Intracellular Levels of the LIS1 Protein Correlate with Clinical and Neuroradiological Findings in Patients with Classical Lissencephaly Antonella Fogli, PhD,*† Renzo Guerrini, MD,† Francesca Moro, PhD,*‡ Emilio Fernandez-Alvarez, MD,§ Marie Odile Livet, MD,  Alessandra Renieri, MD,¶ Maddalena Cioni, MD,# Daniela T. Pilz, MD,** Pierangelo Veggiotti, MD,†† Elena Rossi, PhD,‡ Andrea Ballabio, MD,* and Romeo Carrozzo, MD*‡ We report on the genotype–phenotype correlation in 7 patients with classical lissencephaly carrying a heterozygous subtle mutation in the LIS1 gene. Six patients showed a mutation predicted to encode for a truncated protein, and one mutation altered a splicing site, resulting in skipping of exon 4. Western blot analysis performed on the lymphoblastoid cell line of 2 patients bearing truncating mutations indicated that the mutated allele did not produce a detectable amount of the LIS1 protein; whereas the analysis performed on the fibroblasts from the patient with a splice-site mutation was suggestive of partial protein synthesis from the mutated allele. Although clinical and magnetic resonance imaging find- ings of patients with truncating mutations did not differ from those observed in patients with a heterozygous deletion, the patient bearing the exon-skipping mutation had less severe clinical and brain involvement. Our data suggest that truncating mutations in the LIS1 gene are relatively common among patients with classical lissencephaly not bearing a heterozygous deletion at 17p13.3, and strengthen the relevance of correct intracellular dosage of the LIS1 protein in the neuronal migration process. Fogli A, Guerrini R, Moro F, Fernandez-Alvarez E, Livet MO, Renieri A, Cioni M, Pilz DT, Veggiotti P, Rossi E, Ballabio A, Carrozzo R. Intracellular levels of the LIS1 protein correlate with clinical and neuroradiological findings in patients with classical lissencephaly. Ann Neurol 1999;45:154 –161 Classical lissencephaly or generalized agyria–pachygyria is a severe human brain malformation manifested by a smooth cerebral surface, resulting from an arrest in neuronal migration at 8 to 14 weeks of gestation. 1,2 The neocortex is abnormally thick and poorly orga- nized, with four to six primitive layers, and diffuse neuronal heterotopia. 3,4 Classical lissencephaly is either found in patients with Miller-Dieker syndrome in association with a characteristic facial dysmorphism, or occurs without peculiar facial features in patients with isolated lissen- cephaly sequence (ILS). 2 Almost all of the patients with Miller-Dieker syndrome have either cytogenetically visible or submicroscopic deletions involving chromo- some 17p13.3, whereas about 40% of patients with ILS show submicroscopic deletions occurring at the same locus (Pilz DT and Ledbetter DH, personal communication). In 1993, a gene mapping to the critical region for lissencephaly and indicated as LIS1 was isolated. This gene was initially considered to be involved in classical lissencephaly, based on the observation of nonoverlap- ping deletions detected by the LIS1 cDNA in 2 inde- pendent patients. 5 Subsequently, the finding of an ap- parently balanced translocation disrupting the LIS1 gene, and of three heterozygous subtle mutations (one missense, one frameshift, and one exon-skipping) in patients not bearing a deletion at 17p13.3, confirmed LIS1 as the “chromosome 17” lissencephaly gene. 6,7 The LIS1 gene is ubiquitously expressed 5 and it en- codes for the 45-kd subunit of the intracytoplasmic From the *Telethon Institute of Genetics and Medicine (TIGEM), San Raffaele Biomedical Science Park and ‡Cytogenetic Laboratory, San Raffaele Hospital, Milan; †Institute of Child Neurology and Psychiatry, University of Pisa, and Institute for Medical Research Stella Maris Foundation, Pisa; ¶Department of Molecular Biology and #Institute of Pediatrics, University of Siena, Siena; and ††Insti- tute of Child Neurology and Psychiatry, Institute for Medical Re- search Casimiro Mondino Foundation, Pavia, Italy; §Pediatric Neu- rology, Sant Joan de De ´u Hospital, Barcelona, Spain;  Pediatrics and Pediatric Neurology, Regional Hospital and University of Mar- seille, Marseille, France; and **Department of Human Genetics, University of Chicago, Chicago, IL. Received Aug 25, 1998, and in revised form Oct 21. Accepted for publication Oct 23, 1998. Address correspondence to Dr Carrozzo, Servizio di Genetica Med- ica, Ospedale San Raffaele, Via Olgettina 60, 20132 Milan, Italy. 154 Copyright © 1999 by the American Neurological Association