The continuously evolving phenotype of succinic semialdehyde dehydrogenase deficiency.

The objective of the study is to evaluate the evolving phenotype and genetic spectrum of patients with succinic semialdehyde dehydrogenase deficiency (SSADHD) in long-term follow-up. Longitudinal clinical and biochemical data of 22 pediatric and 9 adult individuals with SSADHD from the patient registry of the International Working Group on Neurotransmitter related Disorders (iNTD) were studied with in silico analyses, pathogenicity scores and molecular modeling of ALDH5A1 variants. Leading initial symptoms, with onset in infancy, were developmental delay and hypotonia. Year of birth and specific initial symptoms influenced the diagnostic delay. Clinical phenotype of 26 individuals (median 12 years, range 1.8-33.4 years) showed a diversifying course in follow-up: 77% behavioral problems, 76% coordination problems, 73% speech disorders, 58% epileptic seizures and 40% movement disorders. After ataxia, dystonia (19%), chorea (11%) and hypokinesia (15%) were the most frequent movement disorders. Involvement of the dentate nucleus in brain imaging was observed together with movement disorders or coordination problems. Short attention span (78.6%) and distractibility (71.4%) were the most frequently behavior traits mentioned by parents while impulsiveness, problems communicating wishes or needs and compulsive behavior were addressed as strongly interfering with family life. Treatment was mainly aimed to control epileptic seizures and psychiatric symptoms. Four new pathogenic variants were identified. In silico scoring system, protein activity and pathogenicity score revealed a high correlation. A genotype/phenotype correlation was not observed, even in siblings. This study presents the diversifying characteristics of disease phenotype during the disease course, highlighting movement disorders, widens the knowledge on the genotypic spectrum of SSADHD and emphasizes a reliable application of in silico approaches.

Fabry Disease and Central Nervous System Involvement: From Big to Small, from Brain to Synapse.

Fabry disease (FD) is an X-linked lysosomal storage disorder (LSD) secondary to mutations in the GLA gene that causes dysfunctional activity of lysosomal hydrolase α-galactosidase A and results in the accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3). The endothelial accumulation of these substrates results in injury to multiple organs, mainly the kidney, heart, brain and peripheral nervous system. The literature on FD and central nervous system involvement is scarce when focusing on alterations beyond cerebrovascular disease and is nearly absent in regard to synaptic dysfunction. In spite of that, reports have provided evidence for the CNS' clinical implications in FD, including Parkinson's disease, neuropsychiatric disorders and executive dysfunction. We aim to review these topics based on the current available scientific literature.

Impact of COVID19 pandemic on patients with rare diseases in Spain, with a special focus on inherited metabolic diseases.

Introduction: The Covid-19 pandemic soon became an international health emergency raising concern about its impact not only on physical health but also on quality of life and mental health. Rare diseases are chronically debilitating conditions with challenging patient care needs. We aimed to assess the quality of life and mental health of patients with rare diseases in Spain, with a special focus on inherited metabolic disorders (IMD). Methods: A prospective case-control study was designed, comparing 459 patients suffering from a rare disease (including 53 patients with IMD) and 446 healthy controls. Quality of life (QoL) and mental health were assessed using validated scales according to age: KINDL-R and the Pediatric Symptom Checklist (PSC) for children and the WhoQoL-Bref questionnaire, GAD and PHQ-9 in adults. Results: First, children and adults (but not adolescents) with IMD showed greater psychological effects than controls (p = 0.022, p = 0.026 respectively). Second, when comparing QoL, only adult patients with IMD showed worse score than controls (66/100 vs 74,6/100 respectively, p = 0.017). Finally, IMD had better quality of life than other rare neurological and genetic diseases (p = 0.008) or other rare diseases (p < 0.001 respectively) but similar alteration of the mental status. Conclusions: Our data show that the pandemic had a negative impact on mental health that is more evident in the group of patients with IMD. Young age would behave as a protective factor on the perception of QoL. Furthermore, patients with IMD show a better QoL than other rare diseases.

Impact of the SARS-CoV-2 pandemic on the health of individuals with intoxication-type metabolic diseases-Data from the E-IMD consortium.

