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Autosomal dominant nocturnal frontal lobe epilepsy. A video-polysomnographic and genetic appraisal of 40 patients and delineation of the epileptic syndrome.

A Oldani, M Zucconi, R Asselta, M Modugno, M T Bonati, L Dalprà, M Malcovati, M L Tenchini, S Smirne, L Ferini-Strambi
DOI: http://dx.doi.org/10.1093/brain/121.2.205 205-223 First published online: 1 February 1998

Summary

A number of clinical and aetiological studies have been performed, during the last 30 years, on patients with abnormal nocturnal motor and behavioural phenomena. The aetiological conclusions of these studies were often conflicting, suggesting either an epileptic or a non-epileptic origin. Among the clinical characteristics of these patients, the familial clustering was one thoroughly accepted. A nocturnal familial form of frontal lobe epilepsy (autosomal dominant nocturnal frontal lobe epilepsy, ADNFLE), often misdiagnosed as parasomnia, has been recently described in some families. In one large Australian kindred, a missense mutation in the second transmembrane domain of the neuronal nicotinic acetylcholine receptor alpha 4 subunit (CHRNA4) gene, located on chromosome 20 q13.2-13.3, has been reported to be associated with nocturnal frontal lobe epilepsy. We performed an extensive clinical and video-polysomnographic study in 40 patients complaining of repeated abnormal nocturnal motor and/or behavioural phenomena, from 30 unrelated Italian families. Thirty-eight patients had an electroclinical picture strongly suggesting the diagnosis of ADNFLE. They had a wide clinical spectrum, ranging from nocturnal enuresis to sleep-related violent behaviour, thus including all the main features of the so-called 'typical' parasomnias. The video-polysomnographic recording confirmed the wide spectrum of abnormal manifestations, including sudden awakenings with dystonic/ dyskinetic movements (in 42.1% of patients), complex behaviours (13.2%) and sleep-related violent behaviour (5.3%). The EEG findings showed ictal epileptiform abnormalities predominantly over frontal areas in 31.6% of patients. In another 47.4% of patients the EEG showed ictal rhythmic slow activity over anterior areas. Only 18.4% of the patients had already received a correct diagnosis of epilepsy. In 73.3% of the patients treated with anti-epileptic drugs the seizures were readily controlled. Pedigree analysis on 28 of the families was consistent with autosomal dominant transmission with reduced penetrance (81%). DNAs from 20 representative affected individuals were sequenced in order to check for the presence of the missense mutation in the CHRNA4 gene found in the Australian kindred affected by ADNFLE. Nucleotide sequence analysis did not reveal the presence of this mutation, but it did confirm the presence of two other base substitutions, not leading to amino acid changes. These two intragenic polymorphisms, together with a closely linked restriction fragment length polymorphism at the D20S20 locus, have been used for linkage analysis of ADNFLE to the terminal region of the long arm of chromosome 20 in five compliant families. The results allowed us to exclude linkage of ADNFLE to this chromosomal region in these families, thus confirming the locus heterogeneity of the disorder. Large and full video-polysomnographical studies are of the utmost importance in order to clarify the real prevalence of both nocturnal frontal lobe epilepsy and parasomnias, and to provide a correct therapy.