Pharmacogenetics and Treatment Response in Narcolepsy Type 1: Relevance of the Polymorphisms of the Drug Transporter Gene ABCB1

Objective Narcolepsy type 1 (NT1) is a chronic hypersomnia clinically characterized by daytime sleepiness and cataplexy. Narcolepsy type 1 treatments target individual symptoms: wake-promoting agents (eg, modafinil) are effective for sleepiness, antidepressants (eg, venlafaxine) on cataplexy, whereas sodium oxybate on both. Narcolepsy type 1 patients variably respond to modafinil and venlafaxine independently of individual clinical features. Given the potential influence of drug transmembrane transport (glycoprotein-P) on drug response, we explored the relation between genetic polymorphisms in the ABCB1 gene and clinical response to modafinil/venlafaxine in NT1. Methods Individual drug response and genotypes were assessed in 107 NT1 patients (males/females, 64/43; mean age, 38 21 years) treated with modafinil and/or venlafaxine at stable doses for at least 3 months. Minisequencing was performed to detect single-nucleotide polymorphisms in ABCB1. Patients with different responses to treatment were contrasted by Fisher exact test and multivariate analysis. Results The ABCB1 diplotype was significantly associated with clinical response to modafinil, with the CGC-TTT (1236/2677/3435) being more frequent in the modafinil responder versus nonresponder group (P = 0.013). Conversely, no significant associations with clinical response to venlafaxine were found. Conclusions The ABCB1 variants modulate therapeutic response to modafinil and may partly explain pharmacoresistance in NT1 patients.