Biotin Homeostasis and Human Disorders: Recent Findings and Perspectives.

Biotin (vitamin B7, or vitamin H) is a water-soluble B-vitamin that functions as a cofactor for carboxylases, i.e., enzymes involved in the cellular metabolism of fatty acids and amino acids and in gluconeogenesis; moreover, as reported, biotin may be involved in gene regulation. Biotin is not synthesized by human cells, but it is found in food and is also produced by intestinal bacteria. Biotin status/homeostasis in human individuals depends on several factors, including efficiency/deficiency of the enzymes involved in biotin recycling within the human organism (biotinidase, holocarboxylase synthetase), and/or effectiveness of intestinal uptake, which is mainly accomplished through the sodium-dependent multivitamin transporter. In the last years, administration of biotin at high/"pharmacological" doses has been proposed to treat specific defects/deficiencies and human disorders, exhibiting mainly neurological and/or dermatological symptoms and including biotinidase deficiency, holocarboxylase synthetase deficiency, and biotin-thiamine-responsive basal ganglia disease. On the other hand, according to warnings of the Food and Drug Administration, USA, high biotin levels can affect clinical biotin-(strept)avidin assays and thus lead to false results during quantification of critical biomarkers. In this review article, recent findings/advancements that may offer new insight in the abovementioned research fields concerning biotin will be presented and briefly discussed.

The Effect of Neuronal CoQ10 Deficiency and Mitochondrial Dysfunction on a Rotenone-Induced Neuronal Cell Model of Parkinson's Disease.

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder currently affecting the ageing population. Although the aetiology of PD has yet to be fully elucidated, environmental factors such as exposure to the naturally occurring neurotoxin rotenone has been associated with an increased risk of developing PD. Rotenone inhibits mitochondrial respiratory chain (MRC) complex I activity as well as induces dopaminergic neuronal death. The aim of the present study was to investigate the underlying mechanisms of rotenone-induced mitochondrial dysfunction and oxidative stress in an in vitro SH-SY5Y neuronal cell model of PD and to assess the ability of pre-treatment with Coenzyme Q10 (CoQ10) to ameliorate oxidative stress in this model. Spectrophotometric determination of the mitochondrial enzyme activities and fluorescence probe studies of reactive oxygen species (ROS) production was assessed. Significant inhibition of MRC complex I and II-III activities was observed, together with a significant loss of neuronal viability, CoQ10 status, and ATP synthesis. Additionally, significant increases were observed in intracellular and mitochondrial ROS production. Remarkably, CoQ10 supplementation was found to reduce ROS formation. These results have indicated mitochondrial dysfunction and increased oxidative stress in a rotenone-induced neuronal cell model of PD that was ameliorated by CoQ10 supplementation.

The Ubiquinone-Ubiquinol Redox Cycle and Its Clinical Consequences: An Overview.

Coenzyme Q10 (CoQ10) plays a key role in many aspects of cellular metabolism. For CoQ10 to function normally, continual interconversion between its oxidised (ubiquinone) and reduced (ubiquinol) forms is required. Given the central importance of this ubiquinone-ubiquinol redox cycle, this article reviews what is currently known about this process and the implications for clinical practice. In mitochondria, ubiquinone is reduced to ubiquinol by Complex I or II, Complex III (the Q cycle) re-oxidises ubiquinol to ubiquinone, and extra-mitochondrial oxidoreductase enzymes participate in the ubiquinone-ubiquinol redox cycle. In clinical terms, the outcome of deficiencies in various components associated with the ubiquinone-ubiquinol redox cycle is reviewed, with a particular focus on the potential clinical benefits of CoQ10 and selenium co-supplementation.

ACR Appropriateness Criteria® Dizziness and Ataxia: 2023 Update.

