Childhood absence epilepsy (CAE), one of the most common epilepsies in children, is genetically and phenotypically heterogeneous. One of the genes responsible for human CAE associated with tonic-clonic seizures has been mapped to chromosome band 8q24 by genetic linkage analysis and is termed ECA1. Recently, we isolated and mapped the JRK/JH8 gene, a human homologue of the mouse epilepsy gene, jerky, on 8q24. The epilepsy phenotype of the mice with inactivated jerky gene as well as its chromosomal localization proposed JRK/JH8 as a prominent candidate for the CAE gene. To confirm whether the JRK/JH8 gene is responsible for ECA1, we performed mutational analyses in the coding region of JRK/JH8 in two CAE families mapped on 8q24, using heteroduplex and direct sequencing methods. We identified seven nucleotide changes, two of which lead to amino acid substitutions. However, these changes did not co-segregate with the disease phenotype. In addition, we redefined the location of JRK/JH8 to be more than 4 Mb distant from D8S502 and ECA1. Thus, negative results of mutation analyses and detailed physical mapping exclude JRK/JH8 as the ECA1 gene.