Genetics of convulsive disorders

Abstract

Certain difficulties and misconceptions regarding the terms heredity and epilepsy were considered primarily from the geneticist''s point of view. The two terms are not mutually exclusive, for a trait such as a convulsive disorder may be dependent upon both hereditary and environmental factors for its expression. The difficulties of defining what constitutes an affected individual for purposes of a genetic analysis were also considered. It has been suggested that the genes responsible for convulsions may be divided into 3 major categories: threshold genes, cerebral disease genes, and "epilepsy" genes. The interaction and irregular expression of these genes may be influenced by the phenomena of expressivity, penetrance, and chronicity. For the purposes of the present and subsequent papers, certain general methods of listing and comparing different orders of near relatives of convulsant and nonconvulsant probands were presented. The prevalence of children with a history of having had at least 1 con- vulsion, among 1,000 admissions, was found to be 11.50[plus or minus]1.01%. If children who were admitted because of their convulsions are omitted, the prevalence is reduced to 8.76+0.91%. The prevalence is reduced still further to 6.55[plus or minus].80% if children who had convulsions as an associated symtom of their disease are also omitted. The prevalence of individuals with a history of having had at least 1 convulsion among most of the different orders of near relatives of convulsant patients of a pedi-atric hospital was significantly higher than that for the near relatives of nonconvulsant patients who were drawn from the same hospital population. When all the near relatives (parents, siblings, aunts and uncles, grandparents, and cousins) are considered together, the prevalence for the convulsant group (3.79[plus or minus]0.45%) is 2.9 times and significantly higher (P=<.001) than for the control group (1.31[plus or minus]0.15%). It is concluded that the data strongly suggest a familial distribution for convulsions among the near relatives of this highly heterogeneous group of children with a history of convulsions; however, the distribution is probably not uniformly spread throughout all the families.