Inherited myoclonus-dystonia: evidence supporting genetic heterogeneity

Inherited myoclonus-dystonia (IMD) is a new term used to describe an autosomal dominant form of myoclonus. Recently a family with IMD was linked to a region on chromosome 11q23 and a possible mutation identified in the D2 dopamine receptor. We have identified a large family with 12 affected individuals. Using linkage analysis and direct sequencing, the D2 receptor gene was excluded as a cause of myoclonus in this family. These results indicate that the Val154Ile D2 receptor substitution is not the universal cause of IMD. This suggests either that it is a rare, family specific polymorphism not causative of IMD, or that IMD is genetically heterogeneous.