Rare monogenic forms of Parkinson's disease (PD) are promoting our understanding 
of the molecular pathways involved in the common, non-Mendelian forms of the 
disease. Here, we focus on PARK7, an autosomal recessive form of early-onset 
parkinsonism caused by mutations in the DJ-1 gene. We first review the genetics 
of this form and the rapidly expanding knowledge about the structure and 
biochemical properties of the DJ-1 protein. We also discuss how DJ-1 dysfunction 
might lead to neurodegeneration, and the implications of this novel piece of 
information for the pathogenesis of the common PD forms. Although much work 
remains to be done to clarify the biology of DJ-1, its proposed activity as a 
molecular chaperone and/or as oxidative sensor appear intriguing in the light of 
the current theories on the pathogenesis of PD.