Diagnostic evaluation of a patient with dizziness or vertigo is complicated by a lack of standardized nomenclature, significant overlap in symptom descriptions, and the subjective nature of the patient's symptoms. Although dizziness is an imprecise term often used by patients to describe a feeling of being off-balance, in many cases dizziness can be subcategorized based on symptomatology as vertigo (false sense of motion or spinning), disequilibrium (imbalance with gait instability), presyncope (nearly fainting or blacking out), or lightheadedness (nonspecific). As such, current diagnostic paradigms focus on timing, triggers, and associated symptoms rather than subjective descriptions of dizziness type. Regardless, these factors complicate the selection of appropriate diagnostic imaging in patients presenting with dizziness or vertigo. This document serves to aid providers in this selection by using a framework of definable clinical variants. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Coexistence of Retinitis Pigmentosa and Ataxia in Patients with PHARC, PCARP, and Oliver-McFarlane Syndromes.

Retinitis pigmentosa (RP) is an inherited retinal dystrophy caused by the loss of photoreceptors and retinal pigment epithelial atrophy, leading to severe visual impairment or blindness. RP can be classified as nonsyndromic or syndromic with complex clinical phenotypes. Three unrelated Polish probands affected with retinitis pigmentosa coexisting with cerebellar ataxia were recruited for this study. Clinical heterogeneity and delayed appearance of typical disease symptoms significantly prolonged the patients' diagnostic process. Therefore, many clinical and genetic tests have been performed in the past. Here, we provide detailed clinical and genetic analysis results of the patients. Whole-exome sequencing (WES) and targeted NGS analysis allow the identification of four novel and two previously reported variants in the following genes: ABHD12, FLVCR1, and PNPLA6. The use of next-generation sequencing (NGS) methods finally allowed for confirmation of the clinical diagnosis. Ultra-rare diseases such as PHARC, PCARP, and Oliver-McFarlane syndromes were diagnosed in patients, respectively. Our findings confirmed the importance of the application of next-generation sequencing methods, especially in ultra-rare genetic disorders with overlapping features.

Reversible encephalitis-like episodes in fragile X-associated tremor/ataxia syndrome: a case report.

BACKGROUND: Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by CGG repeat expansion of FMR1 gene. Both FXTAS and neuronal intranuclear inclusion disease (NIID) belong to polyglycine diseases and present similar clinical, radiological, and pathological features, making it difficult to distinguish these diseases. Reversible encephalitis-like attacks are often observed in NIID. It is unclear whether they are presented in FXTAS and can be used for differential diagnosis of NIID and FXTAS. CASE PRESENTATION: A 63-year-old Chinese male with late-onset gait disturbance, cognitive decline, and reversible attacks of fever, consciousness impairment, dizziness, vomiting, and urinary incontinence underwent neurological assessment and examinations, including laboratory tests, electroencephalogram test, imaging, skin biopsy, and genetic test. Brain MRI showed T2 hyperintensities in middle cerebellar peduncle and cerebrum, in addition to cerebellar atrophy and DWI hyperintensities along the corticomedullary junction. Lesions in the brainstem were observed. Skin biopsy showed p62-positive intranuclear inclusions. The possibilities of hypoglycemia, lactic acidosis, epileptic seizures, and cerebrovascular attacks were excluded. Genetic analysis revealed CGG repeat expansion in FMR1 gene, and the number of repeats was 111. The patient was finally diagnosed as FXTAS. He received supportive treatment as well as symptomatic treatment during hospitalization. His encephalitic symptoms were completely relieved within one week. CONCLUSIONS: This is a detailed report of a case of FXTAS with reversible encephalitis-like episodes. This report provides new information for the possible and rare features of FXTAS, highlighting that encephalitis-like episodes are common in polyglycine diseases and unable to be used for differential diagnosis.

4-Hydroxybenzoic acid rescues multisystemic disease and perinatal lethality in a mouse model of mitochondrial disease.

