Stretch-activated ion channel TMEM63B associates with developmental and epileptic encephalopathies and progressive neurodegeneration

By converting physical forces into electrical signals or triggering intracellular cascades, stretch-activated ion channels (SACs) allow the cell to respond to osmotic and mechanical stress. Knowledge of the pathophysiological mechanisms underlying associations of SACs with human disease is limited. Here we describe 16 unrelated patients, with severe early onset developmental and epileptic encephalopathy (DEE), intellectual disability, and severe motor and cortical visual impairment, associated with progressive neurodegenerative brain changes, carrying ten distinct de novo variants of TMEM63B , encoding for a highly conserved SAC. Variants were missense, including the recurrent V44M in 7/16 patients, or in-frame, and affected conserved residues located in transmembrane regions of the protein. In 12 patients, haematological abnormalities co-occurred, such as macrocytosis and haemolysis, requiring blood transfusions in some. We modelled V44M, R443H, and T481N in transfected Neuro2a cells and demonstrated leak inward cation currents across the mutated channel even in isotonic conditions, while the response to hypo-osmotic challenge was impaired, as were the Ca2+ transients generated under hypo-osmotic stimulation. Ectopic expression of the V44M and G580C variants in Drosophila resulted in early death. TMEM63B -associated DEE represents a novel clinicopathological entity in which altered cation conductivity results in a severe neurological phenotype with progressive brain damage and early onset epilepsy, associated with haematological abnormalities in most patients. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Tuscany Region Call for Health 2018 (grant DECODE-EE); Fondazione Cassa di Risparmio di Firenze (Human Brain Optical Mapping Project); Broad Institute of MIT and Harvard Center for Mendelian Genomics (Broad CMG); National Human Genome Research Institute, the National Eye Institute, and the National Heart, Lung and Blood Institute grant UM1 HG008900; National Human Genome Research Institute grant R01 HG009141; Fondazione Telethon, Telethon Undiagnosed Diseases Program (grant GSP15001); Japan Agency for Medical Research and Development (AMED) under grant numbers JP22ek0109486, JP22ek0109549, and JP22ek0109493; Takeda Science Foundation; Australian NHMRC Centre for Research Excellence in Neurocognition (1117394) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Paediatric Ethics Committees of the Tuscany Region, Italy I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Data availability The data supporting the findings of this study are available within the article and/or its Supplementary material. Any additional raw data are available on request from the corresponding author.