Dominant mitochondrial membrane protein-associated neurodegeneration (MPAN) variants cluster within a specific C19orf12 isoform

Mitochondria membrane protein-associated neurodegeneration (MPAN) neurodegenerative disorder is typically associated with biallelic C19orf12 variants. Here we describe a new and review candidate previous monoallelic de novo C19orf12 variants to define loss of function mutations located in the putative non-membrane spanning C19orf12 isoform as the potential basis of monoallelic MPAN.     

Retrospective analysis of 17 patients with mitochondrial membrane protein-associated neurodegeneration diagnosed in Russia

IntroductionMitochondrial membrane protein-associated neurodegeneration (MPAN) is a rare neurological syndrome caused by pathogenic variants in the C19orf12 and is characterized by iron deposition in the basal ganglia and substantia nigra. Only a limited number of cohort studies were published to date and the prevalence of MPAN remains uncertain.MethodsRecruited subjects with MPAN in Russia were diagnosed by whole-exome sequencing or Sanger sequencing of the C19orf12 gene. Data of over 14000 whole exome sequencing analyses was used to calculate the estimated disease frequency. RNA analysis was performed by RT-PCR. QSVanalyzer software was used to quantify the allelic disbalance.ResultsWe describe the clinical and molecular characterizations of 17 patients with MPAN. DNA analysis detected three previously undescribed pathogenic/likely pathogenic variants in the C19orf12 gene. The estimated disease frequency was calculated to be 1:619150. We describe unusual clinical observations in several cases. One patient showed severe neurogenic muscle weakness along with a lack of marked spasticity or optic nerve atrophy. In another mild clinical case with the NM_001031726.3:c.204_214del (p.(Gly69Argfs*10)) variant in a heterozygous state, a marked allelic disbalance was observed on the RNA level with reduced expression level of the wild-type allele. Thus, this case became the first one of a possible regulatory variant causing MPAN.ConclusionWe reported a detailed clinical and molecular characterization of the third-largest MPAN cohort. We expanded the mutational and clinical spectrum of MPAN. Moreover, we calculated the estimated MPAN frequency in the Russian population for the first time.     

Mitochondrial membrane protein-associated neurodegeneration: a case report and literature review

Mitochondrial membrane protein-associated neurodegeneration (MPAN) is an autosomal recessive disorder caused by mutation in the C19orf12 gene. We report a compound heterozygous c.[32C>T];[205G>A;424A>G] (p.[Thr11Met];[Gly69Arg;Lys142Glu]) Czech patient who manifested with right foot dystonia, impaired handwriting, attention deficit, and signs of iron accumulation on brain MRI. Gradually, he developed dysarthria, spastic-dystonic gait, pedes cavi, and atrophy of leg muscles. Additionally, we report demographic parameters, clinical signs, and allelic frequencies of C19orf12 mutations of all published MPAN cases. We compared the most frequent mutations, p.Thr11Met and p.Gly69ArgfsX10; the latter was associated with younger age at onset and more frequent optic atrophy in homozygotes.     

Mitochondrial Membrane Protein–Associated Neurodegeneration Mimicking Juvenile Amyotrophic Lateral Sclerosis

BackgroundMitochondrial membrane protein associated neurodegeneration (MPAN) is the third most common subtype of neurodegeneration with brain iron accumulation (NBIA) and caused by mutations of the orphan gene C19ORF12 encoding a transmembrane mitochondrial protein. Like other NBIA disorders, the hallmark of neuropathology is iron deposition in the basal ganglia, but the clinical presentation is highly variable.MethodsWe present the relevant clinical history, neurological examination, electrophysiological and neuroimaging tests of a currently ten-year-old girl. The genetic analysis was carried out by exome sequencing focused on known NBIA and juvenile amyotrophic lateral sclerosis (ALS) genes.ResultsThe patient presented at four years of age with progressive lower extremity weakness and generalized hypotonia. She was initially diagnosed with juvenile ALS based on clinical signs, negative brain magnetic resonance imaging (MRI) and electromyography findings. As the disease progressed, a repeat brain MRI showed iron deposition in the basal ganglia at nine years of age. Exome sequencing of genes known to be associated with NBIA revealed a compound heterozygous mutation of C19ORF12 gene.ConclusionsA C19orf12 gene mutation should be considered in young children with clinical signs of progressive upper and lower motor neuron disease. Finding iron accumulation in the basal ganglia helps to focus the genetic testing, but it may not be apparent for several years.     

