CONCORDANCE OF COMMON MOVEMENT-DISORDERS AMONG FAMILIAL CASES

Multicase families are frequently utilized in studies of movement diso rders (MDs). We report families with two or more MD cases seen at the Movement Disorder Clinic, Saskatoon (MDCS). In 30% of the MD probands, there was either a history or documentation of at least one secondary MD case in the family. Only those MD cases that were seen at the MDCS were considered in this study. A total of 56 probands and 77 secondar y MD cases were seen at the MDCS between 1968 and 1996. In 24 (31.2%) of the secondary cases, the diagnosis was different from that in the p roband. In 46 families (82%), only one secondary case was seen, and th e diagnosis was concordant with the proband in 71.7%. In the remaining 10 families with two or more secondary cases, the diagnosis was conco rdant in 64.5% of cases. The largest subgroup was Parkinson's disease (PD)-40 probands and 53 secondary cases. Of these secondary cases, 73. 6% had PD. The concordance rate was 91% in essential tremor, but only 12.5% if the proband had essential tremor + parkinsonism. Considering that a large proportion of secondary cases have a diagnosis discordant with the proband, we recommend that, wherever possible, MD diagnosis in secondary cases be based on clinical assessment.