Abstracts

Juvenile myoclonic epilepsy (JME) accounts for 4 to 11% of all epilepsies. Previous analyses of 258 JME probands revealed classic JME or cJME (73%) and childhood absence evolving to JME or CAE/JME (17%) as the two most common subsyndromes. Here, we calculate and contrast the risks of having epilepsy in relatives of both subsyndromes. Each class/degree relative was examined separately for history of epilepsy. Offspring were analyzed separately. For risk calculations, we used the lifetime prevalence of having epilepsy reported by the Rochester study considering a frequency of familial history of epilepsy of 3%. An estimated prevalence of 0.00045 for JME and 0.00066 for childhood absences was used for the risk calculations. The risk of having seizures was 3 times higher in CAE/JME when compared to general population and cJME. In CAE/JME, this risk is high for all relatives in first, second and third degree (3.1 to 3.8). In cJME, the relative risks for JME exhibit a genetic pattern with risks decreasing with increasing distance of relationship. In cJME, the relative risk of developing JME in both nuclear members and second degree relatives is higher that of the general population. In cJME, parents and siblings have 69 to 136 times higher risk of having JME and 11 to 20 times of having absence compared to general population. However the risk of developing absences for second-degree relatives is not more than the risk for absences in the general population. These suggest a major gene for cJME. Parents and second degree relatives of families with CAE/JME, have 15 to 36 times the risk of having JME compared to general population. Frequency of myoclonic seizures was higher in JME when compared to CAE/JME (39.5% vs. 6.3%). The risk for JME in relatives was 2 times higher in JME families compared to families with CAE/JME. In contrast, frequency of absences was higher in CAE/JME compared to those of cJME (40.5% vs. 6.8%). When the prevalence of CAE in general population was used, the risk for absences in relatives were considerably higher in CAE/JME. The risk of tonic-clonic seizures was similar in both groups (30.2% in JME and 27.8% in CAE/JME). The risk of having a mother with seizures was increased (1.9 in CAE/JME and 1.5 in JME families) but the risk of affectedness in the father was not increased (relative risk of 1 in both subyndromes). Separate genes (more than one), responsible for the complex inheritance of cJME and CAE/JME are influenced by maternal genes. (Supported by NINDS: 5RO1NS042376-03)