Young-Onset Parkinsonism in a Hong Kong Chinese Man With Adult-Onset Hallervorden–Spatz Syndrome

Case report: Novel compound heterozygous variants in the PANK2 gene in a Chinese patient diagnosed with ASD and ADHD

The PANK2 gene, which encodes mitochondrial pantothenate kinase 2 protein, is the disease-causing gene for pantothenate kinase-associated neurodegeneration (PKAN). We report a case of atypical PKAN with autism-like symptoms presenting with speech difficulties, psychiatric symptoms, and mild developmental retardation. Magnetic resonance imaging (MRI) of the brain showed the typical "eye-of-the-tiger" sign. Whole-exon sequencing revealed PANK2 p.Ile501Asn/p.Thr498Ser compound heterozygous variants. Our study highlights the phenotypic heterogeneity of PKAN, which can be confused with autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD) and requires careful clinical identification.

Typical pantothenate kinase-associated neurodegeneration caused by compound heterozygous mutations in PANK2 gene in a Chinese patient: a case report and literature review

Pantothenate kinase-associated neurodegeneration (PKAN) is a rare genetic neurodegenerative disorder with brain iron accumulation characterized as dysarthria, spasticity, cognitive impairment, parkinsonism, and retinopathy. PKAN is caused by biallelic mutations in the mitochondrial pantothenate kinase 2 (PANK2) gene. Herein, we report a 4-year-old patient with PKAN from a Han Chinese family, who presented with developmental regression, progressive inability to walk, and limb tremors. Neuroimaging demonstrated "eye-of-the-tiger" sign. Whole exome sequencing (WES) identified compound heterozygous mutations of c.1213T>G (p.Tyr405Asp) and c.1502T>A (p.Ile501Asn) in PANK2 gene. In addition, a review of all known PANK2 variants observed in reported PKAN patients was conducted, to improve understanding of the genotype-phenotype associations that occur in PKAN patients.

Lifetime risk of autosomal recessive neurodegeneration with brain iron accumulation (NBIA) disorders calculated from genetic databases

Background

Neurodegeneration with brain iron accumulation (NBIA) are a group of clinically and genetically heterogeneous diseases characterized by iron overload in basal ganglia and progressive neurodegeneration. Little is known about the epidemiology of NBIA disorders. In the absence of large-scale population-based studies, obtaining reliable epidemiological data requires innovative approaches.

Methods

All pathogenic variants were collected from the 13 genes associated with autosomal recessive NBIA (PLA2G6, PANK2, COASY, ATP13A2, CP, AP4M1, FA2H, CRAT, SCP2, C19orf12, DCAF17, GTPBP2, REPS1). The allele frequencies of these disease-causing variants were assessed in exome/genome collections: the Genome Aggregation Database (gnomAD) and our in-house database. Lifetime risks were calculated from the sum of allele frequencies in the respective genes under assumption of Hardy-Weinberg equilibrium.

Findings

The combined estimated lifetime risk of all 13 investigated NBIA disorders is 0.88 (95% confidence interval 0.70–1.10) per 100,000 based on the global gnomAD dataset (n = 282,912 alleles), 0.92 (0.65–1.29) per 100,000 in the European gnomAD dataset (n = 129,206), and 0.90 (0.48–1.62) per 100,000 in our in-house database (n = 44,324). Individually, the highest lifetime risks (>0.15 per 100,000) are found for disorders caused by variants in PLA2G6, PANK2 and COASY.

Interpretation

This population-genetic estimation on lifetime risks of recessive NBIA disorders reveals frequencies far exceeding previous population-based numbers. Importantly, our approach represents lifetime risks from conception, thus including prenatal deaths. Understanding the true lifetime risk of NBIA disorders is important in estimating disease burden, allocating resources and targeting specific interventions.

PANK2 p.A170fs：a novel pathogenetic mutation, compound with PANK2 p.R440P, causing pantothenate kinase Associated neurodegeneration in a Chinese family

AIM

Pantothenate kinase associated neurodegeneration (PKAN) is a severe autosomal recessive rare disease and characterized by iron accumulation in the basal ganglia. To investigate the pathogenesis of this disease in two sibling patients with PANK in a Chinese family, whole-exome variant detection and functional analysis were performed.

