PLA2G6mutations and Parkinsonism: Long-term follow-up of clinical features and neuropathology

Clinical, neuroimaging and genetic findings in Brazilian patients with neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) encompasses a clinically and genetically heterogeneous group of rare disorders. Here, we report clinical, neuroimaging and genetic studies in twenty three Brazilian NBIA patients. In thirteen subjects, deleterious variants were detected in known NBIA-causing genes (PANK2, PLA2G6, C9ORF12, WDR45 and FA2H), including previously unreported variants in PANK2 and PLA2G6. Two patients carried rare, likely pathogenic variants in genes not previously associated with NBIA: KMT2A c.11785A > C (p.Ile3929Leu), and TIMM8A c.127T > C (p.Cys43Arg), suggesting an expansion of their associated phenotypes to include NBIA. In eight patients the etiology remains unsolved, suggesting variants undetectable by the adopted methods, or the existence of additional NBIA-causing genes.

A novel variant of PLA2G6 gene related early-onset parkinsonism: a case report and literature review

This study reported a case of early-onset parkinsonism associated with a novel variant of the PLA2G6 gene. The boy first started showing symptoms at the age of 11, with gait instability and frequent falls. As the disease progressed, his gait instability worsened, and he developed difficulties with swallowing and speaking, although there was no apparent decline in cognitive function. An MRI of the head revealed significant atrophy of the cerebellum. The initial diagnosis for the boy was early-onset parkinsonism, classified as Hoehn-Yahr grade 5.Genomic sequencing of the patient indicated that he had compound heterozygous variations in the PLA2G6 gene: c.1454G>A (p.Gly485Glu) and c.991G>T (p.Asp331Tyr). Pedigree analysis revealed that his younger brother also carried the same variant, albeit with milder symptoms. The patient's unaffected mother was found to be a carrier of the c.991G>T variant. Additionally, this study reviewed 62 unrelated families with PLA2G6 gene-related early-onset parkinsonism. The analysis showed a higher proportion of female probands, with a mean age of onset of ~23.0 years. Primary symptoms were predominantly bradykinesia and psychosis, with tremors being relatively rare. Cerebellar atrophy was observed in 41 patients (66.1%). Among the reported mutations, the most common mutation was c.991G>T, presenting in 21 families (33.9%), followed by c.2222G>A in eight families (12.9%). Other mutations were less common. Notably, the c.991G>T mutation was exclusive to Chinese families and was a prevalent mutation among this population. The initial symptoms varied significantly among patients with different mutations.

The role of the PLA2G6 gene in neurodegenerative diseases

PLA2G6-associated neurodegeneration (PLAN) represents a continuum of clinically and genetically heterogeneous neurodegenerative disorders with overlapping features. Usually, it encompasses three autosomal recessive diseases, including infantile neuroaxonal dystrophy or neurodegeneration with brain iron accumulation (NBIA) 2A, atypical neuronal dystrophy with childhood-onset or NBIA2B, and adult-onset dystonia-parkinsonism form named PARK14, and possibly a certain subtype of hereditary spastic paraplegia. PLAN is caused by variants in the phospholipase A2 group VI gene (PLA2G6), which encodes an enzyme involved in membrane homeostasis, signal transduction, mitochondrial dysfunction, and α-synuclein aggregation. In this review, we discuss PLA2G6 gene structure and protein, functional findings, genetic deficiency models, various PLAN disease phenotypes, and study strategies in the future. Our primary aim is to provide an overview of genotype-phenotype correlations of PLAN subtypes and speculate on the role of PLA2G6 in potential mechanisms underlying these conditions.

Genetic Movement Disorders Commonly Seen in Asians

The increasing availability of molecular genetic testing has changed the landscape of both genetic research and clinical practice. Not only is the pace of discovery of novel disease-causing genes accelerating but also the phenotypic spectra associated with previously known genes are expanding. These advancements lead to the awareness that some genetic movement disorders may cluster in certain ethnic populations and genetic pleiotropy may result in unique clinical presentations in specific ethnic groups. Thus, the characteristics, genetics and risk factors of movement disorders may differ between populations. Recognition of a particular clinical phenotype, combined with information about the ethnic origin of patients could lead to early and correct diagnosis and assist the development of future personalized medicine for patients with these disorders. Here, the Movement Disorders in Asia Task Force sought to review genetic movement disorders that are commonly seen in Asia, including Wilson's disease, spinocerebellar ataxias (SCA) types 12, 31, and 36, Gerstmann-Sträussler-Scheinker disease, PLA2G6-related parkinsonism, adult-onset neuronal intranuclear inclusion disease (NIID), and paroxysmal kinesigenic dyskinesia. We also review common disorders seen worldwide with specific mutations or presentations that occur frequently in Asians.

