Shawn K. Westaway

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.

PLA2G6, encoding a phospholipase A2, is mutated in neurodegenerative disorders with high brain iron.

Neurodegenerative disorders with high brain iron include Parkinson disease, Alzheimer disease and several childhood genetic disorders categorized as neuroaxonal dystrophies. We mapped a locus for infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation (NBIA) to chromosome 22q12-q13 and identified mutations in PLA2G6, encoding a calcium-independent group VI phospholipase A2, in NBIA, INAD and the related Karak syndrome. This discovery implicates phospholipases in the pathogenesis of neurodegenerative disorders with iron dyshomeostasis.

Neurodegeneration associated with genetic defects in phospholipase A2

Objective: Mutations in the gene encoding phospholipase A2 group VI (PLA2G6) are associated with two childhood neurologic disorders: infantile neuroaxonal dystrophy (INAD) and idiopathic neurodegeneration with brain iron accumulation (NBIA). INAD is a severe progressive psychomotor disorder in which axonal spheroids are found in brain, spinal cord, and peripheral nerves. High globus pallidus iron is an inconsistent feature of INAD; however, it is a diagnostic criterion of NBIA, which describes a clinically and genetically heterogeneous group of disorders that share this hallmark feature. We sought to delineate the clinical, radiographic, pathologic, and genetic features of disease resulting from defective phospholipase A2. Methods: We identified 56 patients clinically diagnosed with INAD and 23 with idiopathic NBIA and screened their DNA for PLA2G6 mutations. Results: Eighty percent of patients with INAD had mutations in PLA2G6, whereas mutations were found in only 20% of those with idiopathic NBIA. All patients with two null mutations had a more severe phenotype. On MRI, nearly all mutation-positive patients had cerebellar atrophy, and half showed brain iron accumulation. We observed Lewy bodies and neurofibrillary tangles in association with PLA2G6 mutations. Conclusion: Defects in phospholipase A2 lead to a range of phenotypes. PLA2G6 mutations are associated with nearly all cases of classic infantile neuroaxonal dystrophy but a minority of cases of idiopathic neurodegeneration with brain iron accumulation, and genotype correlates with phenotype. Cerebellar atrophy predicts which patients are likely to be mutation-positive. The neuropathologic changes that are caused by defective phospholipase A2 suggest a shared pathogenesis with both Parkinson and Alzheimer diseases.

Mitochondrial Localization of Human PANK2 and Hypotheses of Secondary Iron Accumulation in Pantothenate Kinase‐Associated Neurodegeneration

Abstract: Mutations in the pantothenate kinase 2 gene (PANK2) lead to pantothenate kinase‐associated neurodegeneration (PKAN, formerly Hallervorden‐Spatz syndrome). This neurodegenerative disorder is characterized by iron accumulation in the basal ganglia. Pantothenate kinase is the first enzyme in the biosynthesis of coenzyme A from pantothenate (vitamin B5). PANK2, one of four human pantothenate kinase genes, is uniquely predicted to be targeted to mitochondria. We demonstrate mitochondrial localization of PANK2 and speculate on mechanisms of secondary iron accumulation in PKAN. Furthermore, PANK2 uses an unconventional translational start codon, CUG, which is polymorphic in the general population. The variant sequence, CAG (allele frequency: 0.05), leads to skipping of the mitochondrial targeting signal and cytosolic localization of PANK2. This common variant may cause mitochondrial dysfunction and impart susceptibility to late‐onset neurodegenerative disorders with brain iron accumulation, including Parkinsons disease.

HARP syndrome is allelic with pantothenate kinase–associated neurodegeneration

Abstract—HARP (hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa, and pallidal degeneration) is a rare syndrome with many clinical similarities to pantothenate kinase–associated neurodegeneration (PKAN, formerly Hallervorden–Spatz syndrome). Despite these common features, lipoprotein abnormalities have not been reported in PKAN. After the recent discovery of the genetic defect in PKAN, we report a homozygous nonsense mutation in exon 5 of the PANK2 gene that creates a stop codon at amino acid 371 (R371X) in the original HARP patient. This finding establishes that HARP is part of the PKAN disease spectrum.

Alzheimer Disease Pathology in Cognitively Healthy Elderly:A Genome-wide Study

Many elderly individuals remain dementia-free throughout their life. However, some of these individuals exhibit Alzheimer disease neuropathology on autopsy, evidenced by neurofibrillary tangles (NFTs) in AD-specific brain regions. We conducted a genome-wide association study to identify genetic mechanisms that distinguish non-demented elderly with a heavy NFT burden from those with a low NFT burden. The study included 299 non-demented subjects with autopsy (185 subjects with low and 114 with high NFT levels). Both a genotype test, using logistic regression, and an allele test provided consistent evidence that variants in the RELN gene are associated with neuropathology in the context of cognitive health. Immunohistochemical data for reelin expression in AD-related brain regions added support for these findings. Reelin signaling pathways modulate phosphorylation of tau, the major component of NFTs, either directly or through β-amyloid pathways that influence tau phosphorylation. Our findings suggest that up-regulation of reelin may be a compensatory response to tau-related or beta-amyloid stress associated with AD even prior to the onset of dementia.