MATERIALS AND METHODS

Clinical and radiographic investigations were performed in the two brother patients. Whole exome sequencing (WES) was used in mutation detection, and the mutations were confirmed by Sanger sequencing. A longevity cohort genetic database was applied as Chinese urban controls. Bioinformatic analysis was performed to predict the pathogenicity.

RESULTS

Compound heterozygous mutations of PANK2 were detected in two sibling brothers with PKAN in a Chinese family: c.510_522del (p.A170fs) and c.1319G > C (p.R440P) in the transcript NM_153638. PANK2: c.510_522del (p.A170fs) was absent in public data and the Chinese urban controls. Bioinformatics analysis showed that the above two variants were pathogenicity.

CONCLUSIONS

We identified a rare compound heterozygous combination of PANK2 mutations found in a Chinese family in which two sibling brothers suffered from PKAN. PANK2 c.510_522del (p.A170fs) was the first reported to be a PKAN pathogenic variant.

Atypical pantothenate kinase-associated neurodegeneration with PANK2 mutations : clinical description and a review of the literature

Panthothenate kinase-associated neurodegeneration (PKAN) is arare neurodegeneration caused by mutations in the pantothenate kinase (PANK2) gene, which is located on chromosome 20p13. These mutations result in iron accumulation in the brain basal ganglia leading to parkinsonism, dysarthria, spasticity, cognitive impairment, and retinopathy. Herein, we report acase of adult-onset PKAN who presented with young-onset action tremor, bradykinesia, dysarthria, and bilateral interossei atrophy.  Neuroimaging demonstrated "eye-of-the-tiger signs". Through analyzing PANK2 gene, PANK2 NM_153638:c.1133A>G (p.Asp378 Gly) and PANK2 NM_153638:c.1502 T > A (p.lle501Asn), were detected. In addition, we reviewed the clinical and genetic features and therapeutic strategies for patients with PKAN.

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.

Novel PANK2 mutation in a Chinese boy with PANK2-associated neurodegeneration: A case report and review of Chinese cases

RATIONALE

Pantothenate kinase-associated neurodegeneration (PKAN), also called Hallervorden-Spatz Syndrome (HSS), is a rare neurodegeneration with brain iron accumulation from pantothenate kinase 2 gene (PANK2) mutation characterized as extrapyramidal symptoms. However, few studies involving PKAN patients were reported in China. This study was conducted to identify the genetic mutations in a Chinese boy with PKAN, and to review all PANK2 mutations reported in Chinese cases with PKAN.

PATIENT CONCERN

We reported a 23-year-old Chinese boy with PKAN, exhibiting difficulty in writing and manipulation using right hand with slow progression for 12 years. He spoke with a severe stutter when he was 15 years old.

DIAGNOSIS

Considering results of magnetic resonance images, brain computed tomography and medical history, the case was suspected to be related to genetic factors.

INTERVENTIONS

Whole exome sequencing was arranged, and the mutations were identified in his parents' genome.

OUTCOMES

In the present study, whole exome sequencing revealed 2 novel mutations (c.1696C > G in exon 7 and c.1160_c.1161insG in exon3) of the PANK2 gene in the proband. c.1696C > G and c.1160_c.1161insG, respectively, were confirmed in his father and mother. We also reviewed 14 different PANK2 mutations, most of which were missense type in Chinese cases. Those mutations did not show apparent hotspots, but exon 3 and 4 were frequently involved.

LESSONS

Two novel compound heterozygous mutations were identified and considered to be pathogenic in PKAN patients. This review of the reports indicated that atypical PKAN is the more common phenotype in China and no apparent genotype-phenotype correlation was found.