Case Report: A case of PLA2G6 gene-related early-onset Parkinson's disease and review of literature

Background

Early onset Parkinson's disease (EOPD) is a neurodegenerative disease associated with the action ofto genetic factors. A mutated phospholipase A2 type VI gene (PLA2G6) is considered to be one of pathogenic genes involved in EOPD development. Although EOPD caused by a mutated PLA2G6 has been recorded in major databases, not all mutant genotypes have been reported. Here, we report a case of PLA2G6-related EOPD caused by a novel compound heterozygous mutation.

Case presentation

The case was an of 26-year-old young male with a 2-year course of disease. The onset of the disease was insidious and developed gradually. The patient presented with unsteady walking, bradykinesia, unresponsiveness, and decreased facial expression. Auxiliary examination showed a compound heterozygous mutation of the PLA2G6gene with c.991G > T and c.1427 + 1G > A. Mild atrophy of the cerebrum and cerebellum was detected on brain MRI. The patient was diagnosed with EOPD. We administered treatment with Madopar, which was effective. After a two-year disease course, we observed progression to stage 5 according to the Hoehn-Yahr Scale (without medicine in the off-stage). An MDS-UPDRS III score of 62 was obtained, with characteristics of severe disease and rapid progress. The diagnosis was an EOPD phenotype caused by a combination of mutations at the c.991G > T and c.1427 + 1G > A sites of the PLA2G6gene.

Conclusion

After active treatment, the disease was set under control, with no significant progression during the three-month follow-up period. Dyskinesia did not recur after reducing the Madopar dose. The freezing sign was slightly decreased and the wearing-off was delayed to 2 h.

PLA2G6-associated neurodegeneration in four different populations-case series and literature review

BACKGROUND

PLA2G6-Associated Neurodegeneration, PLAN, is subdivided into: Infantile neuroaxonal dystrophy, atypical neuroaxonal dystrophy, and adult-onset dystonia parkinsonism [1]. It is elicited by a biallelic pathogenic variant in phospholipase A2 group VI (PLA2G6) gene. In this study we describe new cases and provide a comprehensive review of previously published cases.

METHODS

Eleven patients, from four different institutions and four different countries. All underwent a comprehensive chart review.

RESULTS

Ages at onset ranged from 1 to 36 years, with a median of 16 and a mean of 16.18 ± 11.91 years. Phenotypic characteristics were heterogenous and resembled that of patients with infantile neuroaxonal dystrophy (n = 2), atypical neuroaxonal dystrophy (n = 1), adult-onset dystonia parkinsonism (n = 1), complex hereditary spastic paraparesis (n = 3), and early onset Parkinson's disease (n = 2). Parental genetic studies were performed for all patients and confirmed with sanger sequencing in five. Visual evoked potential illustrated optic atrophy in P4. Mineralization was evident in brain magnetic resonance imaging of P1, P2, P4, P5, P7, and P11. Single photon emission computed tomography was conducted for three patients, revealed decreased perfusion in the occipital lobes for P10. DaTscan was performed for P11 and showed decreased uptake in the deep gray matter, bilateral caudate nuclei, and bilateral putamen. Positive response to Apomorphine was noted for P10 and to Baclofen in P2, and P3.

CONCLUSIONS

PLAN encompasses a wide clinical spectrum. Age and symptom at onset are crucial when classifying patients. Reporting new variants is critical to draw more attention to this condition and identify biomarkers to arrive at potential therapeutics.

