Electrical activity emerges in the third trimester of pregnancy, plays an important role in the construction of cortical maps, and is impaired in patients with severe early epileptic encephalopathies (EOEE). EOEE are rare and severe epileptic syndromes characterized by epilepsy that begins within the first three months of life and is associated with rapid deterioration of motor, cognitive and behavioral skills. There is a genetic basis for the EOEE. Together with other laboratories, the investigators have identified de novo pathogenic variants in the KCNQ2 gene encoding the Kv7.2 subunit of the Kv7 / M potassium channel, a channel known to control neuronal excitability in the brain and spinal cord. via the current M (IM). Pathogenic variants of the KCNQ2 gene represent the main cause of EOEE and the term KCNQ2-related epileptic encephalopathy (KCNQ2-REE) is now used to define this condition. KCNQ2-REE patients have a remarkably homogeneous phenotype at the start, with epilepsy that begins in the first days after birth, seizures that result in tonic muscle spasms that last from 1 to 10 seconds, and an interictal EEG called suppression-burst. That is, paroxysmal bursts of activity interspersed with periods of electrical silence. In this group, more than 50% of the patients present a remission of the epilepsy and a quasi-normalization of the EEG which can occur a few weeks to several months after the onset of the seizures. Despite this positive evolution in terms of seizures, the developmental progression is abnormal and the phenotype is severe with an absence of language, autistic behavior and a subsequent development of motor disorders such as diplegia, spasticity, ataxia or dystonia. The ambition of this project is to increase knowledge of epileptic encephalopathies linked to KCNQ2 at the clinical and molecular levels, to decipher the pathophysiological mechanisms and to propose therapeutic strategies. This project aims to better describe the clinical, EEG, imaging, developmental and long-term follow-up characteristics of patients carrying the KCNQ2 mutation identified in the laboratory.