In the recent years, many genes involved in inherited neurological disorders have been identified, and the achievement of the human genome project should accelerate their discovery. For common disorders which are of multifactorial origin, the identification of genetic susceptibility factors is still difficult. However, the study of rare monogenic forms of these disorders has proven to be fruitful. An example is Parkinson's disease, in which mutations in the alpha synculein gene are responsible for an autosomal dominant form. The study of alpha-synculein led to the conclusion that this protein is a major component of Lewy bodies, which constitute the pathological hallmark of the disease. The study of autosomal recessive forms allowed to demonstrate the relative frequency and the large variety of mutations in the Parkin gene. Parkin is probably involved in ubiquitination of proteins before their degradation by the proteasome and the identification of its cellular targets should allow the understanding of the specificity of neurodegenerative process in the human disease.