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Clinical features and ATTCT repeat expansion in spinocerebellar ataxia type 10.

BACKGROUND: Spinocerebellar ataxia type 10, an autosomal dominant disease characterized by ataxia and seizures, is caused by a large expansion of an unstable ATTCT pentanucleotide repeat. OBJECTIVES: To characterize the phenotypic expression of spinocerebellar ataxia type 10 and to examine the genotype-phenotype correlations in 2 large families. DESIGN: Clinical characterization and genotype-phenotype correlation. SETTING: Studies at 2 medical schools with private practice referral. PATIENTS: Twenty-two affected individuals from 2 large Mexican American pedigrees. RESULTS: Of the 22 individuals, ataxia was the initial symptom in 21; seizure disorders developed in 11, mostly within several years following the onset of ataxia. The seizure frequency was different in the 2 families: 3 (25%) of 12 had seizures in family 1, and 8 (80%) of 10 had seizures in family 2 (P =.01). A brain magnetic resonance imaging or computed tomographic scan showed cerebellar atrophy in all patients examined. An electroencephalogram demonstrated epileptiform discharges in 4 of 8 patients studied. Although anticipation was apparent in both families, only family 1 showed a strong inverse correlation between age of onset and repeat number (r(2) = 0.79, P =.001). In family 1, 8 transmissions, of which 7 were paternal, resulted in an average gain of 1940 repeats. In contrast, despite anticipation, 2 affected male subjects transmitted their expanded alleles to 8 progenies, with an average loss of 755 repeats, in family 2. CONCLUSIONS: Seizure is an integral part of the spinocerebellar ataxia type 10 phenotype, with documented morbidity and mortality. Family-dependent factors may alter the frequency of the seizure phenotype and the pattern of intergenerational repeat size changes, making the genotype-phenotype correlation complex.

Adult↗

Localized 1H NMR measurements of 2-pyrrolidinone in human brain in vivo.

Localized 1H NMR homonuclear J editing spectroscopy was used to measure the concentration of 2-pyrrolidinone (PRDN) in the human occipital lobe of five normal and six epileptic subjects taking vigabatrin. PRDN is a lactam cyclization product of gamma-aminobutyric acid (GABA). From a localized volume of 13.5 cm3 in the occipital cortex, the concentration of PRDN ranged from 0.2 to 0.3 micromol/g in normal subjects, whereas in epileptic subjects on vigabatrin PRDN was elevated to 0.6 +/- 0.1 micromol/g. The elevated PRDN in patients on vigabatrin was in accord with raised GABA levels compared with normals. 1H NMR measurements of PRDN will be important in assessment of the role of this metabolite for improved seizure control.

Adult↗

Temporal neocortical role in ictal experiential phenomena.

Resection of a left temporal neocortical tumor, preserving the amygdala and hippocampus, permanently abolished ictal illusions in a 20-year-old man, suggesting that neocortical epileptic discharge is essential in the production of the experiential phenomena of seizures. In light of other works demonstrating amygdala and hippocampal participation, we propose that ictal experiential phenomena represent simultaneous epileptic discharge of the temporal neocortex and the limbic system.

Adult↗

Differential neural activity in the human temporal lobe evoked by faces of family members and friends.

In 6 patients, depth electrodes revealed differential evoked responses to familiar versus novel faces. These differential responses were obtained in the amygdala, hippocampus, and temporal neocortex but not in the dorsolateral frontal or cingulate cortex. The limbic and temporal structures that differentiated novel from familiar faces did not respond differentially to variations in luminance. Limbic structures and temporal cortex thus appear to participate in face recognition and in encoding the familiarity of visual experiences.

Adult↗

Autoantibodies to glutamic acid decarboxylase in palatal myoclonus and epilepsy.

We report the presence of serum autoantibodies directed against glutamic acid decarboxylase in a patient with epilepsy and palatal myoclonus not associated with brain lesions. Glutamic acid decarboxylase antibody reactivity was dependent on the presence of carboxy-terminal amino acids, similar to that reported in patients with stiff-man syndrome. Marked reduction in the frequency of epileptic attacks and improvement in palatal myoclonus occurred when benzodiazepine was administered and phenytoin was gradually tapered. Testing for anti-glutamic acid decarboxylase antibodies may be indicated in patients with palatal myoclonus and with convulsive disorders refractory to therapy.

Adult↗

Vigabatrin increases human brain homocarnosine and improves seizure control.