Common Variants in CASQ2, GPD1L, and NOS1AP Are Significantly Associated With Risk of Sudden Death in Patients With Coronary Artery Disease

Background— Recent evidence suggests a genetic component for sudden cardiac death (SCD) in subjects with coronary artery disease (CAD). We conducted a systematic candidate-gene approach using haplotype-tagging single nucleotide polymorphisms (htSNPs) to identify genes associated with SCD risk in the context of CAD. Methods and Results— We investigated 1424 htSNPs representing 18 genes with mutations described in patients with ventricular arrhythmias in 291 subjects from the Oregon Sudden Unexpected Death Study (Ore-SUDS). The Ore-SUDS is an ongoing prospective investigation of SCD in the Portland, OR, metropolitan area (population, 1 000 000). SCD cases were ascertained from multiple sources and medical records were reviewed to determine the presence of CAD. A total of 36 SNPs were associated with risk of SCD (uncorrected probability values <0.01) in the initial study sample. These SNPs were subsequently tested for replication in an independent case-control study sample from the Ore-SUDS (n=688). The association analysis in the replication stage revealed 6 SNPs associated with SCD: CASQ2 region (rs17500488, P=0.04; rs3010396, P=0.007; rs7366407; P=0.04), NOS1AP (rs12084280, P=0.04; rs10918859, P=0.02), and 1 SNP located ≈26 kb upstream of GPD1L (rs9862154, P=0.04). Conclusions— Common variations in or near CASQ2, GPD1L, and NOS1AP are associated with increased risk of SCD in patients with CAD. These findings provide further evidence for overlap between the genetic architecture of rare and common forms of SCD, and replication in additional populations is warranted.

Infantile neuroaxonal dystrophy: What's most important for the diagnosis?

BACKGROUND AND AIMS Infantile neuroaxonal dystrophy is a rare neurodegenerative disorder, with onset in the first 2 years of life. Mutations in the PLA2G6 gene were identified in patients with infantile neuroaxonal dystrophy. Our purpose was to review clinical, neurophysiologic, neuroradiologic and neuropathological features of our patients in order to identify the earliest signs of disease. We also correlate these data with the genotype in the mutation positive patients. METHODS We reviewed the clinical reports, neurophysiologic and neuropathological studies and brain imaging of our patients. In five patients molecular analysis of the PLA2G6 gene was performed. RESULTS We report 10 patients with infantile neuroaxonal dystrophy. Earliest symptoms presented between 6 and 18 months of age. The first manifestations were arrest in the acquisition of milestones or regression. The first neurological signs were generalized hypotonia and pyramidal signs. Fast rhythms on EEG were observed in all patients. Brain imaging studies showed cerebellar atrophy in all patients, with signal hyperintensity in the cerebellar cortex on T2-weighted images in five. All cases had characteristic axonal spheroids on skin biopsy. Mutations in the PLA2G6 gene were identified in the five patients studied. Three of them had the same homozygous mutations 2370T> G, Y790X. CONCLUSIONS Though mutations were detected in the patients studied, a clear genotype-phenotype correlation could not be ascertained. In the appropriate clinical context, characteristic brain imaging and fast rhythms on EEG can support the decision to perform molecular analysis and avoid skin biopsy to confirm diagnosis.

Discordant expression of miR-103/7 and pantothenate kinase host genes in mouse

miR-103 and miR-107, microRNAs hosted by pantothenate kinase genes, are proposed to regulate cellular lipid metabolism. microRNA-mediated regulation is complex, potentially affecting expression of the host gene, related enzymes within the same pathway, or apparently distinct targets. Using qRT-PCR, we demonstrate that miR-103 and miR-107 expression does not correlate with expression of host pantothenate kinase genes in mouse tissues. The miR-103/7 family thus provides an intriguing model for dissecting microRNA transcription, processing and coordinated function within host genes.

Novel compound heterozygous mutations in the PANK2 gene in a chinese patient with atypical pantothenate kinase- associated neurodegeneration

We investigated the presence of mutations in the pantothenate kinase (PANK2) gene in a 27‐year‐old male Chinese patient with atypical pantothenate kinase‐associated neurodegeneration (PKAN), formerly Hallervorden‐Spatz syndrome. Automated DNA sequence analyses revealed compound heterozygous mutations in the exon 3 and 5. This patient had a 10‐year history of PKAN characterized by a slight tremor of the right hand when writing at onset and a slow progressive rigidity of the neck and the right arm and resting tremor in upper extremities. Dysarthria, dysphagia, and dystonic‐athetoid movements of the face and right fingers were marked. Magnetic resonance showed the typical “eye‐of‐the‐tiger” sign.