NRXN1α+/- is associated with increased excitability in ASD iPSC-derived neurons.

BACKGROUND: NRXN1 deletions are identified as one of major rare risk factors for autism spectrum disorder (ASD) and other neurodevelopmental disorders. ASD has 30% co-morbidity with epilepsy, and the latter is associated with excessive neuronal firing. NRXN1 encodes hundreds of presynaptic neuro-adhesion proteins categorized as NRXN1α/ß/γ. Previous studies on cultured cells show that the short NRXN1ß primarily exerts excitation effect, whereas the long NRXN1α which is more commonly deleted in patients involves in both excitation and inhibition. However, patient-derived models are essential for understanding functional consequences of NRXN1α deletions in human neurons. We recently derived induced pluripotent stem cells (iPSCs) from five controls and three ASD patients carrying NRXN1α+/- and showed increased calcium transients in patient neurons. METHODS: In this study we investigated the electrophysiological properties of iPSC-derived cortical neurons in control and ASD patients carrying NRXN1α+/- using patch clamping. Whole genome RNA sequencing was carried out to further understand the potential underlying molecular mechanism. RESULTS: NRXN1α+/- cortical neurons were shown to display larger sodium currents, higher AP amplitude and accelerated depolarization time. RNASeq analyses revealed transcriptomic changes with significant upregulation glutamatergic synapse and ion channels/transporter activity including voltage-gated potassium channels (GRIN1, GRIN3B, SLC17A6, CACNG3, CACNA1A, SHANK1), which are likely to couple with the increased excitability in NRXN1α+/- cortical neurons. CONCLUSIONS: Together with recent evidence of increased calcium transients, our results showed that human NRXN1α+/- isoform deletions altered neuronal excitability and non-synaptic function, and NRXN1α+/- patient iPSCs may be used as an ASD model for therapeutic development with calcium transients and excitability as readouts.

Fifteen-minute consultation: Approach to investigation and management of childhood dystonia.

Dystonia is a hyperkinetic movement disorder characterised by sustained or intermittent muscle contractions causing abnormal movements, postures or both. Dystonia is a challenging condition to diagnose and treat. Dystonia is often under-recognised in children, particularly in cerebral palsy, and frequently coexists with spasticity. This guide aims to simplify the approach to diagnosis, investigation and treatment of childhood-onset dystonia. The principle of treatment is similar regardless of the underlying aetiology: identification of potential triggers and consideration of both pharmacological and surgical options.

KMT2B-related disorders: expansion of the phenotypic spectrum and long-term efficacy of deep brain stimulation.

Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5-37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden's Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at 6 months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 16.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.

X-linked infantile spinal muscular atrophy (SMAX2) caused by novel c.1681G>A substitution in the UBA1 gene, expanding the phenotype.

X-linked infantile spinal muscular atrophy (SMAX2), OMIM 301830, is a rare, severe form of spinal muscular atrophy, caused by variants in the Ubiquitin like modifier-activating enzyme 1 (UBA1) gene. Clinical features reported to date include marked hypotonia, areflexia, arthrogryposis, contractures, myopathic facies and tongue fibrillations. Previous reports have included a history of contractures. We report a male patient presenting following a normal pregnancy with typical symptoms of X-linked infantile spinal muscular atrophy including hypotonia, weakness, areflexia and respiratory insufficiency, however contractures were absent. There was a significant family history of neuromuscular disease on the maternal side, with several male relatives all dying before the age of six months. Creatine Kinase was mildly elevated, MRI Brain was normal and neurophysiological testing revealed a diffuse motor neuronopathy. Genetic testing for SMN1 gene was normal. UBA1 sequencing revealed a maternally inherited hemizygous familial variant [c.1681G>A p. (Asp561Asn)], which has not been previously reported.

FARS2 Causing Complex Hereditary Spastic Paraplegia With Dysphonia: Expanding the Disease Spectrum.

Herein we present two siblings with hereditary spastic paraplegia caused by novel compound heterozygous variant and deletion in FARS2 and expansion of the disease spectrum to include dysphonia.

NRXN1 deletion syndrome; phenotypic and penetrance data from 34 families.

