Unverricht-Lundborg disease: absence of nonallelic genetic heterogeneity.

Unverricht-Lundborg disease is a clinically recognizable form of progressive myoclonus epilepsy. Recently, in several families of both Finnish and Mediterranean extraction segregating Unverricht-Lundborg disease, the gene for this disease was linked to the same region of the long arm of chromosome 21. We performed linkage analysis in eight families, including four of neither Baltic nor Mediterranean origin, using a polymorphic (CA)n repeat marker for the human liver-type 6 phosphofructokinase (PFKL) gene, previously mapped to 21q22.3. No recombinations were observed between the disease phenotype and the PFKL marker and a maximum lod score of 5.63 was obtained. These findings confirm tight linkage between PFKL and the gene for Unverricht-Lundborg disease and strongly suggest a lack of nonallelic genetic heterogeneity of the disease.