The p.Thr11Met mutation in c19orf12 is frequent among adult Turkish patients with MPAN

IntroductionMutations in the C19orf12 gene cause mitochondrial membrane protein associated neurodegeneration (MPAN), an autosomal recessive form of neurodegeneration with brain iron accumulation (NBIA). A limited number of patients with C19orf12 mutations, particularly those with adult onset of symptoms, have been reported.MethodsWe sequenced the entire coding region of C19orf12 in 15 Turkish adult probands with idiopathic NBIA. We also performed haplotype analysis in families with a recurrent C19orf12 mutation. Clinical features were collected using a standardized form.ResultsNine of our 15 probands (60%) carried the homozygous c.32C > T mutation in C19orf12 (predicted protein effect: p.Thr11Met). This homozygous mutation co-segregated with the disease in all affected relatives available for testing (16 homozygous subjects).Haplotypes across the C19orf12 locus were identical for a very small region, closest to the mutation, suggesting an old founder, or, two independent founders. The clinical phenotype was characterized by adult onset in most cases (mean 24.5 years, range 10–36), and broad spectrum, including prominent parkinsonism, pyramidal signs, psychiatric disturbances, cognitive decline, and motor axonal neuropathy, in various combinations. On T2- or susceptibility weighted-MRI images, all patients displayed bilateral hypointensities in globus pallidus and substantia nigra, without an eye-of-the-tiger sign; however, hyperintense streaking of the medial medullary lamina between the external and internal parts of globus pallidus was observed frequently.ConclusionThe C19orf12 p.Thr11Met mutation is frequent among adult Turkish patients with MPAN. These findings contribute to the characterization of this important NBIA form, and have direct implications for genetic testing of patients of Turkish origin.     

Mitochondrial protein associated neurodegeneration – Case report

Neurodegeneration with brain iron accumulation (NBIA) is a group of genetic disorders with a progressive extrapyramidal syndrome and excessive iron deposition in the brain, particularly in the globus pallidus and substantia nigra. We present the case of a 31-year-old woman with mitochondrial protein associated neurodegeneration (MPAN). MPAN is a new identified subtype of NBIA, caused by mutations in C19orf12 gene. The typical features are speech and gait disturbances, dystonia, parkinsonism and pyramidal signs. Common are psychiatric symptoms such as impulsive or compulsive behavior, depression and emotional lability. In almost all cases, the optic atrophy has been noted and about 50% of cases have had a motor axonal neuropathy. In the MRI on T2- and T2*-weighted images, there are hypointense lesions in the globus palidus and substantia nigra corresponding to iron accumulation.     

Novel case of neurodegeneration with brain iron accumulation 4 (NBIA4) caused by a pathogenic variant affecting splicing

Neurodegeneration with brain iron accumulation type 4 (NBIA4) also known as MPAN (mitochondria protein-associated neurodegeneration) is a rare neurological disorder which main feature is brain iron accumulation most frequently in the globus pallidus and substantia nigra. Whole exome sequencing (WES) in a 12-year-old patient revealed 2 variants in the C19orf12 gene, a previously reported common 11 bp deletion c.204_214del11, p.(Gly69Argfs*10) and a novel splicing variant c.193+5G>A. Functional analysis of novel variant showed skipping of the second exon, resulting in a formation of a truncated nonfunctional protein. This is the first functionally annotated pathogenic splicing variant in NBIA4.     

Clinical and imaging characteristics of late onset mitochondrial membrane protein-associated neurodegeneration (MPAN)

ABSTRACT

Young onset dementias present significant diagnostic challenges. We present the case of a 35-year-old Kuwaiti man with social withdrawal, drowsiness, irritability, anxiety, aphasia, memory loss, hypereflexia, and Parkinsonism. Brain MRI showed bilateral symmetric gradient echo hypointensities in the globi pallidi and substantiae nigrae. Left cortical hypometabolism was seen on brain fluorodeoxyglucose positron emission tomography. A cortical brain biopsy revealed a high Lewy body burden. Genetic testing revealed a homozygous p.T11M mutation in the C19orf12 gene consistent with mitochondrial membrane protein-associated neurodegeneration. This is the oldest onset age of MPAN reported.     

