Genetic linkage studies in autosomal dominant parkinsonism: evaluation of seven candidate genes.

Linkage studies were performed in three families (A, B, and C) with autosomal dominantly inherited parkinsonism affecting multiple members in three generations. Affected individuals exhibited the cardinal signs and symptoms of Parkinson's disease, with a mean age of onset of 51, 62, and 61 years in Families A, B, and C, respectively. Parkinsonian symptoms responded to L-dopa treatment, and an [18F]6-fluoro-L-dopa positron emission tomography scan in 1 affected member of Family B showed decreased striatal uptake typical of Parkinson's disease. Ancestors of all three families were traced to a small region in northern Germany and southern Denmark, suggesting the possibility of a common mutation. Linkage studies were performed with polymorphic markers associated with the following candidate genes: the genes for glutathione peroxidase (GPX1, 3q11), tyrosine hydroxylase (TH, 11p15.5), brain-derived neurotrophic factor (BDNF, 11p14), catalase (CAT, 11p13), amyloid precursor protein (APP, 21q21), copper-zinc superoxide dismutase (SOD1, 21q21), and debrisoquin 4-hydroxylase (CYP2D6, 22q13.1). Summed lod scores for all families excluded linkage to the genes GPX1, TH, APP, SOD1, and CYP2D6, as well as to the chromosomal region containing the genes CAT and BDNF. If families were analyzed individually, exclusion was possible for two (Family A), six (Family B), and five (Family C) of the seven candidate genes. There was strong evidence against linkage for the remaining loci in all families analyzed individually, except for TH, which was uninformative in Families A and B, and CYP2D6, which gave slightly positive pairwise lod scores in Family A. Our results indicate that the candidate genes investigated are not involved in the etiology of parkinsonism in these families.