Objective: To identify cohorts with existing olfactory data within the Global Parkinson’s Genetics Program (GP2, http://gp2.org/). To support harmonisation across cohorts and facilitate future expansion of smell testing, particularly in under-represented populations.

Background: GP2 is an international collaborative program aimed at accelerating research into the genetic architecture of PD. Olfactory dysfunction is a common early feature of Parkinson’s disease (PD) yet smell test data availability within GP2 remains limited. To address this, we initiated a smell testing outreach project.

Method: A request for expression of interest (RFEI) form was circulated to GP2 investigators to query smell testing data availability globally. Outreach calls were conducted to review which smell tests are being used worldwide, whether data are shareable and whether investigators would be interested in leading smell testing projects. Data requests were sent to investigators with objective olfactory data at the end of 2025. Data outreach is ongoing to encourage data submission across the network.

Results: Investigators representing 29 cohorts responded to the RFEI, with representation across Europe, the Americas, Africa, Asia and Oceania. Investigators representing 16 cohorts reported objective psychophysical smell test data, while 13 reported subjective olfactory data only. To date, 5 cohorts have contributed extended olfactory data, capturing smell test type, version, raw scores and hyposmia thresholds, totalling 3277 participants. Additional cohorts have submitted basic olfactory data (raw scores only), and we aim to continue our harmonisation efforts throughout 2026.

Conclusion: The smell testing outreach project has established a framework for engaging investigators interested in olfactory data sharing and analyses, with 5 cohorts contributing 3277 participants so far. We aim to perform the largest olfactory GWAS to date, starting in 2027. We are particularly interested in engaging with new investigators to set up smell testing collections in under-represented populations.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/smell-testing-in-the-global-parkinsons-genetics-program-gp2/