Inherited and de novo mutations in sporadic cases of DYT1-dystonia.

A study of Danish probands with primary torsion dystonia is presented. The probands were examined clinically and biochemically to exclude secondary dystonia. Mutation analyses for the GAG-deletion in the DYT1 gene were performed on 107 probands; and the mutation was detected in three. All three probands had the classical phenotype of DYT1-dystonia, but only one had a family history of dystonia. The other two probands had, obviously, sporadic DYT1-dystonia, one of which was caused by a de novo mutation, while the other one had a parent being an asymptomatic carrier. De novo mutations in the DYT1 gene are seldom reported although independent founder mutations are known to have occurred. The frequency of DYT1-dystonia was low in our study even though several probands had early onset generalised dystonia. None of the probands in our study with other types of dystonia had the GAG-deletion as reported in other studies. The difficulties in genetic counselling concerning the heterogeneity of dystonia exemplified by DYT1-dystonia are outlined.