The clinical phenotype of X-linked recessive torsion dystonia was documented in 42 affected individuals from 21 families. In 7 families, there were 9 sibships (core families) with 2 or more affected individuals available for evaluation. The ages of the patients ranged from 29 to 79 years with a mean of 46.2 +/- 10.1 years; the mean age of onset of dystonia was 35.0 +/- 8.0 years with a range of 12 to 48 years; and the mean duration of illness was 11.1 +/- 7.9 years. First manifestations were noted in the lower extremities in 36%, the axial musculature in 29%, the upper extremities in 23%, and in the head in 12% of the cases. The majority of patients displayed gait abnormalities (90%), leg dystonia (79%), oromandibular dystonia (64%), neck dystonia (57%), blepharospasm (57%), and truncal dystonia (52%). The disease generalized in 90% of the cases within 1 to 11 years of onset (median duration, 5 years). Overall, the condition was disabling, but the Fahn-Marsden disability score did not correlate with age of onset, duration of illness, site of onset, rate of generalization, or presence of parkinsonism. Thirty-six percent of the cases displayed at least 1 of the following "parkinsonian symptoms": bradykinesia, tremor, rigidity, loss of postural reflexes and a shuffling gait. Parkinsonism was diagnosed as definite in 14%, probable in 2%, and possible in 19% of the cases. Given this high association of dystonia and parkinsonism, we propose to call the disorder X-linked dystonia-parkinsonism syndrome (XDP).(ABSTRACT TRUNCATED AT 250 WORDS)