Characterizing TMEM63B: a novel mechanosensitive ion channel coding gene whose mutations cause developmental and epileptic encephalopathy with white matter abnormalities

This project has been funded thanks to the Joint Call Fondazione Cariplo and Fondazione Telethon 2025.

Developmental and epileptic encephalopathies (DEEs) are severe neurodevelopmental disorders characterized by intellectual disability and early-onset epilepsy, imposing a main medical and socio-economic burden. Using advanced genetic testing, we recently identified 17 patients carrying variants of TMEM63B who exhibited severe developmental delay, drug-resistant neonatal or early infantile epilepsy, and progressive neurodegeneration. TMEM63B is an ion channel that allows cells to respond to mechanical and pressure stimuli by converting physical forces into electrical signals. Through functional studies, we demonstrated that some of the identified variants cause an activation of the channel without specific stimuli and impair the response to calcium without affecting channel sensitivity to the osmotic stimulation. To model the effects exerted by TMEM63B variants in the patients’ brains, we will study different patient-specific brain cell populations obtained by differentiating induced pluripotent stem cells (iPSCs) reprogrammed from skin cells of two patients carrying two different TMEM63B variants. We will first generate the target brain cell population using specific differentiation protocols and assess whether the two variants alter the TMEM63B protein expression or localization. Then, we will evaluate whether they affect channel properties and cell function in normal conditions and under specific channel-activating stimuli. Characterizing morpho-functional anomalies induced by TMEM63B variants in brain cell populations involved in some of the symptoms observed in our patients (i.e. epilepsy, white matter damage and neurodegeneration) will be instrumental for defining the pathophysiological mechanisms underlying TMEM63B-related DEE and speed-up the identification of possible therapeutic targets.