Homocarnosine, a dipeptide of gamma-aminobutyric acid (GABA) and histidine, is thought to be an inhibitory neuromodulator synthesized in subclasses of GABAergic neurons. Homocarnosine is present in human brain in greater amounts (0.4-1.0 micromol/g) than in other animals. The antiepileptic drug vigabatrin increases human cerebrospinal fluid homocarnosine linearly with daily dose. By using 1H nuclear magnetic resonance spectroscopy, serial occipital lobe GABA and homocarnosine concentrations were measured in 11 patients started on vigabatrin. Daily low-dose (2 g) vigabatrin increased both homocarnosine and GABA. Larger doses of vigabatrin (4 g) further increased homocarnosine but changed GABA levels minimally. Seizure control improved with increasing homocarnosine and GABA concentrations. Patients whose seizure control improved with the addition of vigabatrin had higher mean homocarnosine, but the same mean GABA concentrations, than those whose seizure control did not improve. Increased homocarnosine may contribute to improved seizure control.

Adult↗

Firing of human hippocampal units in relation to voluntary movements.

During certain movements (termed "type I," "instrumental," or "voluntary"), the rodent hippocampal EEG is dominated by regular 7-10 Hz waves. This "theta rhythm" is accompanied by increased firing of hippocampal interneurons and dentate gyrus granule cells. No obvious theta rhythm is present in comparable situations in humans or other primates. However, a widespread scalp negativity (the "readiness potential") starts approximately 1 second before spontaneous key presses at long intervals. The readiness potential has been recorded in the monkey hippocampus. In this study, action potentials were recorded in the human hippocampus in relation to various movements. During a broadly ranging interview including various movements and memory tests, hippocampal units were found that fired during movements of the tongue and/or hands. Only movements that required a high degree of effort were effective. Other hippocampal units appeared to be correlated with either the transitions between tasks or the interruptions within tasks. In a second experiment, hippocampal units were found to change their firing in the seconds preceding spontaneous key presses. These data indicate that, like the rodent hippocampus, human hippocampal neuronal activity is strongly influenced by movement.

Action Potentials↗

Prenatal diagnosis of a mosaic supernumerary marker iso (8p) (tetrasomy 8p): discordance between chorionic villi culture and amniotic fluid karyotypes.

We describe the first case of mosaic supernumerary marker iso (8p) displaying a karyotype discordance between chorionic villi (CV) and amniotic fluid (AF) cultures during prenatal cytogenetic diagnosis. In the first trimester, cytogenetic analysis after chorionic villi sampling (CVS) was normal in all metaphases in the short-term cytotrophoblast cell culture, but an undefined supernumerary marker was detected in 60% of mesenchymal cells in the long-term CV culture. Informed of the mosaicism, the couple selected amniotic fluid sampling as a second-trimester confirmatory diagnostic procedure. The supernumerary marker was absent in all of the 25 available AF cells metaphases. The prospective parents received genetic counselling and were informed that the discordance could be interpreted as a placental confined mosaicism or as a true foetal mosaicism with low percentage of affected cells. The couple opted to continue the pregnancy. In the second month of life, the child had abnormal development with severe psychomotor delay and frequent episodes of epilepsy. Postnatal cytogenetic extensive re-evaluation discovered that the previously detected supernumerary marker was indeed an isochromosome (8p) rearrangement present at low frequency in 5% of the blood lymphocytes.

Amniocentesis↗

Memory for emotional words following unilateral temporal lobectomy.

We recently reported that patients who had received unilateral temporal lobectomy, including the amygdala and hippocampus, show impaired acquisition in a fear conditioning task (LaBar, LeDoux, Spencer, & Phelps, 1995), indicating a deficit in emotional memory. In the present paper, we examined performance of these patients on two verbal, emotional memory tasks in an effort to determine the extent of this deficit. In Experiment 1, subjects were asked to recall emotional and non-emotional words. In Experiment 2, subjects were asked to recall neutral words which were embedded in emotional and non-emotional sentence contexts. Both temporal lobectomy subjects and normal controls showed enhanced recall for emotional words (Experiment 1) and enhanced recall for neutral words embedded in emotional sentence contexts (Experiment 2). These results suggest that the deficit seen in emotional memory following unilateral temporal lobectomy is not a global deficit and may be limited to specific circumstances where emotion influences memory performance. Several hypotheses concerning the discrepancy between the present studies and the fear conditioning results (LaBar et al., 1995) are discussed.