Coenzyme Q (CoQ) deficiency syndrome is conventionally treated with limited efficacy using exogenous CoQ10. Poor outcomes result from low absorption and bioavailability of CoQ10 and the clinical heterogenicity of the disease. Here, we demonstrate that supplementation with 4-hydroxybenzoic acid (4HB), the precursor of the benzoquinone ring in the CoQ biosynthetic pathway, completely rescues multisystemic disease and perinatal lethality in a mouse model of CoQ deficiency. 4HB stimulates endogenous CoQ biosynthesis in tissues of Coq2 mutant mice, normalizing mitochondrial function and rescuing cardiac insufficiency, edema, and neurodevelopmental delay. In contrast, exogenous CoQ10 supplementation falls short in fully restoring the phenotype. The treatment is translatable to human use, as proven by in vitro studies in skin fibroblasts from patients with pathogenic variants in COQ2. The therapeutic approach extends to other disorders characterized by deficiencies in the production of 4HB and early steps of CoQ biosynthesis and instances of secondary CoQ deficiency.

A novel MT-ATP6 variant associated with complicated ataxia in two unrelated Italian patients: case report and functional studies.

BACKGROUND: MT-ATP6 is a mitochondrial gene which encodes for the intramembrane subunit 6 (or A) of the mitochondrial ATP synthase, also known asl complex V, which is involved in the last step of oxidative phosphorylation to produce cellular ATP through aerobic metabolism. Although classically associated with the NARP syndrome, recent evidence highlights an important role of MT-ATP6 pathogenic variants in complicated adult-onset ataxias. METHODS: We describe two unrelated patients with adult-onset cerebellar ataxia associated with severe optic atrophy and mild cognitive impairment. Whole mitochondrial DNA sequencing was performed in both patients. We employed patients' primary fibroblasts and cytoplasmic hybrids (cybrids), generated from patients-derived cells, to assess the activity of respiratory chain complexes, oxygen consumption rate (OCR), ATP production and mitochondrial membrane potential. RESULTS: In both patients, we identified the same novel m.8777 T > C variant in MT-ATP6 with variable heteroplasmy level in different tissues. We identifed an additional heteroplasmic novel variant in MT-ATP6, m.8879G > T, in the patients with the most severe phenotype. A significant reduction in complex V activity, OCR and ATP production was observed in cybrid clones homoplasmic for the m.8777 T > C variant, while no functional defect was detected in m.8879G > T homoplasmic clones. In addition, fibroblasts with high heteroplasmic levelsof m.8777 T > C variant showed hyperpolarization of mitochondrial membranes. CONCLUSIONS: We describe a novel pathogenic mtDNA variant in MT-ATP6 associated with adult-onset ataxia, reinforcing the value of mtDNA screening within the diagnostic workflow of selected patients with late onset ataxias.

Mitochondrial dysfunction in brain tissues and Extracellular Vesicles Fragile X-associated tremor/ataxia syndrome.

OBJECTIVE: Mitochondrial impairments have been implicated in the pathogenesis of Fragile X-associated tremor/ataxia syndrome (FXTAS) based on analysis of mitochondria in peripheral tissues and cultured cells. We sought to assess whether mitochondrial abnormalities present in postmortem brain tissues of patients with FXTAS are also present in plasma neuron-derived extracellular vesicles (NDEVs) from living carriers of fragile X messenger ribonucleoprotein1 (FMR1) gene premutations at an early asymptomatic stage of the disease continuum. METHODS: We utilized postmortem frozen cerebellar and frontal cortex samples from a cohort of eight patients with FXTAS and nine controls and measured the quantity and activity of the mitochondrial proteins complex IV and complex V. In addition, we evaluated the same measures in isolated plasma NDEVs by selective immunoaffinity capture targeting L1CAM from a separate cohort of eight FMR1 premutation carriers and four age-matched controls. RESULTS: Lower complex IV and V quantity and activity were observed in the cerebellum of FXTAS patients compared to controls, without any differences in total mitochondrial content. No patient-control differences were observed in the frontal cortex. In NDEVs, FMR1 premutation carriers compared to controls had lower activity of Complex IV and Complex V, but higher Complex V quantity. INTERPRETATION: Quantitative and functional abnormalities in mitochondrial electron transport chain complexes IV and V seen in the cerebellum of patients with FXTAS are also manifest in plasma NDEVs of FMR1 premutation carriers. Plasma NDEVs may provide further insights into mitochondrial pathologies in this syndrome and could potentially lead to the development of biomarkers for predicting symptomatic FXTAS among premutation carriers and disease monitoring.

