Olfactory deficits and cardiac 123I‐MIBG in Parkinson's disease related to the LRRK2 R1441G and G2019S mutations

Abstract

It has been proposed that olfactory tests and metaiodobenzylguanidine cardiac scintigraphy may help diagnose idiopathic Parkinson's disease in the premotor phase. However, it is not clear what value these tests have in all patients with Parkinson's disease and, particularly, in those who carry mutations in LRRK2. The objective was to analyze olfactory dysfunction and the changes in cardiac I-metaiodobenzylguanidine uptake in patients with Parkinson's disease carrying the R1441G and G2019S mutations in LRRK2, and in patients with Parkinson's disease with no known mutations. Patients with Parkinson's disease were screened for R1441G and G2019S LRRK2 gene mutations and classified as LRRK2 mutation carriers or noncarriers. A total of 190 patients with Parkinson's disease (44 LRRK2 mutation carriers) were tested for olfactory dysfunction using the Brief Smell Identification Test. Cardiac (123) I-metaiodobenzylguanidine scintigraphy was performed on 90 patients with Parkinson's disease (27 LRRK2 mutation carriers). Thirty-six percent of patients with LRRK2 mutations have hyposmia, compared to 75% of noncarrier patients with Parkinson's disease (P < .001). Sixty-six percent of LRRK2 mutation carriers have low early metaiodobenzylguanidine uptake, compared to 86% of noncarriers (P = .048). Similarly, the heart/mediastinum ratio in delayed metaiodobenzylguanidine images appeared to differ between these groups of patients with Parkinson's disease, although these results did not reach statistical significance. The data obtained indicate that olfactory and cardiac impairment is less prevalent when Parkinson's disease is associated with mutations in LRRK2, although the underlying mechanisms for this difference remain unclear. Thus, such screening would be less useful to detect the premotor phase in asymptomatic relatives who carry mutations in LRRK2 than in cases not associated with LRRK2.