Elevation of blood β-carboline alkaloids in essential tremor

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Abstract
Background: β-Carboline alkaloids are normal body constituents but are also potent tremor-producing chemicals that are naturally present in the food chain. Objective: To explore the hypothesis that high concentrations of β-carboline alkaloids are associated with essential tremor (ET). Methods: One hundred cases and 100 controls were frequency matched on age, sex, and ethnicity. Blood concentrations of harmane and harmine were quantified by high-performance liquid chromatography, blinded to clinical information. Results: The mean log blood concentration of harmane was higher in cases than controls (0.72 ± 0.53 vs 0.51 ± 0.64 g−10/mL; p = 0.01). A nonparametric test on nontransformed data (median harmane = 5.21 g−10/mL in cases and 2.28 g−10/mL in controls) confirmed this difference (p = 0.005). The mean log blood concentration of harmine was 0.20 ± 0.48 g−10/mL in cases and 0.10 ± 0.65 g −10/mL in controls (p = 0.20). Log harmane concentrations were stratified based on the median value; 62% of cases vs 39% of controls had a high log harmane concentration (p = 0.001). Mean log harmane concentration was similar in the cases with (0.74 ± 0.58 g−10/mL) and without (0.71 ± 0.50 g−10/mL) an affected relative (p = 0.83). Conclusions: Blood concentrations of harmane were measured in ET cases compared with controls. Concentrations were elevated in cases with and without a family history of ET.