Genetic testing in Parkinson disease—who should be assessed?

Genetic Testing in Parkinson's Disease

Genetic testing for persons with Parkinson's disease is becoming increasingly common. Significant gains have been made regarding genetic testing methods, and testing is becoming more readily available in clinical, research, and direct-to-consumer settings. Although the potential utility of clinical testing is expanding, there are currently no proven gene-targeted therapies, but clinical trials are underway. Furthermore, genetic testing practices vary widely, as do knowledge and attitudes of relevant stakeholders. The specter of testing mandates financial, ethical, and physician engagement, and there is a need for guidelines to help navigate the myriad of challenges. However, to develop guidelines, gaps and controversies need to be clearly identified and analyzed. To this end, we first reviewed recent literature and subsequently identified gaps and controversies, some of which were partially addressed in the literature, but many of which are not well delineated or researched. Key gaps and controversies include: (1) Is genetic testing appropriate in symptomatic and asymptomatic individuals without medical actionability? (2) How, if at all, should testing vary based on ethnicity? (3) What are the long-term outcomes of consumer- and research-based genetic testing in presymptomatic PD? (4) What resources are needed for clinical genetic testing, and how is this impacted by models of care and cost-benefit considerations? Addressing these issues will help facilitate the development of consensus and guidelines regarding the approach and access to genetic testing and counseling. This is also needed to guide a multidisciplinary approach that accounts for cultural, geographic, and socioeconomic factors in developing testing guidelines. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

An approach to finding brain-situated mutations in sporadic Parkinson's disease

Sporadic Parkinson's disease (PD) is thought to have a major genetic component, but the variants involved remain mostly unknown. One possible reason for the difficulty in finding mutations underlying PD is that rare predominantly brain-situated somatic mutations underlie the disease; these mutations would be missed by analysing blood DNA only. To test the feasibility of looking for somatic mutations in PD brain tissue, we compared copy number variants (CNVs) between 8 PD and 26 control brains using Affymetrix 6.0 arrays. The median number of CNVs per brain, and the overall proportion of amplifications and deletions, were similar in PD and control brains. In 7 of the 8 PD brains, however, a total of 45 CNVs were found that were not present in control brains. Twelve of these CNVs overlapped with one or more genes, some of which are involved in pathways suspected in the pathogenesis of PD, or are rare. This study shows that PD brain CNVs can be detected, and raises the possibility that brain-situated mutations could underlie some cases of PD. A method of undertaking a definitive study of brain somatic mutations in PD, using massively parallel sequencing and multiple tissues, is suggested.