Enlarged perivascular spaces and their association with motor, cognition, MRI markers and cerebrovascular risk factors in male fragile X premutation carriers.

FMR1 premutation carriers (55-200 CGG repeats) are at risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS), a neurodegenerative disorder associated with motor and cognitive impairment. Bilateral hyperintensities of the middle cerebellar peduncles (MCP sign) are the major radiological hallmarks of FXTAS. In the general population, enlarged perivascular spaces (PVS) are biomarkers of small vessel disease and glymphatic dysfunction and are associated with cognitive decline. Our aim was to determine if premutation carriers show higher ratings of PVS than controls and whether enlarged PVS are associated with motor and cognitive impairment, MRI features of neurodegeneration, cerebrovascular risk factors and CGG repeat length. We evaluated 655 MRIs (1-10 visits/participant) from 229 carriers (164 with FXTAS and 65 without FXTAS) and 133 controls. PVS in the basal ganglia (BG-EPVS), centrum semiovale, and midbrain were evaluated with a semiquantitative scale. Mixed-effects models were used for statistical analysis adjusting for age. In carriers with FXTAS, we revealed that (1) BG-PVS ratings were higher than those of controls and carriers without FXTAS; (2) BG-PVS severity was associated with brain atrophy, white matter hyperintensities, enlarged ventricles, FXTAS stage and abnormal gait; (3) age-related increase in BG-PVS was associated with cognitive dysfunction; and (4) PVS ratings of all three regions showed robust associations with CGG repeat length and were higher in carriers with the MCP sign than carriers without the sign. This study demonstrates clinical relevance of PVS in FXTAS especially in the basal ganglia region and suggests microangiopathy and dysfunctional cerebrospinal fluid circulation in FXTAS physiopathology.

Fragile X-associated tremor/ataxia syndrome treated with multitarget deep brain stimulation.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive hereditary neurodegenerative disorder which causes intention tremor and cerebellar ataxia. It typically affects the ageing population. Deep brain stimulation (DBS) is widely accepted in the treatment of common movement disorders and has been trialled in treating rare and complex neurodegenerative disorders. We report a case of a man in his 40s with a long history of tremor affecting his hands. MRI brain revealed high T2 signal in the middle cerebellar peduncles. Genetic testing revealed FMR1 premutation confirming the diagnosis of FXTAS. Subsequently, he was treated with multitarget DBS of the ventralis intermediate nucleus and ventralis oralis posterior nuclei bilaterally, with excellent neurological function at 9 years follow-up. This case suggests multitarget DBS for FXTAS with neurophysiology-guided DBS programming can provide excellent long-term tremor suppression in selected patients.

Role of fragile X messenger ribonucleoprotein 1 in the pathophysiology of brain disorders: a glia perspective.

Fragile X messenger ribonucleoprotein 1 (FMRP) is a widely expressed RNA binding protein involved in several steps of mRNA metabolism. Mutations in the FMR1 gene encoding FMRP are responsible for fragile X syndrome (FXS), a leading genetic cause of intellectual disability and autism spectrum disorder, and fragile X-associated tremor-ataxia syndrome (FXTAS), a neurodegenerative disorder in aging men. Although FMRP is mainly expressed in neurons, it is also present in glial cells and its deficiency or altered expression can affect functions of glial cells with implications for the pathophysiology of brain disorders. The present review focuses on recent advances on the role of glial subtypes, astrocytes, oligodendrocytes and microglia, in the pathophysiology of FXS and FXTAS, and describes how the absence or reduced expression of FMRP in these cells can impact on glial and neuronal functions. We will also briefly address the role of FMRP in radial glial cells and its effects on neural development, and gliomas and will speculate on the role of glial FMRP in other brain disorders.

