Infantile parkinsonism-dystonia: a dopamine "transportopathy"

Cluster-Dominated Electrochemiluminescence of Tertiary Amines in Polyethyleneimine Nanoparticles: Mechanism Insights and Sensing Application

Designing and screening highly efficient and cost-effective luminophores have always been a challenge to develop sensitive electrochemiluminescence (ECL) biosensors. Herein, polyethyleneimine nanoparticles (PEI NPs), a kind of nonconjugated polymer (NCP) NPs with tertiary amine clusters, were developed as an ECL luminophore. Specifically, PEI NPs were synthesized by a one-step hydrothermal method using PEI and formaldehyde. The properties of PEI NPs were investigated in detail using photochemical and electrochemical techniques. The results showed cluster-dominated luminescence of tertiary amines in PEI NPs via "through-space conjugation". This non-negligible ECL performance (at 631 nm) was also verified by the initiated reduction-oxidation process. With persulfate as a coreactant, PEI NPs acted as both the luminophore and coreaction accelerator to enhance the ECL intensity remarkably, which was eightfold higher than that of isolated PEI. Moreover, choosing dopamine as the model target, a highly sensitive "signal off" ternary ECL sensor was constructed utilizing PEI NPs as the luminophore. Dopamine could be oxidized to benzoquinone at the sensing interface, quenching the signal via ECL energy transfer. Free from any signal amplification, the proposed sensor achieved a low detection limit (4.3 nM) for target monitoring with good selectivity and stability. This strategy not only provides a unique perspective for designing novel efficient and facile ECL luminophores of tertiary amines but also broadens the biological application of NCP NPs.

DNAJC6 Mutations Disrupt Dopamine Homeostasis in Juvenile Parkinsonism-Dystonia

Background

Juvenile forms of parkinsonism are rare conditions with onset of bradykinesia, tremor and rigidity before the age of 21 years. These atypical presentations commonly have a genetic aetiology, highlighting important insights into underlying pathophysiology. Genetic defects may affect key proteins of the endocytic pathway and clathrin‐mediated endocytosis (CME), as in DNAJC6‐related juvenile parkinsonism.

Objective

To report on a new patient cohort with juvenile‐onset DNAJC6 parkinsonism‐dystonia and determine the functional consequences on auxilin and dopamine homeostasis.

Methods

Twenty‐five children with juvenile parkinsonism were identified from a research cohort of patients with undiagnosed pediatric movement disorders. Molecular genetic investigations included autozygosity mapping studies and whole‐exome sequencing. Patient fibroblasts and CSF were analyzed for auxilin, cyclin G–associated kinase and synaptic proteins.

Results

We identified 6 patients harboring previously unreported, homozygous nonsense DNAJC6 mutations. All presented with neurodevelopmental delay in infancy, progressive parkinsonism, and neurological regression in childhood. ¹²³I‐FP‐CIT SPECT (DaTScan) was performed in 3 patients and demonstrated reduced or absent tracer uptake in the basal ganglia. CSF neurotransmitter analysis revealed an isolated reduction of homovanillic acid. Auxilin levels were significantly reduced in both patient fibroblasts and CSF. Cyclin G–associated kinase levels in CSF were significantly increased, whereas a number of presynaptic dopaminergic proteins were reduced.

Conclusions

DNAJC6 is an emerging cause of recessive juvenile parkinsonism‐dystonia. DNAJC6 encodes the cochaperone protein auxilin, involved in CME of synaptic vesicles. The observed dopamine dyshomeostasis in patients is likely to be multifactorial, secondary to auxilin deficiency and/or neurodegeneration. Increased patient CSF cyclin G–associated kinase, in tandem with reduced auxilin levels, suggests a possible compensatory role of cyclin G–associated kinase, as observed in the auxilin knockout mouse. DNAJC6 parkinsonism‐dystonia should be considered as a differential diagnosis for pediatric neurotransmitter disorders associated with low homovanillic acid levels. Future research in elucidating disease pathogenesis will aid the development of better treatments for this pharmacoresistant disorder. © 2020 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Recombinant Adeno-Associated Virus-mediated rescue of function in a mouse model of Dopamine Transporter Deficiency Syndrome

Dopamine Transporter Deficiency Syndrome (DTDS) is a rare autosomal recessive disorder caused by loss-of-function mutations in dopamine transporter (DAT) gene, leading to severe neurological disabilities in children and adults. DAT-Knockout (DAT-KO) mouse is currently the best animal model for this syndrome, displaying functional hyperdopaminergia and neurodegenerative phenotype leading to premature death in ~36% of the population. We used DAT-KO mouse as model for DTDS to explore the potential utility of a novel combinatorial adeno-associated viral (AAV) gene therapy by expressing DAT selectively in DA neurons and terminals, resulting in the rescue of aberrant striatal DA dynamics, reversal of characteristic phenotypic and behavioral abnormalities, and prevention of premature death. These data indicate the efficacy of a new combinatorial gene therapy aimed at rescuing DA function and related phenotype in a mouse model that best approximates DAT deficiency found in DTDS.

