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Biomedical subjects

I E Scheffer

Publications and source records attributed to I E Scheffer.

At least 37 records · Page 2Linked to original sources
PubMed2001

Mutant GABA(A) receptor gamma2-subunit in childhood absence epilepsy and febrile seizures.

Epilepsies affect at least 2% of the population at some time in life, and many forms have genetic determinants. We have found a mutation in a gene encoding a GABA(A) receptor subunit in a large family with epilepsy. The two main phenotypes were childhood absence epilepsy (CAE) and febrile seizures (FS). There is a recognized genetic relationship between FS and CAE, yet the two syndromes have different ages of onset, and the physiology of absences and convulsions is distinct. This suggests the mutation has age-dependent effects on different neuronal networks that influence the expression of these clinically distinct, but genetically related, epilepsy phenotypes. We found that the mutation in GABRG2 (encoding the gamma2-subunit) abolished in vitro sensitivity to diazepam, raising the possibility that endozepines do in fact exist and have a physiological role in preventing seizures.

Age of Onset↗
PubMed2001

Severe myoclonic epilepsy of infancy: extended spectrum of GEFS+?

PURPOSE: Severe myoclonic epilepsy of infancy (SMEI) is an intractable epilepsy of early childhood of unknown etiology. It is often associated with a family history of seizure disorders, but epilepsy phenotypes have not been well described. We sought to characterize the seizure phenotypes of relatives to better understand to the genetic basis of SMEI. METHODS: Probands with SMEI were identified, and systematic family studies were performed. Epilepsy syndromes were characterized in affected family members. RESULTS: Twelve probands with SMEI were identified. Eleven of the 12 probands with SMEI had a family history of seizures, and the twelfth was the result of a consanguineous marriage. We found that 16.7% of full siblings and 8.3% of parents had definite seizures. A total of 39 affected family members was identified. The most common phenotype was febrile seizures in 14, febrile seizures plus in seven, partial epilepsy in two, and there were single individuals with SMEI, myoclonic-astatic epilepsy, Lennox-Gastaut syndrome, and 13 cases with unclassified or unconfirmed seizures. CONCLUSIONS: The family history of seizures in SMEI is in keeping with the spectrum of seizure phenotypes seen in generalized epilepsy with febrile seizures plus (GEFS+). Our findings suggest that SMEI is the most severe phenotype in the GEFS+ spectrum.

Adolescent↗
PubMed2001

Genetics of the epilepsies.

Recent molecular insights into the human idiopathic epilepsies have suggested the central role of ligand-gated and voltage-gated ion channels in their etiology. So far, genes coding for sodium and potassium channel subunits as well as a nicotinic cholinergic receptor subunit have been identified for mendelian idiopathic epilepsies. In vitro and in vivo studies of mutations demonstrate functional changes, allowing new insights into mechanisms underlying hyperexcitability. Similarly, spontaneous murine epilepsy models have been associated with calcium channel molecular defects. The major challenge before us in understanding the genetics of the epilepsies is to identify genes for common forms of epilepsy following complex inheritance. Once such genes are discovered, the gene-gene-environmental interactions producing specific epilepsy syndromes can be explored.

Animals↗
PubMed2001

Near-total absence of the cerebellum.

We report five cases of near-total absence of the cerebellum with accompanying pontine hypoplasia. The cerebellar remnant in each case comprised only antero-superior masses, the posterior fossa being otherwise fluid filled. Three of these patients, two teenagers and an infant, presented a fairly consistent clinical and neuroradiological phenotype, and a few similar cases are recorded in the literature. The cerebellar remnant was irregular and asymmetrical, and no ventral pontine prominence was discernible. In at least the older two, cerebellar motor functions were not greatly compromised, and intellectual handicap was of a mild degree. We propose that these cases represent a distinct entity of "near-total absence of the cerebellum with flat ventral pons, and relatively mild clinical affection". All cases have been sporadic, implying that the risk of recurrence within a family may be low. Quite different clinical pictures, of considerably greater severity, are demonstrated in the remaining two cases. One had pontocerebellar hypoplasia type 2, while the other had a complex cerebellar and cerebral malformation.

Adolescent↗
PubMed2000

CHRNB2 is the second acetylcholine receptor subunit associated with autosomal dominant nocturnal frontal lobe epilepsy.