Cerebral Iron Deposition in Neurodegeneration

Disruption of cerebral iron regulation appears to have a role in aging and in the pathogenesis of various neurodegenerative disorders. Possible unfavorable impacts of iron accumulation include reactive oxygen species generation, induction of ferroptosis, and acceleration of inflammatory changes. Whole-brain iron-sensitive magnetic resonance imaging (MRI) techniques allow the examination of macroscopic patterns of brain iron deposits in vivo, while modern analytical methods ex vivo enable the determination of metal-specific content inside individual cell-types, sometimes also within specific cellular compartments. The present review summarizes the whole brain, cellular, and subcellular patterns of iron accumulation in neurodegenerative diseases of genetic and sporadic origin. We also provide an update on mechanisms, biomarkers, and effects of brain iron accumulation in these disorders, focusing on recent publications. In Parkinson’s disease, Friedreich’s disease, and several disorders within the neurodegeneration with brain iron accumulation group, there is a focal siderosis, typically in regions with the most pronounced neuropathological changes. The second group of disorders including multiple sclerosis, Alzheimer’s disease, and amyotrophic lateral sclerosis shows iron accumulation in the globus pallidus, caudate, and putamen, and in specific cortical regions. Yet, other disorders such as aceruloplasminemia, neuroferritinopathy, or Wilson disease manifest with diffuse iron accumulation in the deep gray matter in a pattern comparable to or even more extensive than that observed during normal aging. On the microscopic level, brain iron deposits are present mostly in dystrophic microglia variably accompanied by iron-laden macrophages and in astrocytes, implicating a role of inflammatory changes and blood–brain barrier disturbance in iron accumulation. Options and potential benefits of iron reducing strategies in neurodegeneration are discussed. Future research investigating whether genetic predispositions play a role in brain Fe accumulation is necessary. If confirmed, the prevention of further brain Fe uptake in individuals at risk may be key for preventing neurodegenerative disorders.

Dissecting the Phenotype and Genotype of PLA2G6-Related Parkinsonism

BACKGROUND

Complex parkinsonism is the commonest phenotype in late-onset PLA2G6-associated neurodegeneration.

OBJECTIVES

The aim of this study was to deeply characterize phenogenotypically PLA2G6-related parkinsonism in the largest cohort ever reported.

METHODS

We report 14 new cases of PLA2G6-related parkinsonism and perform a systematic literature review.

RESULTS

PLA2G6-related parkinsonism shows a fairly distinct phenotype based on 86 cases from 68 pedigrees. Young onset (median age, 23.0 years) with parkinsonism/dystonia, gait/balance, and/or psychiatric/cognitive symptoms were common presenting features. Dystonia occurred in 69.4%, pyramidal signs in 77.2%, myoclonus in 65.2%, and cerebellar signs in 44.6% of cases. Early bladder overactivity was present in 71.9% of cases. Cognitive impairment affected 76.1% of cases and psychiatric features 87.1%, the latter being an isolated presenting feature in 20.1%. Parkinsonism was levodopa responsive but complicated by early, often severe dyskinesias. Five patients benefited from deep brain stimulation. Brain magnetic resonance imaging findings included cerebral (49.3%) and/or cerebellar (43.2%) atrophy, but mineralization was evident in only 28.1%. Presynaptic dopaminergic terminal imaging was abnormal in all where performed. Fifty-four PLA2G6 mutations have hitherto been associated with parkinsonism, including four new variants reported in this article. These are mainly nontruncating, which may explain the phenotypic heterogeneity of childhood- and late-onset PLA2G6-associated neurodegeneration. In five deceased patients, median disease duration was 13.0 years. Brain pathology in three cases showed mixed Lewy and tau pathology.

CONCLUSIONS

Biallelic PLA2G6 mutations cause early-onset parkinsonism associated with dystonia, pyramidal and cerebellar signs, myoclonus, and cognitive impairment. Early psychiatric manifestations and bladder overactivity are common. Cerebro/cerebellar atrophy are frequent magnetic resonance imaging features, whereas brain iron deposition is not. Early, severe dyskinesias are a tell-tale sign. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

PLA2G6 variants associated with the number of affected alleles in Parkinson's disease in Japan

This study aimed to evaluate genotype-phenotype correlations of Parkinson's disease (PD) patients with phospholipase A2 group V (PLA2G6) variants. We analyzed the DNA of 798 patients with PD, including 78 PD patients reported previously, and 336 in-house controls. We screened the exons and exon-intron boundaries of PLA2G6 using the Ion Torrent system and Sanger method. We identified 21 patients with 18 rare variants, such that 1, 9, and 11 patients were homozygous, heterozygous, and compound heterozygous, respectively, with respect to PLA2G6 variants. The allele frequency was approximately equal between patients with familial PD and those with sporadic PD. The PLA2G6 variants detected frequently were identified in the early-onset sporadic PD group. Patients who were homozygous for a variant showed more severe symptoms than those who were heterozygous for the variant. The most common variant was p.R635Q in our cohort, which was considered a risk variant for PD. Thus, the variants of PLA2G6 may play a role in familial PD and early-onset sporadic PD.

