Disturbios do desenvolvimento cortical e epilepsia autossomica dominante com auras auditivas : estudos geneticos e moleculares / Malformations of cortical development and autosomal dominant partial epilepsy with auditory features

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Temporal Lobe Epilepsy (TLE) and malformations of cortical development (MCD) are two of the most important causes of epilepsy. Extensive molecular genetic studies have resulted in gene discovery for MCD such as periventricular nodular heterotopia (PNH), lisencephaly/ subcortical band heterotopia spectrum (LIS-SBH), schizencephaly, polymicrogyria and for a subtype of TLE, the autossomic dominant partial epilepsy with auditory features (ADPEAF). The main goals of this project were 1) to screen for mutations in the four main genes responsible for abnormal cortical development (FLN1, LIS1, DCX and EMX2) in a large cohort of patients with different types of cortical malformations 2) to map the loci for ADPEAF and 3) to investigate molecular mechanisms of mutations identified. Mutation screening was performed by the polymerase chain reactions (PCR). PCR products were analyzed by denaturing high performance liquid chromatography (DHPLC) and were subsequently sequenced using standard automatic sequencer. In addition, HUMARA marker and Real Time PCR were performed to study molecular mechanisms resulting from the mutations identified. Linkage analysis was carried out by amplifying microsatellites markers by PCR and analyzing alleles with Fragment profiler® software and MLINK® package program. We have studied a total of 108 patients with MCD. Thirteen had PNH, 19 had the LIS-SBH spectrum, 46 individuals had schizencephaly and 30 had polymicrogyria. In addition we have identified four families segregating ADPEAF. Two families were considered informative for linkage analysis. We found a G987C mutation that alters the splicing site of the 6th intron of the FLN1 gene in two related patients with classical PNH findings, skewed X chromosome inactivation was detected as the possible mechanism responsible for clinical differences between the two patients. In the LIS-SBH group, one patient with agyria/pachygyria had an A1385C transversion, which changes a histidine for a proline in amino acid 277 of the LIS1 protein. Furthermore, in the group of the schizencephalies and polymicrogyria we have detected only neutral variants in the EMX2 gene. Linkage analysis in ADPEAF showed linkage to chromosome 10q in only one family. Automatic sequencing identified a mutation in the LGI1 gene. In addition, neuroimaging studies showed cortical malformations in patients with LGI1 mutations. Mutation and genetics analysis of the LGI gene family and MASS1 in other pedigrees failed to show a role for these genes in the etiology of ADPEAF. A genome wide scan performed in a large family segregating ADPEAF point to a potential candidate region on chromosome 6q22, which was not confirmed after further investigation with additional microsatellite markers. We conclude that: a) Mosaicism, mutations in non coding regions, large deletions and the presence of atypical cases could have contributed for the low frequency of mutations found in patients with PNH and the LIS-SBH spectrum b) we found mutations in the FLN1 gene in familial cases of bilateral PNH, c) the pathologic mechanism of this mutation is the splicing site destruction of the 6th FLN1 gene intron, d) phenotypic differences between the two related patients harboring this FLN1 mutation were explained by a non random X chromosome inactivation, e) missense mutations in the LIS1 gene are a rare finding in patients with the LIS-SBH spectrum and its localization in latter WD domains are not always related with less severe LIS, f) schizencephaly and polymicrogyria appear not to have a genetic background in the EMX2, since our study detected only a neutral polymorphism in these patients, g) ADPEAF is a genetically heterogeneous entity, since mutations in the LGI1 gene were identified only in one family with this syndrome, h) cortical malformation in the left temporal lobe was detected by the first time in individuals with ADPEAF and LGI1 mutations, i) MASS1 and LGI gene family were not involved with ADPEAF etiology in the other pedigrees studied, j) a potential candidate locus to contain the second gene responsible for ADPEAF was identified in chromosome 6q22, however additional studies failed to confirm linkage in this region

ASSUNTO(S)

genetics cortex cerebral sistema nervoso central genetica central nervous system cerebral cortex

ACESSO AO ARTIGO

Documentos Relacionados