Sonographic alteration of substantia nigra is related to parkinsonism-predominant course of X-linked dystonia-parkinsonism.

•X-linked dystonia-parkinsonism manifests with predominant parkinsonism or dystonia.•Substantia nigra hyperechogenicity indicates a course with predominant parkinsonism.•Substantia nigra hyperechogenicity is clustered in some families of XDP patients.•Substantia nigra hyperechogenicity is proposed to reflect a genetic disease modifier.