A locus on mouse Ch10 influences susceptibility to limbic seizure severity: fine mapping and in silico candidate gene analysis.

Identification of genes contributing to mouse seizure susceptibility can reveal novel genes or pathways that provide insight into human epilepsy. Using mouse chromosome substitution strains and interval-specific congenic strains (ISCS), we previously identified an interval conferring pilocarpine-induced limbic seizure susceptibility on distal mouse chromosome 10 (Ch10). We narrowed the region by generating subcongenics with smaller A/J Ch10 segments on a C57BL/6J (B6) background and tested them with pilocarpine. We also tested pilocarpine-susceptible congenics for 6-Hz ECT (electroconvulsive threshold), another model of limbic seizure susceptibility, to determine whether the susceptibility locus might have a broad effect on neuronal hyperexcitability across more than one mode of limbic seizure induction. The ISCS Line 1, which contained the distal 2.7 Mb segment from A/J (starting at rs29382217), was more susceptible to both pilocarpine and ECT. Line 2, which was a subcongenic of Line 1 (starting at rs13480828), was not susceptible, thus defining a 1.0 Mb critical region that was unique to Line 1. Bioinformatic approaches identified 45 human orthologs within the unique Line 1 susceptibility region, the majority syntenic to human Ch12. Applying an epilepsy network analysis of known and suspected excitability genes and examination of interstrain genomic and brain expression differences revealed novel candidates within the region. These include Stat2, which plays a role in hippocampal GABA receptor expression after status epilepticus, and novel candidates Pan2, Cdk2, Gls2 and Cs, which are involved in neural cell differentiation, cellular remodeling and embryonic development. Our strategy may facilitate discovery of novel human epilepsy genes.

Acute and chronic responses to the convulsant pilocarpine in DBA/2J and A/J mice.

Characterizing the responses of different mouse strains to experimentally-induced seizures can provide clues to the genes that are responsible for seizure susceptibility, and factors that contribute to epilepsy. This approach is optimal when sequenced mouse strains are available. Therefore, we compared two sequenced strains, DBA/2J (DBA) and A/J. These strains were compared using the chemoconvulsant pilocarpine, because pilocarpine induces status epilepticus, a state of severe, prolonged seizures. In addition, pilocarpine-induced status is followed by changes in the brain that are associated with the pathophysiology of temporal lobe epilepsy (TLE). Therefore, pilocarpine can be used to address susceptibility to severe seizures, as well as genes that could be relevant to TLE. A/J mice had a higher incidence of status, but a longer latency to status than DBA mice. DBA mice exhibited more hippocampal pyramidal cell damage. DBA mice developed more ectopic granule cells in the hilus, a result of aberrant migration of granule cells born after status. DBA mice experienced sudden death in the weeks following status, while A/J mice exhibited the most sudden death in the initial hour after pilocarpine administration. The results support previous studies of strain differences based on responses to convulsants. They suggest caution in studies of seizure susceptibility that are based only on incidence or latency. In addition, the results provide new insight into the strain-specific characteristics of DBA and A/J mice. A/J mice provide a potential resource to examine the progression to status. The DBA mouse may be valuable to clarify genes regulating other seizure-associated phenomena, such as seizure-induced neurogenesis and sudden death.

Classification of partial seizure symptoms in genetic studies of the epilepsies.

OBJECTIVES: To develop standardized definitions for classification of partial seizure symptoms for use in genetic research on the epilepsies, and evaluate inter-rater reliability of classifications based on these definitions. METHODS: The authors developed the Partial Seizure Symptom Definitions (PSSD), which include standardized definitions of 41 partial seizure symptoms within the sensory, autonomic, aphasic, psychic, and motor categories. Based on these definitions, two epileptologists independently classified partial seizures in 75 individuals from 34 families selected because one person had ictal auditory symptoms or aphasia. The data used for classification consisted of standardized diagnostic interviews with subjects and family informants, and medical records obtained from treating neurologists. Agreement was assessed by kappa. RESULTS: Agreement between the two neurologists using the PSSD was "substantial" or "almost perfect" for most symptom categories. CONCLUSIONS: Use of standardized definitions for classification of partial seizure symptoms such as those in the Partial Seizure Symptom Definitions should improve reliability and accuracy in future genetic studies of the epilepsies.

Familial clustering of seizure types within the idiopathic generalized epilepsies.

OBJECTIVE: To examine the genetic relationships among epilepsies with different seizure types--myoclonic, absence, and generalized tonic-clonic--within the idiopathic generalized epilepsies (IGEs). BACKGROUND: Careful phenotype definition in the epilepsies may allow division into groups that share susceptibility genes. Examination of seizure type, a phenotypic characteristic less complex than IGE syndrome, may help to define more homogeneous subgroups. METHODS: Using the approach that found evidence of distinct genetic effects on myoclonic vs absence seizures in families from the Epilepsy Family Study of Columbia University, the authors examined an independent sample of families from Australia and Israel. They also examined the familial clustering of generalized tonic-clonic seizures (GTCs) within the IGEs in two combined data sets. Families were defined as concordant if all affected members had the same type of seizure or IGE syndrome, as appropriate for the analysis performed. RESULTS: The proportion of families concordant for myoclonic vs absence seizures was greater than expected by chance in the Australian families. In addition, GTCs clustered in families with IGEs to a degree greater than expected by chance. CONCLUSIONS: These results provide additional evidence for distinct genetic effects on myoclonic vs absence seizures in an independent set of families and suggest that there is a genetic influence on the occurrence of generalized tonic-clonic seizures within the idiopathic generalized epilepsies.

