Heterozygous inherited mutations in their principle subunits K<sub>v</sub> 7.2/KCNQ2 and K<sub>v</sub> 7.3/KCNQ3 cause benign familial neonatal epilepsy whereas patients with de novo heterozygous K<sub>v</sub> 7.2 mutations are associated with early-onset epileptic encephalopathy and neurodevelopmental disorders characterized by intellectual disability, developmental delay and autism.
SCN2A mutations have been described in a very broad spectrum of clinical phenotypes including benign (familial) neonatal/infantile seizures and early infantile epileptic encephalopathies (EIEE) as Ohtahara syndrome (OS), Dravet syndrome (DS), epilepsy of infancy with migrating focal seizures and West syndrome (WS).
Variants in the SCN2A gene cause a broad spectrum of epilepsy syndromes of variable severity including benign neonatal-infantile epilepsy (BFNIE), developmental and epileptic encephalopathies (DEE), and other neuropsychiatric disorders.
Linkage mapping in two mutation-negative BFNE families excluded linkage to KCNQ2, KCNQ3, and SCN2A, but linkage to KCNQ2could not be excluded in the third mutation-negative BFNE family.
Thirty-three families fulfilled clinical criteria for benign familial neonatal epilepsy (BFNE); 27 of these families had KCNQ2 mutations, one had a KCNQ3 mutation, and two had SCN2A mutations.
In addition to benign familial neonatal epilepsy (BFNE), KCNQ2 mutations have been recently found in families with one or more family members with a severe outcome, including drug-resistant seizures with psychomotor retardation, electroencephalogram (EEG) suppression-burst pattern (Ohtahara syndrome), and distinct neuroradiological features, a condition that was named "KCNQ2 encephalopathy."
In addition to benign familial neonatal epilepsy (BFNE), KCNQ2 mutations have been recently found in families with one or more family members with a severe outcome, including drug-resistant seizures with psychomotor retardation, electroencephalogram (EEG) suppression-burst pattern (Ohtahara syndrome), and distinct neuroradiological features, a condition that was named "KCNQ2 encephalopathy."
To demonstrate the functionality of the kick-in methodology, we generated two mouse lines with separate mutant versions of the voltage-dependent potassium channel Kv7.2 (Kcnq2): p.Tyr284Cys (Y284C) and p.Ala306Thr (A306T); both variations have been associated with benign familial neonatal epilepsy.
Heterozygous mutations in the genes KCNQ2 and SCN2A cause the two other autosomal dominant seizure disorders of infancy: benign familial neonatal epilepsy and benign familial neonatal-infantile epilepsy.
Missense mutations in SCN2A, encoding the brain sodium channel NaV 1.2, have been described in benign familial neonatal-infantile seizures (BFNIS), a self-limiting disorder, whereas several SCN2A de novo nonsense mutations have been found in patients with more severe phenotypes including epileptic encephalopathy.
Interestingly, in the majority of the cases, the initial epileptic features of these patients were comparable to those previously described in the case of benign familial neonatal epilepsy (BFNE) also caused by KCNQ2 mutations.
PRRT2 mutations were recently identified in benign familial infantile epilepsy (BFIE) and infantile convulsions with paroxysmal choreoathetosis (ICCA) but no abnormalities have so far been identified in their phenotypically similar seizure disorder of benign convulsions with mild gastroenteritis (CwG), while mutations in KCNQ2 and KCNQ3 have been recognized in benign familial neonatal epilepsy (BFNE).
Mutations in SCN2A, the gene encoding α2 subunit of the neuronal sodium channel, are associated with a variety of epilepsies: benign familial neonatal-infantile seizures (BFNIS); genetic epilepsy with febrile seizures plus (GEFS+); Dravet syndrome (DS); and some intractable childhood epilepsies.
KCNQ2-5 channels are predominantly expressed in neurons and are important determinants of cellular excitability, as indicated by the occurrence of human genetic mutations in KCNQ channels that underlie inheritable disorders including, in the case of KCNQ2/3, the syndrome of benign familial neonatal convulsions.
The molecular pathogenesis of benign childhood epilepsy with centrotemporal spikes (BECTS) remains unclear whereas mutations of the KCNQ2 and KCNQ3 genes have been identified as causes of benign familial neonatal convulsions.
The band 2q24 constitutes the smallest commonly deleted segment in these patients, and contains the voltage-gated sodium channel genes SCN1A and SCN2A, associated with Dravet syndrome and benign familial neonatal-infantile seizures, respectively.
We identified two novel SCN2A mutations causing benign familial neonatal-infantile seizures and analysed the functional consequences of these mutations in a neonatal and an adult splice variant of the human Na(+) channel Na(V)1.2 expressed heterologously in tsA201 cells together with beta1 and beta2 subunits.