PROGRESS IN MAPPING HUMAN EPILEPSY GENES

The chromosomal loci for seven epilepsy genes have been identified in chromosomes 1q, 6p, 8q, 16p, 20q, 21q, and 22q. In 1987, the first epi lepsy locus was mapped in a common benign idiopathic generalized epile psy syndrome, juvenile myoclonic epilepsy (JME). Properdin factor or B f, human leukocyte antigen (HLA), and DNA markers in the HLA-DQ region were genetically linked to JME and the locus, named EJM1, was assigne d to the short arm of chromosome 6. Our latest studies, as well as tho se by White-house et al., show that not all families with JME have the ir genetic locus in chromosome 6p, and that childhood absence epilepsy does not map to the same EJM1 locus. Recent results, therefore, favor genetic heterogeneity for JME and for the common idiopathic generaliz ed epilepsies. Heterogeneity also exists in benign familial neonatal c onvulsions, a rare form of idiopathic generalized epilepsy. Two loci a re now recognized; one in chromosome 20q (EBN1) and another in chromos ome 8q. Heterogeneity also exists for the broad group of debilitating and often fatal progressive myoclonus epilepsies (PME). The gene locus (EPM1) for both the Baltic and Mediterranean types of PME or Unverric ht-Lundborg disease is the same and is located in the long arm of chro mosome 21. Lafora type of PME does not map to the same EPM1 locus in c hromosome 21. PME can be caused by the juvenile type of Gaucher's dise ase, which maps to chromosome 1q, by the juvenile type of neuronal cer oid lipofuscinoses (CLN3), which maps to chromosome 16p, and by the '' cherry-red-spot-myoclonus'' syndrome of Guazzi or sialidosis type I, w hich has been localized to chromosome 10. A point mutation in the mito chondrial tRNA(Lys) coding gene can also cause PME in children and adu lts (MERFF).