B

9 kb

9 kb

point mutations, deletions

a 1

90%

dodecamer repeat expansion

dodecamer repeat expansion

normal

'i expanded

Fig. 3 a Southern blot analysis of patients homozygous or compound heterozygous for the repeat and another mutation. DNA is digested with EcoRI (see Fig. 1a) and probed with the cystatin B cDNA. Compound heterozygotes carry a normal-size and a larger-size allele. The large allele varies between patients. b Sequence of dodecamer repeat area from a normal individual with three repeats and from a patient with more than 50 uninterrupted repeats of the dodecamer. c The point mutations account for only a small percentage of the mutant alleles (10%). The repeat expansion in the promoter is the most common defect in progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) even in patients with different haplotypes. N normal individual

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