Long-term treatment response and fluorodopa positron emission tomographic scanning of parkinsonism in a family with dopa-responsive dystonia

Dopa‐responsive dystonia (DRD) is one form of childhood‐onset idiopathic torsion dystonia. Adult‐onset parkinsonism has appeared in several previously unaffected members in families with DRD suggesting that this may be an additional phenotypical expression of the disease. We report a family with DRD in which 2 women and 1 man, unaffected by dystonia, developed tremor‐onset parkinsonism after age 50 years. The women continue on a low dosage of levodopa after 9 and 13 years of treatment, with a stable, nearly complete, symptomatic response. This contrasts to the typical long‐term treatment complications observed in patients with Parkinson's disease. We assessed nigrostriatal dopaminer‐gic function in the proband, with typical DRD, and the 2 women with parkinsonism using 6‐{18F}fluoro‐L‐dopa positron emission tomography. All 3 had normal striatal 6‐{18F}fluoro‐L‐dopa uptake. These observations provide compelling evidence that “benign” adult‐onset parkinsonism may be an expression of the disease in some members of families with DRD and does not support consideration of the DRD gene as a risk factor for development of Parkinson's disease. There may be considerable clinical heterogeneity in DRD depending on the age at onset.