Early-Onset Parkinson's Disease Caused by PLA2G6 Compound Heterozygous Mutation, a Case Report and Literature Review

PLA2G6 has been certified as a causative gene in patients with autosomal recessive early-onset Parkinson's disease (EOPD). We reported an EOPD case caused by PLA2G6 gene mutation, and performed neurological examination, genetic analysis, and multimodal neuroimaging to describe this phenotype. A compound heterozygous mutation c.991G>T/c.1472+1G>A was detected in this patient. Heterozygous for the c.991G>T and c.1472+1G>A were separately detected in his parents. Pathogenicity of these two mutations were predicted according to the American college of medical genetics and genomics (ACMG) guideline. MRI assessment showed absence of bilateral “swallow tail sign” and cerebellar atrophy in this patient, while no obvious difference in brain iron accumulation between PLA2G6 mutant PD patient and healthy controls. Cerebellar abnormalities may be a marker for diagnosis and evaluation of PLA2G6 mutation Parkinsonism. However, the iron accumulation in PD may not be the result of PLA2G6 mutation.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

Dystonia and Parkinson's disease: What is the relationship?

Dystonia and Parkinson's disease are closely linked disorders sharing many pathophysiological overlaps. Dystonia can be seen in 30% or more of the patients suffering with PD and sometimes can precede the overt parkinsonism. The response of early dystonia to the introduction of dopamine replacement therapy (levodopa, dopamine agonists) is variable; dystonia commonly occurs in PD patients following levodopa initiation. Similarly, parkinsonism is commonly seen in patients with mutations in various DYT genes including those involved in the dopamine synthesis pathway. Pharmacological blockade of dopamine receptors can cause both tardive dystonia and parkinsonism and these movement disorders syndromes can occur in many other neurodegenerative, genetic, toxic and metabolic diseases. Pallidotomy in the past and currently deep brain stimulation largely involving the GPi are effective treatment options for both dystonia and parkinsonism. However, the physiological mechanisms underlying the response of these two different movement disorder syndromes are poorly understood. Interestingly, DBS for PD can cause dystonia such as blepharospasm and bilateral pallidal DBS for dystonia can result in features of parkinsonism. Advances in our understanding of these responses may provide better explanations for the relationship between dystonia and Parkinson's disease.

Identification of a novel mutation in PLA2G6 gene and phenotypic heterogeneity analysis of PLA2G6-related neurodegeneration

INTRODUCTION

This study reports a novel mutation site of the phospholipase A2 group VI (PLA2G6) gene, and analyzes the information of 67 previously published cases to elucidate PLA2G6 phenotype-genotype variations.

METHODS

We collected clinical data and examined gene mutation sites from one Chinese patient with adult-onset ataxia and her family. Next-generation sequencing (NGS) and Sanger sequencing were used to verify possible mutations. PolyPhen-2, SIFT, and MutationTaster were used to predict their pathogenicity. For analyzing the distribution frequency of the mutation, 597 healthy controls were recruited. We also analyzed the clinical and genetic information of 67 cases from 23 studies in Pubmed database.

RESULTS

A novel compound heterozygous mutation of the PLA2G6 gene, c.1648delC and c.991G > T, was found in the Chinese patient, and classified as pathogenic. The c.1648delC variation was absent in ExAC, 1000G, dbSNP databases and the 597 healthy controls. Of the 67 cases, 29 presented ataxia. The signs of cerebellar atrophy appeared in the MRIs of most patients, while signs of iron accumulation were absent in older-aged patients with a compound heterozygous mutation. Thirty-eight patients showed no ataxia. A negative or mild extrapyramidal symptom accompanied by a low age, a homogenous mutation, while moderate or severe extrapyramidal symptoms were associated with an old age and a compound heterozygous mutation.

CONCLUSION

A novel compound heterozygous mutation of the PLA2G6 gene, c.1648delC and c.991G > T, is associated with adult onset ataxia. Phenotype-genotype variations of PLA2G6 are predicted to be caused by the loss of protein or enzyme activity of phospholipase-2.

