Abstract: Objective: To assess the value of baseline clinical and imaging biomarkers in a cohort of asymptomatic LRRK2 G2019S carriers for predicting conversion to Parkinson disease (PD) at 4 years. Methods: Thirty-two asymptomatic carriers of LRRK2 G2019S mutation underwent baseline and 4-year evaluation including clinical examination (Unified Parkinson?s Disease Rating Scale, part III, olfaction University of Pennsylvania Smell Identification Test [UPSIT]) and dopamine transporter (DaT) SPECT (123I-ioflupane). Visual and semiquantitative analysis of images was performed. The specific striatal binding ratio was calculated (striatal region of interest [ROI] 2 occipital ROI/ occipital ROI). Results: Three carriers, asymptomatic at baseline, had converted to PD at 4-year evaluation. Twenty-three participants were fully evaluated. PD converters had lower striatal DaT binding at baseline than nonconverters (p 50.002). A baseline scan with a ratio of bilateral striatal uptake below 1 predicted conversion to PD within the 4-year period with high sensitivity and specificity (area under the curve 1; p 5 0.006). The slope of DaT binding decline between the 2 scans was similar in PD converters and nonconverters. Age-adjusted UPSIT score at baseline and at 4 years was similar in both groups. Conclusions: Semiquantitative DaT-SPECT could be used to predict early conversion to PD in asymptomatic carriers of the LRRK2 G2019S mutation. Rate of conversion to PD at 4 years in this cohort aged ;64 years was 12%. The slope of DaT binding decline on DaT-SPECT imaging seems to be similar across different stages of the premotor period

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