Fluorescence in situ hybridization analysis with LIS1 specific probes reveals a high deletion mutation rate in isolated lissencephaly sequence

Purpose: Recent revision of the lissencephaly critical region on chromosome 17p13.3 and confirmation of LIS1 as the causative gene for classical lisse ncephaly has allowed the development and application of fluorescence in sit u hybridization (FISH) probes corresponding directly to this gene. Method: We have analyzed patients with isolated lissencephaly sequence (ILS) by FIS H with probes at D17S379, an anonymous locus distal to LIS1, and with LIS1 specific probes. Results: In 110 patients with ILS, a deletion at D17S379 w as detected in 23.6%. Of those patients without a deletion, 32 were availab le for further study with LIS1 probes. Deletions were found in eight additi onal individuals. Conclusion: The overall deletion mutation rate detectable by FlSH with LIS1 probes is approximate to 40%. This rate is significantly higher than the deletion rate observed at D17S379. This indicates that FIS H studies using probes specific to LIS1 should be undertaken as the initial diagnostic assay for the evaluation of patients with ILS, and the high fre quency of deletions raises the possibility of "hotspots" for chromosome bre akage in this region.