Adult↗

Functional roles of Broca's area and SMG: evidence from cortical stimulation mapping in a deaf signer.

The importance of the left hemisphere in language function has been firmly established and current work strives to understand regional specializations within the perisylvian language areas. This paper reports a case study of a deaf user of American Sign Language undergoing an awake cortical stimulation mapping procedure. Patterns of sign errors accompanying electrical stimulation of Broca's area and the supramarginal gyrus (SMG) are reported. Our findings show Broca's area to be involved in the motor execution of sign language. These data demonstrate that the linguistic specificity of Broca's area is not limited to speech behavior. In addition, unusual semantic-phonological errors were observed with stimulation to the SMG; these data may implicate the SMG in the binding of linguistic features in the service of language production. Taken together, these findings provide important insight into the linguistic specificity of Broca's area and the functional role of the supramarginal gyrus in language processing.

Anomia↗

Timing and localization of movement-related spectral changes in the human peri-Rolandic cortex: intracranial recordings.

Event-related spectral power (ERSP) was measured from intracranial EEG and used to characterize the time-course and localization of the Rolandic mu rhythms in 12 patients during the delayed recognition of words or faces (DR) and the discrimination of simple lateralized visual targets (LVD). On each trial, the subject decided whether to make manual response (Go) or not (NoGo). ERSP increased on both Go and NoGo trials in peri-Rolandic regions of all subjects with a peak latency of approximately 330-ms poststimulus and duration of 260 ms during the DR task. The peak of this ERSP increase preceded movement by approximately 300 ms. All subjects produced a subsequent movement specific ERSP decrease of peri-Rolandic mu rhythms (starting approximately 90 ms before the average reaction time) with an peak latency of approximately 800 ms and duration of approximately 520 ms. The LVD task produced bilateral movement-selective readiness potentials and reproduced the movement-specific late ERSP decreases seen in the DR task (strongest from 7-24 Hz). Furthermore, the LVD task demonstrated that the late movement-related ERSP decrease is larger for the contralateral hand. However, the LVD task did not consistently reproduce the early ERSP increase seen in the DR task. Movement-related ERSP decreases were widespread, occurring in pre- and post-Rolandic as well as primary-motor, supplemental motor, and cingulate cortical regions. Other cortical areas including frontal, temporal, and occipital regions did not show movement-related ERSP changes. Peri-Rolandic ERSP decreases in mu rhythms correlate with the generation of a motor command. The early increases in mu may reflect a transient state of motor inhibition just prior to motor execution.

Brain Mapping↗

Hemispheric control of unilateral and bilateral responses to lateralized light stimuli after callosotomy and in callosal agenesis.

Normally, simple digital or manual responses to a light stimulus in the right or left visual hemifields are performed faster with uncrossed hand-field combinations than with crossed hand-field combinations. Because of the organization of visual and motor pathways, the integration of uncrossed responses is assumed to occur within a single hemisphere, whereas a time-consuming interhemispheric transfer via the corpus callosum is considered to be necessary for the integration of crossed responses. However, callosal transfer may be dispensable for those crossed responses which can be controlled through ipsilaterally descending motor pathways by the hemisphere receiving the visual stimulus. We investigated crossed-uncrossed differences (CUDs) in speed of simple visuomotor responses to lateralized flashes in one subject with total section of the corpus callosum and two subjects with complete callosal agenesis. We recorded the reaction times as well as the premotor times, as indicated by the electromyographic latencies of the prime movers, of three types of responses: a distal response involving a thumb flexion, a proximal response chiefly involving a forearm flexion and an axial response involving a shoulder elevation. Further, the three types of responses to a single lateralised flash were performed both unilaterally and bilaterally. The three acallosal subjects showed CUDs greatly exceeding normal values on distal responses, either unilateral or bilateral, and on unilateral proximal responses. These abnormally long CUDs stood in sharp contrast to the insignificant CUDs exhibited by the same subjects on bilateral proximal responses and on unilateral and bilateral axial responses in agreement with correspondingly insignificant CUDs reported for normal subjects. These results confirm that a callosal contribution is important for the execution of fast distal and unilateral proximal responses to a visual stimulus directed to the hemisphere ipsilateral to the responding hand. By contrast, the other types of crossed responses appear to be efficiently coordinated across the midline without the aid of the corpus callosum. This is in keeping with the hypothesis that they are governed by a bilaterally distributed motor system which is preferentially activated for the execution of symmetrical bilateral movements, employing axial and proximal limb muscles.

Accidents, Traffic↗