Genetics of Parkinson's disease and the role of genetic testing

Highly-penetrant variants in different genes (including: SNCA, LRRK2, VPS35, VPS13C, PARK2, PINK1, and PARK7) are established as rare causes of monogenic forms of Parkinson's disease (PD). Several other genes have recently been nominated to be disease-causing, but for these, the evidence remains inconclusive and additional studies are required. Of note, some variants with reduced penetrance in the LRRK2 and the GBA gene are known to act as strong risk factors for the development of PD, and they are especially prevalent in some populations. Last, common variants of very small effect size, modulating the risk for developing of PD, have also been identified by genome-wide association studies (GWAS) in more than 90 chromosomal loci. With the notable exception of some populations, only a minority of PD cases are explained by identifiable mutations in single genes. Moreover, no specific treatment is currently available for PD, based on a specific genetic etiology. While this situation might change in the future, still, at the moment, genetic testing for PD remains useful in order to provide an accurate etiological diagnosis, and to offer patients and relatives counselling about the risk to unaffected persons, and disease course. Due to the potential implications in the psychological, social, and professional domains for both patients and relatives, the genetic testing for diagnostic, and especially for predictive purposes, should be performed by a professional team, including neurologists, genetic counsellors, and psychologists. These procedure should always include pre-test and post-test genetic counselling.