POINT MUTATIONS AND AN INTRAGENIC DELETION IN LIS1, THE LISSENCEPHALYCAUSATIVE GENE IN ISOLATED LISSENCEPHALY SEQUENCE AND MILLER-DIEKER SYNDROME

Classical lissencephaly (smooth brain) or generalized agyria-pachygyri a is a severe brain malformation which results from an arrest of neuro nal migration at 9-13 weeks gestation, It has been observed in several malformation syndromes including Miller-Dieker syndrome (MDS) and iso lated lissencephaly sequence (ILS), A gene containing P-transducin lik e repeats, now known as LIS1, was previously mapped to the ILS/MDS chr omosome region on 17p13.3. We recently localized the classical lissenc ephaly critical region to the LISI gene locus by molecular analysis of key ILS and MDS patients, We have now characterized the structure of LISI, which consists of 11 exons, and have searched for the presence o f subtle mutations in 19 ILS patients who showed no gross rearrangemen ts of LISI, Single strand conformational polymorphism (SSCP) analysis revealed band-shifts for three patients, each involving a different co ding exon, which were not observed in their respective parental DNAs. Sequence analysis identified these de novo mutations as a dA-->dG tran sition in exon VI at nucleotide 446, a dC-->dT transition in exon VIII at nucleotide 817, and a 22 bp deletion at the exon IX-intron 9 junct ion from nucleotide 988 to 1002+7, which causes skipping of exon IX in the mature LIS1 transcript, These changes are predicted to result in an H149R amino acid substitution, an R273X premature translation termi nation, and abolition of amino acids 301-334, in the respective LIS1 p roteins. These data thus confirm LIS1 as the gene responsible for clas sical lissencephaly in ILS and MDS.