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Unverricht―Lundborg disease (ULD) is a type of autosomal recessive progressive myoclonus epilepsy (PME). The molecular basis for ULD involves mutations in the gene encoding cystatin B, a cysteine protease inhibitor. The gene is located on chromosome 21 at q22.3 [1]. This mutation leads to the multiplication of the C4GC4GCG minisatellite sequence repeats. The normal range of repeats is 2―3, with a premutation range of 12―17, and a causative disease range of 30―80 repeats. However, the number of repeats does not correlate with the disease phenotype.