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is an uncommon, idiopathic partial epilepsy characterized by clusters of motor seizures occurring in sleep. We describe a mutation of the beta2 subunit of the nicotinic acetylcholine receptor, effecting a V287M substitution within the M2 domain. The mutation, in an evolutionary conserved region of CHRNB2, is associated with ADNFLE in a Scottish family. Functional receptors with the V287M mutation are highly expressed in Xenopus oocytes and characterized by an approximately 10-fold increase in acetylcholine sensitivity. CHRNB2 is a new gene for idiopathic epilepsy, the second acetylcholine receptor subunit implicated in ADNFLE.

Acetylcholine↗
PubMed2000

Phenotypic characterization of an alpha 4 neuronal nicotinic acetylcholine receptor subunit knock-out mouse.

Neuronal nicotinic acetylcholine receptors (nAChR) are present in high abundance in the nervous system (Decker et al., 1995). There are a large number of subunits expressed in the brain that combine to form multimeric functional receptors. We have generated an alpha(4) nAChR subunit knock-out line and focus on defining the behavioral role of this receptor subunit. Homozygous mutant mice (Mt) are normal in size, fertility, and home-cage behavior. Spontaneous unconditioned motor behavior revealed an ethogram characterized by significant increases in several topographies of exploratory behavior in Mt relative to wild-type mice (Wt) over the course of habituation to a novel environment. Furthermore, the behavior of Mt in the elevated plus-maze assay was consistent with increased basal levels of anxiety. In response to nicotine, Wt exhibited early reductions in a number of behavioral topographies, under both unhabituated and habituated conditions; conversely, heightened levels of behavioral topographies in Mt were reduced by nicotine in the late phase of the unhabituated condition. Ligand autoradiography confirmed the lack of high-affinity binding to radiolabeled nicotine, cytisine, and epibatidine in the thalamus, cortex, and caudate putamen, although binding to a number of discrete nuclei remained. The study confirms the pivotal role played by the alpha(4) nAChR subunit in the modulation of a number of constituents of the normal mouse ethogram and in anxiety as assessed using the plus-maze. Furthermore, the response of Mt to nicotine administration suggests that persistent nicotine binding sites in the habenulo-interpeduncular system are sufficient to modulate motor activity in actively exploring mice.

Aggression↗
PubMed2000

Periventricular nodular heterotopia in patients with filamin-1 gene mutations: neuroimaging findings.

BACKGROUND: The filamin-1 (FLN-1) gene is responsible for periventricular nodular heterotopia (PNH), which is an X-linked dominant neuronal migration disorder. OBJECTIVE: To review the clinical and imaging findings in a series of patients with documented filamin-1 mutations. MATERIALS AND METHODS: A retrospective review of the medical records and MR studies of a series of patients with PNH and confirmed FLN-1 mutations was done. There were 16 female patients (age range: .67-71 years; mean = 28.6) with filamin-1 gene mutations. RESULTS: In six of the patients the same mutation was inherited in four generations in one pedigree. In a second pedigree, a distinct mutation was found in two patients in two generations. In a third pedigree, a third mutation was found in four patients in two generations. The remaining four patients had sporadic de novo mutations that were not present in the parents. Ten patients had seizures, and all patients had normal intelligence. In all 16 patients MR demonstrated bilateral near-continuous PNH. There were no consistent radiographic or clinical differences between patients carrying different mutations. CONCLUSION: Patients with confirmed FLN-1 gene mutations are usually female and have a distinctive MR pattern of PNH. Other female patients with this same MR pattern probably harbor FLN-1 mutations and risk transmission to their progeny. This information is important for genetic counseling.

Adolescent↗
PubMed2000

A new locus for generalized epilepsy with febrile seizures plus maps to chromosome 2.