The SARS-CoV-2 pandemic challenges healthcare systems worldwide. Within inherited metabolic disorders (IMDs) the vulnerable subgroup of intoxication-type IMDs such as organic acidurias (OA) and urea cycle disorders (UCD) show risk for infection-induced morbidity and mortality. This study (observation period February 2020 to December 2021) evaluates impact on medical health care as well as disease course and outcome of SARS-CoV-2 infections in patients with intoxication-type IMDs managed by participants of the European Registry and Network for intoxication type metabolic diseases Consortium (E-IMD). Survey's respondents managing 792 patients (n = 479 pediatric; n = 313 adult) with intoxication-type IMDs (n = 454 OA; n = 338 UCD) in 14 countries reported on 59 (OA: n = 36; UCD: n = 23), SARS-CoV-2 infections (7.4%). Medical services were increasingly requested (95%), mostly alleviated by remote technologies (86%). Problems with medical supply were scarce (5%). Regular follow-up visits were reduced in 41% (range 10%-50%). Most infected individuals (49/59; 83%) showed mild clinical symptoms, while 10 patients (17%; n = 6 OA including four transplanted MMA patients; n = 4 UCD) were hospitalized (metabolic decompensation in 30%). ICU treatment was not reported. Hospitalization rate did not differ for diagnosis or age group (p = 0.778). Survival rate was 100%. Full recovery was reported for 100% in outpatient care and 90% of hospitalized individuals. SARS-CoV-2 impacts health care of individuals with intoxication-type IMDs worldwide. Most infected individuals, however, showed mild symptoms and did not require hospitalization. SARS-CoV-2-induced metabolic decompensations were usually mild without increased risk for ICU treatment. Overall prognosis of infected individuals is very promising and IMD-specific or COVID-19-related complications have not been observed.

Monoamine neurotransmitters in early epileptic encephalopathies: New insights into pathophysiology and therapy.

AIM: To study neurotransmitter status in children with early epileptic and developmental and epileptic encephalopathy (DEE) and to explore the clinical response to dopaminergic and serotoninergic therapies in a group of patients. METHOD: Two hundred and five patients (111 males [54.1.%] and 94 females [45.9%], mean age 10 months at the onset of epilepsy [SD 1 year 1 month], range 0-3 year) with epileptic encephalopathy/DEE were recruited, including those with West syndrome, Ohtahara syndrome, early myoclonic encephalopathy, epilepsy of infancy with migrating focal seizures, myoclonic encephalopathy in non-progressive disorders, infantile spasms, Doose syndrome, Lennox-Gastaut syndrome, Landau-Kleffner syndrome, and those unclassified. Cerebrospinal fluid (CSF) neurotransmitter studies and patients' medical records were reviewed. Additionally, we present clinical data of 10 patients with low CSF neurotransmitter levels who received dopaminergic/serotoninergic treatments. RESULTS: Abnormal neurotransmitter values were identified in 68 (33%) patients. 5-Hydroxyindoleacetic acid (5-HIAA) deficit was the most prevalent alteration (91%). Low CSF 5-HIAA levels were significantly higher in 1- to 3-year-old children. A negative significant correlation was found between 5-HIAA levels and epilepsy duration before CSF study (Spearman's ρ=-0.191, p=0.007). Abnormalities in deep grey matter were associated with low levels of CSF homovanillic acid and 5-HIAA. Ten patients with low CSF neurotransmitter levels received dopamine and/or serotonin therapies. Six of them showed initial decrease of seizure frequency and severity and maintained improvement in some neurodevelopmental skills. INTERPRETATION: A considerable number of patients showed neurotransmitter abnormalities. Age at seizure onset and duration of epilepsy before CSF study were the principal factors related to neurotransmitter depletion. Early monoamine supplementation would seem advisable as a neuroprotective strategy. WHAT THIS PAPER ADDS: 5-Hydroxyindoleacetic acid homeostasis is especially vulnerable in patients with epileptic encephalopathy/developmental and epileptic encephalopathy. Age of seizure onset and duration of epilepsy are determinants of neurotransmitter depletion.

Volumetric study of brain MRI in a cohort of patients with neurotransmitter disorders.