PLA2G6-Associated Neurodegeneration (PLAN): Review of Clinical Phenotypes and Genotypes

Phospholipase A2 group VI (PLA2G6)-associated neurodegeneration (PLAN) includes a series of neurodegenerative diseases that result from the mutations in PLA2G6. PLAN has genetic and clinical heterogeneity, with different mutation sites, mutation types and ethnicities and its clinical phenotype is different. The clinical phenotypes and genotypes of PLAN are closely intertwined and vary widely. PLA2G6 encodes a group of VIA calcium-independent phospholipase A2 proteins (iPLA₂β), an enzyme involved in lipid metabolism. According to the age of onset and progressive clinical features, PLAN can be classified into the following subtypes: infantile neuroaxonal dystrophy (INAD), atypical neuroaxonal dystrophy (ANAD) and parkinsonian syndrome which contains adult onset dystonia parkinsonism (DP) and autosomal recessive early-onset parkinsonism (AREP). In this review, we present an overview of PLA2G6-associated neurodegeneration in the context of current research.

Genetic analysis of ATP13A2, PLA2G6 and FBXO7 in a cohort of Chinese patients with early-onset Parkinson's disease

Several genes have already been certified as causative genes in patients with autosomal recessive early-onset Parkinson's syndrome with pyramidal tract signs, including ATP13A2, PLA2G6 and FBXO7. Variants in these three genes may also play roles in early-onset Parkinson's disease (EOPD). In order to investigate the contribution of genetic variants in these three genes to Chinese sporadic EOPD patients, we screened 101 Chinese sporadic EOPD patients and 83 age- and sex-matched healthy controls using direct sequencing. Interpretation of those detected variants was performed based on the guidelines developed by the American College of Medical Genetics and Genomics (ACMG). Two missense variants, p.G360E and p.T733M, with "uncertain significance" classification were identified in the ATP13A2 gene and five synonymous variants were significantly over-represented in EOPD patients. Two missense variants, p.R53C and p.T319M, were absent in both our control group and online databases, classified as "likely pathogenic" in the PLA2G6 gene. Only benign variants were identified in the FBXO7 gene. These results indicate that rare variants of PLA2G6 may contribute to PD susceptibility in Chinese population, the ATP13A2 might be associated with higher risk for sporadic EOPD, while the FBXO7 gene doesn't seem to be a risk factor to develop sporadic PD in Chinese population. Further biochemical and molecular biological studies needs to be conducted to support our main results in our future researches.

Neuropathology of genetic synucleinopathies with parkinsonism: Review of the literature

Clinical-pathological studies remain the gold-standard for the diagnosis of Parkinson's disease (PD). However, mounting data from genetic PD autopsies challenge the diagnosis of PD based on Lewy body pathology. Most of the confirmed genetic risks for PD show heterogenous neuropathology, even within kindreds, which may or may not include Lewy body pathology. We review the literature of genetic PD autopsies from cases with molecularly confirmed PD or parkinsonism and summarize main findings on SNCA (n = 25), Parkin (n = 20, 17 bi-allelic and 3 heterozygotes), PINK1 (n = 5, 1 bi-allelic and 4 heterozygotes), DJ-1 (n = 1), LRRK2 (n = 55), GBA (n = 10 Gaucher disease patients with parkinsonism), DNAJC13, GCH1, ATP13A2, PLA2G6 (n = 8 patients, 2 with PD), MPAN (n = 2), FBXO7, RAB39B, and ATXN2 (SCA2), as well as on 22q deletion syndrome (n = 3). Findings from autopsies of heterozygous mutation carriers of genes that are traditionally considered recessively inherited are also discussed. Lewy bodies may be present in syndromes clinically distinctive from PD (eg, MPAN-related neurodegeneration) and absent in patients with clinical PD syndrome (eg, LRRK2-PD or Parkin-PD). Therefore, the authors can conclude that the presence of Lewy bodies are not specific to the diagnosis of PD and that PD can be diagnosed even in the absence of Lewy body pathology. Interventions that reduce alpha-synuclein load may be more justified in SNCA-PD or GBA-PD than in other genetic forms of PD. The number of reported genetic PD autopsies remains small, and there are limited genotype-clinical-pathological-phenotype studies. Therefore, larger series of autopsies from genetic PD patients are required. © 2017 International Parkinson and Movement Disorder Society.