Generalized epilepsy with febrile seizures plus (GEFS+) is a recently recognized but relatively common form of inherited childhood-onset epilepsy with heterogeneous epilepsy phenotypes. We genotyped 41 family members, including 21 affected individuals, to localize the gene causing epilepsy in a large family segregating an autosomal dominant form of GEFS+. A genomewide search examining 197 markers identified linkage of GEFS+ to chromosome 2, on the basis of an initial positive LOD score for marker D2S294 (Z=4.4, recombination fraction [straight theta] = 0). A total of 24 markers were tested on chromosome 2q, to define the smallest candidate region for GEFS+. The highest two-point LOD score (Zmax=5.29; straight theta=0) was obtained with marker D2S324. Critical recombination events mapped the GEFS+ gene to a 29-cM region flanked by markers D2S156 and D2S311, with the idiopathic generalized epilepsy locus thereby assigned to chromosome 2q23-q31. The existence of the heterogeneous epilepsy phenotypes in this kindred suggests that seizure predisposition determined by the GEFS+ gene on chromosome 2q could be modified by other genes and/or by environmental factors, to produce the different seizure types observed.

Age of Onset↗
PubMed2000

Genetics of the epilepsies.

Recent molecular insights into the human idiopathic epilepsies have suggested the central role of ligand-gated and voltage-gated ion channels in their etiology. So far, genes coding for sodium and potassium channel subunits as well as a nicotinic cholinergic receptor subunit have been identified for Mendelian idiopathic epilepsies. In vitro and in vivo studies of mutations demonstrate functional changes, allowing new insights in mechanisms underlying hyperexcitability. Similarly, spontaneous murine epilepsy models have been associated with calcium channel molecular defects. The major challenge before us in understanding the genetics of the epilepsies is to identify genes for common forms of epilepsy following complex inheritance. Once such genes are discovered, the gene-gene-environmental interactions producing specific epilepsy syndromes can be explored.

Epilepsy↗
PubMed2000

Independent occurrence of the CHRNA4 Ser248Phe mutation in a Norwegian family with nocturnal frontal lobe epilepsy.

PURPOSE: To describe the clinical features of a family from Northern Norway in which autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is associated with a Ser248Phe amino acid exchange in the second transmembrane domain of the neuronal nicotinic acetylcholine receptor alpha4 subunit (CHRNA4). We also tested for evidence of a de novo mutation or founder effect by comparing haplotypes with the original Australian family where the Ser248Phe mutation was first described. METHODS: Clinical details were obtained from 19 family members. Personal interviews and genetic analysis were carried out in 17. Parts of the coding region of CHRNA4 were sequenced, and two known polymorphisms (bp555/FokI, bp594/CfoI) were typed by restriction analysis. RESULTS: Eleven individuals had ADNFLE. The haplotypes of the mutation-carrying alleles of affected individuals from the Northern Norwegian and the Australian ADNFLE family are different. The phenotypic expressions are remarkably similar. CONCLUSIONS: The Ser248Phe mutation occurred independently in both families. Given the rarity of the disease, this suggests that not only the position of a mutation in the coding sequence but also the type of an amino acid exchange is important for the etiology of ADNFLE. The phenotypic similarity of these two families with different genetic backgrounds suggests that the Ser248Phe mutation largely determines the phenotype, with relatively little influence of other background genes.

Adolescent↗
PubMed2000

A de novo mutation in sporadic nocturnal frontal lobe epilepsy.

Autosomal dominant nocturnal frontal lobe epilepsy is sometimes due to mutations in CHRNA4. The commoner presentation of sporadic nocturnal frontal lobe epilepsy has not been associated with genetic defects. A 30-year-old woman diagnosed as having sporadic nocturnal frontal lobe epilepsy was found to have a de novo Ser252Leu CHRNA4 mutation. A pattern is emerging of site-specific mutation within the second transmembrane domain of CHRNA4 in association with autosomal dominant nocturnal frontal lobe epilepsy and sporadic nocturnal frontal lobe epilepsy in families with different ethnic backgrounds.

Adult↗
PubMed2000

Autosomal dominant rolandic epilepsy with speech dyspraxia.

Autosomal Dominant Rolandic Epilepsy with Speech Dyspraxia (ADRESD) is a rare disorder which highlights the relationship between Benign Rolandic Epilepsy (BRE) and speech and language disorders. Subtle speech and language disorders have recently been well characterised in BRE. ADRESD is associated with long term, more severe speech and language difficulties. The time course of rolandic epilepsy in ADRESD is typical of that of BRE. ADRESD is inherited in an autosomal dominant manner with anticipation. It is postulated that the anticipation may be due to an, as yet unidentified, triplet repeat expansion in a gene for rolandic epilepsy. BRE follows complex inheritance but it is possible that ADRESD may hold some valuable clues to the pathogenesis of BRE.

