of hyposignal in T2 sequences in medial globus pallidus, with central hypersignal, which gave rise to a tiger's eye image. Other aetiologies, such as Wilson's disease, gangliosidosis GM1, hypoprebetalipoproteinemia, hexosaminidase A deficiency, aminoacidurias and infantile Huntingdon's chorea, were precluded. In the 20-year-old male the initial manifestations at the age of 17 were superposed over Gilles de la Tourette syndrome, with complex motor and vocal tics, palilalia, behavioural disorders and postural instability. The 13-year-old patient presented symptoms of chorea, hemiballic movements and dystonia in the lower limbs, which limited walking at the age of 12. The 28-year-old female patient presented a progressive rigid akinetic syndrome, with dementia and partial response to levodopa.

CONCLUSIONS

The clinical spectrum of HSS is broad and its differential diagnosis must include hemiballism, Tourette syndrome and juvenile Parkinsonism.

Pantothenate kinase-associated neurodegeneration: MR imaging, proton MR spectroscopy, and diffusion MR imaging findings

We herein report the case of a 15-year-old male patient with pantothenate kinase-associated neurodegeneration. The classic "eye-of-the-tiger" appearance was initially present on the globus pallidi on T2-weighted MR images and had disappeared by the time of the 10-month follow-up examination. Fluid-attenuated inversion recovery images revealed marked hypointensity in the globus pallidi and dentate nuclei and high signal intensity changes in the deep cerebral white matter. Proton MR spectroscopy revealed markedly decreased N-acetylaspartate in the globus pallidi, associated with decreased N-acetylaspartate and increased myoinositol in the deep cerebral white matter. Diffusion MR images (b=1000 s/mm(2)) were negative (normal appearing) for deep cerebral white matter lesions, whereas apparent diffusion coefficient values were slightly increased (1.08-1.12 x 10(-3) mm(2)/s), compared with the apparent diffusion coefficient values from the normal white matter regions. Apparent diffusion coefficient values in the globus pallidi were lower than those in the unaffected thalamus.

A novel pantothenate kinase gene (PANK2) is defective in Hallervorden-Spatz syndrome

Hallervorden-Spatz syndrome (HSS) is an autosomal recessive neurodegenerative disorder associated with iron accumulation in the brain. Clinical features include extrapyramidal dysfunction, onset in childhood, and a relentlessly progressive course. Histologic study reveals iron deposits in the basal ganglia. In this respect, HSS may serve as a model for complex neurodegenerative diseases, such as Parkinson disease, Alzheimer disease, Huntington disease and human immunodeficiency virus (HIV) encephalopathy, in which pathologic accumulation of iron in the brain is also observed. Thus, understanding the biochemical defect in HSS may provide key insights into the regulation of iron metabolism and its perturbation in this and other neurodegenerative diseases. Here we show that HSS is caused by a defect in a novel pantothenate kinase gene and propose a mechanism for oxidative stress in the pathophysiology of the disease.

Superoxide dismutase-like immunoreactivity in spheroids in Hallervorden-Spatz disease

Iron accumulation in the basal ganglia and spheroid formation are pathological hallmarks of Hallervorden-Spatz disease (HS). Since an overaccumulation of iron (iron thesaurosis) that exceeds the binding capacity of ferritin could cause oxidative damage, we studied the possible role of oxidative stress in the pathogenesis of HS. The basal ganglia and spinal cord from patients with HS were investigated at autopsy, using histochemistry for iron and immunohistochemistry for Cu/Zn superoxide dismutase (SOD1), Mn superoxide dismutase (SOD2) and ferritin. SOD1-like immunoreactivity (IR), SOD2-IR and ferritin-IR occurred frequently in spheroids observed in the basal ganglia, and associated iron accumulation indicated the possible existence of increased oxidative stress in HS patients. Spheroids in the spinal cord showed intense SOD1-IR and SOD2-IR in HS, in sharp contrast with the occasional weak SOD1-IR and SOD2-IR observed in spheroids from patients with amyotrophic lateral sclerosis (ALS). Neither increased ferritin-IR nor iron accumulation were observed in spinal spheroids from HS and ALS patients. These data may suggest that, at least in the spinal cord, SOD1-IR and SOD2-IR in spheroids in HS patients do not result from oxidative stress directly related to iron accumulation.

Hallervorden-Spatz disease: cysteine accumulation and cysteine dioxygenase deficiency in the globus pallidus

We describe neurochemical abnormalities found in the brains of 2 patients with autopsy-confirmed Hallervorden-Spatz (HS) disease. In 1 patient, contents of cystine and of glutathione-cysteine mixed disulfide in the globus pallidus were markedly elevated above values for appropriate control subjects. Activity of cysteine dioxygenase, which converts cysteine to cysteine sulfinic acid, was reduced in the globus pallidus, but normal in the frontal cortex and putamen of both patients. gamma-Aminobutyric acid content was markedly decreased in the globus pallidus and substantia nigra of both patients. These results suggest that cysteine accumulates locally in the globus pallidus in Hallervorden-Spatz disease as a result of an enzymatic block in the metabolic pathway from cysteine to taurine. Accumulated cysteine may chelate iron, accounting for the local increase in iron content in Hallervorden-Spatz disease. The combined excess of cysteine and ferrous iron may generate free radicals that damage neuronal membranes to cause the typical morphological changes observed in this disorder.