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Background: Variants in dehydrodolichol diphosphate synthetase (DHDDS) and nuclear undecaprenyl pyrophosphate synthase 1 (NUS1) cause a neurodevelopmental disorder, classically with prominent epilepsy. Recent reports suggest a complex movement disorder and an overlapping phenotype has been postulated due to their combined role in dolichol synthesis. Cases: We describe three patients with heterozygous variants in DHDDS and five with variants affecting NUS1. They bear a remarkably similar phenotype of a movement disorder dominated by multifocal myoclonus. Diagnostic clues include myoclonus exacerbated by action and facial involvement, and slowly progressive or stable, gait ataxia with disproportionately impaired tandem gait. Myoclonus is confirmed with neurophysiology, including EMG of facial muscles. Literature Review: Ninety‐eight reports of heterozygous variants in DHDDS, NUS1 and chromosome 6q22.1 structural alterations spanning NUS1, confirm the convergent phenotype of hypotonia at birth, developmental delay, multifocal myoclonus, ataxia, dystonia and later parkinsonism with or without generalized epilepsy. Other features include periodic exacerbations, stereotypies, anxiety, and dysmorphisms. Although their gene products contribute to dolichol biosynthesis, a key step in N‐glycosylation, transferrin isoform profiles are typically normal. Imaging is normal or non‐specific. Conclusions: Recognition of their shared phenotype may expedite diagnosis through chromosomal microarray and by including DHDDS/NUS1 in movement disorder gene panels. [ABSTRACT FROM AUTHOR]

Isolated Craniocervical Dystonia Without Initial Neuropsychiatric Manifestations Associated with NMDA-Receptor Antibodies We describe a patient presenting with isolated craniocervical dystonia and serum and cerebrospinal fluid (CSF) NMDAR antibody positivity, without other manifestations of encephalitis at presentation. Keywords: NMDA; craniocervical dystonia; autoimmune encephalitis EN NMDA craniocervical dystonia autoimmune encephalitis 680 682 3 04/18/23 20230401 NES 230401 N-methyl-D-aspartate receptor (NMDAR) encephalitis classically manifests as varying combinations of neuropsychiatric disturbance, autonomic dysfunction, hypoventilation, and salient movement disorders. [Extracted from the article]

Background: Variants in EIF2AK2 have been recently associated with a spectrum of neurological disease encompassing isolated dystonia to fever‐related neurological decompensation, movement disorders and leukodystrophy. Case: A 32‐year old patient presented with childhood‐onset episodes of neurological decompensation after febrile illness, progressive anarthria, dystonia and spasticity. The T2/FLAIR MRI showed bilateral posterolateral putamen hyperintensities and white matter changes suggestive of leukodystrophy. Initial extensive metabolic workup and whole genome sequencing (WGS) was unremarkable. Re‐analysis of the WGS data revealed a variant in exon 3 of the EIF2AK2 gene [(NM_001135651.3): c.92C > G (p.Pro31Arg)]. EIF2AK2‐associated disorders should be incorporated into the differential diagnosis of the syndrome of fever‐related neurological decompensation with movement disorders, especially in the presence of abnormal neuroimaging. Literature review: Disease‐causing variants in EIF2AK2 have been reported in 24 individuals from 16 families in the literature to date. Two broad phenotypes have been described, including: (1) childhood‐onset generalized dystonia and a normal brain MRI; and (2) early childhood‐onset developmental delay combined with movement disorders, spasticity, and seizures in some. Notably, 92% of these patients have neurological deterioration after febrile illness or other physiological stress. Hypomyelination or delayed myelination and thin corpus callosum are seen in most patients and lower medullary lessions are common. Basal ganglia lesions have been reported previously in one case. Conclusions: EIF2AK2‐associated disorders should be incorporated into the differential diagnosis of the syndrome of fever‐related neurological decompensation with movement disorders, especially in the presence of abnormal neuroimaging. [ABSTRACT FROM AUTHOR]

Genetic early-onset parkinsonism presenting from infancy to adolescence (≤21 years old) is a clinically diverse syndrome often combined with other hyperkinetic movement disorders, neurological and imaging abnormalities. The syndrome is genetically heterogeneous, with many causative genes already known. With the increased use of next-generation sequencing in clinical practice, there have been novel and unexpected insights into phenotype-genotype correlations and the discovery of new disease-causing genes. It is now recognized that mutations in a single gene can give rise to a broad phenotypic spectrum and that, conversely different genetic disorders can manifest with a similar phenotype. Accurate phenotypic characterization remains an essential step in interpreting genetic findings in undiagnosed patients. However, in the past decade, there has been a marked expansion in knowledge about the number of both disease-causing genes and phenotypic spectrum of early-onset cases. Detailed knowledge of genetic disorders and their clinical expression is required for rational planning of genetic and molecular testing, as well as correct interpretation of next-generation sequencing results. In this review we examine the relevant literature of genetic parkinsonism with ≤21 years onset, extracting data on associated movement disorders as well as other neurological and imaging features, to delineate syndromic patterns associated with early-onset parkinsonism. Excluding PRKN (parkin) mutations, >90% of the presenting phenotypes have a complex or atypical presentation, with dystonia, abnormal cognition, pyramidal signs, neuropsychiatric disorders, abnormal imaging and abnormal eye movements being the most common features. Furthermore, several imaging features and extraneurological manifestations are relatively specific for certain disorders and are important diagnostic clues. From the currently available literature, the most commonly implicated causes of early-onset parkinsonism have been elucidated but diagnosis is still challenging in many cases. Mutations in ∼70 different genes have been associated with early-onset parkinsonism or may feature parkinsonism as part of their phenotypic spectrum. Most of the cases are caused by recessively inherited mutations, followed by dominant and X-linked mutations, and rarely by mitochondrially inherited mutations. In infantile-onset parkinsonism, the phenotype of hypokinetic-rigid syndrome is most commonly caused by disorders of monoamine synthesis. In childhood and juvenile-onset cases, common genotypes include PRKN, HTT, ATP13A2, ATP1A3, FBX07, PINK1 and PLA2G6 mutations. Moreover, Wilson's disease and mutations in the manganese transporter are potentially treatable conditions and should always be considered in the differential diagnosis in any patient with early-onset parkinsonism. [ABSTRACT FROM AUTHOR]