Vitamin E nomenclature. Is RRR-α-tocopherol the only vitamin E?

It has generally been accepted that vitamin E refers to a group of tocochromanols, α-, ß-, γ-, and δ-tocopherols and the corresponding four tocotrienols. Recently, Azzi and colleagues proposed to restrict the term vitamin E only to RRR-α-tocopherol, not to other tocopherols and tocotrienols (Azzi A et al. Free Radic Biol Med. 2023; 207:178-180. doi: 10.1016/j.freeradbiomed.2023.06.029). The aim of this paper is to express our opinion on the nomenclature of vitamin E based on available scientific data. In our opinion, it would be inappropriate to exclude all the tocochromanols other than RRR-α-tocopherol from the vitamin E group at this stage when the molecular mechanisms showing how vitamin E deficiency causes diseases such as ataxia and how vitamin E prevents/reverses such diseases are not elucidated. Understanding of whole functions of tocochromanols including underlying mechanisms and dynamics is essential before revision of currently accepted definition of vitamin E. The potential roles of γ-tocopherol and tocotrienols are discussed despite whether they are vitamin function should be clarified in the future studies.

Sensory ataxic polyneuropathy unmasking late-onset urea cycle defect.

A 63-year-old man with type 2 diabetes mellitus, alcohol consumption in moderation, and three episodes of hepatic encephalopathy presented with symmetrical lower limb distal weakness, sensory ataxia, thickened palpable nerves, mood disturbances for seven years, and a family history of schizophreniform disorders. Nerve conduction studies showed demyelinating sensorimotor polyradiculoneuropathy. CSF analysis showed mild albumino-cytological dissociation. MRI brain and lumbosacral plexus showed thickened fifth cranial nerves and lumbosacral roots. He was treated with steroids for a provisional diagnosis of chronic inflammatory polyneuropathy and became encephalopathic. EEG showed triphasic waves. Serum ammonia was 201 micrograms/dL. Further evaluation suggested ornithine transcarbamylase (OTC) deficiency. The patient underwent hemodialysis with a low protein diet, rifaximin, and sodium benzoate, with subsequent recovery.

Predictors of Clinically Important Neuroimaging Findings in Children Presenting Pediatric Emergency Department.

OBJECTIVE: The aim of the study is to evaluate predictors of clinically important neuroimaging results, that is, computed tomography and magnetic resonance imaging in children in an academic pediatric emergency department (PED) from 2015 to 2019. METHODS: This study was conducted in an academic PED. The patient's demographic and clinical characteristics of PED visits and neuroimaging findings requested at the PED were recorded for January 1, 2015, to December 31, 2019. In addition, descriptive statistics and logistic regression analyses were conducted. We described and determined the predictors of clinically important neuroimaging findings in children. RESULTS: Clinically important neuroimaging findings were detected in patients with blurred vision ( P = 0.001), ataxia ( P = 0.003), unilateral weakness ( P = 0.004), and altered level of consciousness ( P = 0.026). Clinically important neuroimaging was found 9.4 times higher in patients with altered level of consciousness, 7.4 times higher in patients with focal weakness, 4.6 times higher in patients with blurred vision, and 3.5 times more in patients presenting with ataxia. CONCLUSIONS: Advanced neuroimaging, especially for selected patients in PED, can improve the quality of health care for patients. On the other hand, irrelevant neuroimaging findings can lead physicians away from prompt diagnosis and accurate management. According to our study, advanced neuroimaging can be performed in the early period for both diagnosis and early treatment, especially in selected patients with ataxia, blurred vision, altered consciousness, and unilateral weakness. In other cases, clinicians may find more supporting evidence.

