Idiopathic dystonia occurs in both hereditary and sporadic forms. In t
his report, we studied the age of onset and family history of 260 pati
ents (probands) with idiopathic adult-onset dystonia (IAD), cranial or
cervical. The mean age at onset of these patients was (45.71 +/- 15.8
5) years. Forty-nine probands had a positive family history of dystoni
a or tremor in first- and second-degree relatives, and 7 had affected
siblings only. The significance of tremor as a part of clinical manife
station of dystonia was evidenced by a high frequency of postural or a
ction tremor in patients and relatives. Retrospectively, we examined t
he age of onset of dystonia (cervical or cranial) on successive genera
tions in 49 families. Age of onset of clinical symptoms was earlier, b
y an average of 21.25 years, in the second generation than in the firs
t generation. The mean age at onset of affected family members differe
d significantly between successive generations in these 49 families (p
= 1.11 x 10(-8)). Our results suggest a tendency for earlier onset of
dystonia and worsening of disease phenotype in succeeding generations
in the same family. These findings are most compatible with genetic a
nticipation and suggest that an unstable trinucleotide repeat is most
likely involved in adult-onset primary cranial or cervical dystonia. I
n addition, tremor as an integral part of dystonia needs further evalu
ation by molecular genetic studies.