C19orf12 mutation causing mitochondrial membrane-protein Associated Neurodegeneration masquerading as spastic paraplegia

Mitochondrial Membrane-protein Associated Neurodegeneration (MPAN) is a rare disease, caused by C19orf12 mutations and up to 29 different mutations have been described. We report a young woman presented with spastic paraparesis due to C19orf12 gene. MPAN presenting like Hereditary spastic paraplegia-43 is rare and the genetic mutation had been described only once in the literature.     

C19orf12 mutations in neurodegeneration with brain iron accumulation mimicking juvenile amyotrophic lateral sclerosis

Mutations in C19orf12 have been recently identified as the molecular genetic cause of a subtype of neurodegeneration with brain iron accumulation (NBIA). Given the mitochondrial localization of the gene product the new NBIA subtype was designated mitochondrial membrane protein-associated neurodegeneration. Frequent features in the patients described so far included extrapyramidal signs and pyramidal tract involvement. Here, we report three C19orf12-mutant patients from two families presenting with predominant upper and lower motor neuron dysfunction mimicking amyotrophic lateral sclerosis with juvenile onset. While extrapyramidal signs were absent, all patients showed neuropsychological abnormalities with disinhibited or impulsive behavior. Optic atrophy was present in the simplex case. T2-weighted cranial MRI showed hypointensities suggestive of iron accumulation in the globi pallidi and the midbrain in all patients. Sequence analysis of C19orf12 revealed a novel mutation, p.Gly66del, compound heterozygous with known mutations in all patients. These patients highlight that C19orf12 defects should be considered as a differential diagnosis in patients with juvenile onset motor neuron diseases. Patients have to be examined carefully for neuropsychological abnormalities, optic neuropathy, and signs of brain iron accumulation in MRI.     

Review: Insights into molecular mechanisms of disease in neurodegeneration with brain iron accumulation: unifying theories

Neurodegeneration with brain iron accumulation (NBIA) is a group of disorders characterized by dystonia, parkinsonism and spasticity. Iron accumulates in the basal ganglia and may be accompanied by Lewy bodies, axonal swellings and hyperphosphorylated tau depending on NBIA subtype. Mutations in 10 genes have been associated with NBIA that include Ceruloplasmin (Cp) and ferritin light chain (FTL), both directly involved in iron homeostasis, as well as Pantothenate Kinase 2 (PANK2), Phospholipase A2 group 6 (PLA2G6), Fatty acid hydroxylase 2 (FA2H), Coenzyme A synthase (COASY), C19orf12, WDR45 and DCAF17 (C2orf37). These genes are involved in seemingly unrelated cellular pathways, such as lipid metabolism, Coenzyme A synthesis and autophagy. A greater understanding of the cellular pathways that link these genes and the disease mechanisms leading to iron dyshomeostasis is needed. Additionally, the major overlap seen between NBIA and more common neurodegenerative diseases may highlight conserved disease processes. In this review, we will discuss clinical and pathological findings for each NBIA‐related gene, discuss proposed disease mechanisms such as mitochondrial health, oxidative damage, autophagy/mitophagy and iron homeostasis, and speculate the potential overlap between NBIA subtypes.     

Is there heart disease in cases of neurodegeneration associated with mutations in C19orf12?

IntroductionIn mitochondrial membrane protein-associated neurodegeneration (MPAN), a subtype of neurodegeneration with brain iron accumulation (NBIA), patients suffer from optic nerve atrophy and dementia, which are also typical for another group of diseases, the mitochondrial diseases (MD). Around 30% of patients with MD have heart disease, commonly cardiomyopathy and arrhythmias, and 10% experience a major adverse cardiovascular event. The aim of this study was to assess cardiac involvement in MPAN.MethodsThirteen patients with MPAN were evaluated after written informed consent. All patients had echocardiography and 12 patients had 24-h Holter electrocardiogram (ECG) monitoring using 3-channel digital recorders.ResultsEchocardiography revealed normal values for the dimensions of all heart chambers. The systolic function of the left ventricle was normal in all cases. Right ventricle systolic impairment was found in three patients. 24-hour Holter ECG revealed predominant resting tachycardia during daytime with no physiological slowing of heart rate during sleep in seven cases. No significant arrhythmias were found. In nine patients, selected heart rate variability (HRV) parameters were lower than reference values.ConclusionCardiomyopathy, typical of MD, was not found in patients with MPAN. There were no significant arrhythmias, but disturbances in the circadian rhythm of the heart rate were observed in most cases. The decrease in HRV may reflect an early sign of autonomic dysfunction. A standard cardiac work-up is recommended for patients with MPAN to assess if additional treatment is needed.     