The spectrum of phenotypes associated with heterozygous deletions of neurexin-1 (NRXN1) is diverse and includes: autism spectrum disorder, attention deficit hyperactivity disorder, intellectual disability, seizures, schizophrenia, mood disorders and congenital malformations. Reduced penetrance and variable expressivity of deletions in this gene remain a challenge for genetic counselling. We clinically reviewed 67 NRXN1 deletions from 34 families to document the phenotype and determine odds ratio. Thirty-four probands (5 adults, 29 children (<16 years)) were initially identified from a cohort clinically referred for arrayCGH. A further 33 NRXN1 deletions (16 with established phenotype) from the families were identified following cascade screening. Speech and language delay was a consistent clinical presentation. Pedigree analysis of the inherited group revealed numerous untested relatives with a history of mental health and developmental issues, most notably in the NRXN1ß isoform patients. Our study highlights the complex nature of the NRXN1 phenotype in this population.

Increased Ca2+ signaling in NRXN1α+/- neurons derived from ASD induced pluripotent stem cells.

Background: Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a high co-morbidity of epilepsy and associated with hundreds of rare risk factors. NRXN1 deletion is among the commonest rare genetic factors shared by ASD, schizophrenia, intellectual disability, epilepsy, and developmental delay. However, how NRXN1 deletions lead to different clinical symptoms is unknown. Patient-derived cells are essential to investigate the functional consequences of NRXN1 lesions to human neurons in different diseases. Methods: Skin biopsies were donated by five healthy donors and three ASD patients carrying NRXN1α+/- deletions. Seven control and six NRXN1α+/- iPSC lines were derived and differentiated into day 100 cortical excitatory neurons using dual SMAD inhibition. Calcium (Ca2+) imaging was performed using Fluo4-AM, and the properties of Ca2+ transients were compared between two groups of neurons. Transcriptome analysis was carried out to undercover molecular pathways associated with NRXN1α+/- neurons. Results: NRXN1α+/- neurons were found to display altered calcium dynamics, with significantly increased frequency, duration, and amplitude of Ca2+ transients. Whole genome RNA sequencing also revealed altered ion transport and transporter activity, with upregulated voltage-gated calcium channels as one of the most significant pathways in NRXN1α+/- neurons identified by STRING and GSEA analyses. Conclusions: This is the first report to show that human NRXN1α+/- neurons derived from ASD patients' iPSCs present novel phenotypes of upregulated VGCCs and increased Ca2+ transients, which may facilitate the development of drug screening assays for the treatment of ASD.

Status dystonicus due to missense variant in ARX: Diagnosis and management.

Movement disorders are increasingly identified in infantile encephalopathies due to single gene disorders (e.g. SCN2A, CDKL5, ARX). The associated movement disorder can be challenging to recognise and treat. We report a 2 year-old boy with a background history of Ohtahara syndrome due to a missense variant in ARX (the aristaless-related homeobox gene) who subsequently developed status dystonicus. ARX is a transcription factor that plays a critical role in cortical neuronal development and is associated with a range of important neurodevelopmental disorders depending on the site of the pathogenic variant. Cases of status dystonicus are described with variants affecting the polyalanine expansion region of ARX but have not been reported previously with variants affecting the aristaless domain of ARX as in this case. Dystonic episodes posed a challenge in recognition and treatment, including confusion with status epilepticus. We discuss the difficulties in diagnosis and management of status dystonicus, an underreported life-threatening emergency in children.

Noninvasive continuous cardiac output and cerebral perfusion monitoring in term infants with neonatal encephalopathy: assessment of feasibility and reliability.