PURPOSE: Inborn errors of neurotransmitters are rare monogenic diseases. In general, conventional neuroimaging is not useful for diagnosis. Nevertheless, advanced neuroimaging techniques could provide novel diagnosis and prognosis biomarkers. We aim to describe cerebral volumetric findings in a group of Spanish patients with neurotransmitter disorders. METHODS: Fifteen 3D T1-weighted brain images from the International Working Group on Neurotransmitter related Disorders Spanish cohort were assessed (eight with monoamine and seven with amino acid disorders). Volumes of cortical and subcortical brain structures were obtained for each patient and then compared with those of two healthy individuals matched by sex and age. RESULTS: Regardless of the underlying disease, patients showed a smaller total cerebral tissue volume, which was apparently associated with clinical severity. A characteristic volumetric deficit pattern, including the right Heschl gyrus and the bilateral occipital gyrus, was identified. In severe cases, a distinctive pattern comprised the middle and posterior portions of the right cingulate, the left superior motor area and the cerebellum. In succinate semialdehyde dehydrogenase deficiency, volumetric affection seems to worsen over life. CONCLUSION: Despite the heterogeneity and limited size of our cohort, we found novel and relevant data. Total volume deficit appears to be a marker of severity, regardless of the specific neurotransmitter disease and irrespective of the information obtained from conventional neuroimaging. Volumetric assessment of individual brain structures could provide a deeper knowledge about pathophysiology, disease severity and specific clinical traits.

Integrative Approach to Predict Severity in Nonketotic Hyperglycinemia.

OBJECTIVE: Glycine encephalopathy, also known as nonketotic hyperglycinemia (NKH), is an inherited neurometabolic disorder with variable clinical course and severity, ranging from infantile epileptic encephalopathy to psychiatric disorders. A precise phenotypic characterization and an evaluation of predictive approaches are needed. METHODS: Longitudinal clinical and biochemical data of 25 individuals with NKH from the patient registry of the International Working Group on Neurotransmitter Related Disorders were studied with in silico analyses, pathogenicity scores, and molecular modeling of GLDC and AMT variants. RESULTS: Symptom onset (p < 0.01) and diagnosis occur earlier in life in severe NKH (p < 0.01). Presenting symptoms affect the age at diagnosis. Psychiatric problems occur predominantly in attenuated NKH. Onset age ≥ 3 months (66% specificity, 100% sensitivity, area under the curve [AUC] = 0.87) and cerebrospinal fluid (CSF)/plasma glycine ratio ≤ 0.09 (57% specificity, 100% sensitivity, AUC = 0.88) are sensitive indicators for attenuated NKH, whereas CSF glycine concentration ≥ 116.5µmol/l (100% specificity, 93% sensitivity, AUC = 0.97) and CSF/plasma glycine ratio ≥ 0.15 (100% specificity, 64% sensitivity, AUC = 0.88) are specific for severe forms. A ratio threshold of 0.128 discriminates the overlapping range. We present 10 new GLDC variants. Two mild variants resulted in attenuated, whereas 2 severe variants or 1 mild and 1 severe variant led to severe phenotype. Based on clinical, biochemical, and genetic parameters, we propose a severity prediction model. INTERPRETATION: This study widens the phenotypic spectrum of attenuated NKH and expands the number of pathogenic variants. The multiparametric approach provides a promising tool to predict disease severity, helping to improve clinical management strategies. ANN NEUROL 2022;92:292-303.

Clinical features and health-related quality of life in adult patients with mucopolysaccharidosis IVA: the Spanish experience.

BACKGROUND: Mucopolysaccharidosis (MPS) IVA or Morquio A syndrome is a progressive and disabling disease characterized by a deficiency of the enzyme N-acetylgalactosamine-6-sulphate sulphatase. Its clinical presentation is very heterogeneous and poorly understood in adults. The aim of this study was to describe the clinical manifestations of MPS IVA in adult patients in Spain and to assess their health-related quality of life (HRQoL). RESULTS: Thirty-three patients from nine reference centres participated in the study. The median age was 32 (interquartile range [IQR]: 20.5-40.5) years. The phenotype was classical in 54.5% of patients, intermediate in 33.3% of patients, and non-classical in 12.1% of patients. The most common clinical manifestation was bone dysplasia, with a median height of 118 (IQR: 106-136) cm. Other frequent clinical manifestations were hearing loss (75.7%), ligamentous laxity (72.7%), odontoid dysplasia (69.7%), limb deformities that required orthopaedic aids (mainly hip dysplasia and genu valgus) (63.6%), and corneal clouding (60.6%). In addition, 36.0% of patients had obstructive sleep apnoea/hypopnoea syndrome and 33.3% needed non-invasive ventilation. Cervical surgery and varisation osteotomy were the most common surgical interventions (36.4% each). Almost 80% of patients had mobility problems and 36.4% used a wheelchair at all times. Furthermore, 87.9% needed help with self-care, 33.3% were fully dependent, and 78.8% had some degree of pain. HRQoL according to the health assessment questionnaire was 1.43 (IQR: 1.03-2.00) in patients with the non-classical phenotype, but 2.5 (IQR: 1.68-3.00) in those with the classical phenotype. Seven patients were initiated on enzyme replacement therapy (ERT), but two of them were lost to follow-up. Lung function improved in four patients and slightly worsened in one patient. The distance achieved in the six-minute walk test increased in the four patients who could perform it. HRQoL was better in patients treated with elosulfase alfa, with a median (IQR) of 1.75 (1.25-2.34) versus 2.25 (1.62-3.00) in patients not treated with ERT. CONCLUSIONS: The study provides real-world data on patients with MPS IVA. Limited mobility, difficulties with self-care, dependence, and pain were common, together with poor HRQoL. The severity and heterogeneity of clinical manifestations require the combined efforts of multidisciplinary teams.

