Linkage of benign familial infantile convulsions to chromosome 16p12-q12 suggests allelism to the infantile convulsions and choreoathetosis syndrome.
The syndrome of benign familial infantile convulsions (BFIC) is an autosomal dominant epileptic disorder that is characterized by convulsions, with onset at age 3-12 mo and a favorable outcome. BFIC had been linked to chromosome 19q, whereas the infantile convulsions and choreoathetosis (ICCA) syndrome, in which BFIC is associated with paroxysmal dyskinesias, had been linked to chromosome 16p12-q12. BFIC appears to be frequently associated with paroxysmal dyskinesias, because many additional families from diverse ethnic backgrounds have similar syndromes that have been linked to the chromosome 16 ICCA region. Moreover, one large pedigree with paroxysmal kinesigenic dyskinesias only, has also been linked to the same genomic area. This raised the possibility that families with pure BFIC may be linked to chromosome 16 as well. We identified and studied seven families with BFIC inherited as an autosomal dominant trait. Genotyping was performed with markers at chromosome 19q and 16p12-q12. Although chromosome 19q could be excluded, evidence for linkage in the ICCA region was found, with a maximum two-point LOD score of 3.32 for markers D16S3131 and SPN. This result proves that human chromosome 16p12-q12 is a major genetic locus underlying both BFIC and paroxysmal dyskinesias. The unusual phenotype displayed by one homozygous patient suggests that variability of the ICCA syndrome could be sustained by genetic modifiers.