Parkinson's Disease and Metal Storage Disorders: A Systematic Review

Metal storage disorders (MSDs) are a set of rare inherited conditions with variable clinical pictures including neurological dysfunction. The objective of this study was, through a systematic review, to identify the prevalence of Parkinsonism in patients with MSDs in order to uncover novel pathways implemented in Parkinson’s disease. Human studies describing patients of any age with an MSD diagnosis were analysed. Foreign language publications as well as animal and cellular studies were excluded. Searches were conducted through PubMed and Ovid between April and September 2018. A total of 53 publications were identified including 43 case reports, nine cross-sectional studies, and one cohort study. The publication year ranged from 1981 to 2018. The most frequently identified MSDs were Pantothenate kinase-associated neurodegeneration (PKAN) with 11 papers describing Parkinsonism, Hereditary hemochromatosis (HH) (7 papers), and Wilson’s disease (6 papers). The mean ages of onset of Parkinsonism for these MSDs were 33, 53, and 48 years old, respectively. The Parkinsonian features described in the PKAN and HH patients were invariably atypical while the majority (4/6) of the Wilson’s disease papers had a typical picture. This paper has highlighted a relationship between MSDs and Parkinsonism. However, due to the low-level evidence identified, further research is required to better define what the relationship is.

Nomenclature of genetic movement disorders: Recommendations of the international Parkinson and movement disorder society task force

The system of assigning locus symbols to specify chromosomal regions that are associated with a familial disorder has a number of problems when used as a reference list of genetically determined disorders,including (I) erroneously assigned loci, (II) duplicated loci, (III) missing symbols or loci, (IV) unconfirmed loci and genes, (V) a combination of causative genes and risk factor genes in the same list, and (VI) discordance between phenotype and list assignment. In this article, we report on the recommendations of the International Parkinson and Movement Disorder Society Task Force for Nomenclature of Genetic Movement Disorders and present a system for naming genetically determined movement disorders that addresses these problems. We demonstrate how the system would be applied to currently known genetically determined parkinsonism, dystonia, dominantly inherited ataxia, spastic paraparesis, chorea, paroxysmal movement disorders, neurodegeneration with brain iron accumulation, and primary familial brain calcifications. This system provides a resource for clinicians and researchers that, unlike the previous system, can be considered an accurate and criterion-based list of confirmed genetically determined movement disorders at the time it was last updated.

Inborn errors of metabolism and expanded newborn screening: review and update

Inborn errors of metabolism (IEM) are a phenotypically and genetically heterogeneous group of disorders caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, more than 1000 different IEM have been identified. While individually rare, the cumulative incidence has been shown to be upwards of 1 in 800. Clinical presentations are protean, complicating diagnostic pathways. IEM are present in all ethnic groups and across every age. Some IEM are amenable to treatment, with promising outcomes. However, high clinical suspicion alone is not sufficient to reduce morbidities and mortalities. In the last decade, due to the advent of tandem mass spectrometry, expanded newborn screening (NBS) has become a mandatory public health strategy in most developed and developing countries. The technology allows inexpensive simultaneous detection of more than 30 different metabolic disorders in one single blood spot specimen at a cost of about USD 10 per baby, with commendable analytical accuracy and precision. The sensitivity and specificity of this method can be up to 99% and 99.995%, respectively, for most amino acid disorders, organic acidemias, and fatty acid oxidation defects. Cost-effectiveness studies have confirmed that the savings achieved through the use of expanded NBS programs are significantly greater than the costs of implementation. The adverse effects of false positive results are negligible in view of the economic health benefits generated by expanded NBS and these could be minimized through increased education, better communication, and improved technologies. Local screening agencies should be given the autonomy to develop their screening programs in order to keep pace with international advancements. The development of biochemical genetics is closely linked with expanded NBS. With ongoing advancements in nanotechnology and molecular genomics, the field of biochemical genetics is still expanding rapidly. The potential of tandem mass spectrometry is extending to cover more disorders. Indeed, the use of genetic markers in T-cell receptor excision circles for severe combined immunodeficiency is one promising example. NBS represents the highest volume of genetic testing. It is more than a test and it warrants systematic healthcare service delivery across the pre-analytical, analytical, and post-analytical phases. There should be a comprehensive reporting system entailing genetic counselling as well as short-term and long-term follow-up. It is essential to integrate existing clinical IEM services with the expanded NBS program to enable close communication between the laboratory, clinicians, and allied health parties. In this review, we will discuss the history of IEM, its clinical presentations in children and adult patients, and its incidence among different ethnicities; the history and recent expansion of NBS, its cost-effectiveness, associated pros and cons, and the ethical issues that can arise; the analytical aspects of tandem mass spectrometry and post-analytical perspectives regarding result interpretation.

