Blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentration in dystonia cases vs. controls

Background: Harmane (1-methyl-9H-pyrido[3,4 b]indole) (HA) is a potent neurotoxin that has been linked to two neurological diseases, essential tremor and Parkinson's disease. Blood harmane concentrations [HA] are elevated in patients with both diseases. An important question is whether HA is specifically linked with these diseases or alternatively, is a non-specific marker of neurological illness. Objectives: We assessed whether blood [HA] was elevated in patients with a third neurological disease, dystonia, comparing them to controls. Methods: Blood [HA] was quantified by high performance liquid chromatography. Subjects comprised 104 dystonia cases and 107 controls. Results: Mean log blood [HA] in dystonia cases was similar to that of controls (0.41±0.51g^-10/ml vs. 0.38±0.61g^-10/ml, t=0.42, p=0.68). In unadjusted and adjusted logistic regression analyses, log blood [HA] was not associated with the outcome (diagnosis of dystonia vs. control): odds ratio (OR)_unadjusted=1.11, 95% confidence interval (CI)=0.69-1.79, p=0.68; OR_adjusted=1.07, 95% CI=0.58-1.97, p=0.84. Conclusions: In contrast to the elevated blood [HA] that has been reported in patients with essential tremor and Parkinson's disease, our data demonstrate that blood [HA] was similar in patients with dystonia and controls. These findings provide the first support for the notion that an elevated blood [HA] is not a broad feature of neurological disease, and may be a specific feature of certain tremor disorders.