Thiamine is a crucial cofactor involved in the maintenance of carbohydrate metabolism and participates in multiple cellular metabolic processes within the cytosol, mitochondria, and peroxisomes. ...Currently, four genetic defects have been described causing impairment of thiamine transport and metabolism: SLC19A2 dysfunction leads to diabetes mellitus, megaloblastic anemia and sensory‐neural hearing loss, whereas SLC19A3, SLC25A19, and TPK1‐related disorders result in recurrent encephalopathy, basal ganglia necrosis, generalized dystonia, severe disability, and early death. In order to achieve early diagnosis and treatment, biomarkers play an important role. SLC19A3 patients present a profound decrease of free‐thiamine in cerebrospinal fluid (CSF) and fibroblasts. TPK1 patients show decreased concentrations of thiamine pyrophosphate in blood and muscle. Thiamine supplementation has been shown to improve diabetes and anemia control in Rogers' syndrome patients due to SLC19A2 deficiency. In a significant number of patients with SLC19A3, thiamine improves clinical outcome and survival, and prevents further metabolic crisis. In SLC25A19 and TPK1 defects, thiamine has also led to clinical stabilization in single cases. Moreover, thiamine supplementation leads to normal concentrations of free‐thiamine in the CSF of SLC19A3 patients. Herein, we present a literature review of the current knowledge of the disease including related clinical phenotypes, treatment approaches, update of pathogenic variants, as well as in vitro and in vivo functional models that provide pathogenic evidence and propose mechanisms for thiamine deficiency in humans.
Article Note: Belen Perez-Duenas and Davide Tonduti are both senior authors of this manuscript. Relevant conflicts of interest/financial disclosures: The authors have no potential conflicts of ...interest to disclose. Funding agencies: For #2genetic diagnosis was performed based on a research project funded by Instituto de Salud Carlos III, grant/award number: PI18/01319. Corrections added on 12 March 2021 after first online publication: Correspondence address updated for Belen Perez-Duenas. CAPTION(S): Figure S1. Xxx APPENDIX S1. Supporting Information Byline: Silvia Masnada, Diego Martinelli, Marta Correa-Vela, Emanuele Agolini, Heidy Baide-Mairena, Anna Marce-Grau, Cecilia Parazzini, Pierangelo Veggiotti, Belen Perez-Duenas, Davide Tonduti
Objective
Mutations in the genes encoding neuronal ion channels are a common cause of Mendelian neurological diseases. We sought to identify novel de novo sequence variants in cases with early ...infantile epileptic phenotypes and neurodevelopmental anomalies.
Methods
Following clinical diagnosis, we performed whole exome sequencing of the index cases and their parents. Identified channel variants were expressed in Xenopus oocytes and their functional properties assessed using two‐electrode voltage clamp.
Results
We identified novel de novo variants in KCNA6 in four unrelated individuals variably affected with neurodevelopmental disorders and seizures with onset in the first year of life. Three of the four identified mutations affect the pore‐lining S6 α‐helix of KV1.6. A prominent finding of functional characterization in Xenopus oocytes was that the channel variants showed only minor effects on channel activation but slowed channel closure and shifted the voltage dependence of deactivation in a hyperpolarizing direction. Channels with a mutation affecting the S6 helix display dominant effects on channel deactivation when co‐expressed with wild‐type KV1.6 or KV1.1 subunits.
Significance
This is the first report of de novo nonsynonymous variants in KCNA6 associated with neurological or any clinical features. Channel variants showed a consistent effect on channel deactivation, slowing the rate of channel closure following normal activation. This specific gain‐of‐function feature is likely to underlie the neurological phenotype in our patients. Our data highlight KCNA6 as a novel channelopathy gene associated with early infantile epileptic phenotypes and neurodevelopmental anomalies.
Summary
Objective
To gain insight into the mechanisms underlying KCNQ2 encephalopathy by examining the electrophysiologic properties of mutant Kv7.2 channels in different multimeric configurations.
...Methods
We analyzed the genotype‐phenotype relationship in 4 patients with KCNQ2 encephalopathy and performed electrophysiologic analysis of M‐currents mediated by homomeric Kv7.2 or heteromeric Kv7.2/Kv7.3 channels.
Results
Negligible or no current was recorded in cells expressing homomeric E130K, W270R, or G281R de novo mutants, and it was reduced by more than 90% for the L243F maternally inherited mutant. The E130K and G281R mutants presented a marked dominant‐negative behavior, whereas the current density was partially reduced (L243F) or not affected (W270R) when coexpressed with wild‐type Kv7.2 subunits. In contrast, the extent of Kv7.3 “rescue,” which yields negligible currents on its own, followed the sequence E130K > L243F > W270R, whereas no rescue was observed with the G281R mutant. No significant effects on current density were observed when subunits were expressed in a 0.5:0.5:1.0 (Kv7.2:mutant:Kv7.3) DNA ratio to mimic the genetic balance. There was an increase in sensitivity to phosphatidylinositol 4,5‐bisphosphate (PIP2) depletion for W270R/Kv7.3, but no substantial differences were observed when the mutated subunits were coexpressed with Kv7.2 or both Kv7.2 and Kv7.3.
