Abstracts

Migration of post-mitotic neurons from the ventricular zone to form the cortical plate comprises one of the most critical stages in brain development. Mutations in two genes, [italic]LIS1[/italic] and [italic]DCX[/italic] are responsible for neuronal migration disorders including classical lissencephaly (LIS) and subcortical band heterotopia (SBH). More than one hundred deletions and forty-one intragenic mutations, have been described in the [italic]LIS1[/italic] gene in patients with LIS but only five missense mutations were reported until now. The objective of this study is to report a new missense mutation in a patient with lissencephaly
All patients included in the study had high resolution MRI scans performed in a 2T scanner with T1- and T2-weighted images in three orthogonal planes or CT scans. We searched for mutations in the coding exons of [italic]LIS1[/italic] and [italic]DCX[/italic] genes in all patients. In addition, a total of 50 unrelated normal control subjects were also genotyped. PCR reactions were performed with primers designed to amplify the entire coding region and intron/exon boundaries of the [italic]LIS1[/italic] and [italic]DCX[/italic] genes. PCR samples were analyzed by the single-strand conformation polymorphism (SSCP) method. The nucleotide sequence of all fragments showing an altered mobility in the SSCP experiment were subsequently determined using the Big Dye Terminator Sequencing kit for megaBACE[reg]1000.
A total of 15 patients were analyzed, 5 of them have SBH and 10 have LIS. SSCP analysis revealed one patient of the LIS group with altered band shift in exon 8 of the [italic]LIS1[/italic] gene and 7 patients (4 of the SBH and 3 of the LIS group) with abnormal migration patterns for exon 11 of the [italic]LIS1[/italic] gene. SSCP analysis of the [italic]DCX[/italic] gene did not show any abnormal band shift. Sequencing of the abnormal PCR fragment amplified from exon 8 of the [italic]LIS1[/italic] gene showed a A [rarr] C transversion which predicts a changes of a histidine for a proline in position 277 of the protein. MRI of this patient showed abnormalities more severe in the posterior regions, with agyria in the parietal and occipital lobes and pachygiria in temporal and frontal lobes. The abnormality found in exon 11 of the[italic] LIS1[/italic] gene was a C [rarr]T substitution in the beginning of the 3[acute]untranslated region whish was also present in nine control subjects.
The malformation pattern of this patient is more severe in the posterior regions, a typical characteristic of individuals with [italic]LIS1[/italic] mutations. Otherwise this patient seems to have a LIS grade (3a), probably more severe than expected for individuals with missense mutations in [italic]LIS1[/italic].The new missense mutation we describe changes a basic histidine for a nonpolar proline. It is localized in the 5^th WD domain of the lis1 protein, which is very conserved in different species, and is probably involved in interactions with b spectrin, a cytoskeletal protein.
[Supported by: CAPES and FAPESP]