Insights into the expanding phenotypic spectrum of inherited disorders of biogenic amines.

Inherited disorders of neurotransmitter metabolism are rare neurodevelopmental diseases presenting with movement disorders and global developmental delay. This study presents the results of the first standardized deep phenotyping approach and describes the clinical and biochemical presentation at disease onset as well as diagnostic approaches of 275 patients from the registry of the International Working Group on Neurotransmitter related Disorders. The results reveal an increased rate of prematurity, a high risk for being small for gestational age and for congenital microcephaly in some disorders. Age at diagnosis and the diagnostic delay are influenced by the diagnostic methods applied and by disease-specific symptoms. The timepoint of investigation was also a significant factor: delay to diagnosis has decreased in recent years, possibly due to novel diagnostic approaches or raised awareness. Although each disorder has a specific biochemical pattern, we observed confounding exceptions to the rule. The data provide comprehensive insights into the phenotypic spectrum of neurotransmitter disorders.

Assessment of intellectual impairment, health-related quality of life, and behavioral phenotype in patients with neurotransmitter related disorders: Data from the iNTD registry.

Inherited disorders of neurotransmitter metabolism are a group of rare diseases, which are caused by impaired synthesis, transport, or degradation of neurotransmitters or cofactors and result in various degrees of delayed or impaired psychomotor development. To assess the effect of neurotransmitter deficiencies on intelligence, quality of life, and behavior, the data of 148 patients in the registry of the International Working Group on Neurotransmitter Related Disorders (iNTD) was evaluated using results from standardized age-adjusted tests and questionnaires. Patients with a primary disorder of monoamine metabolism had lower IQ scores (mean IQ 58, range 40-100) within the range of cognitive impairment (<70) compared to patients with a BH4 deficiency (mean IQ 84, range 40-129). Short attention span and distractibility were most frequently mentioned by parents, while patients reported most frequently anxiety and distractibility when asked for behavioral traits. In individuals with succinic semialdehyde dehydrogenase deficiency, self-stimulatory behaviors were commonly reported by parents, whereas in patients with dopamine transporter deficiency, DNAJC12 deficiency, and monoamine oxidase A deficiency, self-injurious or mutilating behaviors have commonly been observed. Phobic fears were increased in patients with 6-pyruvoyltetrahydropterin synthase deficiency, while individuals with sepiapterin reductase deficiency frequently experienced communication and sleep difficulties. Patients with BH4 deficiencies achieved significantly higher quality of life as compared to other groups. This analysis of the iNTD registry data highlights: (a) difference in IQ and subdomains of quality of life between BH4 deficiencies and primary neurotransmitter-related disorders and (b) previously underreported behavioral traits.

Unraveling Molecular Pathways Altered in MeCP2-Related Syndromes, in the Search for New Potential Avenues for Therapy.

Methyl-CpG-binding protein 2 (MeCP2) is an X-linked epigenetic modulator whose dosage is critical for neural development and function. Loss-of-function mutations in MECP2 cause Rett Syndrome (RTT, OMIM #312750) while duplications in the Xq28 locus containing MECP2 and Interleukin-1 receptor-associated kinase 1 (IRAK1) cause MECP2 duplication syndrome (MDS, OMIM #300260). Both are rare neurodevelopmental disorders that share clinical symptoms, including intellectual disability, loss of speech, hand stereotypies, vasomotor deficits and seizures. The main objective of this exploratory study is to identify novel signaling pathways and potential quantitative biomarkers that could aid early diagnosis and/or the monitoring of disease progression in clinical trials. We analyzed by RT-PCR gene expression in whole blood and microRNA (miRNA) expression in plasma, in a cohort of 20 females with Rett syndrome, 2 males with MECP2 duplication syndrome and 28 healthy controls, and correlated RNA expression with disease and clinical parameters. We have identified a set of potential biomarker panels for RTT diagnostic and disease stratification of patients with microcephaly and vasomotor deficits. Our study sets the basis for larger studies leading to the identification of specific miRNA signatures for early RTT detection, stratification, disease progression and segregation from other neurodevelopmental disorders. Nevertheless, these data will require verification and validation in further studies with larger sample size including a whole range of ages.