LGI1 mutations in autosomal dominant partial epilepsy with auditory features.

OBJECTIVE: S: Mutations in LGI1 cause autosomal dominant partial epilepsy with auditory features (ADPEAF), a form of familial temporal lobe epilepsy with auditory ictal manifestations. The authors aimed to determine what proportion of ADPEAF families carries a mutation, to estimate the penetrance of identified mutations, and to identify clinical features that distinguish families with and without mutations. METHODS: The authors sequenced LGI1 in 10 newly described ADPEAF families and analyzed clinical features in these families and others with mutations reported previously. RESULTS: Three of the families had missense mutations in LGI1 (C42R, I298T, and A110D). Penetrance was 54% in eight families with LGI1 mutations the authors have identified so far (five reported previously and three reported here). Excluding the original linkage family, the authors have found mutations in 50% (7/14) of tested families. Families with and without mutations had similar clinical features, but those with mutations contained significantly more subjects with auditory symptoms and significantly fewer with autonomic symptoms. In families with mutations, the most common auditory symptom type was simple, unformed sounds (e.g., buzzing and ringing). In two of the newly identified families with mutations, some subjects with mutations had idiopathic generalized epilepsies. CONCLUSIONS: LGI1 mutations are a common cause of autosomal dominant partial epilepsy with auditory features. Current data do not reveal a clinical feature that clearly predicts which families with autosomal dominant partial epilepsy with auditory features have a mutation. Some families with LGI1 mutations contain individuals with idiopathic generalized epilepsies. This could result from either an effect of LGI1 on risk for generalized epilepsy or an effect of co-occurring idiopathic generalized epilepsy-specific genes in these families.

Genetic influences on myoclonic and absence seizures.

OBJECTIVE: To examine the relationship between genotype and phenotype in idiopathic generalized epilepsies (IGEs) using a novel approach that focuses on seizure type rather than syndrome. METHODS: The authors evaluated whether the genetic effects on myoclonic seizures differ from the genetic effects on absence seizures. For this purpose, they studied 34 families containing 2 or more members with IGEs and assessed whether the number of families concordant for seizure type exceeded that expected by chance. The authors performed a similar analysis to examine the genetic contributions to juvenile myoclonic epilepsy (JME), juvenile absence epilepsy (JAE), and childhood absence epilepsy (CAE). RESULTS: The observed number of families concordant for seizure type (myoclonic, absence, or both) was greater than expected (20 vs 7.51; p < 0.0001). The observed number of families concordant for syndrome was greater than expected when JME was compared with absence epilepsies (JAE+CAE) (17 vs 11.9; p < 0.012) but not when JAE was compared with CAE (8 vs 6.82; p = 0.516). CONCLUSIONS: These results provide evidence for distinct genetic effects on absence and myoclonic seizures, suggesting that examining the two seizure types separately would be useful in linkage studies of idiopathic generalized epilepsies. The approach presented here can also be used to discover other clinical features that could direct division of epilepsies into groups likely to share susceptibility genes.

Autosomal dominant partial epilepsy with auditory features: defining the phenotype.

The authors previously reported linkage to chromosome 10q22-24 for autosomal dominant partial epilepsy with auditory features. This study describes seizure semiology in the original linkage family in further detail. Auditory hallucinations were most common, but other sensory symptoms (visual, olfactory, vertiginous, and cephalic) were also reported. Autonomic, psychic, and motor symptoms were less common. The clinical semiology points to a lateral temporal seizure origin. Auditory hallucinations, the most striking clinical feature, are useful for identifying new families with this synome.

Tympanoplasty for the anterior-superior perforation in children.

Anterior-superior perforations of the tympanic membrane have proven more difficult to repair than other perforations, and many investigators have found such repairs to be problematic. We report a technique in which the tympanic membrane is released from the malleus, and the graft is placed medical to the remnant, lateral to the malleus, and medial to the tympanomeatal flap. In a series of 42 cases the short-term surgical success rate (represented by an intact graft at 6 months) was 98%, with 95% of ears remaining free of reperforation to the end of follow-up. Postoperatively, 90% of children had an air-bone gap of 20 dB or less and 100% of children had an air-bone gap of 30 dB or less. Eighty-seven percent of subjects demonstrated a speech reception threshold (SRT) of 20 dB or better, whereas 100% of subjects demonstrated an SRT of 30 dB or better. These results compare favorably with those reported at this institution for repair of perforations of any quadrant in children, and those of other investigators for anterior superior perforations in adults.