BackgroundNoninvasive hemodynamic monitoring of infants with neonatal encephalopathy (NE) undergoing therapeutic hypothermia (TH) would be a potentially useful clinical tool. We aimed to assess the feasibility and reliability of noninvasive cardiac output monitoring (NICOM) and near-infrared spectroscopy (NIRS) in this cohort.MethodsNICOM and NIRS were commenced to measure cardiac output (CO), systemic vascular resistance (SVR), blood pressure (BP), and cerebral regional oxygen saturations (SctO2) during TH and rewarming. NICOM measures of CO were also compared with simultaneous echocardiography-derived CO (echo-CO).ResultsTwenty infants with a median gestation of 40 weeks were enrolled. There was a strong correlation between NICOM- and echo-CO (r2=0.79, P<0.001). NICOM-CO was systematically lower than echo-CO with a bias of 27% (limits of agreement 3-51%). NICOM illustrated lower CO during TH, which increased during rewarming. SctO2 increased over the first 30 h of TH and stayed high for the remainder of the study. There was a rise in SVR over the first 30 h of TH and a decrease during rewarming (all P<0.05).ConclusionsNoninvasive hemodynamic assessment of infants with NE is feasible and illustrates potentially important changes. Larger studies are needed to assess the clinical applicability of those methods in this cohort.

Left ventricular rotational mechanics in infants with hypoxic ischemic encephalopathy and preterm infants at 36 weeks postmenstrual age: A comparison with healthy term controls.

BACKGROUND AND AIMS: There is a paucity of data on left ventricle (LV) rotational physiology in neonates. We aimed to assess rotational mechanics in infants with hypoxic ischemic encephalopathy (HIE) and premature infants (<32 weeks) at 36 weeks postmenstrual age (PMA) (preterm group) and compare them with healthy term controls (term controls). We also compared the parameters in preterm infants with and without chronic lung disease (CLD). METHODS: Echocardiography was performed within 48 hours of birth or at 36 weeks PMA. LV basal and apical rotation, twist (and torsion=twist/LV length), twist rate (LVTR), and untwist rate (LVUTR) were measured. One-way ANOVA was used to compare values. RESULTS: There was no difference in gestation (40.0 [39.1-40.3] vs 39.9 [39.0-40.9], P>.05) or birthweight (3.7 [3.4-4.1] vs 3.5 [3.2-3.9], P>.05) between the HIE group (n=16) and term controls (n=30). The preterm group (n=35) had a gestation and weight of 36.0 [34.6-36.3] weeks and 2.3 [2.0-2.4] kg. The HIE group had lower twist, torsion, LVTR, and LVUTR than the other two groups. The preterm group had a more negative (clockwise) basal rotation while the term group had a more positive (counterclockwise) apical rotation. Preterm infants with CLD had higher apical rotation, twist, and torsion when compared to infants without CLD. CONCLUSION: Infants with HIE have reduced rotational mechanics. Preterm infants at 36 weeks PMA have comparable measurements of twist to term infants. This is achieved by predominant basal rather than apical rotation. Infants with CLD have increased apical rotation.

Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2.

Childhood onset motor neuron diseases or neuronopathies are a clinically heterogeneous group of disorders. A particularly severe subgroup first described in 1894, and subsequently called Brown-Vialetto-Van Laere syndrome, is characterized by progressive pontobulbar palsy, sensorineural hearing loss and respiratory insufficiency. There has been no treatment for this progressive neurodegenerative disorder, which leads to respiratory failure and usually death during childhood. We recently reported the identification of SLC52A2, encoding riboflavin transporter RFVT2, as a new causative gene for Brown-Vialetto-Van Laere syndrome. We used both exome and Sanger sequencing to identify SLC52A2 mutations in patients presenting with cranial neuropathies and sensorimotor neuropathy with or without respiratory insufficiency. We undertook clinical, neurophysiological and biochemical characterization of patients with mutations in SLC52A2, functionally analysed the most prevalent mutations and initiated a regimen of high-dose oral riboflavin. We identified 18 patients from 13 families with compound heterozygous or homozygous mutations in SLC52A2. Affected individuals share a core phenotype of rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia, severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs), hearing loss, optic atrophy and respiratory insufficiency. We demonstrate that SLC52A2 mutations cause reduced riboflavin uptake and reduced riboflavin transporter protein expression, and we report the response to high-dose oral riboflavin therapy in patients with SLC52A2 mutations, including significant and sustained clinical and biochemical improvements in two patients and preliminary clinical response data in 13 patients with associated biochemical improvements in 10 patients. The clinical and biochemical responses of this SLC52A2-specific cohort suggest that riboflavin supplementation can ameliorate the progression of this neurodegenerative condition, particularly when initiated soon after the onset of symptoms.