Brain MR patterns in inherited disorders of monoamine neurotransmitters: An analysis of 70 patients.

Inherited monoamine neurotransmitter disorders (iMNDs) are rare disorders with clinical manifestations ranging from mild infantile hypotonia, movement disorders to early infantile severe encephalopathy. Neuroimaging has been reported as non-specific. We systematically analyzed brain MRIs in order to characterize and better understand neuroimaging changes and to re-evaluate the diagnostic role of brain MRI in iMNDs. 81 MRIs of 70 patients (0.1-52.9 years, 39 patients with tetrahydrobiopterin deficiencies, 31 with primary disorders of monoamine metabolism) were retrospectively analyzed and clinical records reviewed. 33/70 patients had MRI changes, most commonly atrophy (n = 24). Eight patients, six with dihydropteridine reductase deficiency (DHPR), had a common pattern of bilateral parieto-occipital and to a lesser extent frontal and/or cerebellar changes in arterial watershed zones. Two patients imaged after acute severe encephalopathy had signs of profound hypoxic-ischemic injury and a combination of deep gray matter and watershed injury (aromatic l-amino acid decarboxylase (AADCD), tyrosine hydroxylase deficiency (THD)). Four patients had myelination delay (AADCD; THD); two had changes characteristic of post-infantile onset neuronal disease (AADCD, monoamine oxidase A deficiency), and nine T2-hyperintensity of central tegmental tracts. iMNDs are associated with MRI patterns consistent with chronic effects of a neuronal disorder and signs of repetitive injury to cerebral and cerebellar watershed areas, in particular in DHPRD. These will be helpful in the (neuroradiological) differential diagnosis of children with unknown disorders and monitoring of iMNDs. We hypothesize that deficiency of catecholamines and/or tetrahydrobiopterin increase the incidence of and the CNS susceptibility to vascular dysfunction.

The impact of COVID-19 pandemic on the diagnosis and management of inborn errors of metabolism: A global perspective.

Quantitative estimates for the global impact of COVID-19 on the diagnosis and management of patients with inborn errors of metabolism (IEM) are lacking. We collected relevant data from 16 specialized medical centers treating IEM patients in Europe, Asia and Africa. The median decline of reported IEM related services in March 1st-May 31st 2020 compared to the same period in 2019 were as high as 60-80% with a profound impact on patient management and care for this vulnerable patient group. More representative data along with outcome data and guidelines for managing IEM disorders under such extraordinary circumstances are needed.

Correction to: Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies.

An amendment to this paper has been published and can be accessed via the original article.

Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies.

BACKGROUND: Tetrahydrobiopterin (BH4) deficiencies comprise a group of six rare neurometabolic disorders characterized by insufficient synthesis of the monoamine neurotransmitters dopamine and serotonin due to a disturbance of BH4 biosynthesis or recycling. Hyperphenylalaninemia (HPA) is the first diagnostic hallmark for most BH4 deficiencies, apart from autosomal dominant guanosine triphosphate cyclohydrolase I deficiency and sepiapterin reductase deficiency. Early supplementation of neurotransmitter precursors and where appropriate, treatment of HPA results in significant improvement of motor and cognitive function. Management approaches differ across the world and therefore these guidelines have been developed aiming to harmonize and optimize patient care. Representatives of the International Working Group on Neurotransmitter related Disorders (iNTD) developed the guidelines according to the SIGN (Scottish Intercollegiate Guidelines Network) methodology by evaluating all available evidence for the diagnosis and treatment of BH4 deficiencies. CONCLUSION: Although the total body of evidence in the literature was mainly rated as low or very low, these consensus guidelines will help to harmonize clinical practice and to standardize and improve care for BH4 deficient patients.

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. 123 I-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.

Discovery of Biomarker Panels for Neural Dysfunction in Inborn Errors of Amino Acid Metabolism.

