Summary Epileptic encephalopathies of infancy and childhood comprise a large, heterogeneous group of severe epilepsies characterised by several seizure types, frequent epileptiform activity on EEG, ...and developmental slowing or regression. The encephalopathies include many age-related electroclinical syndromes with specific seizure types and EEG features. With the molecular revolution, the number of known monogenic determinants underlying the epileptic encephalopathies has grown rapidly. De-novo dominant mutations are frequently identified; somatic mosaicism and recessive disorders are also seen. Several genes can cause one electroclinical syndrome, and, conversely, one gene might be associated with phenotypic pleiotropy. Diverse genetic causes and molecular pathways have been implicated, involving ion channels, and proteins needed for synaptic, regulatory, and developmental functions. Gene discovery provides the basis for neurobiological insights, often showing convergence of mechanistic pathways. These findings underpin the development of targeted therapies, which are essential to improve the outcome of these devastating disorders.
Abstract Background Dopamine transporter deficiency syndrome (DTDS) is a primary neurotransmitter disorder caused by loss-of-function mutations in SLC6A3 , which encodes the dopamine transporter ...(DAT). The syndrome is characterised by progressive infantile-onset dystonia-parkinsonism with raised dopamine metabolite homovanillic acid in the cerebrospinal fluid. There are no disease modifying therapies for this life-limiting disorder. The aims of this study were to evaluate the clinical disease spectrum and develop a novel gene therapy approach for DTDS. Methods Patients aged 1–36 years with childhood-onset dystonia-parkinsonism and suggestive neurotransmitter profile had SLC6A3 sequenced. In-vitro functional studies were undertaken for identified missense mutations. We specifically phenotyped DAT knockout (–/–) mice motor behaviour as a model of DTDS and developed a preclinical viral gene therapy construct. We evaluated effects of intracranial delivery of DAT gene therapy in neonatal DAT–/– mice as a proof of concept study. Findings We identified ten new patients harbouring seven novel missense mutations, and found a novel atypical phenotype of juvenile parkinsonism. In-vitro functional characterisation revealed multifactorial disease mechanisms, including abnormal DAT trafficking, glycosylation, and impaired substrate recognition and uptake function. The DAT–/– mouse clearly recapitulated many features of human disease, including reduced survival, early hyperkinesia with later parkinsonism, raised homovanillic acid concentrations, and neurodegeneration. We have evaluated viral gene therapy approaches to target dopaminergic neurons and subsequently delivered DAT via adeno-associated virus type 9 to neonatal DAT–/– mice, with improved survival rates and motor phenotype. Interpretation We report an expanding disease spectrum in DTDS, in which the clinical presentation mimics both cerebral palsy and juvenile parkinsonism. Genotype–phenotype correlation is evident, with in-vitro functional studies demonstrating greater residual DAT function in later-onset milder forms of disease. The preclinical study of viral gene therapy in neonatal mice is promising and will facilitate the longer term aim towards clinical translation for this untreatable disorder. Funding Medical Research Council Clinical Research Training Fellowship, Great Ormond Street Hospital Children's Charity.
Abstract Background Migrating partial seizures of infancy (MPSI) is a severe, pharmacoresistant, early-onset epilepsy syndrome associated with high morbidity and mortality in which the underlying ...causal disease mechanisms are poorly understood. We aimed to describe the clinical, radiological, and pathological features of a national cohort of patients and to investigate the genetic basis of the syndrome. Methods We did a national surveillance study with data from the British Paediatric Neurology Surveillance Unit, with detailed endophenotyping on the referred cases. The genetic approaches that we took for molecular genetic investigation were: multiple gene panel testing of 29 genes associated with early-onset epilepsy, whole exome sequencing, and direct Sanger sequencing of KCNT1 , a recently identified cause of MPSI. The multiple gene panel used Haloplex sequence capture (Agilent, Santa Clara, CA, USA) and Illumina sequencing with a MiSeq platform. For copy number variant analysis we used a custom Roche Nimblegen oligonucleotide 135K aCGH (Roche Diagnostic Ltd, Madison, WI, USA). We analysed sequence data using NextGENe software (Softgenetics, State College, PA USA) and array data using CGH Fusion (InfoQuant, London, UK). We did whole exome sequencing using Illumina paired-end library preparation and sequencing on a Hi-Seq platform. For Sanger sequencing, the genomic KCNT1 DNA sequence was taken from Ensembl and primer pairs for all exons, and flanking intronic regions were designed with primer3 software. Exons were amplified by PCR, sequenced by the BigDye terminator method, and analysed with Chromas/Sequencher software. The research genetic study was approved by the local research ethics committee and specific consent was given by individual parents for genetic studies to be undertaken on a research basis. Findings 14 patients met the electroclinical criteria for a diagnosis of MPSI. Several novel clinical findings (movement disorder and severe gut dysmotility) and electrographic features (hypsarrhythmia, burst suppression) were identified. Novel radiological features included delayed myelination in five patients with white matter hyperintensity on brain MRI in four, and decreased N-acetyl aspartate on magnetic resonance spectroscopy in three of four patients. Putaminal atrophy, evident in one patient, has not been previously reported. Neuropathological findings included bilateral hippocampal gliosis and neuronal loss in two patients who had post-mortem examinations. Genetic investigation showed missense mutations of KCNT1 in three of the nine patients tested. One variant c.2800G>A (p.A934T) was found in several patients and likely to be a common mutation for KCNT1 -MPSI. Another mutation, c.811G>T (p.V271F), is a novel, previously unreported variant, which is highly conserved, absent in control populations, and is predicted to be damaging (Polyphen score 0·733). Interpretation This study is the first national cohort of patients with this rare condition and expands the electroclinical phenotype of MPSI. We have shown that KCNT1 is an important disease-causing gene in MPSI. However the absence of KCNT1 mutations in many patients suggests that this condition is genetically heterogeneous and further genetic causes are yet to be discovered. Funding Neurology Charitable Fund (Alder Hey Children's Hospital), MPSI support group, Action Medical Research, UK Children's Neurological Research Campaign, Roald Dahl's Marvellous Children's Charity, Great Ormond Street Hospital Children's Charities.
Summary The monoamine neurotransmitter disorders consist of a rapidly expanding heterogeneous group of neurological syndromes characterised by primary and secondary defects in the biosynthesis ...degradation, or transport of dopamine, norepinephrine, epinephrine, and serotonin. Disease onset can occur any time from infancy onwards. Clinical presentation depends on the pattern and severity of neurotransmitter abnormalities, and is predominated by neurological features (encephalopathy, epilepsy, and pyramidal and extrapyramidal motor disorders) that are primarily attributed to deficiency of cerebral dopamine, serotonin, or both. Many neurotransmitter disorders mimic the phenotype of other neurological disorders (eg, cerebral palsy, hypoxic ischaemic encephalopathy, paroxysmal disorders, inherited metabolic diseases, and genetic dystonic or parkinsonian syndromes) and are, therefore, frequently misdiagnosed. Early clinical suspicion and appropriate investigations, including analysis of neurotransmitters in CSF, are essential for accurate clinical diagnosis. Treatment strategies focus on the correction of monoamine deficiency by replacement of monoamine precursors, the use of monoamine analogues, inhibition of monoamine degradation, and addition of enzyme cofactors to promote monoamine production.
Summary 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. Funding Birmingham Children's Hospital Research Foundation, Birth Defects Foundation Newlife, Action Medical Research, US National Institutes of Health, Wellchild, and the Wellcome Trust.
PDF
