Frequency of familial aggregation in primary adult-onset cranial cervical dystonia.

Family history of definite/probable dystonia was studied in 36 probands with primary adult-onset cranial/cervical dystonia. Of the 157 relatives who were examined, 8 from 7 families and 11 from 10 families were diagnosed as having definite or probable dystonia, respectively. The frequency of familial occurrence of definite dystonia was 19.4%, 33% when considering both definite and probable dystonia. There was a tendency for relatives affected by either definite or probable dystonia to have the same type of dystonia as the index patient. Similar segregation ratios were found for parents, siblings, and children with either definite or probable dystonia. These observations raise the possibility that probable dystonia represents formes frustes/mild phenotypes of dystonia rather than another movement disorder.