Substantia Nigra Neuromelanin Magnetic Resonance Imaging in LRRK2 Asymptomatic Carriers

Background Neuromelanin (NM)‐sensitive MRI of the substantia nigra is a biomarker of neurodegeneration in Parkinson's disease (PD), which is expected to begin years before motor symptoms emerge, and for which LRRK2 mutation asymptomatic carriers (AC) are at higher risk. Objectives To investigate NM‐MRI in asymptomatic LRRK2 carriers. Methods Asymptomatic first‐degree relatives of LRRK2 ‐PD patients were sequentially recruited. An extensive clinical evaluation and a study of NM using a specific T1‐weighted MRI sequence, were performed. Targeted genetic testing for LRRK2 variants was performed after evaluation. Results Nineteen asymptomatic participants were included, 12 LRRK2‐ G2019S non‐carriers (NC) and 7 AC. Demographics and motor scores, assessed using MDS‐UPRS‐III, did not differ between groups. NM area was smaller in AC when compared to NC (16 mm 2 [14.9–19.1] vs 20.6 mm 2 [19.3–24.0], P = 0.025). Conclusion NM‐MRI can be significantly decreased in LRRK2 ‐G2019S AC. This technique may be a promising biomarker of neurodegeneration in pre‐diagnostic stages of PD.