The P2X 7 receptor is a ligand-gated cation-selective channel that mediates ATP-induced apoptosis of cells of the immune system. We and others have shown that P2X 7 is nonfunctional both in lymphocytes and monocytes from some subjects. To study a possible genetic basis we sequenced DNA coding for the carboxyl-terminal tail of P2X 7 . In 9 of 45 normal subjects a heterozygous nucleotide substitution (1513A3 C) was found, whereas 1 subject carried the homozygous substitution that codes for glutamic acid to alanine at amino acid position 496. Surface expression of P2X 7 on lymphocytes was not affected by this E496A polymorphism, demonstrated both by confocal microscopy and immunofluorescent staining. Monocytes and lymphocytes from the E496A homozygote subject expressed nonfunctional receptor, whereas heterozygotes showed P2X 7 function that was half that of germline P2X 7 . Results of transfection experiments showed that the mutant P2X 7 receptor was nonfunctional when expressed at low receptor density but regained function at a high receptor density. This density dependence of mutant P2X 7 function was also seen on differentiation of fresh monocytes to macrophages with interferon-␥, which up-regulated mutant P2X 7 and partially restored its function. P2X 7 -mediated apoptosis of lymphocytes was impaired in homozygous mutant P2X 7 compared with germline (8.6 versus 35.2%). The data suggest that the glutamic acid at position 496 is required for optimal assembly of the P2X 7 receptor.Purinergic P2X 7 receptors are ligand-gated cation channels, present on cells of the immune and hemopoietic system, that have been shown to mediate the ATP-induced apoptotic death of monocytes (1), macrophages (2), and lymphocytes (3, 4). The P2X 7 receptor family has two transmembrane domains with intracellular amino and carboxyl termini and an oligomeric structure in the plasma membrane based on trimeric or larger complexes of identical subunits (5). Moreover, the P2X7 receptor does not appear to form heteropolymers with other P2X subtypes (6). The genes for both the rat and human P2X 7 receptors have now been cloned and show extensive homology (30 -40%) with the other members of the P2X receptor family, although P2X 7 differs in having a long carboxyl terminus of 240 amino acids from the inner membrane face (7). The genomic structure of P2X 7 consists of 13 exons, with exon 12 and exon 13 coding for the C-terminal tail of this molecule. There is strong evidence that this long carboxyl terminus is necessary for the permeability properties of the P2X 7 receptor, because truncation of this tail abolishes ATP-induced uptake of the fluorescent dye YoPro-1 (8). Studies of P2X 7 of macrophages or lymphocytes as well as of human embryonic kidney cells (HEK-293) expressing the cDNA for P2X 7 have shown features that are most unusual for a channel. These include the slow further dilatation following channel opening (9) and the activation of various proteases including membrane metalloproteases (10) and intracellular caspases (2, 11). The fully ...

We performed genomic mapping of a family with autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and intellectual and psychiatric problems, identifying a disease-associated region on chromosome 9q34.3. Whole-exome sequencing identified a mutation in KCNT1, encoding a sodium-gated potassium channel subunit. KCNT1 mutations were identified in two additional families and a sporadic case with severe ADNFLE and psychiatric features. These findings implicate the sodium-gated potassium channel complex in ADNFLE and, more broadly, in the pathogenesis of focal epilepsies.

Recent findings from studies of two families have shown that mutations in the GABA(A)-receptor gamma2 subunit are associated with generalized epilepsies and febrile seizures. Here we describe a family that has generalized epilepsy with febrile seizures plus (GEFS(+)), including an individual with severe myoclonic epilepsy of infancy, in whom a third GABA(A)-receptor gamma2-subunit mutation was found. This mutation lies in the intracellular loop between the third and fourth transmembrane domains of the GABA(A)-receptor gamma2 subunit and introduces a premature stop codon at Q351 in the mature protein. GABA sensitivity in Xenopus laevis oocytes expressing the mutant gamma2(Q351X) subunit is completely abolished, and fluorescent-microscopy studies have shown that receptors containing GFP-labeled gamma2(Q351X) protein are retained in the lumen of the endoplasmic reticulum. This finding reinforces the involvement of GABA(A) receptors in epilepsy.

SCN1A is part of the SCN1A-SCN2A-SCN3A gene cluster on chromosome 2q24 that encodes for alpha pore forming subunits of sodium channels. The 26 exons of SCN1A are spread over 100 kb of genomic DNA. Genetic defects in the coding sequence lead to generalized epilepsy with febrile seizures plus (GEFS+) and a range of childhood epileptic encephalopathies of varied severity (e.g., SMEI). All published mutations are collated. More than 100 novel mutations are spread throughout the gene with the more debilitating usually de novo. Some clustering of mutations is observed in the C-terminus and the loops between segments 5 and 6 of the first three domains of the protein. Functional studies so far show no consistent relationship between changes to channel properties and clinical phenotype. Of all the known epilepsy genes SCN1A is currently the most clinically relevant, with the largest number of epilepsy related mutations so far characterized.