Phenocopies in a large GCH1 mutation positive family with dopa responsive dystonia: confusing the picture?

Background: Dopa responsive dystonia (DRD) is a disorder characterised by childhood onset dystonia but a wide range of clinical presentations has now been described. Objective: To study a large Canadian family with presumed DRD. Methods: The clinical features of the family were collected before molecular genetic mutational analysis. Results: All nine individuals in whom a clinical diagnosis of DRD was definite or probable were heterozygous for a GCH1 gene deletion. However, eight of nine possibly clinically affected members did not carry the GCH1 mutation. Conclusions: Great care must be taken in diagnosing DRD even in families with the classic phenotype, because of potential phenocopies of the disease.