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.