The distribution of ancestral secondary cases in Parkinson's disease.

Recent evidence suggests a genetic mode of transmission of Parkinson's disease. A multifactorial mechanism is likely, but autosomal dominance with reduced penetrance has not been excluded. The distribution of ancestral second-degree relatives with Parkinson's disease was evaluated in 12 families. Affected relatives were bilaterally distributed more often than would be expected for autosomal dominance. The distribution of ancestral secondary cases suggests a multifactorial etiology for most cases of Parkinson's disease. The possibility of dominant gene inheritance in some families is not entirely ruled out.