The epileptic and nonepileptic spectrum of paroxysmal dyskinesias: Channelopathies, synaptopathies, and transportopathies

Historically, the syndrome of primary paroxysmal dyskinesias was considered a group of disorders as a result of ion channel dysfunction. This proposition was primarily based on the discovery of mutations in ion channels, which caused other episodic neurological disorders such as epilepsy and migraine and also supported by the frequent association between paroxysmal dyskinesias and epilepsy. However, the discovery of the genes responsible for the 3 classic forms of paroxysmal dyskinesias disproved this ion channel theory. On the other hand, novel gene mutations implicating ion channels have been recently reported to produce episodic movement disorders clinically similar to the classic paroxysmal dyskinesias. Here, we review the clinical and pathophysiological aspects of the paroxysmal dyskinesias, further proposing a pathophysiological framework according to which they can be classified as synaptopathies (proline-rich transmembrane protein 2 and myofibrillogenesis regulator gene), channelopathies (calcium-activated potassium channel subunit alpha-1 and voltage-gated sodium channel type 8), or transportopathies (solute carrier family 2 member 1). This proposal might serve to explain similarities and differences among the various paroxysmal dyskinesias in terms of clinical features, treatment response, and natural history. © 2017 International Parkinson and Movement Disorder Society.

Association between COMT Val158Met and DAT1 polymorphisms and depressive symptoms in the obese population

OBJECTIVES

Depressive symptoms are common among patients with obesity. Abnormalities in dopamine signaling involved in the reward circuit may ensue excessive consumption of food, resulting in obesity and leading to neuropsychiatric disorders such as depression. This study sought to investigate the association of polymorphisms in the genes encoding DAT1/SLC6A3 and COMT with the intensity of depressive symptoms in obese subjects.

PARTICIPANTS AND METHODS

Prevalence and severity of depressive symptoms were assessed in a group of 364 obese patients using the Beck Depression Inventory (BDI) and the Hamilton Depression Rating Scale (HDRS). Genetic polymorphisms in DAT1 and COMT were evaluated in peripheral blood samples.

RESULTS

The results indicated an association between DAT1 alleles and depressive symptoms, as well as severity of obesity. Subjects homozygous for the nine-repeat allele scored higher in BDI (P=0.022) and HDRS (P=0.00001), suggesting higher intensity of depression in both sexes. This allele was also associated with the highest body mass index (BMI; P=0.001). Carriers of the Val158Met allele of COMT scored higher on both depression scales (BDI, P=0.0005; HRDS, P=0.002) and had the highest BMI values.

CONCLUSION

Polymorphisms in the DAT1 and COMT genes are associated with a greater intensity of depressive symptoms in the obese population.

Genetics of monoamine neurotransmitter disorders

The monoamine neurotransmitter disorders are a heterogeneous group of inherited neurological disorders involving defects in the metabolism of dopamine, norepinephrine, epinephrine and serotonin. The inheritance of these disorders is mostly autosomal recessive. The neurological symptoms are primarily attributable to cerebral deficiency of dopamine, serotonin or both. The clinical presentations were highly variable and substantial overlaps exist. Evidently, laboratory investigations are crucial for accurate diagnosis. Measurement of neurotransmitter metabolites in cerebral spinal fluid (CSF) is the key to delineate the metabolic defects. Adjuvant investigations including plasma phenylalanine, urine pterins, urine 3-O-methyldopa (3-OMD) and serum prolactin are also helpful to establish the diagnosis. Genetic analyses are pivotally important to confirm the diagnosis which allows specific treatments, proper genetic counselling, prognosis prediction, assessment of recurrent risk in the family as well as prenatal diagnosis. Early diagnosis with appropriate treatment is associated with remarkable response and favourable clinical outcome in several disorders in this group.

What is new for monoamine neurotransmitter disorders?

