Spinocerebellar ataxia type 2 with focal epilepsy--an unusual association

The spinocerebellar ataxias are a rare group of inherited neurodegenerative disorders. Epilepsy has not previously been associated with spinocerebellar ataxia type 2 (SCA2). We describe a family with 3 affected members who had typical phenotypic and MRI features of SCA2. Two had focal epilepsy with complex partial seizures and epileptiform discharges on electroencephalography. Trinucleotide expansions in the pathological range were found in the SCA2 gene, confirming SCA2. Sequencing of the expanded SCA2 gene did not reveal any new mutations that could account for epilepsy. The focal epilepsy was well-controlled with carbamazepine. We hypothesise that the new feature of focal epilepsy is due to co-existence of a separate unlinked epilepsy susceptibility gene with the expanded SCA2 gene. Under this oligogenic model, both genes must be present, and co-inheritance of this susceptibility gene with the expanded SCA2 gene causes a complex interaction which triggers epilepsy.