Linkage studies with the chromosome 20 markers D20S19 and D20S20 were performed in two families with benign familial neonatal convulsions at the Department of Pediatrics, The University of Texas Health Science Center, San Antonio, TX. In the first family with 14 affected, none had seizures after two months of age. In the second family with 13 affected, seizures did not remit until 6 to 24 months; febrile convulsions occurred in two, and one had refractory epilepsy until late adolescence. In family one, the odds were greater than 20,000:1 against linkage at 10% recombination; whereas the data from family two favored linkage with a maximum odds ratio of 45:1 at 6% recombination. It was concluded that this autosomal dominant primary epilepsy of infancy is clinically and genetically heterogeneous. 
COMMENT. These data based on large family pedigrees suggest two distinct genetic loci for benign familial neonatal convulsions. The subtype linked to chromosome 20q may be associated with delayed remission and a higher risk for the development of epilepsy. The authors suggest that absence and benign rolandic epilepsy might also show genetic heterogeneity.