Genetics of Parkinson disease.

During the past decade five genes have been identified that are important in autosomal dominant and autosomal recessive forms of Parkinson disease. The identification of these genes has increased our understanding of the likely pathogenic mechanisms resulting in disease. However, mutations in these genes likely contribute to disease in fewer than 5% of all cases of Parkinson disease. Thus, researchers have continued to search for genes that may influence disease susceptibility. Molecular diagnostic testing is currently available for four of the genes mutated in Parkinson disease. Evidence for reduced penetrance, possible effects of haploinsufficiency, and the identification of nondisease causing polymorphisms within several of these genes has made genetic counseling challenging. Current recommendations are to limit molecular testing only to those individuals who are symptomatic. Furthermore, because treatment is unaltered by the presence or absence of mutations in these genes, restraint is recommended when considering the value of screening for mutations in a clinical setting.