Patients with inborn errors of amino acid metabolism frequently show neuropsychiatric symptoms despite accurate metabolic control. This study aimed to gain insight into the underlying mechanisms of neural dysfunction. Here we analyzed the expression of brain-derived neurotrophic factor (BDNF) and 10 genes required for correct brain functioning in plasma and blood of patients with Urea Cycle Disorders (UCD), Maple Syrup Urine Disease (MSUD) and controls. Receiver-operating characteristic (ROC) analysis was used to evaluate sensitivity and specificity of potential biomarkers. CACNA2D2 (α2δ2 subunit of voltage-gated calcium channels) and MECP2 (methyl-CpG binding protein 2) mRNA and protein showed an excellent neural function biomarker signature (AUC ≥ 0,925) for recognition of MSUD. THBS3 (thrombospondin 3) mRNA and AABA gave a very good biomarker signature (AUC 0,911) for executive-attention deficits. THBS3, LIN28A mRNA, and alanine showed a perfect biomarker signature (AUC 1) for behavioral and mood disorders. Finally, a panel of BDNF protein and at least two large neural AAs showed a perfect biomarker signature (AUC 1) for recognition of psychomotor delay, pointing to excessive protein restriction as central causative of psychomotor delay. To conclude, our study has identified promising biomarker panels for neural function evaluation, providing a base for future studies with larger samples.

Presynaptic disorders: a clinical and pathophysiological approach focused on the synaptic vesicle.

The aim of this report is to present a tentative clinical and pathophysiological approach to diseases affecting the neuronal presynaptic terminal, with a major focus on synaptic vesicles (SVs). Diseases are classified depending on which step of the neurobiology of the SV is predominantly affected: (1) biogenesis of vesicle precursors in the neuronal soma; (2) transport along the axon; (3) vesicle cycle at the presynaptic terminal (exocytosis-endocytosis cycle, with the main purpose of neurotransmitter release). Given that SVs have been defined as individual organelles, we highlight the link between the biological processes disturbed by genetic mutations and the clinical presentation of these disorders. The great majority of diseases may present as epileptic encephalopathies, intellectual disability (syndromic or nonsyndromic) with/without autism spectrum disorder (and other neuropsychiatric symptoms), and movement disorders. These symptoms may overlap and present in patients as a combination of clinical signs that results in the spectrum of the synaptopathies. A small number of diseases may also exhibit neuromuscular signs. In general, SV disorders tend to be severe, early encephalopathies that interfere with neurodevelopment. As a consequence, developmental delay and intellectual disability are constant in almost all the defects described. Considering that some of these diseases might mimic other neurometabolic conditions (and in particular treatable disorders), an initial extensive metabolic workup should always be considered. Further knowledge into pathophysiological mechanisms and biomarkers, as well as descriptions of new presynaptic disorders, will probably take place in the near future.

Gamma-aminobutyric acid levels in cerebrospinal fluid in neuropaediatric disorders.

AIM: Gamma-aminobutyric acid (GABA) is a major modulator in brain maturation and its role in many different neurodevelopmental disorders has been widely reported. Although the involvement of GABA in different disorders has been related to its regulatory function as an inhibitory neurotransmitter in the mature brain, co-transmitter, and signalling molecule, little is known about its role as a clinical biomarker in neuropaediatric disorders. The aim of this study is to report the cerebrospinal fluid (CSF) free-GABA concentrations in a large cohort of patients (n=85) with different neurological disorders. METHOD: GABA was measured in the CSF of neuropaediatric patients using capillary electrophoresis with laser-induced fluorescence detection. Other neurotransmitters (amino acids and monoamines) were also analysed. RESULTS: GABA concentrations in CSF were abnormal, with a greater frequency (44%) than monoamines (20%) in neuropaediatric patients compared with our reference values. Although we included a few patients with inborn errors of metabolism, GABA levels in CSF were more frequently abnormal in metabolic disorders than in other nosological groups. INTERPRETATION: Our work suggests further research into brain GABAergic status in neuropaediatric disorders, which could also lead to new therapeutic strategies. WHAT THIS PAPER ADDS: Homeostasis of GABA seems more vulnerable than that of monoamines in the developing brain. The highest GABA levels are found in the primary GABA neurotransmitter disorder SSADH deficiency. GABA alterations are not specific for any clinical or neuroimaging presentation.

Correction to: Age at disease onset and peak ammonium level rather than interventional variables predict the neurological outcome in urea cycle disorders.

Due to an unfortunate error during the typesetting process, the collaborators were presented incorrectly.