The debate over the etiology of Parkinson's disease (PD) has been spurred by an article in the November 14 Journal of the American Medical Association, in which the authors contend that genetics, not just environmental factors, underlie the most common form of PD.
Margaret Pericak-Vance at Duke University, and coworkers, completed a genetic linkage study on 174 families with two or more members suffering from PD. They found evidence for genetic linkage to six different chromosomal markers. Early-onset PD was linked to a locus on chromosome 6q, which lies within the well-documented parkin gene, while late-onset, or idiopathic, PD was linked to positions on chromosomes 17q and 8p. Levodopa non-responsiveness, a trait of some members of the late-onset group, was linked to markers on chromosome arms 9q and 3q. The markers on 17q and 9q were found near the tau and torsinA genes, respectively, which are implicated in other neurodegenerative diseases.
These findings are contrary to those of Tanner et al, who found no genetic linkage in a study of 161 identical and fraternal twins. It should also be noted that the present work used a logarithm of odds (lod) score of 1.5 or higher as a threshold for linkage, whereas traditionally a lod of 3.0 is considered evidence of a strong link. Scientists at an Iceland biotech company recently reported yet another linkage for late-onset PD (see related news item).—Tom Fagan
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