The monoamine neurotransmitter disorders are increasingly recognized as an expanding group of inherited neurometabolic syndromes caused by disturbances in the synthesis, transport and metabolism of the biogenic amines, including the catecholamines (dopamine, norepinephrine, and epinephrine) and serotonin. Disturbances in monoamine metabolism lead to neurological syndromes that frequently mimic other conditions, such as hypoxic ischemic encephalopathy, cerebral palsy, parkinsonism-dystonia syndromes, primary genetic dystonia and paroxysmal disorders. As a consequence, neurotransmitter disorders are frequently misdiagnosed. Early and accurate diagnosis of these neurotransmitter disorders is important, as many are highly amenable to, and some even cured by, therapeutic intervention. In this review, we highlight recent advances in the field, particularly the recent extensive characterization of known neurotransmitter disorders and identification of novel neurotransmitter disorders. We also provide an overview of current and future research in the field focused on developing novel treatment strategies.

Missense dopamine transporter mutations associate with adult parkinsonism and ADHD

Parkinsonism and attention deficit hyperactivity disorder (ADHD) are widespread brain disorders that involve disturbances of dopaminergic signaling. The sodium-coupled dopamine transporter (DAT) controls dopamine homeostasis, but its contribution to disease remains poorly understood. Here, we analyzed a cohort of patients with atypical movement disorder and identified 2 DAT coding variants, DAT-Ile312Phe and a presumed de novo mutant DAT-Asp421Asn, in an adult male with early-onset parkinsonism and ADHD. According to DAT single-photon emission computed tomography (DAT-SPECT) scans and a fluoro-deoxy-glucose-PET/MRI (FDG-PET/MRI) scan, the patient suffered from progressive dopaminergic neurodegeneration. In heterologous cells, both DAT variants exhibited markedly reduced dopamine uptake capacity but preserved membrane targeting, consistent with impaired catalytic activity. Computational simulations and uptake experiments suggested that the disrupted function of the DAT-Asp421Asn mutant is the result of compromised sodium binding, in agreement with Asp421 coordinating sodium at the second sodium site. For DAT-Asp421Asn, substrate efflux experiments revealed a constitutive, anomalous efflux of dopamine, and electrophysiological analyses identified a large cation leak that might further perturb dopaminergic neurotransmission. Our results link specific DAT missense mutations to neurodegenerative early-onset parkinsonism. Moreover, the neuropsychiatric comorbidity provides additional support for the idea that DAT missense mutations are an ADHD risk factor and suggests that complex DAT genotype and phenotype correlations contribute to different dopaminergic pathologies.

Clinical and molecular characterisation of hereditary dopamine transporter deficiency syndrome: an observational cohort and experimental study

BACKGROUND

dopamine transporter deficiency syndrome is the first identified parkinsonian disorder caused by genetic alterations of the dopamine transporter. We describe a cohort of children with mutations in the gene encoding the dopamine transporter (SLC6A3) with the aim to improve clinical and molecular characterisation, reduce diagnostic delay and misdiagnosis, and provide insights into the pathophysiological mechanisms.

METHODS

11 children with a biochemical profile suggestive of dopamine transporter deficiency syndrome were enrolled from seven paediatric neurology centres in the UK, Germany, and the USA from February, 2009, and studied until June, 2010. The syndrome was characterised by detailed clinical phenotyping, biochemical and neuroradiological studies, and SLC6A3 mutation analysis. Mutant constructs of human dopamine transporter were used for in-vitro functional analysis of dopamine uptake and cocaine-analogue binding.

FINDINGS

children presented in infancy (median age 2·5 months, range 0·5-7) with either hyperkinesia (n=5), parkinsonism (n=4), or a mixed hyperkinetic and hypokinetic movement disorder (n=2). Seven children had been initially misdiagnosed with cerebral palsy. During childhood, patients developed severe parkinsonism-dystonia associated with an eye movement disorder and pyramidal tract features. All children had raised ratios of homovanillic acid to 5-hydroxyindoleacetic acid in cerebrospinal fluid, of range 5·0-13·2 (normal range 1·3-4·0). Homozygous or compound heterozygous SLC6A3 mutations were detected in all cases. Loss of function in all missense variants was recorded from in-vitro functional studies, and was supported by the findings of single photon emission CT DaTSCAN imaging in one patient, which showed complete loss of dopamine transporter activity in the basal nuclei.

INTERPRETATION

dopamine transporter deficiency syndrome is a newly recognised, autosomal recessive disorder related to impaired dopamine transporter function. Careful characterisation of patients with this disorder should provide novel insights into the complex role of dopamine homoeostasis in human disease, and understanding of the pathophysiology could help to drive drug development.