Inherited myoclonus-dystonia: Evidence supporting genetic heterogeneity

Inherited myoclonus-dystonia (IMD) is a new term used to describe an autoso mal 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 dop amine receptor. We have identified a large family with 12 affected individu als. Using linkage analysis and direct sequencing, the D2 receptor gene was excluded as a cause of myoclonus in this family. These results indicate th at 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.