Blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentration in essential tremor cases in Spain

► Environmental correlates for essential tremor (ET) are largely unexplored. ► Harmane (1-methyl-9H-pyrido[3,4-b]indole) is a potent tremor-producing toxin. ► Blood harmane levels were quantified by high performance liquid chromatography. ► Blood harmane levels were elevated in familial ET cases vs. controls in Spain. ► These data extend observations from New York to a second cohort of cases in Spain.