Mutations in the GABAA receptor ␥2 subunit are associated with childhood absence epilepsy and febrile seizures. To understand better the molecular basis of absence epilepsy in man, we developed a mouse model harboring a ␥2 subunit point mutation (R43Q) found in a large Australian family. Mice heterozygous for the mutation demonstrated behavioral arrest associated with 6-to 7-Hz spike-and-wave discharges, which are blocked by ethosuximide, a first-line treatment for absence epilepsy in man. Seizures in the mouse showed an abrupt onset at around age 20 days corresponding to the childhood nature of this disease. Reduced cell surface expression of ␥2(R43Q) was seen in heterozygous mice in the absence of any change in ␣1 subunit surface expression, ruling out a dominant-negative effect. GABA Amediated synaptic currents recorded from cortical pyramidal neurons revealed a small but significant reduction that was not seen in the reticular or ventrobasal thalamic nuclei. We hypothesize that a subtle reduction in cortical inhibition underlies childhood absence epilepsy seen in humans harboring the R43Q mutation.GABAA receptor ͉ genetics ͉ electroencephalogram ͉ trafficking ͉ synapse G ABA A receptors in the adult brain are important for inhibiting the activity of neurons in which they reside. Dysfunction of these receptors caused by familial mutations can give rise to febrile seizures (FS) and a variety of generalized epilepsy phenotypes (1-3). To date, five mutations have been reported in the GABA A ␥2 subunit gene with an array of seizure types seen in patients (1, 4-7). Childhood absence epilepsy (CAE) and FS were the main phenotypes in a large Australian family with an arginine to glutamine mutation at position 43 (R43Q) in the GABA A ␥2 subunit gene (1,8).Understanding how the GABA A ␥2(R43Q) mutation causes epilepsy is difficult. GABA A receptors themselves serve several roles. They regulate moment-to-moment brain function (9), play an important role in brain development (10), and have key roles in neuronal plasticity (11, 12) and response to brain injury (13-15). Epilepsy itself is a complex phenomenon involving the interaction of multiple cell types in networks within and between different brain regions that are likely to be influenced by GABA A receptor dysfunction caused by the R43Q mutation. Furthermore, in vitro analyses of the consequences of this mutation have shown inconsistent findings with a range of deficits in receptor pharmacology, trafficking, kinetics, or assembly (16-23) potentially implicated in disease pathogenesis.Clearly, the complex nature of epileptogenesis demands in vivo investigation. Genetic epilepsies provide a framework on which to investigate the consequences of causative mutations at a range of organizational levels within the brain, creating a chain of understanding from molecules to behavior. Linking this chain is impossible in humans because of the highly invasive methodology required and is severely limited in heterologous expression systems that lack necessary complexity. Mice mod...

Objective: To determine the genes underlying Dravet syndrome in patients who do not have an SCN1A mutation on routine testing. Methods:We performed whole-exome sequencing in 13 SCN1A-negative patients with Dravet syndrome and targeted resequencing in 67 additional patients to identify new genes for this disorder.Results: We detected disease-causing mutations in 2 novel genes for Dravet syndrome, with mutations in GABRA1 in 4 cases and STXBP1 in 3. Furthermore, we identified 3 patients with previously undetected SCN1A mutations, suggesting that SCN1A mutations occur in even more than the currently accepted ;75% of cases. Conclusions:We show that GABRA1 and STXBP1 make a significant contribution to Dravet syndrome after SCN1A abnormalities have been excluded. Our results have important implications for diagnostic testing, clinical management, and genetic counseling of patients with this devastating disorder and their families. Neurology ® 2014;82:1245-1253 GLOSSARY cDNA 5 complementary DNA; dHPLC 5 denaturing high-performance liquid chromatography; FS 5 febrile seizures; GABA 5 g-aminobutyric acid; GEFS1 5 genetic epilepsy with febrile seizures plus; WES 5 whole-exome sequencing; WT 5 wild-type.

The P2X(7) receptor is a ligand-gated cation channel that is highly expressed on mononuclear leukocytes and that mediates ATP-induced apoptosis and killing of intracellular pathogens. There is a wide variation in P2X(7) receptor function between subjects, explained in part by four loss-of-function polymorphisms (R307Q, E496A, I568N, and a 5'-intronic splice site polymorphism), as well as rare mutations. In this study, we report the allele frequencies of 11 non-synonymous P2X(7) polymorphisms and describe a fifth loss-of-function polymorphism in the gene (1096C --> G), which changes Thr(357) to Ser (T357S) with an allele frequency of 0.08 in the Caucasian population. P2X(7) function was measured by ATP-induced ethidium(+) influx into peripheral blood lymphocytes and monocytes and, when compared with wild-type subjects, was reduced to 10-65% in heterozygotes, 1-18% in homozygotes, and 0-10% in compound heterozygotes carrying T357S and a second loss-of-function polymorphism. Overexpression of the T357S mutant P2X(7) in either HEK-293 cells or Xenopus oocytes gave P2X(7) function of approximately 50% that of wild-type constructs. Differentiation of monocytes to macrophages, which also up-regulates P2X(7), restored P2X(7) function to near normal in cells heterozygous for T357S and to a value 50-65% of wild-type in cells homozygous for T357S or compound heterozygous for T357S/E496A. However, macrophages from subjects that are compound heterozygous for either T357S/R307Q or T357S/stop codon had near-to-absent P2X(7) function. These functional deficits induced by T357S were paralleled by impaired ATP-induced apoptosis and mycobacteria killing in macrophages from these subjects. Lymphocytes, monocytes, and macrophages from subjects homozygous for T357S or compound heterozygous for T357S and a second loss-of-function allele have reduced or absent P2X(7) receptor function.