Task matters - challenging the motor system allows distinguishing unaffected Parkin mutation carriers from mutation-free controls

How to communicate and what to disclose to participants in a recall-by-genotype research approach: a multistep empirical study

Recall-by-genotype (RbG) is a bottom-up approach using existing genetic data to design follow-up stratified studies. Genetic information may be partially disclosed at invitation, thus raising ethical issues which call for defined best practices for disclosure and communication in RbG approaches. Within the context of the ProtectMove sub-project of the Cooperative Health Research in South Tyrol (CHRIS) study, we investigated research participant perspectives on RbG communication strategies (Step 1 and 4, questionnaire with a subsample of CHRIS participants with and without previous experience of RbG, respectively). Additionally, we explored researchers' and study personnel's experience with RbG (Step 2 and 3, focus group discussion). In step 1 (N = 95), participants were generally satisfied with the study process. Most (71.6%) wanted to know their carrier status for personal and collective benefit. Tailored disclosure strategies and transparent, effective, and well-thought-out communication approaches were advocated by study personnel (Step 2, N = 6) and researchers (Step 3, N = 7). Challenges in dealing with uncertainty, concerns caused by RbG invitations, and the possibility of misunderstanding were also raised. In step 4 (N = 369), participants valued being informed of study details at the first invitation stage, and generally felt comfortable towards RbG study invitations (58.5%) and to receiving genetic information after the study (58.5-81.6%). Comfort and perceived impact of disclosure of genetic information varied according to the type of variant being potentially disclosed. This study suggested designing communication strategies, based on clear and understandable explanations, sensitive to participant expectations and preferences, developing case-by-case solutions for disclosure.

Diverse Functions of Parkin in Midbrain Dopaminergic Neurons

Parkinson's disease (PD) is characterized by preferential degeneration of midbrain dopaminergic neurons that contributes to its typical clinical manifestation. Mutations in the parkin gene (PARK2) represent a relatively common genetic cause of early onset PD. Parkin has been implicated in PINK1-dependent mitochondrial quantity control by targeting dysfunctional mitochondria to lysosomes via mitophagy. Recent evidence suggests that parkin can be activated in PINK1-independent manner to regulate synaptic function in human dopaminergic neurons. Neuronal activity triggers CaMKII-mediated activation of parkin and its recruitment to synaptic vesicles where parkin promotes binding of synaptojanin-1 to endophilin A1 and facilitates vesicle endocytosis. In PD patient neurons, disruption of this pathway on loss of parkin leads to defective recycling of synaptic vesicles and accumulation of toxic oxidized dopamine that at least in part explains preferential vulnerability of midbrain dopaminergic neurons. These findings suggest a convergent mechanism for PD-linked mutations in parkin, synaptojanin-1, and endophilin A1 and highlight synaptic dysfunction as an early pathogenic event in PD. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Parkinson's disease-linked parkin mutation disrupts recycling of synaptic vesicles in human dopaminergic neurons

Parkin-mediated mitophagy has been studied extensively, but whether mutations in parkin contribute to Parkinson's disease pathogenesis through alternative mechanisms remains unexplored. Using patient-derived dopaminergic neurons, we found that phosphorylation of parkin by Ca2+/calmodulin-dependent protein kinase 2 (CaMK2) at Ser9 leads to activation of parkin in a neuronal-activity-dependent manner. Activated parkin ubiquitinates synaptojanin-1, facilitating its interaction with endophilin A1 and synaptic vesicle recycling. Neurons from PD patients with mutant parkin displayed defective recycling of synaptic vesicles, leading to accumulation of toxic oxidized dopamine that was attenuated by boosting endophilin A1 expression. Notably, combined heterozygous parkin and homozygous PTEN-induced kinase 1 (PINK1) mutations led to earlier disease onset compared with homozygous mutant PINK1 alone, further underscoring a PINK1-independent role for parkin in contributing to disease. Thus, this study identifies a pathway for selective activation of parkin at human dopaminergic synapses and highlights the importance of this mechanism in the pathogenesis of Parkinson's disease.

Participant perspective on the recall-by-genotype research approach: a mixed-method embedded study with participants of the CHRIS study

Recall-by-genotype (RbG) research recruits participants previously involved in genetic research based on their genotype. RbG enables the further study of a particular variant of interest, but in recalling participants, it risks disclosing potentially unwanted or distressing genetic information. Any RbG strategy must therefore be done in a manner that addresses the potential ethical and social issues. As part of an RbG pilot on the penetrance of Parkinson's disease variants, we conducted an empirical mixed-method study with 51 participants of the Cooperative Health Research in South Tyrol (CHRIS) study to understand participant views on RbG research approach. Participants were disclosed the disease under investigation but not the individual variant carrier status. Results showed that participants filtered the information received through personal experience and enacted mechanisms to address the concerns raised by invitation by resorting to personal resources and the support provided by experts. While the non-disclosure of the Parkin variant carrier status was deemed acceptable, disclosing the disease under study was important for participants. Participant preferences for disclosure of the disease under investigation and the carrier status varied according to how the knowledge of individual carrier status was perceived to impact the participant's life. This study provided insights into participant response to the RbG research approach, which are relevant for RbG policy development. A suitable communication strategy and granular options addressing preferences for invitation in the original informed consent are critical for an ethically informed RbG policy.