Age of Onset↗
PubMed1999

Motor cortex localization using functional MRI and transcranial magnetic stimulation.

OBJECTIVE: Congenital brain lesions producing focal seizures may be accompanied by reorganization of the areas responsible for motor and sensory functions within the brain due to a phenomenon that has been termed "neuronal plasticity." This can be studied using functional MRI (fMRI) and transcranial magnetic stimulation (TMS). Using either method, the motor cortex can be localized noninvasively, but to date there have been few studies correlating the level of agreement between the two techniques. METHODS: We used fMRI and TMS to localize the motor cortex in a young woman with intractable focal seizures, congenital left arm weakness, and a dysplastic right hemisphere on MRI. RESULTS: There was excellent agreement in the localization of motor representation for each hand. Both were predominantly located in the left hemisphere. fMRI also showed an area of posterior activation in the right hemisphere, but there was no evidence of descending corticospinal projections from this site using TMS, direct cortical stimulation, and Wada testing. CONCLUSIONS: Functional MRI (fMRI) and transcranial magnetic stimulation (TMS) were successfully used to localize cortical motor function before epilepsy surgery. Each technique demonstrated migration of motor function for the left hand to the left motor cortex. After resection of the dysplastic right precentral gyrus there was no permanent increase in weakness or disability. The two techniques are complementary; fMRI indicates all cortical areas activated by the motor task, whereas TMS identifies only those areas giving rise to corticospinal projections.

Adult↗
PubMed1999

Generalized epilepsy with febrile seizures plus: a common childhood-onset genetic epilepsy syndrome.

We examined the phenotypic variation and clinical genetics in nine families with generalized epilepsy with febrile seizures plus (GEFS+). This genetic epilepsy syndrome with heterogeneous phenotypes was hitherto described in only one family. We obtained genealogical information on 799 individuals and conducted detailed evaluation of 272 individuals. Ninety-one individuals had a history of seizures and 63 had epilepsy consistent with the GEFS+ syndrome. Epilepsy phenotypes were febrile seizures (FS) in 31, febrile seizures plus (FS+) in 15, FS+ with other seizure types (atonic, myoclonic, absence, or complex partial) in 8, and myoclonic-astatic epilepsy in 9 individuals. Inheritance was autosomal dominant with approximately 60% penetrance. This study confirms and expands the spectrum of GEFS+ and provides new insights into the phenotypic relationships and genetics of FS and the generalized epilepsies of childhood. Moreover, the ability to identify large families with this newly recognized common, childhood-onset, generalized genetic epilepsy syndrome suggests that it should be a prime target for attempts to identify genes relevant to FS and generalized epilepsy.

Adult↗
PubMed1999

Genetics of the epilepsies.

Epilepsies, like other common diseases, have complex inheritance, and molecular genetic studies in such conditions are difficult. There has been recent success in identifying the molecular basis of certain epilepsies, particularly in those syndromes with autosomal dominant inheritance. All four genes discovered to date for idiopathic epilepsies code for ion channel subunits, either ligand-gated or voltage-gated. The idiopathic epilepsies thus appear, at least in part, to be a family of channelopathies.

Epilepsy↗
PubMed1999

Epilepsy and paroxysmal movement disorders in families: evidence for shared mechanisms.

The epilepsies have been regarded as clinically distinct from the paroxysmal movement disorders. Recently, a variety of ion channel defects have been identified as the biological basis of certain familial epilepsies and paroxysmal movement disorders. We studied two families with the co-occurrence of epilepsy, movement disorders and migraine. Information was obtained on 147 individuals in the two families. In family WF, there was a co-occurrence of epilepsy (benign infantile convulsions, idiopathic generalized epilepsy), episodic ataxia (with cerebellar atrophy and without myokymia) and common migraine. In family CL, epilepsy (febrile seizures, febrile seizures plus), kinesigenic paroxysmal dyskinesia and migraine (including hemiplegic migraine) were observed in various combinations over 3 generations. The observations in these two families, together with review of the literature, suggest that the co-occurrence of epilepsy (particularly benign infantile convulsions), paroxysmal movement disorders and migraine is not due to chance. Thus, these distinct clinical phenomena could have a shared biological basis and ion channel defects are an attractive possibility.

Adolescent↗