The Genetics of Epilepsy

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Abstract
Summary Among 520 sibships, in which at least one child was an epileptic and for which the family history and clinical findings were quite complete, there were 294 with one parent affected, 222 with neither parent, and 4 with both parents affected. Numerical tests on the pooled data show quite definitely that epilepsy is inherited as if due to a simple autosomal dominant gene with approximately 65% penetrance. Since about 65% of all epilepsy is genetic and since there is about 65 penetrance in genetic epilepsy, the 2 factors effectively balance one another, so that the incidence of epilepsy in the population, 1 in 200, may be taken as the frequency of individuals with a genetic constitution for epilepsy. Assuming random mating, the gene frequency for the dominant gene for epilepsy is 0.0025 and for the normal recessive allele the value is 0.9975. It follows that only about 1 in 160,000 is homozygous for the dominant gene for epilepsy and that 99.5% of the population are genetically normal. For the genetic counselor it is of interest that if one parent has a genetic constitution for epilepsy the frequency among the children is about 36%, and if one child in such a family has epilepsy the empirical probability of another child having epilepsy is about in 1 in 8, which having regard to the standard error, agrees with the degree of concordance (10.3±1.8%) in dizygotic twins, as should be expected.

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