Late-onset and slow-progressing Lafora disease in four siblings with EPM2B mutation.

We report a family with four brothers affected by Lafora disease (LD). Mean age at onset was 19.5 years (range, 17-21). In all cases, the initial obvious symptoms were diffuse myoclonus and occasional generalized tonic-clonic seizures (GTCSs), followed by cognitive difficulties. Severity of myoclonus, seizure diaries, and neurologic and neuropsychological status were finally evaluated in March 2005. The duration of follow-up was >10 years for three subjects. Daily living activities and social interaction were preserved in all cases and, overall, the progression of the disease was slow. Genetic study revealed the homozygous mutation D146N in the EPM2B gene. We suggest that this mutation may be associated with a less severe LD phenotype.