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Deletions of the proximal long arm of chromosome 15 (bands 15q11q13) are found in the majority of patients with two distinct genetic disorders, Angelman syndrome (AS) and Prader-Willi syndrome (PWS). The deleted regions in the two syndromes, defined cytogenetically and by using cloned DNA probes, are similar. However, deletions in AS occur on the maternally inherited chromosome 15, and deletions in PWS occur on the paternally derived chromosome 15. This observation has led to the suggestion that one or more genes in this region show differential expression dependent on parental origin (genetic imprinting). No genes of known function have previously been mapped to this region. We show here that the gene encoding the GABAA (gamma-aminobutyric acid) receptor beta 3 subunit maps to the AS/PWS region. Deletion of this gene (GABRB3) was found in AS and PWS patients with interstitial cytogenetic deletions. Evidence of beta 3 gene deletion was also found in an AS patient with an unbalanced 13;15 translocation but not in a PWS patient with an unbalanced 9;15 translocation. The localization of this receptor gene to the AS/PWS region suggests a possible role of the inhibitory neurotransmitter GABA in the pathogenesis of one or both of these syndromes.
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We studied facial expressions during pathological laughing and crying in 6 patients using EMG investigation. Increased EMG discharges of M. frontalis and M. corrugator supercilii are characteristic of pathological laughing and crying in addition to an increase of EMG discharges of M. orbicularis oculi, M. levator labii superiors, M. zygomaticus major, M. risorius and M. mentalis which we observed during natural laughing. Its patterns of facial expressions are similar to that of crying in normals. From the fact that normals show the same expression of laughing and crying in an extreme emotional outburst, we speculate that pathological laughing and crying is maximal manifestations of facial expressions caused by a release phenomenon of the upper center.
The concurrence of gelastic (laughing) seizures, hypothalamic hamartoma and precocious puberty constitutes a well defined epileptic syndrome in children; moreover mental retardation, neuropsychological deterioration and behavioral disorders have been often observed in these patients. In two cases we studied by means of MRI the appearance and the site of the hamartoma (in the posterior part of the hypothalamus with extension toward the third ventricle). The EEG study was performed by means of repeated recordings, of Computed EEG Topography (CET) and of Ambulatory EEG (A-EEG): in both patients during interictal periods paroxysmal EEG discharges prevailing in temporal or fronto-temporal regions and slight abnormalities of the background activity in the same areas were detected. Laughing seizures were recorded in each patient particularly by means of A-EEG: in case 1 bursts of high-voltage activity ("theta" waves) followed by depression of the background rhythm and by irregular spike discharges located in left temporal region were observed; in patient 2 irregular generalised spike discharges followed by slow waves or by depression of the background activity were seen. The presence of local abnormalities in both patients can support the hypothesis that the cortex, especially of the temporal anterior lobe, is involved in the origin of the laughing seizures. The significance of the mechanisms of secondary generalization as regards the seriousness of the epilepsy and of the mental impairment in these patients is also suggested.
A case of mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes, in which a pituitary growth hormone (GH) secretion deficiency of hypothalamic origin was revealed through neuro-endocrinological examinations, was described. The case was a 10-year-old girl, who had been suffering from generalized tonic seizures since age 5, four episodes of alternating hemiplegia since age 6, stunted growth since age 7, and simple partial motor seizures as well as gelastic seizures since age 8. Marked elevation of lactate and pyruvate in both serum and CSF, abundant ragged red fibers in biopsied muscle, and low density areas in the left occipital lobe and bilateral globus pallidus in addition to diffuse brain atrophy on CT scan and MRI of the head were demonstrated, although the activities of muscle enzymes complex I-IV were within normal ranges. Pituitary GH secretion was deficient under the loadings with insulin, L-DOPA, sleep, and a single growth hormone releasing factor (GRF) administration, but normal GH response was registered under the repetitive stimulation with GRF. Activities of other hormonal axes were normal. It is likely that short stature commonly observed in MELAS patients is due to hypothalamic dysfunction, which might be brought out by chronic ischemia and energy deficiency of the diencephalon based upon mitochondrial abnormality of that region. It is likely that gelastic seizure in this case is due to hypothalamic dysfunction.
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