Epilepsy is among the most frequent findings in many, especially autosomal, 
chromosome aberrations. Its incidence, however, is very variable, and there are 
very few aberrations in which epilepsy is a constant finding. Even siblings and 
monozygotic twins with the same aberration are often discordant for seizure 
disorders. Similar observations can be made for congenital (major) malformations 
in chromosome aberrations. The common explanation is that in these instances 
epilepsy is not caused by the action of a single gene in single or triple dose, 
but is influenced by the combined action of a number of genes within and outside 
of the aneuploid segment. The situation is comparable to a polygenic model of 
inheritance. Gene mutations associated with epilepsy are known, to date, only 
for two disorders: the lissencephaly 1 gene in Miller-Dieker syndrome and 
mutations in the UBE3A gene in Angelman syndrome. Chromosome aberrations in 
which epilepsy is a major and consistent finding include Angelman syndrome due 
to loss of the maternal 15q11.2-q12 segment, tetrasomy of the maternal segment 
15pter-q13 due to an additional inv dup chromosome, Miller-Dieker syndrome due 
to deletion of the 17p13.3 segment including the lissencephaly1 gene, ring 
chromosome 20, and Wolf-Hirschhorn syndrome due to deletion of at least the 
4p16.3 segment.