Pathophysiology and treatment of neurodegeneration with brain iron accumulation in the pediatric population

OPINION STATEMENT

Syndromes of neurodegeneration with brain iron accumulation (NBIA) are characterized by increased iron deposition in the basal ganglia leading to complex progressive neurological symptoms. Several genetically distinct subforms have been recognized. In addition to pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2), further genetic causes continue to be identified. Most of these present in childhood and are inherited following an autosomal recessive trait. However, the clinical and pathological spectrum has broadened and new age-dependent presentations have been described and there is overlap between the different NBIA disorders and with other diseases (such as spastic paraplegias, leukodystrophies and neuronal ceroid lipofuscinosis). Thus, additional clinical information (e.g., radiological findings such as precise patters of deposition of iron or co-occurrence of white matter lesions) may be useful when prioritizing genetic screening. Neuropathological work-up demonstrated variable involvement of iron deposition, but also Lewy bodies, neurofibrillary tangles and spheroid bodies. Treatment remains symptomatic. Here we review characteristic features of NBIA syndromes with a focus on pediatric cases.

Genetics and Pathophysiology of Neurodegeneration with Brain Iron Accumulation (NBIA)

Our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. In addition to the core syndromes of pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2), several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). In parallel, the clinical and pathological spectrum has broadened and new age-dependent presentations are being described. There is also growing recognition of overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies and neuronal ceroid lipofuscinosis which makes a diagnosis solely based on clinical findings challenging. Autopsy examination of genetically-confirmed cases demonstrates Lewy bodies, neurofibrillary tangles, and other hallmarks of apparently distinct neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease. Until we disentangle the various NBIA genes and their related pathways and move towards pathogenesis-targeted therapies, the treatment remains symptomatic. Our aim here is to provide an overview of historical developments of research into iron metabolism and its relevance in neurodegenerative disorders. We then focus on clinical features and investigational findings in NBIA and summarize therapeutic results reviewing reports of iron chelation therapy and deep brain stimulation. We also discuss genetic and molecular underpinnings of the NBIA syndromes.

Excess iron harms the brain: the syndromes of neurodegeneration with brain iron accumulation (NBIA)

Regulation of iron metabolism is crucial: both iron deficiency and iron overload can cause disease. In recent years, our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. These are characterized by excessive iron deposition in the brain, mainly the basal ganglia. Pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2) are the core syndromes, but several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). These conditions show a wide clinical and pathological spectrum, with clinical overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies, and neuronal ceroid lipofuscinosis. Lewy body pathology was confirmed in some clinical subtypes (C19orf12-associated neurodegeneration and PLAN). Research aims at disentangling the various NBIA genes and their related pathways to move towards pathogenesis-targeted therapies. Until then treatment remains symptomatic. Here we will introduce the group of NBIA syndromes and review the main clinical features and investigational findings.

Current concepts and controversies in neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) encompasses at least 7 genetically distinct disorders, and additional causative genes likely await identification. Recent advances have included the characterization of new genes associated with new subtypes of NBIA and also highlighted the phenotypic heterogeneity of this class of disorders. Herein, we summarize current concepts of NBIA pathogenesis and discuss important gaps in current knowledge, outlining key questions in the field.

Neurodegeneration with brain iron accumulation - clinical syndromes and neuroimaging

Iron participates in a wide array of cellular functions and is essential for normal neural development and physiology. However, if inappropriately managed, the transition metal is capable of generating neurotoxic reactive oxygen species. A number of hereditary conditions perturb body iron homeostasis and some, collectively referred to as neurodegeneration with brain iron accumulation (NBIA), promote pathological deposition of the metal predominantly or exclusively within the central nervous system (CNS). In this article, we discuss seven NBIA disorders with emphasis on the clinical syndromes and neuroimaging. The latter primarily entails magnetic resonance scanning using iron-sensitive sequences. The conditions considered are Friedreich ataxia (FA), pantothenate kinase 2-associated neurodegeneration (PKAN), PLA2G6-associated neurodegeneration (PLAN), FA2H-associated neurodegeneration (FAHN), Kufor-Rakeb disease (KRD), aceruloplasminemia, and neuroferritinopathy. An approach to differential diagnosis and the status of iron chelation therapy for several of these entities are presented. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.