Molecular phenotypes of mitochondrial dysfunction in clinically non-manifesting heterozygous PRKN variant carriers

Homozygous or compound heterozygous (biallelic) variants in PRKN are causal for PD with highly penetrant symptom expression, while the much more common heterozygous variants may predispose to PD with highly reduced penetrance, through altered mitochondrial function. In the presence of pathogenic heterozygous variants, it is therefore important to test for mitochondrial alteration in cells derived from variant carriers to establish potential presymptomatic molecular markers. We generated lymphoblasts (LCLs) and human induced pluripotent stem cell (hiPSC)-derived neurons from non-manifesting heterozygous PRKN variant carriers and tested them for mitochondrial functionality. In LCLs, we detected hyperactive mitochondrial respiration, and, although milder compared to a biallelic PRKN-PD patient, hiPSC-derived neurons of non-manifesting heterozygous variant carriers also displayed several phenotypes of altered mitochondrial function. Overall, we identified molecular phenotypes that might be used to monitor heterozygous PRKN variant carriers during the prodromal phase. Such markers might also be useful to identify individuals at greater risk of eventual disease development and for testing potential mitochondrial function-based neuroprotective therapies before neurodegeneration advances.

Ten years of dynamic consent in the CHRIS study: informed consent as a dynamic process

The Cooperative Health Research in South Tyrol (CHRIS) is a longitudinal study in Northern Italy, using dynamic consent since its inception in 2011. The CHRIS study collects health data and biosamples for research, and foresees regular follow-ups over time. We describe the experience with the CHRIS study dynamic consent, providing an overview of its conceptualization and implementation, and of the participant-centered strategies used to assess and improve the process, directly linked to participation and communication. In order to comply with high ethical standards and to allow broadness in the areas of research, CHRIS dynamic consent was conceived as an interactive process: based on a strong governance and an ongoing tailored communication with participants, it aims to promote autonomy and to develop a trust-based engaged relationship with participants, also relevant for retention. Built within an online platform, the consent allows granular choices, which can be changed over time. In a process of co-production, participants views have been investigated and kept into account in policy development. Participants showed a high degree of participation, thus enabling the consolidation of the CHRIS resources. Even though a low change rate was reported in the baseline, participants valued the possibility of changing their informed consent choices. Communication (language-tailored, ongoing, multimedia) was important for participants, and for participation and retention. In our experience, dynamic consent was proven to be a flexible consent model, which allowed to meet ethical and legal standards for participation in research, and to accommodate participants' and researchers' needs.

Frequency of Heterozygous Parkin (PRKN) Variants and Penetrance of Parkinson's Disease Risk Markers in the Population-Based CHRIS Cohort

Mutations in the Parkin (PRKN) gene are the most frequent cause of autosomal recessive early-onset Parkinson's disease (PD). Heterozygous PRKN mutation carriers might also be at increased risk for developing clinical symptoms of PD. Given the high frequency of heterozygous mutations in the general population, it is essential to have better estimates of the penetrance of these variants, and to investigate, which clinical and biochemical markers are present in carriers and thus potentially useful for identifying those individuals at greater risk of developing clinical symptoms later in life. In the present study, we ascertained the frequency of heterozygous PRKN mutation carriers in a large population sample of the Cooperative Health Research in South Tyrol (CHRIS) study, and screened for reported PD risk markers. 164 confirmed heterozygous PRKN mutation carriers were compared with 2,582 controls. A higher number of heterozygous mutation carriers reported a detectable increase in an akinesia-related phenotype, and a higher percentage of carriers had manifested diabetes. We also observed lower resting heart rate in the PRKN mutation carriers. Extending our risk analyses to a larger number of potential carriers and non-carriers using genotype imputation (n = 299 carriers and n = 7,127 non-carriers), from previously published biomarkers we also observed a higher neutrophil-to-lymphocyte ratio (NLR) and lower serum albumin and sodium levels in the heterozygous PRKN variant carriers. These results identify a set of biomarkers that might be useful either individually or as an ensemble to identify variant carriers at greater risk of health issues due to carrier status.