Significance
There was a marked disparity of the impact of these mutations on Kv7.2 function, which varied on association with Kv7.2 or Kv7.3 subunits. Current density of homomeric channels was the most reliable property relating Kv7.2 function to encephalopathy, but other factors are required to explain the milder phenotype for some individuals carrying the maternally inherited L243F mutation. We hypothesize that the role of homomeric Kv7.2 channels for fine‐tuning neuronal connections during development is critical for the severity of the KCNQ2 encephalopathy.
De novo rare damaging variants in genes involved in critical developmental pathways, notably regulation of synaptic transmission, have emerged as a frequent cause of neurodevelopmental disorders ...(NDD). NDD show great locus heterogeneity and for many of the associated genes, there is substantial phenotypic diversity, including epilepsy, intellectual disability, autism spectrum disorder, movement disorders, and combinations thereof. We report two unrelated patients, a young girl with early‐onset refractory epilepsy, severe disability, and progressive cerebral and cerebellar atrophy, and a second girl with mild dysmorphism, global developmental delay, and moderate intellectual disability in whom trio‐based whole‐exome sequencing analysis uncovered de novo missense variants in CHRM1. Biochemical analyses of one of the NDD‐associated variants proved that it caused a reduction in protein levels and impaired cellular trafficking. In addition, the mutated receptor showed defective activation of intracellular signaling pathways. Our data strengthen the concept that brain‐reduced muscarinic signaling lowers the seizure threshold and severely impairs neurodevelopment.
In this work we identified de novo missense mutations in the Muscarinic receptor CHRM1 in patients with neurodevelopmental disorders. Biochemical analyses of one of the mutations showed a defective activation, indicating that brain reduced Muscarinic signaling impairs neurodevelopment.
Chiari Malformation Type 1 (CM-1) is characterized by herniation of the cerebellar tonsils below the foramen magnum and the presence of headaches and other neurologic symptoms. Cranial bone ...constriction is suspected to be the most common biologic mechanism leading to CM-1. However, other mechanisms may also contribute, particularly in the presence of connective tissue disorders (CTDs), such as Ehlers Danlos Syndrome (EDS). Accumulating data suggest CM-1 with connective tissue disorders (CTD+) may have a different patho-mechanism and different genetic risk factors than CM-1 without CTDs (CTD-). To identify CM-1 genetic risk variants, we performed whole exome sequencing on a single large, multiplex family from Spain and targeted sequencing on a cohort of 186 unrelated adult, Caucasian females with CM-1. Targeted sequencing captured the coding regions of 21 CM-1 and EDS candidate genes, including two genes identified in the Spanish family. Using gene burden analysis, we compared the frequency of rare, functional variants detected in CM-1 cases versus publically available ethnically-matched controls from gnomAD. A secondary analysis compared the presence of rare variants in these genes between CTD+ and CTD- CM-1 cases. In the Spanish family, rare variants co-segregated with CM-1 in COL6A5, ADGRB3 and DST. A variant in COL7A1 was present in affected and unaffected family members. In the targeted sequencing analysis, rare variants in six genes (COL7A1, COL5A2, COL6A5, COL1A2, VEGFB, FLT1) were significantly more frequent in CM-1 cases compared to public controls. In total, 47% of CM-1 cases presented with rare variants in at least one of the four significant collagen genes and 10% of cases harbored variants in multiple significant collagen genes. Moreover, 26% of CM-1 cases presented with rare variants in the COL6A5 gene. We also identified two genes (COL7A1, COL3A1) for which the burden of rare variants differed significantly between CTD+ and CTD- CM-1 cases. A higher percentage of CTD+ patients had variants in COL7A1 compared to CTD+ patients, while CTD+ patients had fewer rare variants in COL3A1 than did CTD- patients. In summary, rare variants in several collagen genes are particularly frequent in CM-1 cases and those in COL6A5 co-segregated with CM-1 in a Spanish multiplex family. COL6A5 has been previously associated with musculoskeletal phenotypes, but this is the first association with CM-1. Our findings underscore the contribution of rare genetic variants in collagen genes to CM-1, and suggest that CM-1 in the presence and absence of CTD symptoms is driven by different genes.
Early recognition of SGCE‐myoclonus–dystonia in children Correa‐Vela, Marta; Carvalho, Joao; Ferrero‐Turrion, Julia ...
Developmental medicine and child neurology,
February 2023, 2023-02-00, 20230201, Letnik:
65, Številka:
2
Journal Article
Recenzirano
Aim
To evaluate early dystonic features in children and adolescents with SGCE‐myoclonus–dystonia.
Method
In this cross‐sectional study, 49 patients (26 females and 23 males) with ...SGCE‐myoclonus–dystonia (aged 15y 2mo, SD 12y) with childhood‐onset (2y 10mo, SD 1y 10mo) dystonia were examined using a standardized video recorded protocol. Dystonia was rated using the Writer's Cramp and Gait Dystonia Rating Scales. Disability and impairment for handwriting and walking were also rated.
