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Rapid-onset dystonia-parkinsonism (RPD) is an autosomal dominant movement disorder characterized by sudden onset of persistent dystonia and parkinsonism, generally during adolescence or early adulthood. Symptoms evolve over hours or days, and generally stabilize within a few weeks, with slow or no progression. Other features include little or no response to L-dopa, and low levels of homovanillic acid in the central nervous system. Neuroimaging studies indicate no degeneration of dopaminergic nerve terminals in RDP, suggesting that this disorder results from a functional deficit, as in dystonia, rather than neuronal loss, as in Parkinson's disease. We studied 81 members of two midwestern US families with RDP, 16 of whom exhibited classic features of RDP. We found significant evidence for linkage in these two families to markers on chromosome 19q13, with the highest multipoint LOD score at D19S198 (z = 5.77 at theta = 0.0). The flanking markers D19S587 and D19S900 define a candidate region of approximately 8 cM. Although RDP itself is a rare condition, it is important because it has clinical and biochemical similarities to both Parkinson's disease and dystonia. Identification of the genetic defect in RDP holds promise for understanding the underlying disease processes of both of these more common diseases.

Rapid-onset dystonia-parkinsonism (RDP) is characterized by sudden onset over hours to days of dystonia, dysphagia, dysarthria, and parkinsonism. RDP has been reported by our group in two apparently unrelated families. We now report analysis of cerebrospinal fluid metabolites of dopamine, norepinephrine, and serotonin for mild and severely affected individuals, known asymptomatic gene carriers, and at-risk individuals from both families with RDP. Levels of the dopamine metabolite homovanillic acid (HVA) were decreased in severely affected patients and in some asymptomatic gene carriers. HVA levels increased with treatment in some affected individuals, but this increase did not predict clinical response to carbidopa/levodopa. We suggest that a low HVA level is a biological marker with modest association to the diagnosis of RDP.

As part of a community-based study of Alzheimer's disease (AD) in the African-American population age 65 and over, we have determined apolipoprotein E (Apo E) genotypes in 85 subjects (31 AD patients and 54 controls). The epsilon 4 allele of Apo E was strongly associated with AD in this population sample. The epsilon 4 allele frequency in AD patients was 40.3% compared with 13.9% in the control group, and 22.6% of the AD patients were homozygous for this allele compared with 3.7% of the control subjects (p = 0.01). This study extends the association of Apo E-epsilon 4 and AD to nonwhite populations and provides further evidence that the observed allelic association is biologically relevant.