Mitochondrial dysfunction in Fragile X syndrome and Fragile X-associated tremor/ataxia syndrome: prospect use of antioxidants and mitochondrial nutrients.

Fragile X syndrome (FXS) is a genetic disorder characterized by mutation in the FMR1 gene, leading to the absence or reduced levels of fragile X Messenger Ribonucleoprotein 1 (FMRP). This results in neurodevelopmental deficits, including autistic spectrum conditions. On the other hand, Fragile X-associated tremor/ataxia syndrome (FXTAS) is a distinct disorder caused by the premutation in the FMR1 gene. FXTAS is associated with elevated levels of FMR1 mRNA, leading to neurodegenerative manifestations such as tremors and ataxia.Mounting evidence suggests a link between both syndromes and mitochondrial dysfunction (MDF). In this minireview, we critically examine the intricate relationship between FXS, FXTAS, and MDF, focusing on potential therapeutic avenues to counteract or mitigate their adverse effects. Specifically, we explore the role of mitochondrial cofactors and antioxidants, with a particular emphasis on alpha-lipoic acid (ALA), carnitine (CARN) and Coenzyme Q10 (CoQ10). Findings from this review will contribute to a deeper understanding of these disorders and foster novel therapeutic strategies to enhance patient outcomes.

RFC1: Motifs and phenotypes.

Biallelic intronic expansions (AAGGG)exp in intron 2 of the RFC1 gene have been shown to be a common cause of late-onset ataxia. Since their first description, the phenotypes, neurological damage, and pathogenic variants associated with the RFC1 gene have been frequently updated. Here, we review the various motifs, genetic variants, and phenotypes associated with the RFC1 gene. We searched PubMed for scientific articles published between March 1st, 2019, and January 15th, 2024. The motifs and phenotypes associated with the RFC1 gene are highly heterogeneous, making molecular diagnosis and clinical screening and investigation challenging. In this review we will provide clues to give a better understanding of RFC1 disease. We briefly discuss new methods for molecular diagnosis, the origin of cough in RFC1 disease, and research perspectives.

Multifeature quantitative motor assessment of upper limb ataxia including drawing and reaching.

OBJECTIVE: Voluntary upper limb movements are an ecologically important yet insufficiently explored digital-motor outcome domain for trials in degenerative ataxia. We extended and validated the trial-ready quantitative motor assessment battery "Q-Motor" for upper limb movements with clinician-reported, patient-focused, and performance outcomes of ataxia. METHODS: Exploratory single-center cross-sectional assessment in 94 subjects (46 cross-genotype ataxia patients; 48 matched controls), comprising five tasks measured by force transducer and/or position field: Finger Tapping, diadochokinesia, grip-lift, and-as novel implementations-Spiral Drawing, and Target Reaching. Digital-motor measures were selected if they discriminated from controls (AUC >0.7) and correlated-with at least one strong correlation (rho ≥0.6)-to the Scale for the Assessment and Rating of Ataxia (SARA), activities of daily living (FARS-ADL), and the Nine-Hole Peg Test (9HPT). RESULTS: Six movement features with 69 measures met selection criteria, including speed and variability in all tasks, stability in grip-lift, and efficiency in Target Reaching. The novel drawing/reaching tasks best captured impairment in dexterity (|rho9HPT| ≤0.81) and FARS-ADL upper limb items (|rhoADLul| ≤0.64), particularly by kinematic analysis of smoothness (SPARC). Target hit rate, a composite of speed and endpoint precision, almost perfectly discriminated ataxia and controls (AUC: 0.97). Selected measures in all tasks discriminated between mild, moderate, and severe impairment (SARA upper limb composite: 0-2/>2-4/>4-6) and correlated with severity in the trial-relevant mild ataxia stage (SARA ≤10, n = 20). INTERPRETATION: Q-Motor assessment captures multiple features of impaired upper limb movements in degenerative ataxia. Validation with key clinical outcome domains provides the basis for evaluation in longitudinal studies and clinical trial settings.