Results
Dystonia was present at rest (n=1), posture (n=12), and during specific motor tasks (n=45) such as writing (n=35), walking (n=23), and running (n=20). Most children reported disability while performing these tasks. Early dystonic patterns were identified for writer's cramp and gait dystonia, the latter named the ‘circular shaking leg’, ‘dragging leg’, and ‘hobby‐horse gait’ patterns. Sensory tricks were used by five and eight children to improve dystonia and myoclonus during writing and walking respectively. The rating scales accurately measured the severity of action dystonia and correlated with self‐reported disability.
Interpretation
Children with SGCE‐myoclonus–dystonia show recognizable dystonic patterns and sensory tricks that may lead to an early diagnosis and timely therapeutic approach. Isolated writer's cramp is a key feature in childhood and should prompt SCGE analysis. The proposed action dystonia scales could be used to monitor disease course and response to treatment.
What this paper adds
Most children with SGCE‐myoclonus–dystonia got writer's cramp and had walking and running dystonia.
Writer's cramp was a key feature and should prompt SGCE genetic investigation.
‘Circular shaking leg’, ‘dragging leg’, and ‘hobby‐horse gait’ were recognized as early gait patterns.
Children used sensory tricks to improve myoclonus and dystonia, suggesting common pathophysiological mechanisms.
Action dystonia rating scales are valid tools to assess severity in children.
What this paper adds
Most children with SGCE‐myoclonus–dystonia got writer's cramp and had walking and running dystonia.
Writer's cramp was a key feature and should prompt SGCE genetic investigation.
‘Circular shaking leg’, ‘dragging leg’, and ‘hobby‐horse gait’ were recognized as early gait patterns.
Children used sensory tricks to improve myoclonus and dystonia, suggesting common pathophysiological mechanisms.
Action dystonia rating scales are valid tools to assess severity in children.
This study evaluates early dystonic features in a large cohort of children with SGCE‐MDS, describes recognizable dystonic patterns and sensory tricks, and proposes action dystonia scales that could be used to monitor disease course and response to treatment.
This original article is commented on by Roze on pages 151–152 of this issue.
The neurological phenotype of 3‐hydroxyisobutyryl‐CoA hydrolase (HIBCH) and short‐chain enoyl‐CoA hydratase (SCEH) defects is expanding and natural history studies are necessary to improve clinical ...management. From 42 patients with Leigh syndrome studied by massive parallel sequencing, we identified five patients with SCEH and HIBCH deficiency. Fourteen additional patients were recruited through collaborations with other centres. In total, we analysed the neurological features and mutation spectrum in 19 new SCEH/HIBCH patients. For natural history studies and phenotype to genotype associations we also included 70 previously reported patients. The 19 newly identified cases presented with Leigh syndrome (SCEH, n = 11; HIBCH, n = 6) and paroxysmal dystonia (SCEH, n = 2). Basal ganglia lesions (18 patients) were associated with small cysts in the putamen/pallidum in half of the cases, a characteristic hallmark for diagnosis. Eighteen pathogenic variants were identified, 11 were novel. Among all 89 cases, we observed a longer survival in HIBCH compared to SCEH patients, and in HIBCH patients carrying homozygous mutations on the protein surface compared to those with variants inside/near the catalytic region. The SCEH p.(Ala173Val) change was associated with a milder form of paroxysmal dystonia triggered by increased energy demands. In a child harbouring SCEH p.(Ala173Val) and the novel p.(Leu123Phe) change, an 83.6% reduction of the protein was observed in fibroblasts. The SCEH and HIBCH defects in the catabolic valine pathway were a frequent cause of Leigh syndrome in our cohort. We identified phenotype and genotype associations that may help predict outcome and improve clinical management.
Metabolic adaptation may happen in response to the pressure exerted by the microenvironment and is a key step in survival of metastatic cells. Brain metastasis occurs as a consequence of the systemic ...dissemination of tumor cells, a fact that correlates with poor prognosis and high morbidity due to the difficulty in identifying biomarkers that allow a more targeted therapy. Previously, we performed transcriptomic analysis of human breast cancer patient samples and evaluated the differential expression of genes in brain metastasis (BrM) compared to lung, bone and liver metastasis. Our network approach identified upregulation of glucose-regulated protein 94 (GRP94) as well as proteins related to synthesis of fatty acids (FA) in BrM. Here we report that BrM cells show an increase in FA content and decreased saturation with regard to parental cells measured by Raman spectroscopy that differentiate BrM from other metastases. Moreover, BrM cells exerted a high ability to oxidize FA and compensate hypoglycemic stress due to an overexpression of proteins involved in FA synthesis and degradation (SREBP-1, LXRα, ACOT7). GRP94 ablation restored glucose dependence, down-regulated ACOT7 and SREBP-1 and decreased tumorigenicity in vivo. In conclusion, GRP94 is required for the metabolic stress survival of BrM cells, and it might act as a modulator of lipid metabolism to favor BrM progression.
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