We evaluated an association between essential tremor (ET) and the Parkinson's disease (PD) genes, Leucine Rich Repeat Kinase 2 (LRRK2) and Glucocerebrosidase (GBA). Clinical studies demonstrate an association between ET and PD, suggesting possible shared pathophysiologies, yet LRRK2 has rarely been studied in ET, and GBA, not at all. ET cases (n = 275, including 42 with rest tremor) and controls (n = 289) were enrolled in an epidemiological study (Columbia University). Post-mortem brain tissue samples were obtained on 24 additional ET cases, including 3 with brainstem Lewy bodies. We performed a comprehensive analysis of the LRRK2 gene by genotyping 4 LRRK2 mutations (G2019S, I2020T, R1441C and Y1699C), 2 rare LRRK2 variants (L1114L and I1122V) and 19 LRRK2 SNPs. All GBA exons were sequenced in a subset of 93 Ashkenazi Jewish (AJ) cases, 62 AJ controls and 24 ET brains. LRRK2 mutations were not found in any ET cases or ET brains and none of the LRRK2 SNPs was associated with ET. GBA mutations were found in 7.5% (7/93) of AJ ET cases and 4.8% (3/62) of AJ controls (p = 0.75). 8.3% (2/24) of ET brains carried a GBA mutation. Four different heterozygous mutations were identified, including 3 previously reported mutations (N370S, R496H, and E326K) and 1 new missense variant (R44C). As suggested by several smaller prior reports, the known mutations for the LRRK2 gene are not risk factors for ET. Furthermore, a similar frequency of GBA mutations in AJ ET cases and controls suggests that GBA is not a common cause of ET either.
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