Newly Characterized Forms of Neurodegeneration with Brain Iron Accumulation

Neurodegeneration with brain iron accumulation (NBIA) comprises a group of brain iron deposition syndromes that lead to mixed extrapyramidal features and progressive dementia. Historically, there has not been a clearly identifiable molecular cause for many patients with clinical and radiologic features of NBIA. Recent discoveries have shown that mutations in C19orf12 or WDR45 can lead to NBIA. C19orf12 mutations are inherited in an autosomal recessive manner, and lead to a syndrome similar to that caused by mutations in PANK2 or PLA2G6. In contrast, WDR45 mutations lead to a distinct form of NBIA characterized by spasticity and intellectual disability in childhood followed by the subacute onset of dystonia–parkinsonism in adulthood. WDR45 mutations act in an X-linked dominant manner. Although the function of C19orf12 is largely unknown, WDR45 plays a key role in autophagy. Each of these new forms of NBIA thus leads to a distinct clinical syndrome, and together they implicate new cellular pathways in the pathogenesis of these disorders.     

Dystonia Linked to EIF4A2 Haploinsufficiency: A Disorder of Protein Translation Dysfunction

Background

Protein synthesis is a tightly controlled process, involving a host of translation-initiation factors and microRNA-associated repressors. Variants in the translational regulator EIF2AK2 were first linked to neurodevelopmental-delay phenotypes, followed by their implication in dystonia. Recently, de novo variants in EIF4A2, encoding eukaryotic translation initiation factor 4A isoform 2 (eIF4A2), have been described in pediatric cases with developmental delay and intellectual disability.

Objective

We sought to characterize the role of EIF4A2 variants in dystonic conditions.

Methods

We undertook an unbiased search for likely deleterious variants in mutation-constrained genes among 1100 families studied with dystonia. Independent cohorts were screened for EIF4A2 variants. Western blotting and immunocytochemical studies were performed in patient-derived fibroblasts.

Results

We report the discovery of a novel heterozygous EIF4A2 frameshift deletion (c.896_897del) in seven patients from two unrelated families. The disease was characterized by adolescence- to adulthood-onset dystonia with tremor. In patient-derived fibroblasts, eIF4A2 production amounted to only 50% of the normal quantity. Reduction of eIF4A2 was associated with abnormally increased levels of IMP1, a target of Ccr4-Not, the complex that interacts with eIF4A2 to mediate microRNA-dependent translational repression. By complementing the analyses with fibroblasts bearing EIF4A2 biallelic mutations, we established a correlation between IMP1 expression alterations and eIF4A2 functional dosage. Moreover, eIF4A2 and Ccr4-Not displayed significantly diminished colocalization in dystonia patient cells. Review of international databases identified EIF4A2 deletion variants (c.470_472del, c.1144_1145del) in another two dystonia-affected pedigrees.

Conclusions

Our findings demonstrate that EIF4A2 haploinsufficiency underlies a previously unrecognized dominant dystonia-tremor syndrome. The data imply that translational deregulation is more broadly linked to both early neurodevelopmental phenotypes and later-onset dystonic conditions. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.     

Association of Rare Variants in ARSA with Parkinson's Disease

Background

Several lysosomal genes are associated with Parkinson's disease (PD), yet the association between PD and ARSA remains unclear.

Objectives

To study rare ARSA variants in PD.

Methods

To study rare ARSA variants (minor allele frequency < 0.01) in PD, we performed burden analyses in six independent cohorts with 5801 PD patients and 20,475 controls, followed by a meta-analysis.

Results

We found evidence for associations between functional ARSA variants and PD in four cohorts (P ≤ 0.05 in each) and in the meta-analysis (P = 0.042). We also found an association between loss-of-function variants and PD in the United Kingdom Biobank cohort (P = 0.005) and in the meta-analysis (P = 0.049). These results should be interpreted with caution as no association survived multiple comparisons correction. Additionally, we describe two families with potential co-segregation of ARSA p.E382K and PD.

