Spectrum of KV 2.1 Dysfunction in KCNB1-Associated Neurodevelopmental Disorders.

OBJECTIVE: Pathogenic variants in KCNB1, encoding the voltage-gated potassium channel KV 2.1, are associated with developmental and epileptic encephalopathy (DEE). Previous functional studies on a limited number of KCNB1 variants indicated a range of molecular mechanisms by which variants affect channel function, including loss of voltage sensitivity, loss of ion selectivity, and reduced cell-surface expression. METHODS: We evaluated a series of 17 KCNB1 variants associated with DEE or other neurodevelopmental disorders (NDDs) to rapidly ascertain channel dysfunction using high-throughput functional assays. Specifically, we investigated the biophysical properties and cell-surface expression of variant KV 2.1 channels expressed in heterologous cells using high-throughput automated electrophysiology and immunocytochemistry-flow cytometry. RESULTS: Pathogenic variants exhibited diverse functional defects, including altered current density and shifts in the voltage dependence of activation and/or inactivation, as homotetramers or when coexpressed with wild-type KV 2.1. Quantification of protein expression also identified variants with reduced total KV 2.1 expression or deficient cell-surface expression. INTERPRETATION: Our study establishes a platform for rapid screening of KV 2.1 functional defects caused by KCNB1 variants associated with DEE and other NDDs. This will aid in establishing KCNB1 variant pathogenicity and the mechanism of dysfunction, which will enable targeted strategies for therapeutic intervention based on molecular phenotype. ANN NEUROL 2019;86:899-912.

Preliminary Evidence that Melatonin Is not a Biomarker in Children and Adolescents With Episodic Migraine.

BACKGROUND: To date, there have not been reliable biomarkers to identify impending migraine episodes. A prior study in adults with migraine demonstrated a reduction in the urinary metabolic substrate of melatonin (urinary 6-sulfatoxymelatonin; aMT6s) during a migraine. The aim of this study was to examine whether evening urinary melatonin metabolite levels could predict migraine the next day in children and adolescents with migraine. METHODS: Twenty-one children and adolescents with migraine (aged 5-17 years) were recruited to this observational study conducted at UC San Francisco to provide urine samples for 10 days and maintain a prospective headache diary during the same period. Nightly melatonin metabolite 6-sulfatoxymelatonin in urine was assayed and results from nights preceding migraine were compared to nights preceding a non-headache day. RESULTS: Mean (±SD) aMT6s levels the night prior to a migraine attack were 56.2 ± 39.0 vs 55.4 ± 46.6 ng/mL (P = .915), and mean melatonin metabolite levels the night following migraine were 55.5 ± 46.9 vs 57.0 ± 37.7 ng/mL (P = .841). However, in post hoc exploratory analyses, aMT6s levels were lower the night before a migraine in those who experienced aura or premonitory symptoms. CONCLUSION: While urinary melatonin metabolites do not predict migraine attacks in children and adolescents overall, they may be predictive in those who experience premonitory phase symptoms as part of their migraine attacks.

Neck-Tongue syndrome: A systematic review.

Objective Neck-Tongue syndrome (NTS) is characterized by brief attacks of neck or occipital pain, or both, brought out by abrupt head turning and accompanied by ipsilateral tongue symptoms. As the disorder is rare, we undertook a systematic review of the literature to identify all reported cases in order to phenotype clinically the disorder and subsequently inform clinical diagnostic criteria. Methods Two electronic databases were searched using the search term "neck tongue syndrome". All English language references were reviewed in full. Cases were abstracted using a standardized abstraction form and the references of the retrieved articles were reviewed by hand to identify additional references and cases. Conference proceedings from recent headache meetings were searched. We also report six new cases from our centers. Results There were 39 primary cases, 56% of which were female. Mean age (SD) at onset was 16 (12) years. Twenty (53%) experienced neck pain, seven (18%) occipital pain, and 11 (29%) both. Pain was most often sharp or stabbing and severe, lasting several seconds to several minutes. Eleven experienced numbness and/or tingling in the neck/occiput following the pain. Thirty-six had an accompanying tongue sensory disturbance and three a motor/posture disturbance; five had both. Thirteen had other headaches, and four a family history of Neck-Tongue syndrome. Conclusions Neck-Tongue syndrome typically has pediatric or adolescent onset, suggesting that ligamentous laxity during growth and development may facilitate transient subluxation of the lateral atlantoaxial joint with sudden head turning. Familial cases suggest a genetic predisposition in some individuals. Neck-Tongue syndrome should be re-instated in the International Classification of Headache Disorders.

Missense-depleted regions in population exomes implicate ras superfamily nucleotide-binding protein alteration in patients with brain malformation.

Genomic sequence interpretation can miss clinically relevant missense variants for several reasons. Rare missense variants are numerous in the exome and difficult to prioritise. Affected genes may also not have existing disease association. To improve variant prioritisation, we leverage population exome data to identify intragenic missense-depleted regions (MDRs) genome-wide that may be important in disease. We then use missense depletion analyses to help prioritise undiagnosed disease exome variants. We demonstrate application of this strategy to identify a novel gene association for human brain malformation. We identified de novo missense variants that affect the GDP/GTP-binding site of ARF1 in three unrelated patients. Corresponding functional analysis suggests ARF1 GDP/GTP-activation is affected by the specific missense mutations associated with heterotopia. These findings expand the genetic pathway underpinning neurologic disease that classically includes FLNA. ARF1 along with ARFGEF2 add further evidence implicating ARF/GEFs in the brain. Using functional ontology, top MDR-containing genes were highly enriched for nucleotide-binding function, suggesting these may be candidates for human disease. Routine consideration of MDR in the interpretation of exome data for rare diseases may help identify strong genetic factors for many severe conditions, infertility/reduction in reproductive capability, and embryonic conditions contributing to preterm loss.