Conclusions

Rare functional and loss-of-function ARSA variants may be associated with PD. Further replications in large case–control/familial cohorts are required. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.     

Polygenic Parkinson's Disease Genetic Risk Score as Risk Modifier of Parkinsonism in Gaucher Disease

Background

Biallelic pathogenic variants in GBA1 are the cause of Gaucher disease (GD) type 1 (GD1), a lysosomal storage disorder resulting from deficient glucocerebrosidase. Heterozygous GBA1 variants are also a common genetic risk factor for Parkinson's disease (PD). GD manifests with considerable clinical heterogeneity and is also associated with an increased risk for PD.

Objective

The objective of this study was to investigate the contribution of PD risk variants to risk for PD in patients with GD1.

Methods

We studied 225 patients with GD1, including 199 without PD and 26 with PD. All cases were genotyped, and the genetic data were imputed using common pipelines.

Results

On average, patients with GD1 with PD have a significantly higher PD genetic risk score than those without PD (P = 0.021).

Conclusions

Our results indicate that variants included in the PD genetic risk score were more frequent in patients with GD1 who developed PD, suggesting that common risk variants may affect underlying biological pathways. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.     

Influence of cytochrome 2C19 allelic variants on on-treatment platelet reactivity evaluated by five different platelet function tests

Background

The antiplatelet effect of clopidogrel has been linked to cytochrome P450 2C19 (CYP2C19) carrier status. The presence of loss of function and gain of function variants were found to have a gene-dose effect on clopidogrel metabolism. However, genotyping is only one aspect of predicting response to clopidogrel and several platelet function tests are available to measure platelet response.Patients and methodsWe studied the influence of CYP2C19 allelic variants on on-treatment platelet reactivity as assessed by light transmission aggregometry (LTA), the VerifyNow P2Y12 assay, the VASP assay, multiple electrode aggregometry (MEA), and the Impact-R in 288 patients after stenting for cardiovascular disease. Allelic variants of CYP2C19 were determined with the Infiniti® CYP450 2C19 + assay and categorized into four metabolizer states (ultrarapid, extensive, intermediate, poor).

Results

Platelet reactivity increased linearly from ultrarapid to poor metabolizers using the VerifyNow P2Y12 assay (P = 0.04), the VASP assay (P = 0.02) and the Impact-R (P = 0.04). The proportion of patients with high on-treatment residual platelet reactivity (HRPR) identified by LTA, the VerifyNow P2Y12 assay and the VASP assay increased when the metabolizer status decreased, while no such relationship could be identified for results of MEA and Impact-R. The presence of loss of function variants (*2/*2, *2-8*/wt, *2/*17) was an independent predictor of HRPR in LTA and the VASP assay while it did not reach statistical significance in the VerifyNow P2Y12 assay, MEA, and the Impact-R.

Conclusion

Depending on the type of platelet function test differences in the association of on-treatment platelet reactivity with CYP2C19 carrier status are observed.     

In Vivo Investigation of Glucose Metabolism in Idiopathic and PRKN-Related Parkinson's Disease

Background

Alterations in mitochondrial dysfunction have been implicated in the pathogenesis of Parkinson's disease (PD). Mitochondrial energy production is linked to glucose metabolism, and diabetes is associated with PD. However, studies investigating glucose metabolism in vivo in genetically stratified PD patients and controls have yet to be performed.

Objectives

The objectives of this study were to explore glucose production, gluconeogenesis, and the contribution of gluconeogenesis to glucose production in idiopathic and PRKN PD compared with healthy controls with state-of-the-art biochemical methods.

Methods

We applied a dried-blood sampling/gas chromatography/mass spectrometry approach to monitor fluxes in the Cori cycle in vivo.

Results

The contribution of gluconeogenesis to total glucose production is increased in idiopathic PD patients (n = 33), but not in biallelic PRKN mutation carriers (n = 5) compared with healthy controls (n = 13).

Conclusions

We provide first-time in vivo evidence for alterations in glucose metabolism in idiopathic PD, in keeping with the epidemiological evidence for an association between PD and diabetes. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.     

Genetic screen in a large series of patients with primary progressive aphasia

Introduction

Primary progressive aphasia (PPA) is a neurological syndrome, associated with both frontotemporal dementia and Alzheimer's disease, in which progressive language impairment emerges as the most salient clinical feature during the initial stages of disease.